thank you alot for this information. sorry if understand it wrong. so you are saying that using my opamp as comparator requaries these opamps to have very large bandwith of frequency. and they are not. so you are using op amp with negative feedback configuration with caps so that frequency is limited and doesnt alow curcuit be unstable . did i understand it correctlyThere are 2-Flavors of Regulators,
Linear, which is what you've been working with, and
Switch-Mode-Regulators,
which turn either fully On, or, fully Off, usually at very high Frequencies.
Both use Voltage-Feedback,
and depending on the design,
they may also use Current-Feedback.
Switch-Mode-Regulators require a properly designed Filter-Network on the Output,
but generally speaking,
most Linear-Regulators can be run with no Filtering of the Output.
If a Switching-Regulator is run without a proper Filter-Network,
all kinds of crazy problems are created,
and you will basically have really BAD Voltage-Regulation, and a ton of Electrical "Noise".
You might get away with this if your Load is strictly Resistive,
like a Heating-Element, or an Incandescent-Light-Bulb,
but if there is the slightest amount of Inductance, or Capacitance, in your Load,
you will have serious problems.
Switching-Regulators are usually much more efficient,
and therefore, they Dissipate much less Heat than a Linear-Regulator.
To make a Switch-Mode-Regulator work,
there is usually some additional complexity and Cost -vs- a Linear-Regulator's simplicity.
Also, many Op-Amps can NOT deal with being used as a Comparitor,
especially at High-Frequencies.
The LM358's that You were trying to use are ~$0.10 Cents each,
they are for very un-demanding jobs were CHEAP is the Top-Priority.
The LT1630CN8 Op-Amps that I specified are
the closest thing to a perfect Op-Amp that I've found,
and they ought to be, because the damn things cost ~$8.oo each,
but they have excellent manners in all situations,
so they're very easy to work with.
They will operate as a Comparitor at over 100khz without issues,
and have "Rail-to-Rail" Inputs and Outputs,
which also makes them work really well for DC-Circuits.
And, they're still available in a Through-Hole, 8-Pin-DIP-Package,
which makes them Hobbyist-Friendly.
If you are willing to spend another ~$40 to ~$50 Dollars,
I'll show You how to DIY your own Switch-Mode-Regulator.
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