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FPWM of a buck converter

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alimjoco

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Guys,

If a buck converter is operating at FPWM continuous mode, will it still operate if the load current is low in which it can enter discontinuous mode?

Usually we design the inductor needed to be 1/3 of the Iload max in order to have a good trade off between eff and transient response. If i decide to use a lower inductor which has an inductor ripple current of 300mA. Will it operate if I use a load current less than 150mA. I see in the lab that my buck is still regulating at 100mA(still switching) eventhough I used a smaller inductor..I think that should be in discontinuous mode already. Why is that so.? I think i need to monitor the current thorugh the inductor to be sure.

Thanks
 

1.

If you reduce load, it will result in higher output V (unless regulation is installed). Less current flows in the converter overall.

My simulations do not show it going into an irregular mode.

2.

A smaller inductor will charge more quickly. Current may reach a plateau and stay there, until the transistor/mosfet shuts off.

Then a smaller inductor will also discharge more quickly. This may create an idle period afterward, drawing down the load capacitor.

3.

I think i need to monitor the current thorugh the inductor to be sure.

Good idea. This waveform is a vital indicator as to what's really going on.
 

After reading up on the subject, I see that discontinuous mode refers to the idle time after coil current falls to zero.

So by reducing inductor value, it can result in discontinuous mode.

Theoretically this would indicate you can increase the frequency, if you wish to make most efficient use of the coil.
 

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