Switching regulator load transient

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leekc_84

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Hi all,

Currently I am evaluating switching regulator to provide 5V, 1.2A load, from 3.3V input.

Looking into load transient, output voltage shows a spike up when power on, and spike down when power off. Spike is as high as double of regulated voltage ~10V.

What's the root cause of this scenario? and what mitigation paths are recommended?

Thanks for help...
 

Probably you need to adjust the compensation network of the regulator to avoid spikes, this is crucial in boost (step up) regulators since they tend to be unstable. If your regulator has soft-start feature use it, it may avoid the initial peak. Any information on the circuit used or IC would be useful.
If your system could be damaged in such these situations place a zener in parallel to the output AFTER your have solved the peak problem without the zener. Just in case it might peak in a specific unknown situation.

Ernest
 

Sounds like you need some undervoltage lockout protection on the controller. What controller are you using?
 

Hi, can you show your test setup? Does the controller has soft-start/soft-stop function?
 

Thanks for all the comments.

Actually load current comsumption is about 0.8A, i'll just want to have some margin.

The spike i mentioned is when I observed the AC voltage output. Spike up to +5V when power on the controller.


Sorry my mistake, something to add-on...

When measured the DC voltage, it shows 0 to +5V only, not +10V as describe earlier. I am not sure why AC voltage shows the spike transition when power on/off.
 
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You may face voltage spike due to high inrush current at turn on. Switching on or OFF on SMPS would lead to di/dt at source and this multiplied by Power cord inductance, would inject a voltage into mains. depending upon dI, this may add up or get subtracted from mains voltage. This could be one of the reason for AC side voltage disturbances, when switching load connected to it.
 

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