Abstract: The power supply, as the heart of PC, is closely related to reliable and stable operation of PC. It is critical to test the power supply of PC. In the paper, the time sequence characteristic test and dynamic test of the PC power supply are analyzed, and the key role of the ITECH IT8700 series programmable electronic load is described.

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The computer is an indispensable tool in our life. As for the power supply, as the key component of PC, the performance should comply with the relevant codes and standards, and the load capacity, reliability and compatibility with the motherboard and external equipment have great influence on the reliable and stable operation of the whole system.

A number of items of the computer power supply should be tested. In the paper, the time sequence characteristic test and dynamic test are analyzed. One powerful and high-precision electronic load is needed in both tests. With the individual IT8700 series programmable DC electronic load of ITECH, the function of the electronic load of 1-16 channel(s) can be realized, the value of the dynamic test can reach 25KHZ, and the measurement resolution can reach 0.1mV and 0.01mA.

Time Sequence Characteristic Test

The PC power supply can output the voltage and is also subject to signal linkage to the motherboard. The relationship between the PC power supply and motherboard is called time sequence. The time sequence is an important condition for good combination of the power supply and motherboard, and also a common cause of failure in normal start-up and shutdown of the computer and incompatibility between the power supply and motherboard.

The important factor of the time sequence is the relationship between the output voltage of the power supply and the P.G/PS-ON# signal. The P.G signal is controlled by the power supply, indicating that the power supply is ready. The PS_ON# signal is controlled by the motherboard, indicating whether to turn on the computer. The voltage of the PC power supply must be output to the computer motherboard (such as the CPU, hard disc) with response to certain time sequence requirements before information processing, as shown below:

The corresponding time sequence requirements are as follows:

The test method is as follows:

1. Start-up time: T1＜500mS, full-load, normal power supply voltage, using PS/ON for start-up. The time of rising from +12V, +5V and +3.3V to 95% of the nominal value is T1.

2. +5V, +12V and +3.3V rise edge time: 0.1mS≤T2≤20mS, and using PS/ON for start-up. Measure the lower limit, normal level and upper limit of the power supply voltage respectively once, and use the poorest value.

3. P.G delay: 100mS＜T3＜500mS. Measure the low voltage and normal voltage respectively once under full load. Use PS/ON for start-up/shutdown.

4. P.G duration: T5≥16mS, full load, normal power supply voltage. Conduct measurement with the AC power supply OFF.

5. P.G drop warning time: T6≥1mS, full-load, normal power supply voltage. Shut down the AC and PS/ON and conduct measurement once respectively.

Note: The rise edge time and drop edge time refer to the time between 10% and 95% of the nominal value.

Due to the special synchronous load-pulling function of the IT8700 series multi-channel load of ITECH, the synchronous load-pulling (with the synchronization time less than 10us) can be well controlled in the above time sequence test. Meanwhile, with the built-in GPIB communication interface of the series, the synchronous load-pulling output can be realized.

As the test line has impedance, the voltage drop will occur in the actual test. To ensure the measurement accuracy, the IT8700 series load of ITECH has the function of remote measurement. Users can use this terminal to measure the output terminal voltage of the tested instrument, and the line voltage drop can be compensated in the remote measurement and wiring method, thereby greatly improving the accuracy of measurement.

Dynamic Test

The power supply of constant voltage output is equipped with the feedback control circuit in the design to continuously keep the stable output voltage. As the feedback control circuit has a certain bandwidth, the response of the power supply to load current changes is limited. If the ratio of the phase shift and gain between the input and output of the control circuit is 1 and the degree exceeds 180, the output of the power supply will be unstable, out of control or vibrating. The current changes dynamically during operation of the computer; therefore, the dynamic load test is critical to the PC power supply.

The programmable electronic load can simulate the worst load condition of the power supply in actual operation, such as the rapid rise/drop slope and cycle of the load current. With the 25KHZ dynamic mode of the IT8700 series load, the current changes of the computer in different operating states can be simulated to test the dynamic characteristics of the power supply.

IT8700 Series Programmable Electronic Load of ITECH

With the modular structural design and the globally unique dynamic power distribution technology, the IT8700 series programmable electronic load of ITECH can be used in various tests. Using the individual series electronic load, the functions of the electronic load of 1-16 channel(s) can be realized, and the frame power can be extended to 4,800W, and the measurement resolution can reach 0.1mV and 0.01mA. The 100KHZ List mode and 25KHz dynamic mode can meet the requirements of most tests.

Conclusion

ITECH Electronics has been dedicated to the study of related industrial tests with “power electronic” products as the core. The IT8700 series programmable multi-channel electronic load is one of star products. With high performance and quality, which are the characteristics of ITECH products, this electronic load can be used in the time sequence characteristic test and dynamic characteristic test of the PC power supply, guaranteeing the quality of the PC power supply.