(4) Reading the test results:

A. It is usually measured under the conditions of full load, half load and zero load.

B. The phase should be read under unwrap

C, Gain margin: loop gain when the phase of A/R is zero

Phase margin: Phase value when loop gain is 0dB

As shown in the figure above: the phase margin is 67.4o at 580Hz (line A); The gain margin is 38.1dB. At 18.6KHz (line B), the method and principle of reading the gain margin and phase margin are slightly different. The reason is that the error amplifier (not only GH) is included in the A/R during the switching power supply measurement, which has a 180 degree reverse change.

(5) Requirements for test equipment for loop gain test:

Requirements for test equipment 4395A(network analyzer) frequency coverage range from 10Hz to 50KHz or higher frequency range from 10Hz to 500MHz

Narrow bandwidth IFBW 2Hz to 30KHz

High frequency resolution test points: 2 to 801; Frequency resolution: 1mHz

Log scan Scan mode: log scan

Gain and Phase mode Format: LogMag and Phase Marker function - minimum 4 (2 for each margin) or 8 for Delta-Marker Marker and Delta-Marker small excitation power output power -60dbm to 20dBm

3. Output impedance

(1) Test equipment:

4395A, 41802A*2 (50ohm to 1Mohm adapter), 10441B*2 (probe), 9100-0855 (transformer)

(2) Test block diagram:

A/R lin MAG is the test result. In order to ensure the accuracy of the test, it is necessary to conduct straight-through calibration before the test.

(3) Problems that need to be paid attention to in the test: in order to prevent direct current output from the switching power supply to T1, put the capacitor C in the middle of +out and T1. The impedance of T1 should be less than a few ohms in the frequency range tested, and 470uF is recommended.

(4) Test results:

(5) Requirements of output impedance test on test equipment

Requirements for test equipment 4395A(Network Analyzer)

Frequency range from 100Hz to 100 KHZ and even wider frequency range from 10Hz to 500MHz

High frequency resolution test points: 2 to 801; Frequency resolution: 1mHz

Log scan Scan mode: log scan

Marker function Eight markers

Pass/Fail function The built-in limit line function is used for Pass/Fail tests

Four : Power supply output fluctuation, switching power supply noise test

(1) Test equipment: 4395A, 41802A (50ohm to 1Mohm adapter), 10441B (probe)

(2) Test block diagram

The spectrometer mode is used to observe the characteristics of the output signal

(3) Test results

(4) Power supply output fluctuation, switching power supply noise test requirements on test equipment

Requirements for test equipment 4395A(Spectrum analyzer)

Wide frequency coverage Frequency range from 10Hz to 500MHz

Narrow bandwidth, fast test speed IFBW: 1Hz to 1MHz (narrow IFBW test speed is also very fast)

Log scan Scan mode: log scan

Marker function Eight markers

Pass/Fail function The built-in limit line function is used for Pass/Fail tests