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How to avoid ripples at the out of the regulator

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Nizar_Ib

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How to avoid ripples on the regulator output voltage

Hi,

when my regulator is not connected to the circuit I have a pure output voltage, but when connectiong it to the circuit below I have ripples on the output which confuse the VGs of the FET's and affects the current throw them.
why that happen? and how to avoid it?

17012018.JPG
 

About no information given.

Regulator circuit, ripple frequency and magnitude? How is the regulator supplied? If the ripple voltage is copied from the regulator input, maybe the dropout voltage is undercut.
 

A voltage regulator is supposed to regulate its output voltage. Since your voltage regulator has ripples on its output then it is not regulating. Please post the detailed schematic of your voltage regulator showing its input voltage. What is the frequency of the ripples? Is it mains hum or is it a high oscillation frequency?
 

Re: How to avoid ripples on the regulator output voltage

but when connectiong it to the circuit below...
Click to expand...

All regulators do well when they are left alone.

I am not surprised that the regulator is not doing its job when connected to a variable load. Your regulator is going out of regulator when connected to the circuit.

A simple (almost trivial) solution is to have a big capacitor close to the transistors. If that is still not enough, you are perhaps asking for too much from the poor regulator.
 

Is your voltage regulator feeding Vgate or is it the 12VDC?
If Vgate is high enough then the 12V current will be 12V/0.375 ohms= 32A!
 

Distinguish first between "ripple" as the sawtooth riding
on switched-mode power supply output, and other LDO
output behaviors (like small or large signal oscillation,
overcurrent protection "motorboating", etc.). A LDO ought
to reduce ripple from what's coming in, but many have
such poor HF PSRR that they don't do it very well. And
it's possible to pick the right (wrong) compensation such
that some frequency bends could see no attenuation or
even gain. But in any case if it's real inbound ripple the
frequency ought to be a dead match, while loop or
protection-function "activity" will be something else than
what rides on the source supply.

A couple of measurements ought to narrow down the
source and suggest "solution avenues".
 

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