Full Bridge SMPS With High No Load Voltage?

In my attempt to build an inverter-style plasma cutter, I have run into a problem. How can a full bridge SMPS create a high (270 VDC) near open circuit voltage, but have a relatively low load voltage (90 vdc at

25+ amps)? The high voltage is used to start the arc, and the lower voltage is used to maintain the arc. I'm planning to use a CCM PFC with an output of 220 vdc into a full bridge (current mode, fs=25khz). See
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Reply to
Jeremy Samuels
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It has to act like a current source; persumedly you can alter the feedback to do that.

Reply to
Robert Baer

You could put an extra winding/diode on the output choke and feed that to the output, you would need another diode in the main output to stop it feeding back.

Reply to

Sounds good. The other option is sense the i_out and switch the regulation voltage accordingly. You might find you've got almost all the bits in place to do that already.


Reply to

It's not uncommon to use some parallel source of high voltage that has a comparatively high output impedance. When the heavy arc current starts to flow, the high voltage effectively collapses to the voltage provided by the low impedance supply. This is sometimes done with additional windings on the main transformer, sometimes done as a completely separate circuit. In either case, you can add circuitry to actually switch off the HV when the arc starts if you like. It may or may not be necessary to prevent the HV output from inhibiting LV circuitry through negative feedback. Many such circuits don't have negative feedback, but run at a conversion ratio determined by feedforward (line input) only. Paul Mathews

Reply to
Paul Mathews

That might be an interesting exercise in stability.

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