Marquee indicator type universal charging circuit diagram

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One-piece inductor

The picture below shows the schematic diagram of this marquee indicating universal charging circuit.
1. The circuit composition can be seen from the schematic diagram. The universal charging is essentially a small switching power supply circuit. The whole circuit can be roughly divided into the following parts: input rectification and filtering circuit, switching oscillation circuit, overvoltage protection circuit, secondary rectification and filtering circuit, Regulated output circuit, automatic identification of polarity and charging circuit, horological charging indication circuit, etc.

2, the basic working principle of the circuit When the charger is plugged into the AC power supply, the 220V AC voltage is D1 half-wave rectified and C1 filtered to obtain a DC voltage of about 300V. The switching oscillating circuit composed of elements such as Q1, T1, R1, R3, R4, R5, and C2 converts direct current into high frequency alternating current, and the oscillation process is as follows.


At the moment of power-on, the +300V voltage is supplied to the switching transistor Q1 through the starting resistor R1 to provide a base current lB that increases from nothing. The collector of the Q1 also produces a collector current Io that increases from nothing, and the current flows through The 1-2 winding of the switching transformer T1 generates a self-induced electromotive force that is positive and negative, and also induces a positive and negative mutual electromotive force in the positive feedback winding 3-4 of T1, and the electromotive force is fed back through R3, C2, etc. The base of Ql makes lB further increase, which is a strong positive feedback process.

Under the action of this positive feedback, Q1 quickly enters a saturated state, and transformer T1 stores magnetic field energy. After that, the positive feedback winding continuously charges the capacitor C2, and the polarity is up and down, so that the base voltage of Q1 is continuously decreased, and finally the Q1 is taken out of saturation, and the current of the T11-2 winding is decreasing, and the windings of the T1 are The induced electromotive force is all inverted. At this time, the induced electromotive force of the T13-4 winding is positive and negative. After the electromotive force is fed back to the base of Q1, lB is further reduced, so that it cycles into another strong positive feedback process. Q1 is quickly closed. Then, under the action of self-discharge and +300V reverse charging, C2 will make Q1 base voltage rise again and enter the next cycle, thus generating periodic oscillation, so that Q1 works under constant opening and closing state. .
During the Q1 cut-off period, the polarity of the induced electromotive force of the T1 secondary winding (5-6 winding) is positive and negative, and D3 is turned on. At this time, the electromotive force charges the capacitor C4 and obtains about 10 V at C4. A DC voltage of around 7.6V) supplies power to the load.
An overvoltage protection circuit consisting of D2, C3, and Z1 is also provided outside the T1 positive feedback winding. When the 220V power supply voltage rises abnormally and the output voltage also rises, the Zener diode Z1 in the overvoltage protection circuit will be reversed. The breakdown is turned on, the switching tube is stopped, and the output terminal has no voltage, which serves as a protection.
The base of Q3 is stabilized at about 5V by the 5.1V Zener diode, and the Q3 emitter voltage is about 4.2V.
Q4-Q7 constitutes a charging circuit that automatically switches polarity. When the charged mobile phone battery is connected between U1 and U2, when the battery polarity is left negative right positive as shown in the figure below, Q4 and Q6 on the diagonal will be turned on, Q5 and Q7 will be off, charging current The direction is as shown by the arrow in the figure below; when the battery is reversed, Q5 and Q7 are turned on, Q4 and Q6 are turned off, and the charging current is reversed. That is, regardless of the polarity of the battery, the circuit ensures that the battery is charged with the correct polarity.
LED7 is the power indicator light. When the charger is plugged into 220V AC, the light will be illuminated and will be extinguished during the charging process until the battery is fully charged and then illuminated again.
LEDl-LED6 is connected in series to form three sets of marquee indicating circuits. Under the control of the marquee control chip ZXT-604, three sets of LEDs will alternately emit light. Since these six LEDs are installed on the circuit board in cross layout, During the charging process, a charging indication effect of the marquee (rotation) is formed.
Since Q2 is in a micro-on state when the rechargeable battery is not inserted, its C-pole voltage is only about 1.2V. At this time, only the power indicator LED7 is in a forward-biased state, and the marquee circuit cannot reach the operating voltage. Does not work, LED1 ~ LED6 does not emit light.
During the charging process after plugging in the battery, Q3 is in a saturated conduction state due to the enhanced conduction of Q3, and the C-pole voltage reaches about 7.6V. At this time, the power indicator LED7 is extinguished due to the reverse bias, and the marquee circuit is turned off. When it is powered, LED1~LED6 alternately emit light as a charging indication.

3. The problem that should be paid attention to in the circuit assembly. Although the universal charging is simple and the number of components is small, there are still various problems in the assembly process, mainly the following:
(1) Diode installed in this circuit, D2, D3, D4, D5, Z1 Five diodes have the same shape and color, small size, and the type writing is not easy to identify. If not reminded, students often mistake these five diodes. . The five diodes, D2, D3, and D4 are the same model: 1N4148, D5 model is C5V1, Z1 model is C2, and the latter two are Zener diodes.
(2) Triode is installed incorrectly. Because this circuit uses discrete components, there are 7 triodes, of which Q2 to Q7 are 3 S8050 and S8550 respectively. The former is NPN and the latter is PNP. The difference between words is easy to read. . Switching tube Q1, the installation of wrong polarity is also one of the common mistakes.
(3) Other common errors Electrolytic capacitor polarity is wrong, color ring resistance is not familiar with the fault, and the switch transformer is not measured before installation to confirm whether the three sets of windings are broken, and the LED does not know the polarity and causes the reverse.
(4) The circuit board itself is wrongly corrected. Since this circuit kit is purchased from a small factory, its work is very general, and there are some errors. When installing, some obvious errors should be corrected in advance:
1) There are two places on the circuit board marked with “R2”. The R2 marked as horizontal installation should be left in the actual installation without any components. The R2 marked as vertical installation should be “D2” and the pole Sex should be "left negative right".
2) There is an electrolytic capacitor under the capacitor C2 in the circuit board. The actual number should be C3.
3) There is a light-emitting diode under the D3 in the circuit board. The actual number should be LED3.
It is recommended that after all components have been installed, check that the components are correct and then re-energize the test machine. In addition, the copper foil at the contact between the two power metal sheets and the circuit board should be tinned to prevent oxidation, but the metal power contact pads are not soldered to the top.