The computer is now an indispensable tool in our lives and work. As a key component of the computer, the power supply must not only meet the relevant specifications and standards in performance, but also its load capacity, reliability, and the main board and peripherals. The compatibility of all has a great influence on the reliable and stable operation of the whole system.
Among the many test items of computer power supply, the two key tests of timing characteristic test and dynamic test require a powerful electronic load with high test accuracy. ITECH’s star product IT8700 series multi-input programmable DC electronic load can dynamically test up to 25KHZ, and the measurement resolution can reach 0.1mV 0.01mA. Freely select from 8 types of load modules, which can meet the test requirements of up to 16 channels, and bring users accurate tests in multiple test fields such as electronic components, ATE test systems, solar cells, LEDs, communication tests, aerospace, etc. measuring.
Timing characteristic test
The PC power supply not only outputs voltage, but also has a signal connection with the motherboard. The two have a certain relationship in time sequence. This is called timing. Timing is an important condition for the power supply and the motherboard to work well, and it also causes the computer to fail to switch on and off the power supply normally. The most common cause of incompatibility with the motherboard.
The most important thing in the sequence is the relationship between the power supply output voltage and the PG signal and PS-ON# signal. The PG signal is controlled by the power supply, indicating whether the power supply is ready, and the PS_ON# signal is controlled by the main board, indicating whether to turn on. The voltage of the PC power supply must respond to the output of the computer motherboard (such as CPU, hard disk, etc.) according to a certain timing requirement to process information, as shown in the following figure:
Figure 1 PC power supply voltage timing diagram
The corresponding timing requirements are as follows:
The test method is as follows:
1. Start-up time: T1 is required to be T1 <500mS, full load, normal power supply voltage, PS/ON for power-on, and the time for +12V, +5V & +3.3V to rise to 95% of the nominal value is T1.
2. +5V, +12V, and +3.3V rising edge time: 0.1mS≤T2≤20mS is required, and PS/ON is used for power-on, and the lower limit, normal and upper limit of the power supply voltage are measured once, and the worst is taken.
3. PG delay: 100mS<T3<500mS is required, the full load low voltage and the normal voltage are measured once each, and PS/ON is used as on/off.
4. PG maintenance time: requires T5 ≥16mS, full load, normal power supply voltage, and measurement when AC power supply is turned off.
5. PG drop warning time: requires T6≥1mS, full load, normal power supply voltage, cut off AC and PS/ON, and measure once each.
Note: The rising edge and falling edge time are the time in the range of 10% to 95% of the indicator value.
In the above sequence test, due to the unique synchronous pull function of the IT8700 series, the synchronous pull of the load is well controlled (the synchronization time can reach less than 10us), and the built-in GPIB communication interface of this series can realize the synchronous pull. Output.
Figure 2 IT8700 series electronic load
In the actual test, due to the impedance of the test line, a voltage drop will occur. In order to ensure the measurement accuracy, IT8700 series comes with a remote measurement function. Users can use this terminal to measure the output terminal voltage of the instrument under test, and use the remote measurement wiring method to compensate for the voltage drop on the line, which can greatly improve the measurement accuracy. .
dynamics test
In fact, a constant voltage output power supply has a feedback control loop in the design, which can continuously maintain a stable output voltage for its output voltage. In fact, the feedback control loop has a certain bandwidth, which limits the power supply's response to changes in load current. If the phase shift and gain of the input and output of the control loop are 1 and exceed 180 degrees, the output of the power supply will be unstable, out of control, or oscillating. When the computer is working, the current changes dynamically, rather than always maintaining the same. Therefore, dynamic load testing is extremely important for PC power supplies.
Programmable electronic load can be used to simulate the worst load conditions when the power supply is actually working, such as the rapid rise of the load current, the slope of the fall, the cycle, etc. The IT8700 series has a dynamic mode up to 25KHZ, which can simulate the current changes of the computer under different operating conditions to test the dynamic characteristics of the power supply.
Figure 3 Dynamic diagram of load current
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