Voltage Mode DC-DC Buck Converter

[iscmos]

Can someone give me a clue about the maximum duty cycle and minimum on time of voltage-mode DC-DC buck converter? I konw there is maximum duty cycle and minimum on time for current-mode DC-DC converter, they are dependent on CLK signal, but for voltage-mode, it seems has nothing to do with CLK signal, so does this mean there is no limit for maximum and minimum?Thanks!

 

[eem2am]

i just answered this long but site crashed.

in brief, you can get controllers with all ranges of on and off min/max etc

 

[VVV]

The maximum duty-cycle has nothing to do with the current or voltage mode, it only depends on the internal circuitry. So it can be 100%, even for a voltage-mode buck.

 

[iscmos]

The maximum duty-cycle has nothing to do with the current or voltage mode, it only depends on the internal circuitry. So it can be 100%, even for a voltage-mode buck.

That was I thought, you konw, in theory, the range could vary from 0% to 100%, but if it works in the limited condition, what is the response of DC-DC loop?
Also there is buck-boost converter can resolve this problem, especially when vin is very near to vout.

 

[VVV]

If the duty-cycle is limited by the internal circuiry, then the loop is simply open and the output just follows the input, according to the duty-cycle:
Vout=Dmax*Vin,

so any change in Vin will be reflected at the output, because the loop can no longer work.

 

[eem2am]

Vout = D * Vin

always this.

But iobviously in transient situation the duty cycle may be different...but on constant load this is it

vout = d vin

does not matter vmc or cmc