Electronic – Buck Converter Control Scheme- Why isn’t just a comparator not enough

controldc/dc converter

I am supposed to come up with some control schemes for the converter before understanding the standard PWM control scheme.

Isn't it just enough if the output of the converter is compared with a fixed reference voltage to drive the output to required voltage level? Although I'm not sure there is a lot more to it, this seems to work pretty well.

I've tried simulating this circuit with L,C and R values from an example.


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The required output voltage is 6V. S2 is a voltage controlled switch, controlled by the output of comparator.

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V2(green) is the output of comparator and V1(red) is the output of buck converter.

Best Answer

What you have here is a hysteretic-style buck converter. It may simulate well for a static load, but real-world performance may not be as robust as you'd imagine. A previous answer to this can be found here. In a nutshell, the switching frequency is dependent on the load and will vary greatly. This makes filtering out the ripple challenging.

Try quickly changing the load during the simulation and see what happens.

Now this kind of supply would work well as a pre-regulator, fed into a low-dropout linear regulator. The output of that would be very flat and virtually ripple-free.