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

(3) PFC Circuit

1) Introduction to the PFC Voltage Forming Chip TDA4863G

The TDA4863G chip is designed with several advanced features including low startup current, zero current control, output overvoltage protection, undervoltage lockout, internal start timer, and totem pole drive output. The pin functions and reference voltages are detailed in Table 2, and the internal block diagram can be found in Figure 6.

When the power is initially turned on, the high-level control signal POWER-ON is sent to the gate of the MOS tube QS8 via R39 and DS5, causing QS8 to saturate and turn on. Once the optocoupler IC10 is triggered, both Q14 and Q8 are activated, providing an operating voltage VCC (12V) to IC4. The energy storage inductor L2 secondary induced pulse voltage is then sent to its 5 feet, while also detecting zero current (to minimize MOS tube switching loss). This triggers the bistable multivibrator to begin operation, outputting a PWM drive pulse from its 7-pin to a push-pull amplifier circuit consisting of a resistor R3, transistor Q7, and Q13, exciting the MOS tube Q2 to turn on and off.

When Q2 turns on, the 3-8 winding of the energy storage inductor L2 begins to store energy; when it turns off, it releases energy, boosting the voltage of the capacitor C1 terminal to 400V through D2 and L3, thereby improving the power supply's correction factor. However, if the grid voltage drops, the voltage at pin 3 of IC4 falls below 1V after being divided by resistors R51, R52, R53, and R54. This signals the internal multiplier circuit and current comparator to stop the drive circuit. Additionally, the B voltage resulting from bridge rectification decreases (approximately 1.4 times the grid voltage), and the voltages of R50, R80, R81, and R82 are divided, causing ZD6 and Q18 to shut off. Consequently, the PFC voltage drops to around 70V. Yet, this voltage is divided by resistors R44, R76, R77, and R75 (with R78 disconnected) to the voltage at pin 1 of IC4. When this voltage exceeds 2.5V, the internal drive is activated. Conversely, if the DS poles of resistors R75, R78, and the MOS Q18 break down or if IC1’s pin 1 falls below 0.2V, the internal comparator circuit halts the internal driver circuit.

In the event of overcurrent in the MOS tube Q2, a voltage spike forms across the source overcurrent detecting resistor R47 of Q, prompting the internal current comparator of the 4-pin IC4 to compare and stop the multivibrator from working, achieving overcurrent protection. The PFC voltage forming control circuit is illustrated in Figure 7.

2) Formation of PFC Voltage

The PFC circuit primarily employs Infineon’s TDA4863G chip as the PFC voltage forming module, comprising components such as IC2, IC4, L2, D2, Q14, Q8, Q7, Q13, Q2, Q18, Q16, IC10, and others. In the standby state, since Q14 is in the standby mode, transistor Q8 is turned off, preventing the PFC module IC4 from functioning due to the lack of power supply.

Once the power is turned on for the second time, the high-level control signal POWER-ON is applied to the gate of the MOS tube QS8 via R39 and DS5, saturating and turning on QS8. Controlled by the optocoupler IC10, both Q14 and Q8 are activated, providing an operating voltage VCC (12V) to IC4, while the energy storage inductor L2 secondary induced pulse voltage is sent to its 5 feet, detecting zero current (to reduce MOS tube switching loss). The bistable multivibrator then begins to operate, outputting a PWM drive pulse from its 7-pin to a push-pull amplifier circuit made up of a resistor R3, transistors Q7 and Q13, exciting the MOS tube Q2 to turn on and off. When Q2 is turned on, the 3-8 winding of the energy storage inductor L2 begins storing energy; when it is turned off, it starts releasing energy, boosting the voltage of the capacitor C1 terminal to 400V through D2 and L3, thus enhancing the power supply's correction factor.

If the grid voltage decreases, the voltage at pin 3 of IC4 drops below 1V after being divided by resistors R51, R52, R53, and R54. The internal multiplier circuit and current comparator compare this to stop the drive circuit. Simultaneously, the B voltage caused by bridge rectification also decreases (about 1.4 times the grid voltage), and the voltages of R50, R80, R81, and R82 are divided, causing ZD6 and Q18 to turn off. At this point, the PFC voltage is also low, approximately 70V. However, this voltage is divided by resistors R44, R76, R77, R75 (when R78 is disconnected) to the voltage at pin 1 of IC4, and the internal drive is activated 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 breakdown, or if IC1’s pin 1 is lower than 0.2V, causing the internal comparator circuit to stop the internal driver circuit.

When the MOS tube Q2 experiences overcurrent for some reason, a voltage rise forms across the source overcurrent detecting resistor R47 of Q, and the internal current comparator of the 4-pin IC4 compares this, causing the multivibrator to stop working, achieving 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 chip contains dual operational amplifiers and a 2.5V reference voltage regulator. The pin functions and voltage references are outlined in Table 3, and the internal structure circuit is depicted in Figure 8.

4) The Main Power Supply Circuit

The main power supply circuit is implemented using a current pulse width modulation block UC3845B (IC1) and a half bridge frequency main power supply block IR2184S (IC3).

(1) When the signal board sends the high-level control signal POWER-ON to the pin 1 of the socket CNS 1, the optocoupler IC10 activates transistors Q14 and Q8, providing a working voltage of 12V to IC4’s 7 feet, thus starting the PFC circuit. IC2 detects the PFC circuit’s operation and inputs from its 2 pin, outputting a low level from its 7 pin, causing transistor Q12 to conduct, outputting an 8V voltage from its C pole, and sending it to IC1’s 7 pin. IC1 then begins oscillating internally, outputting a PWM drive pulse from its 6 pin to IC3’s 1 pin. Once 12V power is supplied to IC3’s 5 pin and 145V is formed at its 8 pin, the IC3 internal pulse generator starts working. The 4 pin and 7 pin output low-side and high-side drive pulses, driving the gates of the MOS transistors Q4 and Q3 to alternate between on and off states. This means that when Q3 is turned on, the 400V PFC voltage flows through the DS pole, C11, and the switching transformer T2’s 3-1 winding to the ground, forming a loop and creating a positive and negative electromotive force in the T2 3-1 winding. When Q4 is on, the current flows through the ground to Q4’s SD pole, also forming a positive and negative electromotive force in the T2 3-1 winding, coupling an alternating magnetic field to the secondary winding of T2. Due to mutual inductance, a sinusoidal alternating voltage is induced in the secondary winding, and a synchronous rectifier circuit generates a voltage of 12V and 24V.

A 24V stable sampling control circuit is formed by the optocoupler IC9 and the precision voltage comparator ICS4. When the 24V voltage rises for some reason, the control electrode voltage of ICS4 increases, turning it on. This enhances the primary LED of IC9 and the secondary phototransistor, increasing the current fed back to IC1’s pin 1. The internal current comparison detection causes the PWM drive pulse width to be reduced, lowering the output voltage from the 6 pin, ultimately controlling the duty cycle of the 4 and 7 pin driving pulses output by IC3 to achieve voltage regulation.

(2) Synchronous Rectification Circuit

With the advancement of modern power supply modules towards lower voltage and higher current applications, the switching loss and conduction voltage drop loss of power rectifiers have become significant factors affecting power supply efficiency. In traditional secondary rectifier circuits, Schottky diodes were commonly chosen for their low-voltage, high-current applications, with a turn-on voltage drop generally exceeding 0.4V. As the output voltage of power modules continues to decrease with technological advancements, the efficiency of these modules becomes lower. To improve efficiency and reduce losses, synchronous rectification technology is gradually being adopted. Synchronous rectification technology is typically divided into self-driven and control-driven modes. Currently, the circuit adopts the self-driven mode, utilizing MOS tubes for rectification in the secondary of the switching transformer. Its function is similar to that of an ordinary rectifier diode, but its conduction voltage drop is much smaller than that of an ordinary diode, thus improving the overall circuit efficiency and reducing losses.