ATX power supply core circuit

ATX Power Supply core circuit.

The main conversion circuit of the ATX power supply is the same as the AT power supply, which also uses a "double-tube half-bridge it-excited" circuit. The PWM (pulse width modulation) controller also uses the TL494 control chip, but eliminates the utility switch. Since the utility switch is eliminated, as long as the power line is connected, there will be +300V DC voltage on the converter circuit, while the auxiliary power supply also provides working voltage to the TL494, ready to start the power supply. When the voltage of this pin is +5V, the TL494 pin 8, 11 no output pulse, so that the two switching tubes are cut off, the power supply is in standby mode, no voltage output. When pin 4 is 0V, the TL494 has a trigger pulse to the switch, and the power supply enters normal operation.

ATX power supply

The output of the auxiliary power supply is sent to the TL494, and the other output is divided by a voltage divider circuit to obtain two signal voltages, "+5VSB" and "PS-ON", both of which are +5V. The "+5VSB" output is connected to the "power supply monitoring component" of the ATX motherboard as its operating voltage, requiring the "+5VSB" output to provide 10mA of operating The "+5VSB" output is required to provide 10mA of operating current. The output of the "power monitoring component" is connected to the "PS-ON", and when its trigger button switch (non-lock switch) is not pressed, the "PS-ON" is +5V, which is connected to the "PS-ON". ON" is +5V, which is connected to the positive phase input of voltage comparator U1, while the voltage at the negative phase input of U1 is about 4.5V, so that the output of voltage comparator U1 is +5V, which is sent to the "dead drive control pin" of TL494, so that the ATX power supply is in standby mode. When the motherboard's power monitoring trigger button switch (mounted on the main chassis panel), "PS-ON" becomes low, the voltage comparator U1 output is 0V, so that the ATX host power on. Press the trigger button switch on the panel once more, so that "PS-ON" becomes +5V again, thus turning off the power. At the same time, you can also use the program to control the output of the "power supply monitoring component", so that "PS-ON" becomes +5V and the power is automatically turned off. For example, under the WIN9X platform, the ATX power supply will be automatically shut down when the shutdown command is issued.