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High Voltage Boost Converter - sacrilege?
High Voltage Boost Converter - sacrilege?
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Old 10th January 2019, 10:25 PM   #81
trobbins is offline trobbins  Australia
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This threads smps is a discontinuous flyback - the diode needs a fast turn-on, and although the turn-off (reverse recovery) should be as fast as possible, that is alleviated by the diode current naturally passing through zero at turn-off as well as the reverse voltage just resonantly increasing. The secondary winding is not 'push pull' in the context of general use of that description - both diodes conduct at the same time - one to bump the positive rail up, and the other to bump the negative rail more negative.

The scope plot in post #79 shows a 13.5us period (75kHz), and diode on time of about 6us (about 44% duty cycle). When the diode stops conducting, the diode voltage swings resonantly, as does the FET drain voltage during that portion of the period. The FET is conducting during about the 4us that the diode waveform is flat, and then the fet primary energy flies back to the secondary winding for the diode to pass.

This smps was the topic of another thread here as well: YH11068A 10-32V to 45-390V dc/dc - guess the control ICs

The other smps linked in post #74 is an unregulated isolated pp style with 37kHz ripple, that has the advantage of allowing many fixed secondary voltage levels to be set up (assuming a fixed nominal 12V input level) by either using a full-bridge or doubler rectifier output, and using the range of secondary taps.

Last edited by trobbins; 10th January 2019 at 10:30 PM.
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Old 11th January 2019, 01:48 PM   #82
mondogenerator is offline mondogenerator  England
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Thanks trobbins

Given how simple the circuit is for these PSUs, I am almost tempted to build a heavier duty version (I have some 600V IGBTs somewhere that may suit)

However the whole fly back transformer/coupled inductor subject is vast in itself! I found some pot cores (3C85 ferrite, 0.5" diameter by about an inch E cores) and I spent the last 2 hours trying to find reference to the cores, which I find are discontinued Phillips.

Anyway I think the core material is vaguely suitable, but perhaps I am better off trying to make a simple boost inductor using them?

It would seem far simpler a design exercise for a simple booster (and I probably have some design theory in my uni folders to help out)
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