Absolutely usable switching power supply: Veuve Clicquot 4C7108 power supply

Kaige 4C7108 uses a separately excited single-ended flyback switching power supply, the oscillation circuit uses TDA8380, and the main power supply output voltage is 115V.

The power supply pin of TDA8380 is pin (5), and pin (10) is externally connected to C530 and internal circuit to form a sawtooth wave oscillator. (6) The reference current set by the external pin R522 provides a fixed charge and discharge current for C530, so the oscillation frequency of TDA8380 is determined by the time constant of R522 and C530. This machine is 34KHZ. The forward and reverse excitation currents output by pins (1) and (15) of TDA8380 are sent to the B pole of switching tube Q502, making Q502 work in the switching state. The purpose of using reverse excitation is to enable Q502 to cut off quickly. The forward excitation saturates Q502 and charges C525 at the same time. When Q502 is cut off, the voltage charged on C525 becomes the power supply of the reverse excitation tube. The four diodes D511-D514 maintain a reverse bias of 2.8V when Q502 is turned off.

Voltage stabilizing circuit
The output voltage of the switching power supply is determined by the duty cycle of the switching pulse level, and the switching pulse duty cycle of the TDA8380 is affected by the input voltage level of pin (9).
The voltage stabilizing circuit is mainly composed of Q503, Q504, IC502 and other components. The differential amplifier composed of Q503 and Q504 is the error sampling circuit. D519 provides the reference voltage for the B pole of Q503. The B pole of Q504 changes with the change of the output voltage. When the output voltage is high, the conduction degree of Q504 decreases, the C pole current of Q503 is shunted and reduced, the current of IC502 increases, the internal resistance of IC502's (4) and (5) pins decreases, and the internal resistance of IC501's (9) When the pin voltage decreases, the duty cycle of the width-modulated pulse becomes smaller, which reduces the output voltage and achieves the purpose of voltage stabilization. Adjusting VR504 can change the output voltage.

Protection circuit
1. Overvoltage protection
Overvoltage protection is controlled by IC501 (7) pin. The working voltage of TDA8380 is 9V-20V. If it is lower than 8.4V or higher than 23V, the circuit will be protected. The working voltage of IC501 of this machine is designed to be 15V. The voltage divided by R523 and R524 and sent to IC501 (7) pin is 2.3V. This voltage comes from the feedback circuit of T501 and is proportional to the AC input voltage and the 115V output voltage. If 220V rises or the 115V output is too high, and the voltage at pin (7) of IC501 reaches 3.6V, the protection circuit will start to act.

2. Under-voltage protection:
When the 220V input voltage is too low, such as when the voltage of pin (5) of IC501 is lower than 8.4V, the under-voltage protection circuit starts to act.

3. Overcurrent protection
Overcurrent protection consists of the E-pole current detection resistors R527 and R528 of Q502 and pins (13) and (14) of IC501. The voltage drop on R527 and R528 reflects the E pole current of Q502, which is input by pin (14) of IC501. During normal operation, the voltage of pin (13) is 1.3V and the voltage of pin (14) is 0.1V. When U(13)-U(14)<0.2V, the protection circuit starts to act.

4. Anti-magnetic protection
The anti-magnetic protection circuit is composed of R517 and the internal circuit of IC501 (3) pin. The pulse signal is induced by the feedback winding of T501 (7) and (9) pins, which is divided by R517 and R521 and sent to the (3) pin of IC501. The internal circuit performs demagnetization detection. When it is judged that T501 still has accumulated energy storage, it Temporarily close the strobe gate to delay the switching pulse output.

Slow start circuit
The slow start circuit is controlled by the external capacitor C529 at pin 12 of IC501. When the operating voltage is added to IC501 (5) pin, the oscillation circuit of (10) pin begins to oscillate, but the DC voltage applied to the pulse width modulator is also affected by the slow start circuit. When the power is turned on, C529 is turned on instantly, and the voltage at pin (12) is 0 instantly, making the DC control level also be 0. As C529 is charged, the voltage of pin (12) gradually rises to the normal value (about 2.8V), and the duty cycle of the width-modulated pulse gradually rises from 0 to the rated value. Therefore, the conduction current of Q502 gradually increases. That is, slow start is achieved.

Standby/power-on
In the standby state, Q506 is turned on, Q505 is turned off, there is no 12V row oscillation voltage output, and the row output circuit stops working.