ATX switching power supply technology design based on PS223

The switching power supply takes safety and reliability as the first principle. The power management monitoring chip is used in the design of high-performance and high-power ATX power supply to achieve surge protection soft start and protection functions such as overvoltage, undervoltage, overheating, overcurrent, short circuit, and overtemperature.

Switching Power Supply (SPS) uses modern power electronics technology. It is small, energy-saving, lightweight and highly efficient and is widely used in almost all electronic devices, including various terminal devices dominated by electronic computers, communication equipment, etc.

1 ATX power supply overview and power management monitoring and protection functions

The high-power (350-900 W) ATX power supply specification version formulated by Intel is ATXl2V 2.2. +12 V uses dual-channel output, one +12 V (A) is dedicated to the CPU, and the other +12 V (B) is used to power other devices. The connector output to the motherboard is 24 pins to output two sets of +12 V. The

high-performance switching power supply is designed as active power factor correction PFC (Power Factor Correction), using integrated PFC/PWM controllers such as Champion's CM6800G to provide integrated control of PFC and PWM power level circuits for the power supply, and using power management monitoring chips such as PS223 to provide multiple protections such as overvoltage, overcurrent, overpower, low voltage and short circuit. Temperature is the most important factor affecting the reliability of power supply equipment. According to relevant data analysis, overheating can cause damage to power devices, and an overheating protection circuit needs to be set. The short circuit protection (SCP) and overload protection (OPP) in the protection design are mandatory standards for ATXl2V. They are triggered to protect the power supply when short circuit and total load of each line are overloaded; overcurrent protection (OCP) prevents overload of a certain output of the power supply; overtemperature protection (OTP) prevents overheating inside the power supply; overvoltage/undervoltage protection (OVP/UVP) is used to trigger when the output voltage exceeds/is lower than the standard value by 20-25%. If there is an abnormality in the power supply, the output will be cut off immediately, and all voltages will not be output. At the moment of power on, the fan will stop after a movement, and the power supply is in the protection state.



Figure 1 is a block diagram of the switching power supply conversion process. The switching power supply conversion process is AC input → EMI filter circuit → rectifier circuit → power factor correction circuit → power stage primary side (high voltage side) switching circuit converted into pulse current → main transformer → power stage secondary side (low voltage side) rectifier circuit → voltage adjustment circuit (DC-DC conversion circuit) → filter circuit → power management monitoring → output.

[page]2 Functional features of PS223

PS223 produced by SiTI is a power management monitoring chip specially designed for high-performance, high-power switching power supplies. It has the functions of controlling, generating PG and stabilizing three voltages: +3.3 V, +5 V, +12 V (A), and +12 V (B). It realizes UVP (undervoltage protection), OVP (overvoltage protection), OCP (overcurrent protection), and SCP (short circuit protection) of each output, and provides a control input with self-recovery function, which can be used as OTP (over-temperature protection) or -12 V UVP (undervoltage protection). When the set value on the chip is exceeded, the control circuit will be closed and locked, and the power supply output will be stopped. It can be restarted only after the fault is eliminated. The internal design has overload protection and lightning protection functions to ensure the stable operation of the entire power supply.

2.1 Main performance indicators of PS223

1) Overvoltage/undervoltage protection and lockout; 2) Overcurrent protection and lockout; 3) Fault protection, output shutdown; 4) Power good output and signal protection; 5) Built-in 300 ms power good output delay; 6) 75 ms low voltage/overvoltage delay protection; 7) 38 ms anti-shock protection; 8) 73μs anti-noise protection; 9) Wide power supply voltage range (90~270 V); 10) Special protection for AC power shutdown.

2.2 Description of PS223 Pin Functions

PS223 uses a 16-pin DIP package, and the functions of each pin are as follows: PGI is the MAIN POWER signal output terminal; VSS is the ground terminal; it is the OVP/UVP/OCP protection signal output terminal; it is the REMOTE CONTROL output terminal, which is used to switch SPS; ISl2A is the 12 V (A) OCP comparator V+ input terminal, with a built-in Sink current source for OCP protection operating point adjustment; RI is used to generate an OCP current source through a grounding resistor (R1: 20~80 kΩ); ISl2B is used for the 12 V (B) OCP comparator V+ input terminal, with a built-in Sink current source for OCP protection operating point adjustment; VSl2B is used for the 12 V (B) OCP comparator V- input terminal, 12 V (B) OVP/UVP detection; OTP is an additional protection function, which can be used for OTP (temperature abnormality protection); IS5 is a 5 V OCP comparator V+ input, built-in Sink current source, used for OCP protection working point adjustment; IS33 is 3.3 V OCP comparator V+ input, built-in Sink current source, used for OCP protection working point adjustment; VSl2A is 12 V OCP comparator V- input, 12 V OVP/UVP detection: VS33 is 3.3 V OCP comparator V- input, 3.3 V OVP/UVP detection: VS5 is 5 V OCP comparator V- input, 5 V OVP/UVP detection; VCC is the working power supply 3.8~15 V; PGO is used for PW-OK, and the power supply SPS outputs a normal state signal.

2.3 Description of the main control signals

The ATX switching power supply relies on the combination of PGI (+5 VSB) and control signals to turn the power on and off.

PGI (+5 VSB) is the power supply for the host system in the ATX standby state. It is used for network wake-up WOL (Wake-up On Lan) and power-on circuits, USB interfaces, and the working power supply for automatic opening and closing management. In the standby and controlled startup states, its output voltage is 5 V high level, and is led out from the 9th pin of the ATX plug using a purple line. It

is the control signal for turning the host power on and off or the remote wake-up power of the network computer. When the POWER switch on the host panel is pressed or the network wake-up remote startup is started, PSON is grounded by the electronic switch of the motherboard after the controlled startup. When the signal level of this port is greater than 1.8 V, the main power is off; when the signal level is lower than 1.8 V, the main power is on. Use a green line to input from the 14th pin of the ATX plug.

PGO (PW_OK) is the output signal for the motherboard to detect whether the power supply is good or bad. When the output is above 2 V, the power supply is normal, and when the output is below 1 V, the power supply is faulty. Usually the standby state is zero level, and the controlled startup voltage output is 5 V high level after stabilization. Use the gray wire to lead out from the 8th pin of the ATX plug. This signal is one of the main bases for judging whether the power supply life and quality are qualified.

It is the output terminal of UVP (undervoltage protection), OVP (overvoltage protection), and OCP (overcurrent protection) protection control signals.

[page]3 Application circuit and design

3.1 PS223 typical application circuit

The typical application circuit of PS223 is shown in Figure 2.