Testing method for dynamic indicators of AC regulated power supply

1 Maximum overshoot amplitude of output voltage when source voltage steps

(1) Test conditions

Quantities other than the source voltage should meet the reference conditions. The variable is the source voltage, and the measured value is the maximum overshoot instantaneous value of the output voltage.

(2) Test method

Connect the test circuit as shown in Figure 1.

Figure 1 Power supply dynamic performance test circuit

S1 is a source voltage step control switch. When S1 is in position a, the power supply under test is powered by a higher source voltage. When S1 is in position b, the power supply under test is powered by a lower source voltage. When S1 is quickly switched between a and b, the required source voltage step can be obtained.

The role of R1 and R2 is to ensure that the power supply under test is uninterrupted. The resistance value should be selected so that the supply voltage is close to the lower value when the source voltage step occurs when S1 is not connected to either side.

N is a digital storage oscilloscope, which is used to measure and record the instantaneous value of the output voltage. The digital storage oscilloscope should have a sufficient sampling rate to accurately reflect the transient process of the output voltage change.

T is a synchronous trigger, which starts the generation and measurement of the source voltage step at the same time.

Set the source voltage (position of the voltage regulator) according to the value specified in Table 1, operate switch S1 to generate a source voltage step, and simultaneously record the transient change waveform of the output voltage of the power supply under test.

Table 1 Data processing of source voltage step response test

(3) Test results

The maximum overshoot amplitude should be the instantaneous value of the output voltage overshoot (see Figure 2), and the largest voltage value shall be taken as the test result.

2 Total recovery time of output voltage transient when source voltage step

(1) Test conditions

Quantities other than the source voltage should conform to the reference conditions. The variable is the source voltage and the measured quantity is the total recovery time of the output voltage transient.

Figure 2 Transient characteristics of output voltage under step quantity[page]

Figure 3 Starting impact current and power on/off overshoot test circuit

(2) Test method

The total recovery time of the output voltage transient during a source voltage step is measured simultaneously with the maximum overshoot amplitude of the output voltage.

(3) Test results

The total output voltage transient recovery time when the source voltage steps includes the transient delay time and the transient recovery time (see Figure 2). The maximum measured value is the total recovery time.

3 Maximum overshoot amplitude of output voltage during load step

(1) Test conditions

The other influencing quantities except the load should meet the reference conditions. The change is the output current, and the measured value is the instantaneous value of the maximum overshoot (overshoot or undershoot) of the output voltage.

(2) Test method

Connect the circuit as shown in Figure 1, where:

R3 and R4 are variable resistors used to adjust the size of the load step. R3 is adjusted so that the current flowing through it is equal to 30% IIN and 80% IIN respectively, and R4 is adjusted so that the current flowing through it is equal to 20% IIN.

S2 is the load control switch.

S3 is the load step 20%IIN control switch.

Set the load according to the provisions of Table 2, operate switches S2 and S3 to generate load steps, and record the transient change waveform of the output voltage of the power supply under test.

Table 2 Load step response test

(3) Test results

The maximum overshoot amplitude should be the instantaneous value of the output voltage, and the largest value in the measurement shall be the test result.

4 Total output voltage transient recovery time during load step

(1) Test conditions

The other influencing quantities except the load should meet the reference conditions. The change is the output current, and the measured value is the instantaneous value of the maximum overshoot (overshoot or undershoot) of the output voltage.

(2) Test method

Connect the circuit as shown in Figure 1. The total load step transient recovery time is measured simultaneously with the maximum overshoot amplitude of the load step.

(3) Test results

The total transient recovery time during load step includes transient delay time and transient recovery time. The maximum measured value is the total recovery time.

5Starting surge current

(1) Test conditions

The load is rated and the amount of change is the source voltage (from off to on), which is measured as the instantaneous value of the input current.

(2) Test method

Connect the circuit as shown in Figure 3.

A non-inductive resistor R is connected in series in the source input circuit and has nothing to do with the phase angle switching. A digital storage oscilloscope is used to measure and record the voltage drop of the starting impact current on the resistor R and calculate the maximum instantaneous value of the starting impact current.

The value of resistor R should be selected so that the drop of source voltage when starting surge current occurs is less than 10% of the nominal value of source voltage.

During the measurement, the phase angle switch is measured once every 15° (electrical angle). If there is no phase angle switch, it can be determined by statistical method, and the switch is randomly switched 20 times.

If the power supply under test is not allowed to be started under load, it can be tested under no-load conditions, and "under no-load conditions" should be noted on the test results.

6. Overshoot when turning on or off

(1) Test conditions

The load is the rated value and the amount of change is the source voltage (from off to on or from on to off), which is measured as the instantaneous value of the output voltage.

(2) Test method

Connect the circuit as shown in Figure 3 and connect the storage oscilloscope to the output terminal of the power supply under test. Refer to the test method in 5(2) to perform power-on and power-off tests using a phase angle switch or statistical method (randomly switch the switch 20 times), and measure the overshoot (instantaneous value) of the output voltage.

(3) Test results

The maximum instantaneous value of the switch (shutdown) overshoot in the measurement is taken as the switch (shutdown) overshoot value.