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why so big swing at output of buck converter

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kalahara

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I'm a biginner of switch power supply circuit.
The picture buck.jpg is the top circuit.
I want to achieve a 3.3v at vo node.
vob node is referenced at 0.5v, and sent into negetive input of error amplifier,
and the output of amp is compared with ramp siginal to generate PWM siginal.PWM is sent to driver to generate LDR and HDR siginal, the two siginal are make sure that there is no time for simultaneously on.

after simulation, I found the output siginal vo is oscillating with big swing
as the picture shows in vout.jpg.
Pls kindly tell me where the fault on my cicuit.
thanks.
 

hi kalahara,
few questions:
what was the frequency of oscillation? is it the same with the switching freq?
is your inductor (L1) only 10uH and the output capacitor (C1) only 4.7uF ?
 

Of course, correct loop compensation is needed for loop stability. You can achieve it by behavior model.
 

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