isolated buck converter idea

I was wonder as a proof of concept, will this work? this schematic below works by charging a high current capacitor which has a small amount of series inductance to temporarily limit the current, and after charging, the switch (similar to the H bridge configuration) dumps the charge into a storage/smoothing capacitor.

By using this method, one can eliminate the cost of transformers in isolated buck converters. A control circuit will control the pulse width into the smoothing capacitor through a negative feedback loop (AKA, as the voltage on the storage cap rises to a target value, the PWM will decrease until the high current capacitor is permanently connected to the DC supply. as the voltage drops, the duty cycle will increase to a 50% maximum.)

I am just curious why this might not work, and if it does, does such a system already exist?

Picture of isolated buck converter idea
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iceng3 years ago

Its called a switched capacitor supply.

BUT it works at speeds beyond what a relay cannot do !

So you must use semiconductors and therefore loose any benefit of isolation.

-max- (author)  iceng3 years ago
Ahh, I was think of using MOSFET switches in sort of an H-bridge configuration, but considering that that is not true isolation, especially if a MOSFET fails.

Its feasible

In the sort of transformers used in switchmode supply supplies, making a "transformer" is no more expensive than making an "inductor", and a lot safer.

-max- (author)  steveastrouk3 years ago
Also, how do they wind toroids in factory production anyway?

Very clever machines. Like this one.

http://youtu.be/zT8sJJZyKzc

-max- (author)  steveastrouk3 years ago

lnteresting. I guess small toroids are wound the same way.

iceng -max-3 years ago

I make a wire hanger loom scuttle and wind enough wire on it to pass through the toroid leaving a turn on every pass.

Make sure there is enough room in the center of the wound toroid to still pass the wire scuttle before you start winding 200 turns by hand and get stuck on 150 with no more center space !

-max- (author)  steveastrouk3 years ago
I think the inductance could even be just parasitic and in the PCB traces and capacitor. If the capacitor and transistors can handle high peak currents, there probably is no need to have the inductor!

Similar circuits are used for inverting supplies.