Repair of Chinese chargers for mobile phones. LG mobile phone charger (principal diagram and repair). Pinout of USB connectors for Garmin navigator
Most modern network chargers are assembled according to the simplest pulse circuit, on one high-voltage transistor (Fig. 1.18) according to the blocking generator circuit.
Unlike simpler circuits based on a 50-Hz step-down transformer, the transformer for pulse converters of the same power is much smaller in size, which means that the dimensions, weight and price of the entire converter are smaller. In addition, pulse converters are safer - if in a conventional converter, in the event of a failure of power elements, a high unstabilized (and sometimes even alternating) voltage from the secondary winding of the transformer gets into the load, then in case of any malfunction of the pulse generator (except for the failure of the feedback optocoupler - but it is usually very well protected) there will be no voltage at all at the output.
Rice. 1.18. A simple pulsed blocking oscillator circuit
A description of the principle of operation and calculation of the circuit elements of a high-voltage pulse converter (transformer, capacitors, etc.) can be found at http://www.nxp.com/ acrobat/applicationnotes/AN00055.pdf (1 Mb).
The principle of operation of the device
The alternating mains voltage is rectified by the VD1 diode (although sometimes the generous Chinese put as many as 4 diodes, in a bridge circuit), the current pulse when turned on is limited by the resistor R1. Here it is desirable to put a resistor with a power of 0.25 W - then, when overloaded, it will burn out, performing the function of a fuse.
The converter is assembled on a transistor VT1 according to the classic flyback circuit. Resistor R2 is needed to start generation when power is applied, it is optional in this circuit, but the converter works a little more stable with it. Generation is supported by the capacitor C1, included in the PIC circuit on the AND winding, the generation frequency depends on its capacitance and the parameters of the transformer. When the transistor is unlocked, the voltage at the lower terminals of the windings I and II according to the circuit is negative, at the upper ones it is positive, the positive half-wave through the capacitor C1 opens the transistor even more, the voltage amplitude in the windings increases.
The transistor opens like an avalanche. After some time, as the capacitor C1 charges, the base current begins to decrease, the transistor begins to close, the voltage at the top output of the winding II according to the circuit begins to decrease, through the capacitor C1 the base current decreases even more, and the transistor closes like an avalanche. Resistor R3 is needed to limit the base current during circuit overloads and surges in the AC mains.
At the same time, the self-induction EMF amplitude through the VD4 diode recharges the capacitor C3 - therefore, the converter is called flyback. If you swap the terminals of the winding III and recharge the capacitor C3 during the forward stroke, then the load on the transistor VT1 will increase sharply during the forward stroke (it may even burn out due to too much current), and during the reverse stroke, the self-induction EMF will be unspent and stand out at the collector junction of the transistor - that is, it can burn out from overvoltage.
Therefore, in the manufacture of the device, it is necessary to strictly observe the phasing of all windings (if you confuse the terminals of winding II, the generator simply will not start, since the capacitor C1, on the contrary, will disrupt generation and stabilize the circuit).
The output voltage of the device depends on the number of turns in the windings II and III and on the stabilization voltage of the Zener diode VD3. The output voltage is equal to the stabilization voltage only if the number of turns in the windings II and III is the same, otherwise it will be different. During the reverse stroke, the capacitor C2 is recharged through the diode VD2, as soon as it is charged to about -5 V, the zener diode will begin to pass current, the negative voltage at the base of the transistor VT1 will slightly reduce the amplitude of the pulses on the collector, and the output voltage will stabilize at a certain level. The stabilization accuracy of this circuit is not very high - the output voltage varies within 15 ... 25%, depending on the load current and the quality of the VD3 zener diode.
Alternate device option
A diagram of a better (and more complex) converter is shown in fig. 1.19.
To rectify the input voltage, a diode bridge VD1 and a capacitor C1 are used, the resistor R1 must be at least 0.5 W, otherwise it may burn out when it is turned on, when charging the capacitor C1. The capacitance of capacitor C1, in microfarads, must equal the power of the device, in watts.
The converter itself is assembled according to the already familiar scheme on the transistor VT1. The emitter circuit includes a current sensor on resistor R4 -
Rice. 1.19. Electrical diagram of a more complex converter
as soon as the current flowing through the transistor becomes so large that the voltage drop across the resistor exceeds 1.5 V (with the resistance indicated on the diagram - 75 mA), the transistor VT2 opens slightly through the VD3 diode and limits the base current of the transistor VT1 so that its collector current does not exceeded the above 75 mA. Despite its simplicity, such a protection scheme is quite effective, and the converter turns out to be almost eternal even with short circuits in the load.
To protect the transistor VT1 from self-induction EMF emissions. A smoothing chain VD4-C5-R6 has been added to the scheme. Diode VD4 must be high-frequency - ideally BYV26C, a little worse - UF4004 ... UF4007 or 1N4936, 1N4937. If there are no such diodes, it is better not to install a chain at all!
Capacitor C5 can be anything, however, it must withstand a voltage of 250 ... 350 V. Such a chain can be installed in all similar circuits (if it is not there), including the circuit according to fig. 1.18 - it will significantly reduce the heating of the case of the key transistor and significantly "extend the life" of the entire converter.
Stabilization of the output voltage is carried out using the Zener diode DA1, which is at the output of the device, galvanic isolation is provided by the optocoupler VOl. The TL431 chip can be replaced with any low-power zener diode, the output voltage is equal to its stabilization voltage plus 1.5 V (voltage drop across the optocoupler LED VOl); to protect the LED from overloads, a small resistor R8 is added. As soon as the output voltage becomes slightly higher than the set value, a current will flow through the zener diode, the LED of the optocoupler VOl will start to glow, its phototransistor will open slightly, the positive voltage from the capacitor C4 will slightly open the transistor VT2, which will reduce the amplitude of the collector current of the transistor VT1. The instability of the output voltage of this circuit is less than that of the previous one, and does not exceed 10 ... 20%, also due to the capacitor C1, there is practically no background of 50 Hz at the converter output.
It is better to use an industrial transformer in these circuits, from any similar device. But you can wind it yourself - for an output power of 5 W (1 A, 5 V), the primary winding should contain approximately 300 turns of wire with a diameter of 0.15 mm, winding II - 30 turns of the same wire, winding III - 20 turns of wire with a diameter of 0 .65 mm. Winding III must be very well isolated from the first two, it is advisable to wind it in a separate section (if any). The core is standard for such transformers, with a dielectric gap of 0.1 mm. In extreme cases, you can use a ring with an outer diameter of approximately 20 mm.
Hello radio amateurs!!!
Going through old boards, I came across a couple of switching power supplies from mobile phones and I wanted to restore them and at the same time tell you about their most frequent breakdowns and troubleshooting. The photo shows two universal schemes for such charges, which are most often found:
In my case, the board was similar to the first circuit, but without the LED at the output, which only plays the role of an indicator of the presence of voltage at the output of the block. First of all, you need to deal with the breakdown, below in the photo I outline the details that most often fail:
And we will check all the necessary details using a conventional multimeter DT9208A.
It has everything you need for this. The continuity mode of diodes and transistor junctions, as well as an ohmmeter and a capacitor capacitance meter up to 200 microfarads. This set of functions is more than enough.
When checking radio components, you need to know the base of all parts of transistors and diodes especially.
Now all cell phone manufacturers have agreed and everything that is in stores is charged via a USB connector. This is very good, because chargers have become universal. In principle, a cell phone charger is not.
This is only a 5V DC pulse source, and the charger itself, that is, the circuit that monitors the battery charge and ensures its charge, is located in the cell phone itself. But, the point is not this, but the fact that these “chargers” are now sold everywhere and are already so cheap that the issue of repair disappears somehow by itself.
For example, in a store, “charging” costs from 200 rubles, and on the well-known Aliexpress there are offers from 60 rubles (including delivery).
circuit diagram
A diagram of a typical Chinese charge, copied from the board, is shown in fig. 1. There may also be a variant with the rearrangement of the diodes VD1, VD3 and the zener diode VD4 to a negative circuit - Fig. 2.
And more "advanced" options may have rectifier bridges at the input and output. There may be differences in part numbers. By the way, the numbering on the diagrams is given arbitrarily. But this does not change the essence of the matter.
Rice. 1. A typical diagram of a Chinese network charger for a cell phone.
Despite the simplicity, this is still a good switching power supply, and even a stabilized one, which is quite suitable for powering something other than a cell phone charger.
Rice. 2. Scheme of a network charger for a cell phone with a changed position of the diode and zener diode.
The circuit is based on a high-voltage blocking oscillator, the generation pulse width of which is controlled by an optocoupler, the LED of which receives voltage from a secondary rectifier. The optocoupler lowers the bias voltage based on the key transistor VT1, which is set by resistors R1 and R2.
The load of the transistor VT1 is the primary winding of the transformer T1. Secondary, lowering, is winding 2, from which the output voltage is removed. There is also winding 3, it serves both to create positive feedback for generation, and as a source of negative voltage, which is made on the diode VD2 and capacitor C3.
This negative voltage source is needed to reduce the voltage at the base of the transistor VT1 when the optocoupler U1 opens. The stabilization element that determines the output voltage is the Zener diode VD4.
Its stabilization voltage is such that, in combination with the direct voltage of the IR LED of the optocoupler U1, it gives exactly the necessary 5V that is required. As soon as the voltage on C4 exceeds 5V, the VD4 zener diode opens and current flows through it to the optocoupler LED.
And so, the operation of the device does not raise questions. But what if I need not 5V, but, for example, 9V or even 12V? This question arose along with the desire to organize a network power supply for a multimeter. As you know, popular in amateur radio circles, multimeters are powered by Krona, a compact 9V battery.
And in "field" conditions, this is quite convenient, but in home or laboratory I would like to be powered from the mains. According to the scheme, “charging” from a cell phone is in principle suitable, it has a transformer, and the secondary circuit does not come into contact with the mains. The problem is only in the supply voltage - "charging" gives out 5V, and the multimeter needs 9V.
In fact, the problem with increasing the output voltage is solved very simply. It is only necessary to replace the VD4 zener diode. To get a voltage suitable for powering a multimeter, you need to put a zener diode on a standard voltage of 7.5V or 8.2V. In this case, the output voltage will be, in the first case, about 8.6V, and in the second about 9.3V, which, both, is quite suitable for a multimeter. A zener diode, for example, 1N4737 (this is 7.5V) or 1N4738 (this is 8.2V).
However, another low-power zener diode for this voltage is also possible.
Tests have shown that the multimeter performs well when powered by this power supply. In addition, an old pocket radio powered by Krona was also tried, it worked, only interference from the power supply slightly interfered. The voltage in 9V is not limited at all.
Rice. 3. Voltage adjustment unit for reworking a Chinese charger.
Do you want 12V? - Not a problem! We put the zener diode on 11V, for example, 1N4741. Only you need to replace the capacitor C4 with a higher voltage one, at least 16V. You can get even more stress. If you remove the zener diode at all, there will be a constant voltage of about 20V, but it will not be stabilized.
It is even possible to make a regulated power supply by replacing the zener diode with a regulated zener diode such as the TL431 (Figure 3). The output voltage can be adjusted, in this case, by a variable resistor R4.
Karavkin V. RK-2017-05.
I present another device from the series "Don't Take!"
A simple microUSB cable is included in the kit, which I will test separately with a bunch of other laces.
I ordered this charger out of curiosity, knowing that it is extremely difficult to make a reliable and safe 5V 1A power supply device in such a compact case. Reality is harsh...
Came in a standard bubble wrap.
The case is glossy, wrapped with a protective film.
Dimensions with fork 65x34x14mm 
Charging immediately turned out to be non-working - a good start ...
I had to disassemble and repair the device at the beginning in order to be able to test it.
It is very easy to disassemble - on the latches of the fork itself.
The defect was discovered immediately - one of the wires to the plug fell off, the soldering turned out to be of poor quality. 
The second soldering is no better 
The assembly of the board itself is done normally (for the Chinese), the soldering is good, the board is washed. 
Real device diagram 
What problems were found:
- Pretty weak attachment of the fork to the body. It is not excluded the possibility of her being torn off in the outlet.
- No input fuse. Apparently those very wires to the plug are protection.
- Half-wave input rectifier - unjustified savings on diodes.
- Small input capacitor (2.2uF/400V). For the operation of a half-wave rectifier, the capacitance is clearly insufficient, which will lead to increased voltage ripples on it at a frequency of 50 Hz and to a decrease in its service life.
- Lack of input and output filters. Not a big loss for such a small and low power device.
- The simplest converter circuit on one weak transistor MJE13001.
- A simple ceramic capacitor 1nF / 1kV in the noise suppression circuit (shown separately in the photo). This is a gross violation of the security of the device. The capacitor must be of class at least Y2.
- There is no snubber circuit to dampen surges of the reverse run of the primary winding of the transformer. This impulse often breaks through the power key element when it is heated.
- Lack of protection against overheating, overload, short circuit, output voltage increase.
- The overall power of the transformer obviously does not pull 5W, and its very miniature size casts doubt on the presence of normal insulation between the windings.
Now testing.
Because the device is initially not safe, the connection was made through an additional mains fuse. If something happens, at least it won’t burn and leave without light.
I checked without a case so that you can control the temperature of the elements.
Output voltage without load 5.25V
Power consumption without load less than 0.1W
Under a load of 0.3A or less, charging works quite adequately, the voltage keeps normally 5.25V, the output ripple is insignificant, the key transistor heats up within normal limits.
Under a load of 0.4A, the voltage starts to walk a little in the range of 5.18V - 5.29V, the ripple at the output is 50Hz 75mV, the key transistor heats up within normal limits.
Under a load of 0.45A, the voltage starts to noticeably walk in the range of 5.08V - 5.29V, the ripple at the output is 50Hz 85mV, the key transistor starts to slowly overheat (burns the finger), the transformer is warm.
Under a load of 0.50A, the voltage starts to fluctuate strongly in the range of 4.65V - 5.25V, the ripple at the output is 50Hz 200mV, the key transistor is overheated, the transformer is also quite hot.
Under a load of 0.55A, the voltage jumps wildly in the range of 4.20V - 5.20V, the output ripple is 50Hz 420mV, the key transistor is overheated, the transformer is also quite hot.
With an even greater increase in load, the voltage sags sharply to obscene values.
It turns out that this charge can actually produce a maximum of 0.45A instead of the declared 1A.
Further, the charge was assembled into a case (along with a fuse) and left to work for a couple of hours.
Oddly enough, the charger did not fail. But this does not mean at all that it is reliable - having such circuitry, it will not last long ...
In short circuit mode, the charging died quietly 20 seconds after switching on - the key transistor Q1, resistor R2 and optocoupler U1 broke. Even the additionally installed fuse did not have time to burn out.
For comparison, I’ll show you how the simplest Chinese 5V 2A charger from a tablet looks inside, made in compliance with the minimum acceptable safety standards. 
I take this opportunity to inform you that the lamp driver from the previous review has been successfully finalized, the article has been supplemented.
We examined the scheme of a simple autonomous charger for mobile equipment, operating on the principle of a simple stabilizer with a decrease in battery voltage. This time we will try to assemble a slightly more complex, but more convenient memory. Batteries built into miniature mobile multimedia devices usually have a small capacity, and, as a rule, are designed to play audio recordings for no more than a few tens of hours with the display turned off, or to play several hours of video or several hours of reading e-books. If the mains socket is unavailable or due to bad weather or other reasons, the power supply is turned off for a long time, then various mobile devices with color displays will have to be powered from built-in power sources.
Given that these devices consume a lot of current, their batteries may be depleted before the moment when electricity from the wall outlet becomes available. If you do not want to immerse yourself in primeval silence and peace of mind, then to power pocket devices, you can provide a backup autonomous power source that will help out both during a long trip into the wild, and in case of man-made or natural disasters, when your locality may be on several days or weeks without power.
Scheme of a mobile charger without a 220V network
The device is a linear compensation type voltage stabilizer with low saturation voltage and very low own current consumption. The energy source for this stabilizer can be a simple battery, rechargeable battery, solar or manual power generator. The current consumed by the stabilizer when the load is off is about 0.2 mA at an input supply voltage of 6 V or 0.22 mA at a supply voltage of 9 V. The minimum difference between the input and output voltage is less than 0.2 V at a load current of 1 A! When the input supply voltage changes from 5.5 to 15 V, the output voltage changes by no more than 10 mV at a load current of 250 mA. When the load current changes from 0 to 1 A, the output voltage changes by no more than 100 mV at an input voltage of 6 V and by no more than 20 mV at an input supply voltage of 9 V.
Resettable fuse protects the stabilizer and battery from overload. Reverse diode VD1 protects the device from reverse polarity of the supply voltage. As the supply voltage increases, the output voltage also tends to increase. To keep the output voltage stable, a control unit assembled on VT1, VT4 is used.
An ultra-bright blue LED is used as a reference voltage source, which, simultaneously with the function of a micropower zener diode, is an indicator of the presence of an output voltage. When the output voltage tends to increase, the current through the LED increases, the current through the emitter junction VT4 also increases, and this transistor opens more, VT1 also opens more. which shunts the gate-source of a powerful field-effect transistor VT3.
As a result, the open channel resistance of the field-effect transistor increases and the voltage across the load decreases. The trimmer resistor R5 can adjust the output voltage. Capacitor C2 is designed to suppress the self-excitation of the stabilizer with an increase in load current. Capacitors C1 and SZ - blocking power circuits. Transistor VT2 is included as a micropower zener diode with a stabilization voltage of 8..9 V. It is designed to protect against breakdown by high voltage gate insulation VT3. A gate-source voltage that is dangerous for VT3 may appear at the moment the power is turned on or due to touching the terminals of this transistor.
Details. Diode KD243A can be replaced by any of the series KD212, KD243. KD243, KD257, 1N4001..1N4007. Instead of KT3102G transistors, any similar collectors with a low reverse current are suitable, for example, any of the KT3102, KT6111, SS9014, VS547, 2SC1845 series. Instead of the KT3107G transistor, any of the KT3107, KT6112, SS9015, BC556, 2SA992 series will do. A powerful p-channel field-effect transistor of the IRLZ44 type in the TO-220 package has a low gate-source opening threshold voltage, the maximum operating voltage is 60 V. The maximum direct current is up to 50 A, the open channel resistance is 0.028 Ohm. In this design, it can be replaced by IRLZ44S, IRFL405, IRLL2705, IRLR120N, IRL530NC, IRL530N. The field-effect transistor is mounted on a heat sink with sufficient cooling surface area for a particular application. During installation, the terminals of the field-effect transistor are short-circuited with a wire jumper.
The battery charger can be mounted on a small printed circuit board. As an independent power source, you can use, for example, four pieces of series-connected alkaline galvanic cells with a capacity of 4 Ah (RL14, RL20). This option is preferable if you plan to use this construct relatively infrequently.
If you plan to use this device relatively frequently, or if your player draws significantly more current even when the display is off, then a 6V rechargeable battery, such as a sealed motorcycle battery or a large flashlight, may be worthwhile. You can also use a battery of 5 or 6 pieces of nickel-cadmium batteries connected in series. When hiking, fishing, to recharge batteries and power a handheld device, it may be convenient to use a solar battery capable of delivering a current of at least 0.2 A at an output voltage of 6 V. When powering the player from this stabilized power source, please note that the regulating transistor is turned on into the "minus" circuit, therefore, simultaneous power supply of the player and, for example, a small active speaker system is possible only if both devices are connected to the output of the stabilizer.
The purpose of this circuit is to prevent a critical discharge of a lithium battery. The indicator turns on the red LED when the battery voltage drops to the threshold value. The LED turn-on voltage is set to 3.2V.
The zener diode must have a stabilization voltage below the desired turn-on voltage of the LED. Chip used 74HC04. Setting the display unit consists in selecting the threshold for turning on the LED using R2. The 74NC04 chip makes it so that the LED lights up when discharged to a threshold, which will be set by the trimmer. The current consumption of the device is 2 mA, and the LED itself will light up only at the moment of discharge, which is convenient. I found these 74NC04s on old motherboards, that's why I used them.
Printed circuit board:
To simplify the design, this discharge indicator can not be set, because the SMD chip can not be found. Therefore, the scarf is specially on the side and it can be cut off along the line, and later, if necessary, added separately. In the future, I wanted to put an indicator on the TL431 there, as a more profitable option in terms of details. The field-effect transistor stands with a margin for different loads and without a radiator, although I think you can put weaker analogues, but already with a radiator.
SMD resistors are installed for SAMSUNG devices (smartphones, tablets, etc., they have their own charge algorithm, and I do everything with a margin for the future) and you can not install them at all. Do not install domestic KT3102 and KT3107 and their analogues, I had voltage floating on these transistors due to h21. Take BC547-BC557, that's it. Scheme source: Butov A. Radio designer. 2009. Assembly and adjustment: Igoran .
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