Network power supply on tl494 diagram. Do-it-yourself switching power supply. TL494CN chip design
TL494 in a complete power supply
http://www.radiokot.ru/circuit/power/supply/38/
More than a year has passed since I seriously took up the topic of power supplies. I read the wonderful books by Marty Brown "Power Sources" and Semenov "Power Electronics". As a result, I noticed a lot of errors in the circuits from the Internet, and recently I see only a cruel mockery of my favorite TL494 chip.
I love the TL494 for its versatility, probably there is no such power supply that could not be implemented on it. In this case, I want to consider the implementation of the most interesting half-bridge topology. The control of the half-bridge transistors is made galvanically isolated, this requires a lot of elements, in principle, a converter inside the converter. Despite the fact that there are many half-bridge drivers, it is too early to write off the use of a transformer (GDT) as a driver, this method is the most reliable. Bootstrap drivers exploded, but I have not yet observed the explosion of GDT. The driver transformer is a conventional pulse transformer, calculated using the same formulas as the power transformer, taking into account the buildup scheme. Often I have seen the use of high power transistors in GDT drive. The microcircuit outputs can deliver 200 milliamps of current, and in the case of a well-built driver, this is a lot, I personally swung the IRF740 and even the IRFP460 at a frequency of 100 kilohertz. Let's look at the scheme of this driver:
This circuit is connected to each output winding of the GDT. The fact is that at the moment of dead time, the primary winding of the transformer turns out to be open, and the secondary windings are not loaded, so the discharge of the gates through the winding itself will take an extremely long time, the introduction of a supporting, discharge resistor will prevent the gate from charging quickly and eat a lot of energy wasted. The circuit in the figure is free from these shortcomings. The fronts measured on a real layout were 160ns rising and 120ns falling at the gate of the IRF740 transistor.
The transistors that complement the bridge in the GDT buildup are similarly constructed. The use of bridge buildup is due to the fact that before the tl494 power trigger is triggered upon reaching 7 volts, the output transistors of the microcircuit will be open, if the transformer is turned on as a push-pool, a short circuit will occur. The bridge is stable.
The VD6 diode bridge rectifies the voltage from the primary winding, and if it exceeds the supply voltage, it will return it back to capacitor C2. This happens due to the appearance of a reverse voltage, all the same, the inductance of the transformer is not infinite.
The circuit can be powered through a quenching capacitor, now a 400 volt k73-17 is working at 1.6 microfarads. diodes kd522 or much better than 1n4148, replacement with more powerful 1n4007 is possible. The input bridge can be built on 1n4007 or use a prefabricated kts407. On the board, kts407 was mistakenly used as VD6, in no case should it be put there, this bridge must be made on high-frequency diodes. The VT4 transistor can dissipate up to 2 watts of heat, but it plays a purely protective role, you can use kt814. The remaining transistors are kt361, and replacement with low-frequency kt814 is highly undesirable. The master oscillator tl494 is tuned here to a frequency of 200 kilohertz, which means that in push-pull mode we get 100 kilohertz. We wind the GDT on a ferrite ring 1-2 centimeters in diameter. Wire 0.2-0.3mm. There should be ten times more turns than the calculated value, this greatly improves the shape of the output signal. The more wound - the less you need to load the GDT with resistor R2. I wound 3 windings of 70 turns on a ring with an outer diameter of 18mm. The overestimation of the number of turns and the mandatory loading with the triangular component of the current are connected, it decreases with an increase in the turns, and the loading simply reduces its percentage effect. The printed circuit board is attached, but it does not quite correspond to the circuit, but there are main blocks on it, plus a body kit for one error amplifier and a series stabilizer for power supply from the transformer. The board is made for installation in the section of the power unit board.
Stabilized half-bridge switching power supply
1
Diodes at the output with a recovery time of no more than 100 ns. Diodes from the HER (High Efficiency Rectifier) family meet these requirements. Not to be confused with Schottky diodes. |
Switching power supplies are often used by radio amateurs in homemade designs. With relatively small dimensions, they can provide high output power. With the use of a pulse circuit, it became realistic to obtain an output power from several hundred to several thousand watts. At the same time, the dimensions of the pulse transformer itself are no larger than a matchbox.
Switching power supplies - principle of operation and features
The main feature of switching power supplies is an increased operating frequency, which is hundreds of times greater than the mains frequency of 50 Hz. At high frequencies with a minimum number of turns in the windings, a high voltage can be obtained. For example, to obtain a 12 Volt output voltage at a current of 1 Ampere (in the case of a network transformer), you need to wind 5 turns of wire with a cross section of approximately 0.6–0.7 mm.
If we talk about a pulse transformer, the driving circuit of which operates at a frequency of 65 kHz, then to get 12 Volts with a current of 1A, it is enough to wind only 3 turns with a wire of 0.25–0.3 mm. That is why many electronics manufacturers use a switching power supply.
However, despite the fact that such blocks are much cheaper, more compact, have high power and low weight, they have electronic filling, therefore, they are less reliable when compared with a network transformer. Proving their unreliability is very simple - take any switching power supply without protection and close the output terminals. At best, the block will fail, at worst, it will explode and no fuse will save the block.
Practice shows that the fuse in the switching power supply burns out last, the power switches and the master generator fly out first, then all parts of the circuit in turn.
Pulse power supplies have a number of protections both at the input and at the output, but they do not always save. In order to limit the inrush current at the start of the circuit, almost all SMPS with a power of more than 50 watts use a thermistor that is at the input of the circuits.
Let's now look at the TOP 3 best switching power supply circuits that you can assemble with your own hands.
A simple do-it-yourself switching power supply
Consider how to make the simplest miniature switching power supply. Any novice radio amateur can create a device according to the presented scheme. It is not only compact, but also operates in a wide range of supply voltages.
A home-made switching power supply has a relatively small power, within 2 watts, but it is literally indestructible, not afraid of even long-term short circuits.
Scheme of a simple switching power supply
The power supply is a low-power switching autogenerator type power supply, assembled on just one transistor. The oscillator is powered from the network through a current-limiting resistor R1 and a half-wave rectifier in the form of a diode VD1.
Transformer of a simple switching power supply
The pulse transformer has three windings, collector or primary, base winding and secondary.
An important point is the winding of the transformer - both the printed circuit board and the diagram indicate the beginning of the windings, so there should be no problems. We borrowed the number of turns of the windings from a transformer for charging cell phones, since the circuitry is almost the same, the number of windings is the same.
First we wind the primary winding, which consists of 200 turns, the wire cross section is from 0.08 to 0.1 mm. Then we put the insulation and wind the base winding with the same wire, which contains from 5 to 10 turns.
We wind the output winding on top, the number of its turns depends on what voltage is needed. On average, about 1 volt per turn is obtained.
Video about testing this power supply:
Do-it-yourself stabilized switching power supply on the SG3525
Consider step by step how to make a stabilized power supply on the SG3525 chip. Let's talk about the advantages of this scheme. The first and most important is the stabilization of the output voltage. There is also a soft start, short circuit protection and self-recording.
First, let's look at the device diagram.
Beginners will immediately pay attention to 2 transformers. In the circuit, one of them is power, and the second is for galvanic isolation.
Do not think that because of this the scheme will become more complicated. On the contrary, everything becomes easier, safer and cheaper. For example, if you put a driver at the output of the microcircuit, then you need a strapping for it.
Let's look further. In this scheme, a microstart and self-starter are implemented.
This is a very productive solution, it allows you to get rid of the need for a standby power supply. Indeed, making a power supply for a power supply is not a good idea, but such a solution is just perfect.
Everything works as follows: a capacitor is charged from a constant, and when its voltage exceeds a predetermined level, this block opens and discharges the capacitor into the circuit.
Its energy is quite enough to start the microcircuit, and as soon as it starts, the voltage from the secondary winding begins to feed the microcircuit itself. It is also necessary to add this output resistor to the microstart, it serves as a load.
Without this resistor, the unit will not start. This resistor is different for each voltage and must be calculated from such considerations that at the rated output voltage 1 W of power was dissipated on it.
We consider the resistance of the resistor:
R = U squared/P
R = 24 squared/1
R = 576/1 = 560 ohms.
Also on the diagram there is a soft start. It is implemented using this capacitor.
And current protection, which in the event of a short circuit will begin to reduce the width of the PWM.
The frequency of this power supply is changed with the help of this resistor and a condender.
Now let's talk about the most important thing - stabilizing the output voltage. These elements are responsible for it:
As you can see, 2 zener diodes are installed here. With their help, you can get any voltage at the output.
Calculation of voltage stabilization:
U out \u003d 2 + U stub1 + U stub2
U out \u003d 2 + 11 + 11 \u003d 24V
An error of + - 0.5 V is possible.
In order for the stabilization to work correctly, a voltage margin in the transformer is needed, otherwise, if the input voltage decreases, the microcircuit simply will not be able to produce the desired voltage. Therefore, when calculating the transformer, you should click on this button and the program will automatically add voltage to the secondary winding for a reserve.
Now we can move on to the consideration of the printed circuit board. As you can see, everything is pretty compact here. We also see a place for a transformer, it is toroidal. Without any problems, it can be replaced with a W-shaped one.
The optocoupler and zener diodes are located near the microcircuit, and not at the output.
Well, there was nowhere to put them on the way out. If you don't like it, make your own PCB layout.
You may ask, why not increase the fee and do everything right? The answer is the following: this was done with the expectation that it would be cheaper to order a board in production, since boards larger than 100 square meters. mm are much more expensive.
Well, now it's time to assemble the scheme. Everything is standard here. We solder without any problems. We wind the transformer and install it.
Check the output voltage. If it is present, then it can already be included in the network.
First, let's check the output voltage. As you can see, the block is designed for a voltage of 24V, but it turned out a little less due to the spread of the zener diodes.
This error is not critical.
Now let's check the most important thing - stabilization. To do this, take a 24V lamp with a power of 100W and connect it to the load.
As you can see, the voltage did not subside and the block withstood without problems. You can load even more.
Video about this switching power supply:
We reviewed the TOP 3 best switching power supply circuits. Based on them, you can assemble a simple PSU, devices on the TL494 and SG3525. Step-by-step photos and videos will help you understand all the installation issues.
SWITCH POWER SUPPLY ON TL494 AND IR2110
Most automotive and network voltage converters are based on a specialized TL494 controller, and since it is the main one, it would not be fair not to briefly talk about the principle of its operation.
The TL494 controller is a DIP16 plastic case (there are options in a planar case, but it is not used in these designs). The functional diagram of the controller is shown in Fig.1.
Figure 1 - Block diagram of the TL494 chip.
As can be seen from the figure, the TL494 microcircuit has very developed control circuits, which makes it possible to build converters on its basis for almost any requirements, but first a few words about the functional units of the controller.
ION and undervoltage protection circuits.
The circuit turns on when the power supply reaches the threshold of 5.5..7.0 V (typical value 6.4V). Up to this point, the internal control buses disable the operation of the generator and the logic part of the circuit. No-load current at +15V supply voltage (output transistors disabled) no more than 10 mA. ION +5V (+4.75..+5.25 V, output stabilization not worse than +/- 25mV) provides outflow current up to 10 mA. It is possible to amplify the ION only using an npn-emitter follower (see TI pages 19-20), but the voltage at the output of such a "stabilizer" will strongly depend on the load current.
Generator generates on the timing capacitor Ct (pin 5) a sawtooth voltage of 0..+3.0V (amplitude set by ION) for TL494 Texas Instruments and 0...+2.8V for TL494 Motorola (what can we expect from others?), respectively for TI F =1.0/(RtCt), for Motorola F=1.1/(RtCt).
Permissible operating frequencies
from 1 to 300 kHz, while the recommended range is Rt = 1...500kΩ, Ct=470pF...10uF. In this case, the typical temperature drift of the frequency is (of course, without taking into account the drift of attached components) +/-3%, and the frequency drift depending on the supply voltage is within 0.1% in the entire allowable range.
For remote shutdown
generator, you can use an external key to close the input Rt (6) to the output of the ION, or - close Ct to the ground. Of course, the leakage resistance of the open switch must be taken into account when choosing Rt, Ct.
Resting phase control input
(duty cycle) through the rest phase comparator sets the required minimum pause between pulses in the arms of the circuit. This is necessary both to prevent through current in the power stages outside the IC, and for the stable operation of the trigger - the switching time of the digital part of the TL494 is 200 ns. The output signal is enabled when the saw on Ct exceeds the voltage at control input 4 (DT). At clock frequencies up to 150 kHz at zero control voltage, the rest phase = 3% of the period (equivalent control signal offset 100..120 mV), at high frequencies, the built-in correction extends the rest phase to 200..300 ns.
Using the DT input circuit, it is possible to set a fixed rest phase (R-R divider), soft start mode (R-C), remote shutdown (key), and also use DT as a linear control input. The input circuit is made up of pnp transistors, so the input current (up to 1.0 uA) flows out of the IC and does not flow into it. The current is quite large, so high-resistance resistors (no more than 100 kOhm) should be avoided. See TI, page 23 for an example of surge protection using a TL430 (431) 3-pin zener diode.
Error Amplifiers
- in fact, operational amplifiers with Ku=70..95dB DC voltage (60 dB for early series), Ku=1 at 350 kHz. The input circuits are assembled on pnp transistors, so the input current (up to 1.0 µA) flows out of the IC and does not flow into it. The current is large enough for the op-amp, the bias voltage is also (up to 10mV), so high-resistance resistors in control circuits (no more than 100 kOhm) should be avoided. But thanks to the use of pnp inputs, the input voltage range is from -0.3V to Vsupply-2V
When using an RC frequency-dependent OS, it should be remembered that the output of the amplifiers is actually single-ended (serial diode!), So charging the capacitance (up) will charge it, and down - it will take a long time to discharge. The voltage at this output is in the range of 0..+3.5V (a little more than the amplitude of the generator), then the voltage coefficient drops sharply and at about 4.5V at the output the amplifiers saturate. Likewise, low-resistance resistors should be avoided in the output circuit of amplifiers (OS loops).
Amplifiers are not designed to operate within one cycle of the operating frequency. With a signal propagation delay inside the amplifier of 400 ns, they are too slow for this, and the trigger control logic does not allow (there would be side pulses at the output). In real PN circuits, the cutoff frequency of the OS circuit is selected on the order of 200-10000 Hz.
Trigger and output control logic
- With a supply voltage of at least 7V, if the saw voltage on the generator is greater than on the control input DT, and if the saw voltage is greater than on any of the error amplifiers (taking into account the built-in thresholds and offsets) - the output of the circuit is allowed. When the generator is reset from maximum to zero, the outputs are disabled. A trigger with a two-phase output divides the frequency in half. With a logical 0 at input 13 (output mode), the trigger phases are combined by OR and are fed simultaneously to both outputs, with a logical 1, they are fed paraphase to each output separately.
Output transistors
- npn Darlingtons with built-in thermal protection (but no current protection). Thus, the minimum voltage drop between the collector (usually closed to the positive bus) and the emitter (at the load) is 1.5V (typical at 200 mA), and in a common emitter circuit it is slightly better, 1.1V typical. The maximum output current (with one open transistor) is limited to 500 mA, the maximum power for the entire crystal is 1W.
Switching power supplies are gradually replacing their traditional relatives in sound engineering, since they look noticeably more attractive both economically and overall. The same factor that switching power supplies contribute to the distortion of the amplifier, namely the appearance of additional overtones, is already losing its relevance mainly for two reasons - the modern element base allows you to design converters with a conversion frequency significantly higher than 40 kHz, therefore, the power supply modulation introduced by the power supply will be in ultrasound. In addition, a higher power frequency is much easier to filter out, and the use of two L-shaped LC filters in the power circuits already sufficiently smoothes the ripple at these frequencies.
Of course, there is also a fly in the ointment in this barrel of honey - the difference in price between a typical power supply for a power amplifier and a switching one becomes more noticeable with an increase in the power of this unit, i.e. the more powerful the power supply, the more profitable it is in relation to its typical counterpart.
And that is not all. When using switching power supplies, it is necessary to adhere to the rules for mounting high-frequency devices, namely the use of additional screens, the supply of a common wire to the heat sinks of the power part, as well as the correct wiring of the ground and the connection of shielding braids and conductors.
After a small lyrical digression about the features of switching power supplies for power amplifiers, the actual circuit diagram of a 400W power supply:
Figure 1. Schematic diagram of a switching power supply for power amplifiers up to 400 W
ENLARGE IN GOOD QUALITY
The control controller in this power supply is TL494. Of course, there are more modern ICs for this task, but we use this particular controller for two reasons - it is VERY easy to get. For quite a long time, no quality problems were found in the manufactured power supplies TL494 from Texas Instruments. The error amplifier is covered by the OOS, which makes it possible to achieve a fairly large coefficient. stabilization (ratio of resistors R4 and R6).
After the TL494 controller, there is a half-bridge driver IR2110, which actually controls the gates of power transistors. The use of the driver made it possible to abandon the matching transformer, which is widely used in computer power supplies. The IR2110 driver is loaded on the shutters through the R24-VD4 and R25-VD5 chains accelerating the closing of the field workers.
Power switches VT2 and VT3 work on the primary winding of the power transformer. The midpoint required to obtain an alternating voltage in the primary winding of the transformer is formed by the elements R30-C26 and R31-C27.
A few words about the algorithm of the switching power supply on the TL494:
At the moment the mains voltage of 220 V is applied, the capacitances of the primary power filters C15 and C16 are infected through resistors R8 and R11, which does not allow the diol bridge VD to be overloaded with a short-circuit current of fully discharged C15 and C16. At the same time, capacitors C1, C3, C6, C19 are charged through a line of resistors R16, R18, R20 and R22, a 7815 stabilizer and a resistor R21.
As soon as the voltage on the capacitor C6 reaches 12 V, the zener diode VD1 "breaks through" and current begins to flow through it, charging the capacitor C18, and as soon as the positive terminal of this capacitor reaches a value sufficient to open the thyristor VS2, it will open. This will turn on relay K1, which will shunt the current-limiting resistors R8 and R11 with its contacts. In addition, the opened thyristor VS2 will open the VT1 transistor to the TL494 controller and the IR2110 half-bridge driver. The controller will enter the soft start mode, the duration of which depends on the ratings of R7 and C13.
During a soft start, the duration of the pulses that open the power transistors increase gradually, thereby gradually charging the secondary power capacitors and limiting the current through the rectifier diodes. The duration increases until the amount of secondary power is sufficient to turn on the LED of optocoupler IC1. As soon as the brightness of the optocoupler LED becomes sufficient to open the transistor, the pulse duration will stop increasing (Figure 2).
Figure 2. Soft start mode.
It should be noted here that the duration of the soft start is limited, since the current passing through the resistors R16, R18, R20, R22 is not enough to power the TL494 controller, the IR2110 driver and the relay winding turned on - the supply voltage of these microcircuits will begin to decrease and soon decrease to a value at which TL494 will stop generating control pulses. And just before this moment, the soft start mode should be over and the converter should enter the normal mode of operation, since the main power supply for the TL494 controller and the IR2110 driver is obtained from the power transformer (VD9, VD10 - rectifier with a midpoint, R23-C1-C3 - RC filter , IC3 is a 15 V stabilizer) and that is why the capacitors C1, C3, C6, C19 have such high ratings - they must hold the controller's power supply until it returns to normal operation.
The TL494 stabilizes the output voltage by changing the duration of the control pulses of power transistors at a constant frequency - Pulse Width Modulation - PWM. This is possible only if the value of the secondary voltage of the power transformer is higher than that required at the output of the stabilizer by at least 30%, but not more than 60%.
Figure 3. The principle of operation of the PWM stabilizer.
As the load increases, the output voltage begins to decrease, the optocoupler LED IC1 starts to glow less, the optocoupler transistor closes, reducing the voltage at the error amplifier and thereby increasing the duration of the control pulses until the effective voltage reaches the stabilization value (Figure 3). When the load decreases, the voltage will begin to increase, the LED of the optocoupler IC1 will begin to glow brighter, thereby opening the transistor and reducing the duration of the control pulses until the value of the effective value of the output voltage decreases to a stabilized value. The value of the stabilized voltage is regulated by a tuning resistor R26.
It should be noted that the TL494 controller does not regulate the duration of each pulse depending on the output voltage, but only the average value, i.e. the measuring part has some inertia. However, even with installed capacitors in the secondary power supply with a capacity of 2200 uF, power failures at peak short-term loads do not exceed 5%, which is quite acceptable for HI-FI class equipment. We usually put capacitors in the secondary power supply of 4700 uF, which gives a confident margin for peak values, and the use of a group stabilization choke allows you to control all 4 output power voltages.
This switching power supply is equipped with overload protection, the measuring element of which is the current transformer TV1. As soon as the current reaches a critical value, the thyristor VS1 opens and shunts the power supply of the final stage of the controller. The control pulses disappear and the power supply goes into standby mode, which can be in standby mode for quite a long time, since the VS2 thyristor continues to remain open - the current flowing through the resistors R16, R18, R20 and R22 is enough to keep it open. How to calculate current transformer.
To bring the power supply out of standby mode, you must press the SA3 button, which will shunt the VS2 thyristor with its contacts, the current will stop flowing through it and it will close. As soon as the SA3 contacts open, the VT1 transistor closes itself, removing power from the controller and driver. Thus, the control circuit will switch to the minimum consumption mode - the thyristor VS2 is closed, therefore the relay K1 is off, the transistor VT1 is closed, therefore the controller and driver are de-energized. Capacitors C1, C3, C6 and C19 begin to charge and as soon as the voltage reaches 12 V, the thyristor VS2 will open and the switching power supply will start.
If necessary, put the power supply into standby mode, you can use the SA2 button, when pressed, the base and emitter of the transistor VT1 will be connected. The transistor will close and de-energize the controller and driver. The control impulses will disappear, and the secondary voltages will also disappear. However, the power will not be removed from the relay K1 and the converter will not restart.
This circuitry allows you to assemble power supplies from 300-400 W to 2000 W, of course, that some elements of the circuit will have to be replaced, because according to their parameters they simply cannot withstand heavy loads.
When assembling more powerful options, you should pay attention to the capacitors of the smoothing filters of the primary power supply C15 and C16. The total capacitance of these capacitors must be proportional to the power of the power supply and correspond to the proportion of 1 W of the output power of the voltage converter corresponds to 1 μF of the capacitance of the primary power filter capacitor. In other words, if the power supply is 400 W, then 2 220 uF capacitors should be used, if the power is 1000 W, then 2 470 uF capacitors or two 680 uF capacitors must be installed.
This requirement has two purposes. First, the ripple of the primary supply voltage is reduced, which makes it easier to stabilize the output voltage. Secondly, the use of two capacitors instead of one facilitates the work of the capacitor itself, since the electrolytic capacitors of the TK series are much easier to get, and they are not entirely intended for use in high-frequency power supplies - the internal resistance is too high and at high frequencies these capacitors will heat up. Using two pieces, the internal resistance is reduced, and the resulting heating is already divided between the two capacitors.
When used as power transistors IRF740, IRF840, STP10NK60 and similar ones (for more details on the most commonly used transistors in network converters, see the table at the bottom of the page), you can refuse the VD4 and VD5 diodes altogether, and reduce the values \u200b\u200bof the resistors R24 and R25 to 22 Ohms - power the IR2110 driver is enough to drive these transistors. If a more powerful switching power supply is assembled, then more powerful transistors will be required. Attention should be paid to both the maximum current of the transistor and its dissipation power - pulse stabilized power supplies are very sensitive to the correctness of the supplied snubber and without it, power transistors heat up more because currents formed due to self-induction begin to flow through the diodes installed in the transistors. Learn more about choosing a snubber.
Also, the increase in closing time without a snubber makes a significant contribution to heating - the transistor is longer in linear mode.
Quite often, they forget about one more feature of field-effect transistors - with increasing temperature, their maximum current decreases, and quite strongly. Based on this, when choosing power transistors for switching power supplies, you should have at least a two-fold margin for maximum current for power supplies of power amplifiers and three times for devices operating on a large unchanging load, such as an induction smelter or decorative lighting, powering a low-voltage power tool.
Stabilization of the output voltage is carried out due to the group stabilization choke L1 (DGS). Pay attention to the direction of the windings of this inductor. The number of turns should be proportional to the output voltages. Of course, there are formulas for calculating this winding assembly, but experience has shown that the overall power of the core for a DGS should be 20-25% of the overall power of a power transformer. You can wind until the window is filled by about 2/3, not forgetting that if the output voltages are different, then the winding with a higher voltage should be proportionally larger, for example, you need two bipolar voltages, one for ± 35 V, and the second to power the subwoofer with voltage ±50 V.
We wind the DGS into four wires at once until 2/3 of the window is filled, counting the turns. The diameter is calculated based on the current intensity of 3-4 A / mm2. Let's say we got 22 turns, we make up the proportion:
22 turns / 35 V = X turns / 50 V.
X turns = 22 × 50 / 35 = 31.4 ≈ 31 turns
Next, we cut two wires for ± 35 V and wind 9 more turns for a voltage of ± 50.
ATTENTION! Remember that the quality of stabilization directly depends on how quickly the voltage changes to which the optocoupler diode is connected. To improve the cof styling, it makes sense to connect an additional load to each voltage in the form of 2 W resistors and a resistance of 3.3 kOhm. The load resistor connected to the voltage controlled by the optocoupler must be 1.7 ... 2.2 times less.
Winding data data for network switching power supplies on ferrite rings with a permeability of 2000NM are summarized in table 1.
WINDING DATA FOR PULSE TRANSFORMERS |
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
However, it is far from always possible to find out the brand of ferrite, especially if it is ferrite from line transformers of TVs. You can get out of the situation by finding out the number of turns empirically. More details about this in the video:
Using the above circuitry of a switching power supply, several submodifications were developed and tested, designed to solve a particular problem for various powers. The printed circuit board drawings of these power supplies are shown below.
Printed circuit board for a pulse stabilized power supply with a power of up to 1200 ... 1500 W. Board size 269x130 mm. In fact, this is a more advanced version of the previous printed circuit board. It is distinguished by the presence of a group stabilization choke that allows you to control the magnitude of all power voltages, as well as an additional LC filter. It has fan control and overload protection. The output voltages consist of two bipolar power sources and one bipolar low-current source designed to power the preliminary stages.
The appearance of the printed circuit board of the power supply up to 1500 W. DOWNLOAD IN LAY FORMAT
A stabilized switching power supply with a power of up to 1500 ... 1800 W can be made on a printed circuit board 272x100 mm in size. The power supply is designed for a power transformer made on K45 rings and located horizontally. It has two power bipolar sources that can be combined into one source to power the amplifier with two-level power supply and one bipolar low-current source for preliminary stages.
Circuit board switching power supply up to 1800 W. DOWNLOAD IN LAY FORMAT
This power supply can be used to power high power automotive equipment, such as high power car amplifiers, car air conditioners. The dimensions of the board are 188x123. The used Schottky rectifier diodes can be bridged and the output current can reach 120 A at a voltage of 14 V. In addition, the power supply can produce a bipolar voltage with a load capacity of up to 1 A (the installed integrated voltage stabilizers no longer allow). The power transformer is made on K45 rings, the power voltage filtering choke on yes two K40x25x11 rings. Built-in overload protection.
The appearance of the printed circuit board power supply for automotive equipment DOWNLOAD IN LAY FORMAT
The power supply up to 2000 W is made on two boards 275x99 in size, located one above the other. The voltage is controlled by one voltage. Has overload protection. The file contains several variants of the "second floor" for two bipolar voltages, for two unipolar voltages, for the voltages required for two and three level voltages. The power transformer is located horizontally and is made on K45 rings.
The appearance of the "two-story" power supply DOWNLOAD IN LAY FORMAT
The power supply with two bipolar voltages or one for a two-level amplifier is made on a 277x154 board. It has a group stabilization choke, overload protection. The power transformer is on K45 rings and is located horizontally. Power up to 2000 W.
The appearance of the printed circuit board DOWNLOAD IN LAY FORMAT
Almost the same power supply as above, but has one bipolar output voltage.
The appearance of the printed circuit board DOWNLOAD IN LAY FORMAT
The switching power supply has two power bipolar stabilized voltages and one bipolar low-current. Equipped with fan control and overload protection. It has a group stabilization choke and additional LC filters. Power up to 2000...2400 W. The board has dimensions of 278x146 mm
The appearance of the printed circuit board DOWNLOAD IN LAY FORMAT
The printed circuit board of a switching power supply for a power amplifier with two-level power supply with a size of 284x184 mm has a group stabilization choke and additional LC filters, overload protection and fan control. A distinctive feature is the use of discrete transistors to speed up the closing of power transistors. Power up to 2500...2800 W.
with two-level power supply DOWNLOAD IN LAY FORMAT
A slightly modified version of the previous PCB with two bipolar voltages. Size 285x172. Power up to 3000 W.
The appearance of the printed circuit board of the power supply for the amplifier DOWNLOAD IN LAY FORMAT
Bridge network switching power supply with a power of up to 4000...4500 W is made on a printed circuit board measuring 269x198 mm. It has two bipolar power voltages, fan control and overload protection. Uses a group stabilization choke. It is desirable to use external additional secondary power filters L.
The appearance of the printed circuit board of the power supply for the amplifier DOWNLOAD IN LAY FORMAT
There is much more space for ferrites on the boards than it could be. The fact is that it is far from always necessary to go beyond the limits of the sound range. Therefore, additional areas on the boards are provided. Just in case, a small selection of reference data on power transistors and links where I would buy them. By the way, I have ordered both TL494 and IR2110 more than once, and of course power transistors. True, he took far from the entire range, but marriage has not yet come across.
POPULAR TRANSISTORS FOR SWITCHED POWER SUPPLY |
|||||||
NAME |
VOLTAGE |
POWER |
CAPACITY |
Qg |
|||
This project is one of the longest I've done. One person ordered a power supply for a power amplifier.
Never before had a chance to make such powerful pulses of a stabilized type, although experience in assembling IIP pretty big. There were many problems during the build. Initially, I want to say that the scheme is often found on the network, or more precisely, on the intervalka website, but .... the scheme is initially not ideal, with errors and most likely will not work if assembled exactly according to the scheme from the site.
In particular, I changed the generator connection diagram, took the diagram from the datasheet. I redid the power supply unit of the control circuit, instead of parallel-connected 2-watt resistors, I used a separate SMPS 15 Volt 2 Ampere, which made it possible to get rid of many troubles.
I replaced some components for my convenience and launched everything in parts, setting up each node separately.
A few words about the design of the power supply. This is a powerful switching power supply unit in bridge topology, it has output voltage stabilization, short circuit and overload protection, all these functions are subject to adjustment.
The power in my case is 2000 watts, but the circuit will allow you to remove up to 4000 watts without any problems if you replace the keys, the bridge and stuff electrolytes at 4000 microfarads. At the expense of electrolytes - the capacity is selected based on the calculation of 1 watt - 1 microfarad.
Diode bridge - 30 Amp 1000 Volt - ready-made assembly, has its own separate airflow (cooler)
Mains fuse 25-30 Amp.
Transistors - IRFP460, try to choose transistors with a voltage of 450-700 volts, with the smallest gate capacitance and with the lowest resistance of the open channel of the key. In my case, these switches were the only option, although they can provide a given power in a bridge circuit. They are installed on a common heat sink, it is imperative to isolate them from each other, the heat sink needs intensive cooling.
Soft start relay - 30 amps with 12 volt coil. Initially, when the unit is connected to a 220 volt network, the starting current is not so large that it can burn the bridge and much more, so the soft start mode for power supplies of this rank is necessary. When connected to the network through a limiting resistor (a chain of series-connected resistors 3x22Ohm 5 watts in my case), electrolytes are charged. When the voltage on them is high enough, the control circuit power supply (15 Volts 2 Amperes) is activated, which closes the relay and through the latter the main (power) power is supplied to the circuit.
Transformer - in my case, on 4 rings 45x28x8 2000NM, the core is not critical and everything connected with it will have to be calculated using specialized programs, the same with group stabilization output chokes.
My unit has 3 windings, all providing bipolar voltage. The first (main, power) winding at +/-45 Volts with a current of 20 Amperes - for powering the main output stages (current amplifier) UMZCH, the second +/-55 volts 1.5 Amperes - for powering the differential stages of the amplifier, the third +/- 15 for powering the filter unit.
The generator is built on TL494, tuned to 80 kHz, further driver IR2110 for key management.
The current transformer is wound on a 2000NM 20x12x6 ring - the secondary winding is wound with 0.3mm MGTF wire and consists of 2x45 turns.
Everything is standard in the output part, a bridge of KD2997 diodes is used as a rectifier for the main power winding - with a current of 30 amperes. The bridge for the 55 volt winding is UF5408 diodes, and for the low-power winding of 15 volts - UF4007. Use only fast or ultrafast diodes, although you can use ordinary pulse diodes with a reverse voltage of at least 150-200 Volts (the voltage and current of the diodes depend on the parameters of the winding).
The capacitors after the rectifier are 100 volts (with a margin), the capacity is 1000 microfarads, but of course there will be more amplifiers on the board itself.
Troubleshooting the initial schema.
I will not give my scheme, since it differs little from the one indicated. I can only say that in circuit 15, the TL output is unhooked from 16 and soldered to 13/14 outputs. Next, we remove the resistors R16/19/20/22 2 watts, and feed the control unit with a separate power supply unit 16-18 Volts 1-2 amperes.
Resistor R29 is replaced by 6.8-10 kOhm. We exclude the SA3 / SA4 buttons from the circuit (in no case close them! There will be a boom!). We replace R8 / R9 - they will burn out the first time they are connected, so we replace it with a 5 watt 47-68 Ohm resistor, you can use several series-connected resistors with the specified power.
R42 - we replace it with a zener diode with the desired stabilization voltage. All variable resistors in the circuit are strongly advised to use a multi-turn type, for the most accurate setting.
The minimum voltage stabilization limit is 18-25 Volts, the generation will be disrupted further.
This stabilizer has good characteristics, has a smooth adjustment of current and voltage, good stabilization, tolerates short circuits without problems, is relatively simple and does not require large financial costs. It has a high efficiency due to the pulse principle of operation, the output current can reach up to 15 amperes, which will allow you to build a powerful charger and power supply with current and voltage regulation. If desired, you can increase the output current to 20 or more amperes.
On the Internet of similar devices, each has its own advantages and disadvantages, but the principle of operation is the same for them. The proposed option is an attempt to create a simple and powerful enough stabilizer.
Due to the use of field switches, it was possible to significantly increase the load capacity of the source and reduce the heating on the power switches. With an output current of up to 4 amperes, transistors and a power diode can not be installed on radiators.
The ratings of some components on the diagram may differ from the ratings on the board, because. I developed the board for my needs.
The output voltage adjustment range is from 2 to 28 volts, in my case the maximum voltage is 22 volts, because. I used low-voltage switches and it was risky to raise the voltage above this value, but with an input voltage of about 30 Volts, you can easily get up to 28 Volts at the output. The output current adjustment range is from 60mA to 15A Amperes, depending on the resistance of the current sensor and the power elements of the circuit.
The device is not afraid of short circuits, the current limit will simply work.
A source based on a PWM controller was assembled TL494, the output of the microcircuit is supplemented with a driver for controlling power keys.
I want to draw your attention to the battery of capacitors installed at the output. Capacitors with a low internal resistance of 40-50 volts should be used, with a total capacitance of 3000 to 5000 microfarads.
The load resistor at the output is used to quickly discharge the output capacitors; without it, the measuring voltmeter at the output will work with a delay, because. when the output voltage decreases, the capacitors need time to discharge, and this resistor will quickly discharge them. The resistance of this resistor must be recalculated if a voltage of more than 24 volts is applied to the input of the circuit. The resistor is two watts, designed with a margin of power, it can get warm during operation, this is normal.
How it works:
PWM controller generates control pulses for power switches. In the presence of a control pulse, the transistor, and power through the open channel of the transistor through the inductor, is supplied to the storage capacitor. Do not forget that the choke is an inductive load, which is characterized by the accumulation of energy and return due to self-induction. When the transistor closes, the charge accumulated in the inductor through the Schottky diode will continue to feed the load. The diode in this case will open, because. the voltage from the inductor has reversed polarity. This process will repeat tens of thousands of times per second, depending on the operating frequency of the PWM chip. In fact, the PWM controller always monitors the voltage across the output capacitor.
The stabilization of the output voltage occurs as follows. The non-inverting input of the first error amplifier of the microcircuit (pin 1) receives the output voltage of the stabilizer, where it is compared with the reference voltage that is present at the inverse input of the error amplifier. When the output voltage decreases, the voltage at pin 1 will also decrease, and if it is less than the reference voltage, the PWM controller will increase the pulse duration, therefore, the transistors will be in the open state for more time and more current will be pumped into the inductor, if the output voltage is greater than the reference , the opposite will happen - the microcircuit will reduce the duration of the control pulses. With the specified divider, you can forcefully change the voltage at the non-inverting input of the error amplifier, thereby increasing or decreasing the output voltage of the stabilizer as a whole. For the most accurate voltage adjustment, a tuning multi-turn resistor is used, although a regular one can be used.
The minimum output voltage is about 2 volts, it is set by the specified divider, if you wish, you can play around with the resistance of the resistors to obtain acceptable values for you, it is not recommended to reduce the minimum voltage below 1 volt.
A shunt is installed to monitor the current drawn by the load. To organize the current limiting function, a second error amplifier is used as part of the TL494 PWM controller. The voltage drop across the shunt enters the non-inverting input of the second error amplifier, is again compared with the reference one, and then exactly the same thing happens as in the case of voltage stabilization. The specified resistor can adjust the output current.
The current shunt is made of two low-resistance resistors connected in parallel with a resistance of 0.05 Ohm.
The accumulative choke is wound on a yellow-white ring from the group stabilization filter of a computer power supply.
Since the circuit was planned for a fairly large input current, it is advisable to use two rings stacked together. The winding of the inductor contains 20 turns of wire wound with two strands with a diameter of 1.25 mm in varnish insulation, the inductance is about 80-90 microhenries.