Converter circuits for LEDs using field-effect transistors. LED driver for mc34063. Diagram and description. Which stabilizer to use in a car

Despite the wide selection in LED flashlight stores various designs, radio amateurs are developing their own versions of circuits to power white super-bright LEDs. Basically, the task comes down to how to power an LED from just one battery or accumulator, and conduct practical research.

After a positive result is obtained, the circuit is disassembled, the parts are put into a box, the experiment is completed, and moral satisfaction sets in. Often research stops there, but sometimes the experience of assembling a specific unit on a breadboard turns into a real design, made according to all the rules of art. Below we consider several simple circuits developed by radio amateurs.

In some cases, it is very difficult to determine who is the author of the scheme, since the same scheme appears on different sites and in different articles. Often the authors of articles honestly write that this article was found on the Internet, but it is unknown who published this diagram for the first time. Many circuits are simply copied from the boards of the same Chinese flashlights.

Why are converters needed?

The thing is that the direct voltage drop is, as a rule, no less than 2.4...3.4V, so it is simply impossible to light an LED from one battery with a voltage of 1.5V, and even more so from a battery with a voltage of 1.2V. There are two ways out here. Either use a battery of three or more galvanic cells, or build at least the simplest one.

It is the converter that will allow you to power the flashlight with just one battery. This solution reduces the cost of power supplies, and in addition allows for fuller use: many converters are operational with a deep battery discharge of up to 0.7V! Using a converter also allows you to reduce the size of the flashlight.

The circuit is a blocking oscillator. This is one of the classic electronic circuits, so if assembled correctly and in good working order, it starts working immediately. The main thing in this circuit is to wind transformer Tr1 correctly and not to confuse the phasing of the windings.

As a core for the transformer, you can use a ferrite ring from an unusable board. It is enough to wind several turns of insulated wire and connect the windings, as shown in the figure below.

The transformer can be wound with winding wire such as PEV or PEL with a diameter of no more than 0.3 mm, which will allow you to place a slightly larger number of turns on the ring, at least 10...15, which will somewhat improve the operation of the circuit.

The windings should be wound into two wires, then connect the ends of the windings as shown in the figure. The beginning of the windings in the diagram is shown by a dot. You can use any low-power n-p-n transistor: KT315, KT503 and the like. Nowadays it is easier to find an imported transistor such as BC547.

If you don't have a transistor at hand n-p-n structures, then you can use, for example, KT361 or KT502. However, in this case you will have to change the polarity of the battery.

Resistor R1 is selected based on the best LED glow, although the circuit works even if it is simply replaced with a jumper. The above diagram is intended simply “for fun”, for conducting experiments. So after eight hours of continuous operation on one LED, the battery drops from 1.5V to 1.42V. We can say that it almost never discharges.

To study the load capacity of the circuit, you can try connecting several more LEDs in parallel. For example, with four LEDs the circuit continues to operate quite stably, with six LEDs the transistor begins to heat up, with eight LEDs the brightness drops noticeably and the transistor gets very hot. But the scheme still continues to work. But this is only for scientific research, since the transistor will not work for a long time in this mode.

If you plan to create a simple flashlight based on this circuit, you will have to add a couple more parts, which will ensure a brighter glow of the LED.

It is easy to see that in this circuit the LED is powered not by pulsating, but DC. Naturally, in this case the brightness of the glow will be slightly higher, and the level of pulsations of the emitted light will be much less. Any high-frequency diode, for example, KD521 (), will be suitable as a diode.

Converters with choke

Another simplest diagram is shown in the figure below. It is somewhat more complicated than the circuit in Figure 1, it contains 2 transistors, but instead of a transformer with two windings it only has inductor L1. Such a choke can be wound on a ring from the same energy saving lamp, for which you will need to wind only 15 turns of winding wire with a diameter of 0.3...0.5 mm.

With the specified inductor setting on the LED, you can get a voltage of up to 3.8V (forward voltage drop across the 5730 LED is 3.4V), which is enough to power a 1W LED. Setting up the circuit involves selecting the capacitance of capacitor C1 in the range of ±50% of the maximum brightness of the LED. The circuit is operational when the supply voltage is reduced to 0.7V, which ensures maximum use of battery capacity.

If the considered circuit is supplemented with a rectifier on diode D1, a filter on capacitor C1, and a zener diode D2, you will get a low-power power supply that can be used to power op-amp circuits or other electronic components. In this case, the inductance of the inductor is selected within the range of 200...350 μH, diode D1 with a Schottky barrier, zener diode D2 is selected according to the voltage of the supplied circuit.

With a successful combination of circumstances, using such a converter you can obtain an output voltage of 7...12V. If you plan to use the converter to power only LEDs, zener diode D2 can be excluded from the circuit.

All the considered circuits are the simplest voltage sources: limiting the current through the LED is carried out in much the same way as is done in various key fobs or in lighters with LEDs.

The LED, through the power button, without any limiting resistor, is powered by 3...4 small disk batteries, the internal resistance of which limits the current through the LED to a safe level.

Current Feedback Circuits

But an LED is, after all, a current device. It is not for nothing that the documentation for LEDs indicates direct current. Therefore, true LED power circuits contain current feedback: once the current through the LED reaches a certain value, the output stage is disconnected from the power supply.

Voltage stabilizers work exactly the same way, only there is voltage feedback. Below is a circuit for powering LEDs with current feedback.

Upon closer examination, you can see that the basis of the circuit is the same blocking oscillator assembled on transistor VT2. Transistor VT1 is the control one in the circuit feedback. Feedback works in this scheme in the following way.

LEDs are powered by voltage that accumulates across an electrolytic capacitor. The capacitor is charged through a diode with pulsed voltage from the collector of transistor VT2. The rectified voltage is used to power the LEDs.

The current through the LEDs passes along the following path: the positive plate of the capacitor, LEDs with limiting resistors, the current feedback resistor (sensor) Roc, the negative plate of the electrolytic capacitor.

In this case, a voltage drop Uoc=I*Roc is created across the feedback resistor, where I is the current through the LEDs. As the voltage increases (the generator, after all, works and charges the capacitor), the current through the LEDs increases, and, consequently, the voltage across the feedback resistor Roc increases.

When Uoc reaches 0.6V, transistor VT1 opens, closing the base-emitter junction of transistor VT2. Transistor VT2 closes, the blocking generator stops and stops charging electrolytic capacitor. Under the influence of a load, the capacitor is discharged, and the voltage across the capacitor drops.

Reducing the voltage on the capacitor leads to a decrease in the current through the LEDs, and, as a result, a decrease in the feedback voltage Uoc. Therefore, transistor VT1 closes and does not interfere with the operation of the blocking generator. The generator starts up and the whole cycle repeats again and again.

By changing the resistance of the feedback resistor, you can vary the current through the LEDs within a wide range. Such circuits are called pulse current stabilizers.

Integral current stabilizers

Currently, current stabilizers for LEDs are produced in an integrated version. Examples include specialized microcircuits ZXLD381, ZXSC300. The circuits shown below are taken from the DataSheet of these chips.

The figure shows the design of the ZXLD381 chip. It contains a PWM generator (Pulse Control), a current sensor (Rsense) and an output transistor. There are only two hanging parts. These are LED and inductor L1. A typical connection diagram is shown in the following figure. The microcircuit is produced in the SOT23 package. The generation frequency of 350KHz is set by internal capacitors; it cannot be changed. The device efficiency is 85%, starting under load is possible even with a supply voltage of 0.8V.

The forward voltage of the LED should be no more than 3.5V, as indicated in the bottom line under the figure. The current through the LED is controlled by changing the inductance of the inductor, as shown in the table on the right side of the figure. The middle column shows the peak current, the last column shows the average current through the LED. To reduce the level of ripple and increase the brightness of the glow, it is possible to use a rectifier with a filter.

Here we use an LED with a forward voltage of 3.5V, a high-frequency diode D1 with a Schottky barrier, and a capacitor C1 preferably with a low equivalent series resistance (low ESR). These requirements are necessary in order to increase the overall efficiency of the device, heating the diode and capacitor as little as possible. The output current is selected by selecting the inductance of the inductor depending on the power of the LED.

It differs from the ZXLD381 in that it does not have an internal output transistor and a current sensor resistor. This solution allows you to significantly increase the output current of the device, and therefore use a higher power LED.

An external resistor R1 is used as a current sensor, by changing the value of which you can set the required current depending on the type of LED. This resistor is calculated using the formulas given in the datasheet for the ZXSC300 chip. We will not present these formulas here; if necessary, it is easy to find a datasheet and look up the formulas from there. The output current is limited only by the parameters of the output transistor.

When you turn on all the described circuits for the first time, it is advisable to connect the battery through a 10 Ohm resistor. This will help avoid the death of the transistor if, for example, the transformer windings are incorrectly connected. If the LED lights up with this resistor, then the resistor can be removed and further adjustments can be made.

Boris Aladyshkin

The main electrical parameter of light emitting diodes (LEDs) is their operating current. When we see the operating voltage in the LED characteristics table, we need to understand that we're talking about about the voltage drop across the LED when operating current flows. That is, the operating current determines the operating voltage of the LED. Therefore, only a current stabilizer for LEDs can ensure their reliable operation.

Purpose and principle of operation

Stabilizers must provide a constant operating current for the LEDs when the power supply has problems with voltage deviations from the norm (you will be interested to know). A stable operating current is primarily necessary to protect the LED from overheating. After all, if the maximum permissible current is exceeded, the LEDs fail. Also, the stability of the operating current ensures the constancy of the luminous flux of the device, for example, when batteries are discharged or voltage fluctuations in the supply network.

Current stabilizers for LEDs have different types execution, and the abundance of design options is pleasing to the eye. The figure shows the three most popular semiconductor stabilizer circuits.

Scheme a) - Parametric stabilizer. In this circuit, the zener diode sets a constant voltage at the base of the transistor, which is connected according to the emitter follower circuit. Due to the stability of the voltage at the base of the transistor, the voltage across the resistor R is also constant. By virtue of Ohm's law, the current across the resistor also does not change. Since the resistor current is equal to the emitter current, the emitter and collector currents of the transistor are stable. By including the load in the collector circuit, we obtain a stabilized current.
Scheme b). In the circuit, the voltage across resistor R is stabilized as follows. As the voltage drop across R increases, the first transistor opens more. This leads to a decrease in the base current of the second transistor. The second transistor closes slightly and the voltage on R stabilizes.
Scheme c). In the third circuit, the stabilization current is determined by the initial current of the field-effect transistor. It is independent of the voltage applied between drain and source.

In circuits a) and b), the stabilization current is determined by the value of the resistor R. By using a subline resistor instead of a constant resistor, you can regulate the output current of the stabilizers.

Electronic component manufacturers produce many LED regulator chips. Therefore, at present, integrated stabilizers are more often used in industrial products and amateur radio designs. Read about everything possible ways Connecting LEDs is possible.

Review of famous models

Most chips for powering LEDs are designed as pulse converters voltage. Converters in which the role of an electrical energy storage device is played by an inductor (choke) are called boosters. In boosters, voltage conversion occurs due to the phenomenon of self-induction. One of the typical booster circuits is shown in the figure.

The current stabilizer circuit works as follows. A transistor switch located inside the microcircuit periodically closes the inductor to the common wire. At the moment the switch opens, a self-induction EMF arises in the inductor, which is rectified by a diode. It is characteristic that the self-induction EMF can significantly exceed the voltage of the power source.

As can be seen from the diagram for manufacturing a booster on TPS61160 manufactured by the company Texas Instruments Very few components are required. The main attachments are inductor L1, Schottky diode D1, rectifying impulse voltage at the output of the converter, and R set.

The resistor performs two functions. Firstly, the resistor limits the current flowing through the LEDs, and secondly, the resistor serves as a feedback element (a kind of sensor). The measuring voltage is removed from it, and internal circuits chip stabilize the current flowing through the LED at a given level. By changing the resistor value you can change the current of the LEDs.

The TPS61160 converter operates at a frequency of 1.2 MHz, the maximum output current can be 1.2 A. Using the microcircuit, you can power up to ten LEDs connected in series. The brightness of the LEDs can be changed by applying a variable duty cycle PWM signal to the “brightness control” input. The efficiency of the above circuit is about 80%.

It should be noted that boosters are usually used when the voltage across the LEDs is higher than the voltage of the power supply. In cases where it is necessary to reduce the voltage, linear stabilizers are often used. A whole line of such MAX16xxx stabilizers is offered by MAXIM. A typical connection diagram and internal structure of such microcircuits is shown in the figure.

As can be seen from block diagram, stabilization of the LED current is carried out by a P-channel field-effect transistor. The error voltage is removed from the resistor R sens and supplied to the field control circuit. Since the field-effect transistor operates in linear mode, the efficiency of such circuits is noticeably lower than that of pulse converter circuits.

The MAX16xxx line of ICs are often used in automotive applications. The maximum input voltage of the chips is 40 V, output current is 350 mA. They, like switching stabilizers, allow PWM dimming.

Stabilizer on LM317

Not only specialized microcircuits can be used as a current stabilizer for LEDs. The LM317 circuit is very popular among radio amateurs.

LM317 is a classic linear voltage regulator with many analogs. In our country, this microcircuit is known as KR142EN12A. A typical circuit for connecting LM317 as a voltage stabilizer is shown in the figure.

To turn this circuit into a current stabilizer, it is enough to exclude resistor R1 from the circuit. The inclusion of LM317 as a linear current stabilizer is as follows.

Calculating this stabilizer is quite simple. It is enough to calculate the value of resistor R1 by substituting the current value into the following formula:

The power dissipated by the resistor is equal to:

Adjustable stabilizer

The previous diagram can easily be converted into adjustable stabilizer. To do this, you need to replace the constant resistor R1 with a potentiometer. The diagram will look like this:

How to make a stabilizer for an LED with your own hands

All of the above stabilizer circuits use minimal amount details. Therefore, even a novice radio amateur who has mastered the skills of working with a soldering iron can independently assemble such structures. The designs on the LM317 are especially simple. You don't even need to design a printed circuit board to make them. It is enough to solder a suitable resistor between the reference pin of the microcircuit and its output.

Also, two flexible conductors need to be soldered to the input and output of the microcircuit and the design will be ready. If using a current stabilizer on LM317 it is intended to power powerful LED, the microcircuit must be equipped with a radiator that will ensure heat removal. As a radiator, you can use a small aluminum plate with an area of 15-20 square centimeters.

When making booster designs, you can use filter coils from various power supplies as chokes. For example, ferrite rings from computer power supplies are well suited for these purposes; several dozen turns of enameled wire with a diameter of 0.3 mm should be wound around them.

Which stabilizer to use in a car

Nowadays, car enthusiasts are often engaged in upgrading the lighting technology of their cars, using LEDs or LED strips(read,). It is known that voltage on-board network car can vary greatly depending on the operating mode of the engine and generator. Therefore, in the case of a car, it is especially important to use not a 12-volt stabilizer, but one designed for a specific type of LED.

For a car, we can recommend designs based on LM317. You can also use one of the modifications of a linear stabilizer with two transistors, in which a powerful N-channel field-effect transistor is used as a power element. Below are options for such schemes, including the scheme.

Conclusion

To summarize, we can say that for reliable operation of LED structures, they must be powered using current stabilizers. Many stabilizer circuits are simple and easy to make yourself. We hope that the information provided in the material will be useful to everyone who is interested in this topic.

http://electro-tehnyk. *****/docs/led_lait. htm

LED flashlight with 3-volt converter for LED 0.3-1.5V 0.3-1.5 V LED FlashLight

Typically, a blue or white LED requires 3 - 3.5v to operate, this scheme allows you to power a blue or white LED with low voltage from one AA battery. Normally, if you want to light up a blue or white LED you need to provide it with V, like from a 3 V lithium coin cell.

Details:
Light-emitting diode
Ferrite ring (~10 mm diameter)
Wire for winding (20 cm)
1kOhm resistor
N-P-N transistor
Battery

Parameters of the transformer used:
The winding going to the LED has ~45 turns, wound with 0.25mm wire.
The winding going to the base of the transistor has ~30 turns of 0.1mm wire.
The base resistor in this case has a resistance of about 2K.
Instead of R1, it is advisable to install a tuning resistor, and achieve a current through the diode of ~22 mA; with a fresh battery, measure its resistance, then replacing it with a constant resistor of the obtained value.

The assembled circuit should work immediately.
There are only 2 possible reasons why the scheme will not work.
1. the ends of the winding are mixed up.
2. too few turns of the base winding.
Generation disappears with the number of turns<15.

Place the wire pieces together and wrap them around the ring.
Connect the two ends of different wires together.
The circuit can be placed inside a suitable housing.
The introduction of such a circuit into a flashlight operating on 3V significantly extends the duration of its operation from one set of batteries.

Option to make the flashlight powered by one 1.5V battery.

The transistor and resistance are placed inside the ferrite ring

The white LED runs on a dead AAA battery.

Modernization option "flashlight - pen"

The excitation of the blocking oscillator shown in the diagram is achieved by transformer coupling at T1. The voltage pulses arising in the right (according to the circuit) winding are added to the voltage of the power source and are supplied to the LED VD1. Of course, it would be possible to eliminate the capacitor and resistor in the base circuit of the transistor, but then failure of VT1 and VD1 is possible when using branded batteries with low internal resistance. The resistor sets the operating mode of the transistor, and the capacitor passes the RF component.

The circuit used a KT315 transistor (as the cheapest, but any other with a cutoff frequency of 200 MHz or more) and a super-bright LED were used. To make a transformer, you will need a ferrite ring (approximate size 10x6x3 and permeability of about 1000 HH). The wire diameter is about 0.2-0.3 mm. Two coils of 20 turns each are wound on the ring.
If there is no ring, then you can use a cylinder of similar volume and material. You just have to wind 60-100 turns for each of the coils.
Important point: you need to wind the coils in different directions.

Photos of the flashlight:
The switch is in the "fountain pen" button, and the gray metal cylinder conducts current.

We make a cylinder according to the standard size of the battery.

It can be made from paper, or use a piece of any rigid tube.
We make holes along the edges of the cylinder, wrap it with tinned wire, and pass the ends of the wire into the holes. We fix both ends, but leave a piece of conductor at one end so that we can connect the converter to the spiral.
A ferrite ring would not fit into the lantern, so a cylinder made of a similar material was used.

A cylinder made from an inductor from an old TV.
The first coil is about 60 turns.
Then the second one swings in the opposite direction again for 60 or so. The coils are held together with glue.

Assembling the converter:

Everything is located inside our case: We solder the transistor, the capacitor, the resistor, solder the spiral on the cylinder, and the coil. The current in the coil windings must go in different directions! That is, if you wound all the windings in one direction, then swap the leads of one of them, otherwise generation will not occur.

The result is the following:

We insert everything inside, and use nuts as side plugs and contacts.
We solder the coil leads to one of the nuts, and the VT1 emitter to the other. Glue it. We mark the conclusions: where we have the output from the coils we put “-”, where the output from the transistor with the coil we put “+” (so that everything is like in a battery).

Now you need to make a “lampodiode”.

Attention: There should be a minus LED on the base.

Assembly:

As is clear from the figure, the converter is a “substitute” for the second battery. But unlike it, it has three points of contact: with the plus of the battery, with the plus of the LED, and the common body (through the spiral).

Its location in the battery compartment is specific: it must be in contact with the positive of the LED.

LED flashlight circuit on a DC/DC converter from Analog Device - ADP1110.

Standard typical ADP1110 connection circuit.
This converter chip, according to the manufacturer’s specifications, is available in 8 versions:

	Output voltage
	Adjustable
	Adjustable

Microcircuits with the indices “N” and “R” differ only in the type of housing: R is more compact.
If you bought a chip with index -3.3, you can skip the next paragraph and go to the “Details” item.
If not, I present to your attention another diagram:

It adds two parts that make it possible to obtain the required 3.3 volts at the output to power the LEDs.
The circuit can be improved by taking into account that LEDs require a current source rather than a voltage source to operate. Changes in the circuit so that it produces 60mA (20 for each diode), and the voltage of the diodes will be set to us automatically, the same 3.3-3.9V.

resistor R1 is used to measure current. The converter is designed in such a way that when the voltage at the FB (Feed Back) pin exceeds 0.22V, it will stop increasing the voltage and current, which means the resistance value R1 is easy to calculate R1 = 0.22V/In, in our case 3.6 Ohm. This circuit helps stabilize the current and automatically select the required voltage. Unfortunately, the voltage will drop across this resistance, which will lead to a decrease in efficiency, however, practice has shown that it is less than the excess that we chose in the first case. I measured the output voltage, and it was V. The parameters of the diodes in such a connection should also be as identical as possible, otherwise the total current of 60 mA would not be distributed equally between them, and again we would get different luminosities.

Details
1. Any choke from 20 to 100 microhenry with a small (less than 0.4 Ohm) resistance is suitable. The diagram shows 47 µH. You can make it yourself - wind about 40 turns of PEV-0.25 wire on a ring of µ-permalloy with a permeability of about 50, size 10x4x5.
2. Schottky diode. 1N5818, 1N5819, 1N4148 or similar. Analog Device DOES NOT RECOMMEND the use of 1N4001
3. Capacitors. 47-100 microfarads at 6-10 volts. It is recommended to use tantalum.
4. Resistors. With a power of 0.125 watts and a resistance of 2 ohms, possibly 300 kohms and 2.2 kohms.
5. LEDs. L-53PWC - 4 pieces.

LED flashlight
Voltage converter for powering the DFL-OSPW5111P white LED with a brightness of 30 cd at a current of 80 mA and a radiation pattern width of about 12°.

The current consumed from a 2.41V battery is 143mA; in this case, a current of about 70 mA flows through the LED at a voltage of 4.17 V. The converter operates at a frequency of 13 kHz, the electrical efficiency is about 0.85.
Transformer T1 is wound on a ring magnetic core of standard size K10x6x3 made of 2000NM ferrite.

The primary and secondary windings of the transformer are wound simultaneously (i.e., in four wires).
The primary winding contains - 2x41 turns of wire PEV-2 0.19,
The secondary winding contains 2x44 turns of PEV-2 0.16 wire.
After winding, the terminals of the windings are connected in accordance with the diagram.

Transistors KT529A of the p-n-p structure can be replaced with KT530A of the n-p-n structure, in this case it is necessary to change the polarity of the connection of the battery GB1 and the LED HL1.
The parts are placed on the reflector using wall-mounted installation. Please ensure that there is no contact between the parts and the tin plate of the flashlight, which supplies the minus of the GB1 battery. The transistors are fastened together with a thin brass clamp, which provides the necessary heat removal, and then glued to the reflector. The LED is placed instead of the incandescent lamp so that it protrudes 0.5... 1 mm from the socket for its installation. This improves heat dissipation from the LED and simplifies its installation.
When first turned on, power from the battery is supplied through a resistor with a resistance of 18...24 Ohms so as not to damage the transistors if the terminals of transformer T1 are incorrectly connected. If the LED does not light, it is necessary to swap the extreme terminals of the primary or secondary winding of the transformer. If this does not lead to success, check the serviceability of all elements and correct installation.

Voltage converter for powering an industrial LED flashlight.

Voltage converter to power LED flashlight
The diagram is taken from the Zetex manual for the use of ZXSC310 microcircuits.
ZXSC310- LED driver chip.
FMMT 617 or FMMT 618.
Schottky diode- almost any brand.
Capacitors C1 = 2.2 µF and C2 = 10 µF for surface mounting, 2.2 µF is the value recommended by the manufacturer, and C2 can be supplied from approximately 1 to 10 µF

68 microhenry inductor at 0.4 A

The inductance and resistor are installed on one side of the board (where there is no printing), all other parts are installed on the other. The only trick is to make a 150 milliohm resistor. It can be made from 0.1 mm iron wire, which can be obtained by unraveling the cable. The wire should be annealed with a lighter, thoroughly wiped with fine sandpaper, the ends should be tinned and a piece about 3 cm long should be soldered into the holes on the board. Next, during the setup process, you need to measure the current through the diodes, move the wire, while simultaneously heating the place where it is soldered to the board with a soldering iron.

Thus, something like a rheostat is obtained. Having achieved a current of 20 mA, the soldering iron is removed and the unnecessary piece of wire is cut off. The author came up with a length of approximately 1 cm.

Flashlight on the power source

Rice. 3. Flashlight on a current source, with automatic equalization of current in LEDs, so that LEDs can have any range of parameters (LED VD2 sets the current, which is repeated by transistors VT2, VT3, so the currents in the branches will be the same)
The transistors, of course, should also be the same, but the spread of their parameters is not so critical, so you can take either discrete transistors, or if you can find three integrated transistors in one package, their parameters are as identical as possible. Play around with the placement of the LEDs, you need to choose an LED-transistor pair so that the output voltage is minimal, this will increase the efficiency.
The introduction of transistors leveled out the brightness, however, they have resistance and the voltage drops across them, which forces the converter to increase the output level to 4V. To reduce the voltage drop across the transistors, you can propose the circuit in Fig. 4, this is a modified current mirror, instead of the reference voltage Ube = 0.7V in the circuit in Fig. 3, you can use the 0.22V source built into the converter, and maintain it in the VT1 collector using an op-amp, also built into the converter.

Rice. 4. Flashlight on a current source, with automatic current equalization in LEDs, and with improved efficiency

Since the op-amp output is of the “open collector” type, it must be “pulled up” to the power supply, which is done by resistor R2. Resistances R3, R4 act as a voltage divider at point V2 by 2, so the opamp will maintain a voltage of 0.22*2 = 0.44V at point V2, which is 0.3V less than in the previous case. It is impossible to take an even smaller divider in order to lower the voltage at point V2. bipolar transistor has a resistance Rke and when operating on it the voltage Uke will drop; in order for the transistor to work correctly, V2-V1 must be greater than Uke, for our case 0.22V is quite enough. However, bipolar transistors can be replaced with field-effect transistors, in which the drain-source resistance is much lower, this will make it possible to reduce the divider, so as to make the difference V2-V1 very insignificant.

Throttle. The choke must be taken with minimal resistance, special attention should be paid to the maximum permissible current; it should be on the order of mA.
The rating doesn't matter as much as the maximum current, so Analog Devices recommends something between 33 and 180 µH. In this case, theoretically, if you do not pay attention to the dimensions, then the greater the inductance, the better in all respects. However, in practice this is not entirely true, since we do not have an ideal coil, it has active resistance and is not linear, in addition, the key transistor at low voltages will no longer produce 1.5A. Therefore, it is better to try several coils of different types, designs and different ratings in order to choose the coil with the highest efficiency and the lowest minimum input voltage, i.e. the coil with which the flashlight will glow for the longest possible time.

Capacitors. C1 can be anything. It is better to take C2 with tantalum because it has low resistance, which increases efficiency.

Schottky diode. Any for current up to 1A, preferably with minimal resistance and minimal voltage drop.

Transistors. Any with a collector current of up to 30 mA, coefficient. current amplification of about 80 with a frequency of up to 100 MHz, KT318 is suitable.

LEDs. You can use white NSPW500BS with a glow of 8000 mcd from Power Light Systems.

Voltage transformer ADP1110, or its replacement ADP1073, to use it, the circuit in Fig. 3 will need to be changed, take a 760 µH inductor, and R1 = 0.212/60mA = 3.5 Ohm.

Flashlight on ADP3000-ADJ

Options:
Power supply V, efficiency approx. 75%, two brightness modes - full and half.
The current through the diodes is 27 mA, in half-brightness mode - 13 mA.
In order to obtain high efficiency, it is advisable to use chip components in the circuit.
A correctly assembled circuit does not need adjustment.
The disadvantage of the circuit is the high (1.25V) voltage at the FB input (pin 8).
Currently, DC/DC converters with an FB voltage of about 0.3V are produced, in particular from Maxim, on which it is possible to achieve an efficiency above 85%.

Flashlight diagram for Kr1446PN1.

Resistors R1 and R2 are a current sensor. Operational amplifier U2B - amplifies the voltage taken from the current sensor. Gain = R4 / R3 + 1 and is approximately 19. The gain required is such that when the current through resistors R1 and R2 is 60 mA, the output voltage turns on transistor Q1. By changing these resistors, you can set other stabilization current values.
In principle, there is no need to install an operational amplifier. Simply, instead of R1 and R2, one 10 Ohm resistor is placed, from it the signal through a 1 kOhm resistor is supplied to the base of the transistor and that’s it. But. This will lead to a decrease in efficiency. On a 10 Ohm resistor at a current of 60 mA, 0.6 Volt - 36 mW - is dissipated in vain. If an operational amplifier is used, the losses will be:
on a 0.5 Ohm resistor at a current of 60 mA = 1.8 mW + consumption of the op-amp itself is 0.02 mA let at 4 Volts = 0.08 mW
= 1.88 mW - significantly less than 36 mW.

About the components.

Any low-power op-amp with a low minimum supply voltage can work in place of the KR1446UD2; the OP193FS would be better suited, but it is quite expensive. Transistor in SOT23 package. A smaller polar capacitor - type SS for 10 Volts. The inductance of CW68 is 100 μH for a current of 710 mA. Although the cutoff current of the inverter is 1 A, it works fine. It achieved the best efficiency. I selected the LEDs based on the most equal voltage drop at a current of 20 mA. The flashlight is assembled in a housing for two AA batteries. I shortened the space for the batteries to fit the size of AAA batteries, and in the freed-up space I assembled this circuit using wall-mounted installation. A case that fits three AA batteries works well. You will need to install only two, and place the circuit in place of the third.

Efficiency of the resulting device.
Input U I P Output U I P Efficiency
Volt mA mW Volt mA mW %
3.03 90 273 3.53 62 219 80
1.78 180 320 3.53 62 219 68
1.28 290 371 3.53 62 219 59

Replacing the bulb of the “Zhuchek” flashlight with a module from the company LuxeonLumiledLXHL-NW98.
We get a dazzlingly bright flashlight, with a very light press (compared to a light bulb).
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Power supply: 1 or 2 1.5V batteries, operability maintained up to Uinput = 0.9V
Consumption:
*with switch open S1 = 300mA
*with switch closed S1 = 110mA

LED Electronic Flashlight
Powered by just one AA or AAA AA battery on a microcircuit (KR1446PN1), which is a complete analogue of the MAX756 (MAX731) microcircuit and has almost identical characteristics.

The flashlight is based on a flashlight that uses two AA size AA batteries as a power source.
The converter board is placed in the flashlight instead of the second battery. A contact made of tinned sheet metal is soldered at one end of the board to power the circuit, and at the other there is an LED. A circle made of the same tin is placed on the LED terminals. The diameter of the circle should be slightly larger than the diameter of the reflector base (0.2-0.5 mm) into which the cartridge is inserted. One of the diode leads (negative) is soldered to the circle, the second (positive) goes through and is insulated with a piece of PVC or fluoroplastic tube. The purpose of the circle is twofold. It provides the structure with the necessary rigidity and at the same time serves to close the negative contact of the circuit. The lamp with the socket is removed from the lantern in advance and a circuit with an LED is placed in its place. Before installation on the board, the LED leads are shortened in such a way as to ensure a tight, play-free fit “in place.” Typically, the length of the leads (excluding soldering to the board) is equal to the length of the protruding part of the fully screwed-in lamp base.
The connection diagram between the board and the battery is shown in Fig. 9.2.
Next, the lantern is assembled and its functionality is checked. If the circuit is assembled correctly, then no settings are required.

The design uses standard installation elements: capacitors of the K50-35 type, EC-24 chokes with an inductance of 18-22 μH, LEDs with a brightness of 5-10 cd with a diameter of 5 or 10 mm. Of course, it is possible to use other LEDs with a supply voltage of 2.4-5 V. The circuit has sufficient power reserve and allows you to power even LEDs with a brightness of up to 25 cd!

About some test results of this design.
The flashlight modified in this way worked with a “fresh” battery without interruption, in the on state, for more than 20 hours! For comparison, the same flashlight in the “standard” configuration (that is, with a lamp and two “fresh” batteries from the same batch) worked for only 4 hours.
And one more important point. If you use rechargeable batteries in this design, it is easy to monitor the state of their discharge level. The fact is that the converter on the KR1446PN1 microcircuit starts stably at an input voltage of 0.8-0.9 V. And the glow of the LEDs is consistently bright until the voltage on the battery reaches this critical threshold. The lamp will, of course, still burn at this voltage, but we can hardly talk about it as real.

Rice. 9.2Figure 9.3

The printed circuit board of the device is shown in Fig. 9.3, and the arrangement of elements is in Fig. 9.4.

Turning the flashlight on and off with one button

The circuit is assembled using a CD4013 D-trigger chip and an IRF630 field-effect transistor in the “off” mode. the current consumption of the circuit is practically 0. For stable operation of the D-trigger, a filter resistor and capacitor are connected to the input of the microcircuit; their function is to eliminate contact bounce. It is better not to connect unused pins of the microcircuit anywhere. The microcircuit operates from 2 to 12 volts; any powerful field-effect transistor can be used as a power switch, since the drain-source resistance of the field-effect transistor is negligible and does not load the output of the microcircuit.

CD4013A in SO-14 package, analogue of K561TM2, 564TM2

Simple generator circuits.
Allows you to power an LED with an ignition voltage of 2-3V from 1-1.5V. Short pulses of increased potential unlock the p-n junction. The efficiency of course decreases, but this device allows you to “squeeze” almost its entire resource from an autonomous power source.
Wire 0.1 mm - 100-300 turns with a tap from the middle, wound on a toroidal ring.

LED flashlight with adjustable brightness and Beacon mode

The power supply of the microcircuit - generator with adjustable duty cycle (K561LE5 or 564LE5) that controls the electronic key, in the proposed device is carried out from a step-up voltage converter, which allows the flashlight to be powered from one 1.5 galvanic cell.
The converter is made on transistors VT1, VT2 according to the circuit of a transformer self-oscillator with positive current feedback.
The generator circuit with adjustable duty cycle on the K561LE5 chip mentioned above has been slightly modified in order to improve the linearity of current regulation.
The minimum current consumption of a flashlight with six super-bright white LEDs L-53MWC from Kingbnght connected in parallel is 2.3 mA. The dependence of the current consumption on the number of LEDs is directly proportional.
The "Beacon" mode, when the LEDs flash brightly at a low frequency and then go out, is implemented by setting the brightness control to maximum and turning the flashlight on again. The desired frequency of light flashes is adjusted by selecting the capacitor SZ.
The performance of the flashlight is maintained when the voltage is reduced to 1.1v, although the brightness is significantly reduced
A field-effect transistor with an insulated gate KP501A (KR1014KT1V) is used as an electronic switch. According to the control circuit, it matches well with the K561LE5 microcircuit. The KP501A transistor has the following limit parameters: drain-source voltage - 240 V; gate-source voltage - 20 V. drain current - 0.18 A; power - 0.5 W
It is permissible to connect transistors in parallel, preferably from the same batch. Possible replacement - KP504 with any letter index. For IRF540 field-effect transistors, the supply voltage of the DD1 microcircuit. generated by the converter must be increased to 10 V
In a flashlight with six L-53MWC LEDs connected in parallel, the current consumption is approximately equal to 120 mA when the second transistor is connected in parallel to VT3 - 140 mA
Transformer T1 is wound on a ferrite ring 2000NM K10-6"4.5. The windings are wound in two wires, with the end of the first winding connected to the beginning of the second winding. The primary winding contains 2-10 turns, the secondary - 2 * 20 turns. Wire diameter - 0.37 mm. grade - PEV-2. The inductor is wound on the same magnetic circuit without a gap with the same wire in one layer, the number of turns is 38. The inductance of the inductor is 860 μH

Converter circuit for LED from 0.4 to 3V- runs on one AAA battery. This flashlight increases the input voltage to the desired voltage using a simple DC-DC converter.

The output voltage is approximately 7 W (depending on the voltage of the installed LEDs).

BuildingtheLEDHeadLamp

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As for the transformer in the DC-DC converter. You must do it yourself. The image shows how to assemble the transformer.

Another option for converters for LEDs is _http://belza. cz/ledlight/ledm. htm

Chargers" href="/text/category/zaryadnie_ustrojstva/" rel="bookmark">charger.

Lead acid sealed batteries are the cheapest currently available. The electrolyte in them is in the form of a gel, so the batteries allow operation in any spatial position and do not produce any harmful fumes. They are characterized by great durability if deep discharge is not allowed. Theoretically, they are not afraid of overcharging, but this should not be abused. Rechargeable batteries can be recharged at any time without waiting for them to be completely discharged.
Lead acid sealed rechargeable batteries suitable for use in portable flashlights used in household, on summer cottages, in production.

Fig.1. Electric flashlight circuit

Electric circuit diagram flashlight with a charger for a 6-volt battery, allowing in a simple way prevent deep discharge battery and thus increase its service life is shown in the figure. It contains a factory-made or home-made transformer power supply and a charging and switching device mounted in the flashlight body.
In the author's version, a standard unit intended for powering modems is used as a transformer unit. The output alternating voltage of the unit is 12 or 15 V, the load current is 1 A. Such units are also available with built-in rectifiers. They are also suitable for this purpose.
AC voltage from the transformer unit goes to the charging and switching device containing a plug for connection charger X2, diode bridge VD1, current stabilizer (DA1, R1, HL1), battery GB, toggle switch S1, emergency button S2, incandescent lamp HL2. Each time the toggle switch S1 is turned on, the battery voltage is supplied to relay K1, its contacts K1.1 close, supplying current to the base of transistor VT1. The transistor turns on, passing current through the HL2 lamp. Turn off the flashlight by switching toggle switch S1 to its original position, in which the battery is disconnected from the winding of relay K1.
The permissible battery discharge voltage is selected at 4.5 V. It is determined by the switching voltage of relay K1. You can change the permissible value of the discharge voltage using resistor R2. As the resistor value increases, the permissible discharge voltage increases, and vice versa. If the battery voltage is below 4.5 V, the relay will not turn on, therefore, no voltage will be supplied to the base of the transistor VT1, which turns on the HL2 lamp. This means the battery needs charging. At a voltage of 4.5 V, the illumination produced by the flashlight is not bad. In case of emergency, you can turn on the flashlight at low voltage with the S2 button, provided that you first turn on the S1 toggle switch.
A constant voltage can also be supplied to the input of the charger-switching device, without paying attention to the polarity of the connected devices.
To switch the flashlight to charging mode, you need to connect the X1 socket of the transformer block to the X2 plug located on the flashlight body, and then connect the plug (not shown in the figure) of the transformer block to a 220 V network.
In this embodiment, a battery with a capacity of 4.2 Ah is used. Therefore, it can be charged with a current of 0.42 A. The battery is charged using direct current. The current stabilizer contains only three parts: an integrated voltage stabilizer DA1 type KR142EN5A or imported 7805, an LED HL1 and a resistor R1. The LED, in addition to working as a current stabilizer, also serves as an indicator of the battery charging mode.
Settings electrical diagram flashlight is reduced to adjusting the battery charging current. Charging current(in amperes) is usually chosen ten times less than the numerical value of the battery capacity (in ampere-hours).
To configure it, it is best to assemble the current stabilizer circuit separately. Instead of a battery load, connect an ammeter with a current of 2...5 A to the connection point between the cathode of the LED and resistor R1. By selecting resistor R1, set the calculated charge current using the ammeter.
Relay K1 – reed switch RES64, passport RS4.569.724. The HL2 lamp consumes approximately 1A current.
The KT829 transistor can be used with any letter index. These transistors are composite and have a high current gain of 750. This should be taken into account in case of replacement.
In the author's version, the DA1 chip is installed on a standard finned radiator with dimensions of 40x50x30 mm. Resistor R1 consists of two 12 W wirewound resistors connected in series.

Without a doubt, LEDs are by far the most economical and durable light sources. Appeared in last years new devices of this class have made a kind of revolution in the field of lighting and illumination. Widespread in everyday life LED bulbs, which came with the compact fluorescent lamps(CFLs) to replace uneconomical and short-lived incandescent lamps, and today they are increasingly replacing CFLs. Unfortunately, despite manufacturers’ assurances of durability, estimated at many tens of thousands of hours, LED lamps sometimes fail, much more ahead of schedule. And the reason is often not the quality of the LEDs, but, most likely, the stinginess of manufacturers: in order to save on the cost of lamps, the LEDs in them are forced to work in extreme conditions, at current values close to the maximum permissible, which has a noticeable effect on the rate of degradation of the crystal and phosphors, as well as on the reliability of the lamp. And if you consider that due to the small dimensions of the lamps, unsatisfactory cooling conditions for LEDs are added to the above, it is not surprising that sometimes such lamps fail after just a few hours of operation.

Analysis of faults of burnt-out lamps shows that in 90% of cases one of the LEDs fails, while the driver, as a rule, remains operational. Repairing such lamps is simple, but without taking measures to reduce the current through the remaining LEDs it is often useless: after some time the lamp fails again.

Consider the possibility of restoring a 7 W Elektrostandard lamp. Her appearance and a view of the driver board from the side of the printed conductors are shown in Fig. 1. First, you should find the burnt-out LED in any way and close it with a jumper. Next, you need to reduce the current through the LEDs. To monitor the current, a sensor consisting of two SMD resistors connected in parallel is used (circled in red in Fig. 1). To reduce the current, you need to unsolder them and solder a new one with a resistance of 2 Ohms in place of any of them. After such repairs, the power and luminous output of the lamp will decrease somewhat, but it will still be able to work long time. The above is fully applicable to similar 15 W lamps (Fig. 2). On their board, to reduce the current through the LEDs, you need to unsolder one of the 5.6 Ohm resistors (also circled in red).

Rice. 1. Elektrostandard lamp

Rice. 2. Elektrostandard lamp

But sometimes it is impossible to restore the lamp due to a controller failure. In this case, the LEDs can be powered from another source. Below we consider the option of connecting a board of LED lamps with a power of 5 or 7 W to a twelve-volt source (for example, car battery). Depending on the rated power, these lamps have 12 or 16 LEDs installed, respectively. Such a lamp can be useful for an emergency or car lamp. Since the LEDs are connected in series on the board, and I didn’t want to change the connection diagram by cutting printed conductors and installing wire jumpers, it was decided to make a converter that increases the battery voltage to the level necessary for the LEDs to glow with normal brightness (in in this case respectively up to 35 or 48 V).

A diagram of a simple converter assembled from widely available and inexpensive parts is shown in Fig. 3. Using a Schmitt trigger DD1.1, a master oscillator operating at a frequency of about 25 kHz is built according to a standard circuit. Elements DD1.2-DD1.6 connected in parallel invert the generator signal and increase its load capacity, providing fast charging and discharging of the capacitance of field-effect transistor VT2. The microcircuit is powered from the lamp power supply through a linear voltage regulator DA1, connected according to a standard circuit. The current sensor is resistor R5.

Rice. 3. Circuit of a simple converter

The stabilization circuit works as follows. If the current through the LEDs becomes greater than required, transistor VT1 opens, shunting the input of the Schmitt trigger DD1.1 with resistor R1. In this case, the duration of the control pulses supplied to the gate of the field-effect transistor VT2 decreases, and the duration of the pauses between them, on the contrary, increases. As a result, the current through the LEDs decreases. Current stabilization is carried out in the range of values input voltage from 9 to 15 V, which is quite enough for battery and car lamps. Resistor R3 serves to discharge capacitor C4 after turning off the converter (without it, the LEDs would glow faintly for a long time after turning off the power).

All details of the device are located on printed circuit board(Fig. 4), made of fiberglass foil on one side. Transistor VT2 does not need a heat sink, but if its body heats up noticeably during operation, you can, in addition to the contact pad on the board used as a heat sink, to which its drain pin is soldered, provide it with a small U-shaped heat sink made from a flattened piece copper wire cross section 2.5 mm 2 and length 20 mm. You can solder it either to the indicated area on the board (next to the transistor) or to the heat-sinking flange of the transistor itself. The appearance of the finished unit is shown in Fig. 5. The additional heat sink for the LED panel is made of aluminum alloy sheet, its appearance is also shown in this figure.

Rice. 4. Printed board and parts on it

Rice. 5. Appearance of the finished unit

A few words about the details. In addition to what is indicated in the diagram, any low-power transistor of the n-p-n structure for surface mounting can be used as VT1. Field-effect transistor (VT2) - any with a drain current of at least 2 A and a drain-source voltage of at least 80 V, designed to control logical levels. Possible replacement of the 74НСТ14 (DD1) microcircuit - from the 74НСТ14 or 74АС14 series. Instead of the RGP10J (VD1) diode, you can use a 1N4007, but it will heat up noticeably and the efficiency will decrease. Diodes of the KD226 series operate practically without heating. Throttle L1 is industrially manufactured in a cylindrical body, its type is unknown, and its appearance is shown in Fig. 5 (black cylinder in the lower left corner of the board).

If you cannot find a 5 V SMD integrated stabilizer, you can build a parametric stabilizer on a zener diode into the power circuit of the DD1 microcircuit. You can place it and a ballast resistor with a resistance of 1 kOhm on the microcircuit seat.

A device assembled from serviceable parts requires virtually no adjustment. When you turn on the converter for the first time, it is advisable to power it from laboratory block with an adjustable output voltage, gradually increasing it, starting from 5 V. If the LEDs do not light, you should check the polarity of their connection and the serviceability of the parts.

When using replacement microcircuits instead of those indicated in the diagram (DD1), it may be necessary to select capacitor C1 or inductor L1 for maximum efficiency. It may be necessary to select resistor R5 to obtain a current through the LEDs equal to 100 mA. If you don’t find the required resistor among those available, you can install R5 of obviously slightly higher resistance and select an additional resistor R5 connected in parallel to it (shown in the diagram with dashed lines), a place is provided for it on the board.

Next, you should check the range of input voltage values at which the current is stabilized through the LEDs. You can try to increase the efficiency of the converter by selecting the inductance of inductor L1. When setting up, you should remember that an open LED circuit can lead to breakdown of the field-effect transistor, so you need to be very careful.

Finally, the converter board should be coated with two layers of XB-784 varnish, this will protect it from moisture. When operating such a lamp, remember that when connecting it to a power source, the polarity must be observed.

One day, on the Internet, I came across quite simple circuit converter for powering LEDs from one AA battery. After assembly, I was upset because the circuit turned out to be inoperative. In half an hour, the circuit was brought into working condition, the ratings of the radio components were changed, and unnecessary parts were removed, and the result was a fairly high-quality converter that is capable of powering LEDs with a power of up to 1 Watt.

The circuit itself consists of 4 parts and a throttle. Fortunately, a ready-made SMD choke was found (soldered from the radiotelephone board), but making it is also not a problem. The choke can be made on a ring from fluorescent lamps (available on all energy saving boards), contains 15 turns of wire 0.15 - 0.2 mm.

Unfortunately, I never found a direct conduction transistor in the SMD version and a powerful bipolar transistor of the KT818 series was used, but for compactness I highly recommend using SMD transistors. The second reverse conduction transistor, literally any one will do, for example the well-known KT315.

The basic resistor is 1 kilo-ohm, it is also advisable to use it in the SMD version.
A 1000 picofarad capacitor is not critical, you can deviate by 50% in one direction or another (it worked for me even with a 0.1 microfarad capacitor, but the LED will glow weaker).

For demonstration, the circuit was assembled on a breadboard. The current consumption is 35 - 40 mA, but it increases sharply if you power the LEDs at 1 watt; the circuit does not allow more, since the maximum output current at peak is 300 mA.

The circuit starts at 0.7 volts. The maximum supply voltage is no more than 2.5 volts; if you supply more, the circuit simply will not work. The output voltage is 3.8 volts at the specified inductor parameters.

List of radioelements

Designation	Type	Denomination	Quantity	My notepad
	Bipolar transistor	KT315A	1	To notepad
	Bipolar transistor	KT818A	1	To notepad
C1	Capacitor	1 nF	1	To notepad
	Resistor	1 kOhm	1	To notepad
L1	Inductor		1	To notepad
HL1	Light-emitting diode		1