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Buck Converter voltage mode control

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giraffu

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I understand that there's 2 mode of operations. Discontinuous current and continuous current. The critical resistance is Rb and if the resistive load is higher than the critical resistance the system is in DCM.

That's theoretical and for open loop buck converter. What happens when i add a voltage mode control with a PID controller system for a closed loop buck converter? Will it be the same?
 

Yes, it will be the same. The mode of operation is purely dependent on the Q of the LC tank.
 

Please calculate power stage gain of continuous time equivalent circuit and realize that it will increase and be current dependent in DCM. Respectively a voltage controller that is stable in CCM can become unstable in DCM with insufficient gain margin.
 

Yes i understand that it is current dependent as when the load current decreases below critical current value it will be in DCM and there's an equation for DCM. When i add voltage mode control, am i right to say that no matter DCM or CCM the output voltage will follow my reference voltage and maintain when i varies the output load and input voltage.
 

When i add voltage mode control, am i right to say that no matter DCM or CCM the output voltage will follow my reference voltage and maintain when i varies the output load and input voltage.
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Yes, you seem to be asking can you still regulate a power supply output in either DCM or CCM...yes ..in both

- - - Updated - - -

Thos concerns flyback not buck, but its the same thing with reference to Voltage mode control or current mode control.....it shows how a stable voltage mode controlled converter can go untable when it subsequently goes into DCM....

App Note AN57 on fig. 13, page 9 shows that a voltage mode flyback that is stable in CCM, can go unstable in DCM.
(the plot shows vout when load is stepped from high load in CCM, to lighter load where its in DCM)..

AN57:
https://ac-dc.power.com/design-supp...es/an-57-9-simple-steps-stable-control-loops/

(a stable current mode controlled converter will virtually always be stable in DCM if it had been stable in CCM)
 

When i add voltage mode control, am i right to say that no matter DCM or CCM the output voltage will follow my reference voltage and maintain when i varies the output load and input voltage.
Click to expand...
Yes, but you may need to reduce the controller gain in DCM to keep the control loop stable.
 

A current mode DCM power stage has less gain than a CCM current mode one.
Is it the other way round with voltage mode control and DCM vs CCM?
 

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