Kangshu AP16PCO5 ATX power supply circuit principle and maintenance (2) - Power Circuit - Circuit Diagram - Huaqiang Electronic Network

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Industrial Router Crystal 3.2*2.5mm 3225 26M (26.000MHZ) 12PF 10PPM 20PPM 30PPM

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SMD aluminum electrolytic capacitor

After power-on, the +325V voltage is applied to the 5th pin of the TNY268PN through the 1st and 2nd windings of T2 (the drain of the internal FET, providing the start-up and 5.8V power supply for the internal circuit of the chip), the chip is started, and the T2 is 5-8. The voltage induced by the 4-3 winding is rectified and filtered to generate two groups of power supplies of +5VSB and +13V. +5VSB is standby. The +13V power supply is supplied to the TNY268PN pin 1 through the resistor R32 (10kΩ). Since the internal drain drive current is no longer used to charge the bypass pin capacitor C23, the chip's no-load power consumption is reduced. 50mW), the other way to power the UC3843B.
Tip: The AC start voltage at the time of power-on is AC145V (DC 200V after rectification). After the start-up, when the mains is AC25-270V (about 27.5-75V after rectification), the auxiliary power supply has a stable output, but The normal working range of the main power supply is AC72.5-270V, which is the limit test face for safety without further adjusting the mains input voltage.
(1) The voltage regulation control consists of 4 feet of TNY268PN, optocoupler M7 (SFH615), and precision voltage regulator M9 (TL431). When the output voltage changes, the K-terminal voltage of M9 also changes with the powder, and the internal light-emitting diode of M7 and the internal resistance of the phototransistor change accordingly, which causes the current of the 4-pin current of TNY268PN to change, thus controlling the internal power MOSEFT. Turn on and off, adjust the output voltage to stabilize the voltage. The TNY268PN's 4-pin enable circuit includes a low-impedance source follower circuit with an output of 1.0V, and the current through the circuit is limited to 240WA. When the current flowing out of this pin exceeds 240μA, the output of the enable circuit will generate a logic low (disable) and the power MOSEFT will be turned off.
(2) Undervoltage protection When the voltage of the 1-pin BP terminal of TNY268PN drops from the normal value of 6.3V to 4.8V, the chip stops working, forcing the power MOSFET to turn off and play a protective role. After the voltage is restored, the chip starts working again. The 4 pin of TNY268PN is connected to +325V through resistors R26 and R27. (2MΩ), and the circuit has the function of undervoltage detection.
Tip: After the measured power supply is started, when the mains supply is reduced to AC72.5V, the main power supply will beep, but the main and auxiliary power supplies can work normally. Below AC25V, the auxiliary power supply stops outputting. At this time, even if the mains voltage returns to normal, The secondary power supply also has no powder.
(3) Overcurrent protection When an overload, short circuit or open loop fault occurs, the TNY268PN internal overcurrent comparator detects that the power MOSPET drain current reaches the limit value, the power MOSPET is turned off, and then the chip restarts as specified, once the fault is removed. The chip resumes normal work.
(4) The temperature of the overheat protection chip is set to 135 °C. When the temperature of the substrate exceeds 135 °C when the chip is working, the internal overheat protection circuit is activated, forcing the power MOSEFT to turn off, and the chip starts again when the temperature drops to 70 °C.
(5) Leading edge blanking circuit This circuit disables the current comparator operation for a short period of time during the turn-on of the power MOSEFT, avoiding the MOSEFT reverse recovery time due to the output capacitor and the output rectifier diode, causing a current spike and ending the pulse early.
3. Main power supply working principle The main power supply mainly produces +3.3V, +5V, +12V, -12V power supply for the computer motherboard. The power supply adopts UC3843B current-controlled pulse width modulation integrated circuit, which has the functions of full function, high operating frequency, few pins, simple peripheral components, etc. The voltage regulation rate can reach 0.01%V (very close to the practical power supply). Adjustment rate). The operating frequency is up to 500kHz, the starting current is only 1mA, and the starting circuit is very simple.
When the mains supply is normal, there are four ways to turn off the pulse output of the 6-pin output of the UC3842B:
1) Turn off Vcc;
2) Reduce the voltage of pin 1 to below 1V;
3) Raise the voltage of 2 feet to 2.5V or more;
4) Raise the voltage of the 3-pin to more than 1V.
The power supply is turned on and off by controlling the voltage of the power pin 7 of the M8 (UC3843B), and is realized by the photocoupler M3 (SFH615).
The voltage regulation of the power supply is realized by controlling the level of the 2-pin level of the UC3843B by the photocoupler M2 (SFH615).
(1) Power supply start and stop When the 7-pin power supply voltage of UC3843B reaches the start condition (greater than 8.5V), the power supply starts, and the 6-pin output PWM pulse of UC3843B goes to the G pole of the power MOS switch tube Q1 (K2611), and Q1 starts to guide. Through and off, the switching transformer T1 performs magnetic energy and electric energy conversion, and the secondary winding voltages are filtered by LC to output corresponding DC power for use in the subsequent stage circuit.
This supply voltage is supplied by the secondary power source. The +13V voltage generated by the 4-3 winding of the secondary power supply T2 is controlled by the transistors Q7 (64), Q5 (64), and M3, and then applied to the 7th pin of the UC3843B.
When the main power is turned on, the 2 pin of M3 is low level 0.1V, the internal LED is illuminated, the phototransistor of 4 and 3 feet is turned on, and the 4 pin is 0.1V low level. At this time, Q7 is cut off, Q5 is Through, the voltage of +13V is adjusted by Q5 to form a voltage of about +9.19V, which is applied to pin 7 of UC3843B, and the main power supply starts to work.
Tip: The measured b and e pole voltages of Q5 are about +9.2V and 9.19V respectively (as if the tube is not conducting, the actual voltage drop between b and e is 0.7V, the tube is conducting, it is estimated that the measurement error is Caused by the oscilloscope to measure the b and e pole voltages of Q5 are +10V, 9.3V. ·
When the main power is off, the 2 pin of M3 is 4.2V high, the internal diode does not emit light, the phototransistor of 4 and 3 pins is not conducting, and the +13V voltage is divided by resistor R17 (10kΩ) and R79 (10kΩ). Q7 is saturated and the other channel is adjusted by Q5 to form a voltage of +3.8V applied to the 7th pin of UC3843B. This voltage is lower than the UC3843B starting voltage +8.5V and the minimum working limit voltage +7.6V. Therefore, UC3843B stops working, the main power supply no output.
The function of resistor R76 (101) and diode D21 is to lower the voltage of pin 1 of UC3843B by saturating the Q7 of saturation, further ensuring that the UC3843B has no PWM pulse output, and the main power supply does not start.
Diodes D14, D22, resistor R78 (4.3kΩ), capacitor C63 (10μF/50V), etc. form a soft-start circuit. When UC3843B is powered on, the voltage across C63 cannot be abruptly changed to 0V, the 1 pin of UC3843B is low level, and the UC3843B has no PWM pulse output. When C63 is charged to +4.9V through the +5V reference voltage and R78 is charged to +4.9V, D14 is turned off, and the 1 pin level of UC3843B is not controlled by C63, and UC3843B starts to work.
The function of D22 is to quickly discharge the charge of C63 through the 5-pin internal circuit of UC3843B after power-off, so as to prepare for the next power-on soft-start circuit.
Capacitor C62 (2.2μF /50V), C61 is UC3843B VCC, VREF terminal power supply filter capacitor, which acts as a suppression switch.
Capacitors C6 and C65 (331kF/1kV) form an anti-peak suppression circuit. The function is to absorb the anti-peak high voltage generated by the leakage inductance of the 1st and 3rd windings of T1 when Q1 is turned off, and avoid the anti-peak high voltage and 325V superimposed breakdown Q1.
Resistor R82 (10Ω) is the Q1 gate-to-source current-limiting resistor, which prevents the G-pole input current from being too large and damages the MOs tube input terminal. The resistor R13 (10kΩ) is the bleeder resistor. After shutdown, the gate storage charge is quickly released through R13. Avoid damage to the MOs tube at startup.
Resistor R73 (1.33kΩ) and capacitor C60 are Rt and Ct timing components, which determine the operating frequency of UC3843B. The measured oscillation frequency of this machine is about 71kHz.
Resistor R14 (0.15Ω/2W) is an overcurrent detection resistor. The sampling voltage is passed through the RC filter composed of resistor R11 (91051) and capacitor C59 to the 3 pin of UC3843B. When the pin level is ≥1V, the internal current detection comparator outputs a high level, resets the PWM latch, and the 6 pin stops outputting the PWM pulse to achieve the current limiting protection purpose.
Resistor R68 (47kΩ) and C55 form an error amplifier compensation network. The function is to change the closed-loop gain and frequency response of the internal amplifier of pins 1 and 2 of UC3843B. Capacitor C58 is the ramp compensation capacitor. The function of the sawtooth wave of the 4 pin of UC3843B is The sampling voltage on C58 and R14 is superimposed on the 3 pin of UC3843B to prevent harmonic oscillation and make the circuit work more stable.
(2) The voltage regulation of the output voltage of the main power supply is controlled by two branches of +5V and +12V. The two voltages are controlled, and the other several output voltages are basically guaranteed to be stable.
+5V, +12V voltage regulator control circuit consists of optocoupler M2 (SFH615), precision reference regulator M6 (TL431), +5V sampling resistor R28 (6.2kΩ), +12V sampling resistor R30 (15.8kΩ) and sampling voltage divider adjustable potential It is composed of VR1 (1kΩ) and resistor R29 (2.2kΩ).
When the output voltage of +5V or +12V rises for some reason, the increased DC voltage is divided by the sampling resistor, which will increase the voltage of the M6 ​​R terminal and the voltage of the K terminal, and the internal light of the 1 and 2 feet of the M2. The luminous intensity of the diode is increased, the conduction level of the phototransistor inside the 3 and 4 legs is deepened, the internal resistance is reduced, and the voltage of the 1 pin of the UC3843B is lowered, so that the UC3843B reduces the duty ratio of the 6-pin output pulse and reduces the output of the secondary winding. The voltage stabilizes the output DC voltage at +5V and +12V for voltage regulation purposes. vice versa.
The -12V uses a three-terminal regulator L7912C-V for voltage regulation. The +3.3V uses a regulator circuit consisting of a high-power FET Q2 (P40NF03L) and a precision reference regulator M4 (TL431). At the beginning of power-on, the +5VSB is pre-controlled by diodes D 18 and R22 (510 Ω). When the 12V power supply has an output, 12V is applied to the gate G of Q2 through diode D17, resistor R70 (100Ω), R22, etc., and Q2 is turned on. The self-locking conduction is adjusted by the resistors R51 (10Ω), R19 (2.37kΩ), and M4 voltage regulation, and the +3.3V power supply is output.
(3) Output rectification and filtering circuit +3.3V, +5V, +12V output rectification and filtering circuit from T1 secondary winding, rectifying diode D8 (STPS30L45CT), D7 (STPS2045CT), D6 (STPS20H1000T) and combined choke L4, each Filter capacitor C15 (1000μF / 10V), 13 (1000μF / 6.3V), C11 (1200μF / 16V) and other components. +3.3V is provided by the 7-4 winding of T1; +5V is provided by the 7-5 winding of T1, and a two-stage LC filter circuit is used; +12V is provided by the 7-5 winding of T1 and the 8-6 winding in series; -12V The 3-to-1 winding of the combined coil L4 is supplied and supplied through the three-terminal regulator M1 (L7912C-V).
When the secondary winding of T1 has induced voltage, this voltage passes through the respective rectifier diodes (diodes in the horizontal position at the left end of L4), L4 charges the respective capacitors, and the output voltage is established. When the induced voltage disappears, the rectifier diode is turned off, at this time due to L4 The current in the current cannot be abrupt, the voltage generates a flyback voltage in L4, and the polarity is left negative right positive. This flyback voltage turns on the freewheeling diode (the diode in the vertical position of the left end of L4), and L4 is discharged through the load and the rectifier diode. The continuity of the load current during the turn-off of Q1 is maintained, and the stability of the output voltage is improved.
4. PS224U chip function The power management chip is a 4-channel secondary monitoring IC, which is packaged in a 16-pin DIP package. It has 3.3V, 5V, dual 12V overcurrent, over/under voltage detection protection and locking, fault protection, and built-in 300ms power supply. Output delay, 75ms undervoltage/overcurrent delay protection, 38ms PSON/control, wide power supply range (3.8V-16V) and other functions.
Its internal functional block diagram and pin function are shown in Figure 4 and Figure 5. The pin functions are shown in Table 2.





The chip can reduce circuit components and improve the reliability of the protection circuit. When the auxiliary power supply works normally, the output +5VS power supply is supplied to the 13 pin of M10 through D18. The power supply voltage is limited to 4.3V. Once the auxiliary power supply is not working properly, the +5VS output drops. When the M10's 13-pin power supply drops synchronously below 3.8. When V, the main power supply will not work. After the main power supply is working, the 13-pin power supply of the M10 is supplied by +12V via the diode D17 and the resistor R70 (101) branch, about 10V. D18 and D17 act as isolation to avoid mutual influence.