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Im having trouble understanding how i can achieve a constant output voltage with a varied input voltage. I know how to design a buck converter with a constant output when the input voltage is fixed but not when the input voltage varies.

How do i ensure the output voltage stays constant for a varied input voltage.

Thakyou

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    \$\begingroup\$ Do you understand how you can have a constant output voltage over different loads? Its the same principle as that: you have a feedback and change the duty cycle of the switching mode as required to keep the same voltage. \$\endgroup\$ – Puffafish Sep 25 '20 at 7:52
  • \$\begingroup\$ Usually, feedback. \$\endgroup\$ – Brian Drummond Sep 25 '20 at 11:47
  • \$\begingroup\$ Hey Thanks heaps for the responses. Is there a way to do this a little simplier without feedback? say like designing the buck converter for a certain voltage and then clamping the voltage using a simple circuit ? \$\endgroup\$ – jpg4321 Sep 26 '20 at 1:42
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How do i ensure the output voltage stays constant for a varied input voltage.

You use a method called feedback - the output voltage is compared against a stable reference voltage and, if it rises above the reference voltage the duty cycle of the buck converter is lowered. If it falls below the reference voltage, the duty cycle is increased. For this you will need a voltage reference and an error amplifier.

There are hundreds of books written about this and so, you might imagine, my answer is just giving the very bare essentials of what you need to do to regulate the output voltage.

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  • \$\begingroup\$ Hey andy thank heaps for the answer! Completely understand about the feedback loop method and incorporating a control method. But is there anyway to do this, say design the buck converter for the lowest input voltage (choose L, C and D appropriatley) but clamp the voltage to the lowest operating point even if the input is increased above this? Basically is there a method to achieve a constant output with a varying input without implementing a control law? \$\endgroup\$ – jpg4321 Sep 26 '20 at 1:12
  • \$\begingroup\$ A buck converter needs to have control. There are no buck converters as you describe. If you want a highly lossy zener voltage regulator then that's not a buck converter - it's a zener regulator. Buck converters have a controller that does what I said in the answer. \$\endgroup\$ – Andy aka Sep 26 '20 at 7:30
  • \$\begingroup\$ @jpg4321 if you are now done with this question and answer please formally accept my answer. I would normally say accept an answer but there is only mine. If you still have a query relevant to this question, please leave a comment. \$\endgroup\$ – Andy aka Oct 7 '20 at 8:24
  • \$\begingroup\$ @jpg4321 if you are now done with this question and answer please formally accept my answer. I would normally say accept an answer but there is only mine. If you still have a query relevant to this question, please leave a comment. (repeat). \$\endgroup\$ – Andy aka Oct 11 '20 at 10:17

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