Regarding Load Resistances

uhdam

Hi Every One,

I am working on the Class E DC-DC converters. My circuit is working good for full load (RL-load resistor) and also giving the 90% of efficiency. But, the problem is that how to maintained the output voltage is constant by changing the load resistance from full load to no load.

If you have any document or any ideas please forward to me.

jegues

Sounds like you're looking for a voltage regulator with high load regulation.

uhdam

Hi jegues,

My specifications are Vin=100v;Vo=50v;Po=50w;f=3.5Mhz and Q=5. I tried in the way of changing the duty cycle and also tried to keeping the voltage regulator, but no use.
So, please give me the clear explanation about how to maintained the output voltage is constant by changing the load resistance from full load to no load.

DragonPetter

Is it a buck converter? When you go to full load to no load, does the current draw change from continuous mode to discontinuous mode in the inductor? The duty cycle transfer function on a buck converter changes when you switch from continuous to discontinuous current mode. If you are operating in continuous mode with a ducty cycle of 50%, you may have about half the output voltage as the input voltage. Once you remove the load and the current reduces so much that it operates in discontinuous mode, that same 50% duty cycle will give you an output voltage only slightly less than the input voltage. So, your operating range will cut drastically, and you will be varying your duty cycle probably less than 10%, and even within that 0-10% range, 1-5% variation will give you a wide swing in output voltage (and so your duty cycle/switching FET time resolution needs to increase). You could also add a load resistor that just barely meets the criteria to maintain continuous mode, but I think that is not the best approach unless you need something quick and non-ideal/efficient.

DragonPetter

Also, I think your minimum load will be whatever your feedback circuit losses are, as in the resistor divider. That minimum current has to be enough that you can control.

uhdam

Hello DragonPetter,

How to control the switch with respect to the output voltage?

DragonPetter

The answer to your question is to choose the correct duty cycle.

uhdam

Please let me know that, how can I choose the correct duty cycle? They are any formulae to choose that?
By the way, My circuit is not buck converter.. that is Class E DC-DC converter.