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Measure R between Vin and GND, Vin and SW, SW and GND, Vout and GND
Measure R of feedback resistors, frequency select resistor
Set up a start up test, 1 probe on SW and 1 probe on Vout. Set up oscilloscope to measure waveforms on SW and Vout and make sure to set trigger to single. Then quickly turn on and off the power supply. Hopefully the waveforms show that buck converter works or explain why it doesn’t work.
Load regulation
Vin = 50V, Iout = 1A
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Vin = 50V, Iout = 2A
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Vin = 50V, Iout = 3A
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Vin = 50V, Iout = 4A
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Vin = 22V, Iout = 1A
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Vin = 22V, Iout = 2A
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Load transient
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Vout ripple
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