Analysis and overhaul Yongshenghong FSP241-4F01 power supply principle (below) - Power Circuit - Circuit Diagram

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(3) PFC circuit
1) Introduction to PFC voltage forming chip TDA4863G
The TDA4863G chip features low startup current, zero current control, output overvoltage protection, undervoltage lockout, internal start timer, and totem pole drive output. The pin function and reference voltage are shown in Table 2. The internal block diagram is shown in Figure 6. Show.

2) Formation of PFC voltage
The PFC circuit mainly uses Infineon's TDA4863G chip as the PFC voltage forming module, which is composed of IC2, IC4, L2, D2, Q14, Q8, Q7, Q13, Q2, Q18, Q16, IC10 and other components. In the standby state, since the Q14 is in the standby state, the transistor Q8 is turned off, and the PFC module IC4 does not work due to no power supply.

When the power is turned on twice, the high-level control signal POWER-ON is applied to the gate of the MOs tube QS8 via R39 and DS5, and the QS8 is saturated and turned on. After the optocoupler IC10 is controlled, Q14 and Q8 are both turned on, and the IC4 pin is obtained. Operating voltage VCC (12V), while the energy storage inductor L2 secondary induced pulse voltage is sent to its 5 feet, and detects zero current (purpose: reduce MOs tube switching loss), the bistable multivibrator starts to work, The PWM drive pulse is output from its 7-pin and sent to a push-pull amplifier circuit composed of a resistor R3, a transistor Q7 and a Q13, and the MOs tube Q2 is excited to be turned on and off. The 3-8 winding of the energy storage inductor L2 starts to store energy when Q2 is turned on, starts to release energy when it is turned off, and boosts the voltage of the capacitor C1 terminal to 400V through D2 and L3, thereby increasing the power of the power supply. Correction factor.

If the grid voltage is reduced, the voltage of the 3 pin of IC4 is reduced to less than 1V after the voltage is divided by the resistors R51, R52, R53, and R74. The internal multiplier circuit and the current comparator are compared to stop the drive circuit. At the same time, the B voltage caused by bridge rectification will also decrease (about 1.4 times of the grid voltage), and then the voltages of R50, R80, R81, and R82 will be divided, causing ZD6 and Q18 to be cut off. At this time, the PFC voltage is also low. It is about 70V, but the PFC voltage is divided by the resistors R44, R76, R77, R75 (when R78 is disconnected) to the voltage of pin 1 of IC4, and the internal drive is driven when pin 1 of IC4 is higher than 2.5V. The circuit stops working. If the DS poles of resistors R75, R78 and MOs Q18 are broken down and IC1's 1 pin is lower than 0.2V, the internal comparator circuit will also stop the internal driver circuit from being stopped.

When the MOs tube Q2 is overcurrentd for some reason, a voltage rise is formed across the source overcurrent detecting resistor R47 of Q, and the internal current comparator of the 4-pin IC4 is compared to cause the multivibrator to stop working. The purpose of overcurrent protection. The PFC voltage forming control circuit is shown in Figure 7.

3) Introduction to grid voltage and PFC voltage detection chip FP103

The FP103 has both dual operational amplifiers and a reference voltage 2.5V regulator. The pin function and voltage reference are shown in Table 3. The internal structure circuit is shown in Figure 8.

4. The main power supply circuit of the main power supply circuit is implemented by a current pulse width modulation block UC3845B (IC1) and a half bridge frequency main power supply block IR2184S (IC3).
(1) 12V/24V voltage is formed when the signal board sends the high-level control signal POWER-ON to the pin 1 of the socket CNS 1, through the action of the optocoupler IC10, causing the transistors Q14, Q8 to be turned on, the PFC module IC4 7 feet get working voltage 12V, PFC circuit starts working, IC2 detects PFC circuit work and input from its 2 pin, 7 pin outputs low level, causing transistor Q12 to conduct, output 8V voltage from c pole, send to IC1 7 feet. Then IC1 starts to oscillate internally, and the PWM drive pulse is output from its 6-pin output to the 1st pin of IC3. After 12V power is supplied to the 5th pin of IC3 and 145V is formed by the 8 pin, the IC3 internal pulse generator starts to work. The 4-pin and 7-pin output low-side and high-side drive pulses drive the gates of the MOs transistors Q4 and Q3, respectively, to be in the alternate on and off states. That is, when Q3 is turned on, the 400V PFC voltage flows through the DS pole. , C11 and switching transformer T2 3-1 winding to the ground to form a loop, in the T2 3-1 winding formed a positive and negative negative electromotive force, and when Q4 is on, the current passes through the ground to Q4 SD pole, also in T2 The 3-1 winding forms an electromotive force that is positive and negative, and an alternating magnetic field is coupled to the secondary winding at T2. Due to the mutual inductance, a sinusoidal alternating voltage is induced in the secondary winding, and a synchronous rectifier circuit is used to generate a voltage of 12V and 24V.

A 24V stable sampling control circuit is formed by the optocoupler IC 9 and the precision voltage comparator ICS4. When the 24V voltage rises for some reason. The control electrode voltage of ICS4 is increased, ICS4 is turned on, IC9's primary LED is enhanced, and the secondary phototransistor is enhanced. The current of pin 1 fed back to IC1 is increased. The internal current comparison detection causes the PWM drive pulse width to be occupied. Compared with the reduction, the output voltage of the 6-pin is lowered, and finally the 4, 7-pin driving pulse width duty ratio output of the IC3 is controlled to achieve the purpose of voltage regulation.

(2) Synchronous rectification circuit With the development of modern power supply modules in the direction of low voltage and high current, the switching loss and conduction voltage drop loss of the power rectifier become an important factor of power supply loss, in the traditional secondary rectifier circuit. Schottky diodes are the first choice for low-voltage, high-current applications. The turn-on voltage drop is basically greater than 0.4V. When the output voltage of the power module continues to decrease with the development of the technology, the efficiency of the power module is lower. Improve efficiency and reduce losses, and gradually use synchronous rectification technology to complete. Usually synchronous rectification technology is divided into self-driven and control-driven. At present, the circuit adopts self-driving mode, and uses the MOs tube for rectification in the secondary of the switching transformer. Its function is the same as that of the ordinary rectifier diode, but its conduction voltage drop is much smaller than that of the ordinary diode, so the efficiency of the whole circuit is improved. , reducing the loss.