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A zvs is not controllable. on,off, not much else. To control a resonant SMPS you have to control the input, so you actually have 2 SMPS. A full bridge can be made to adjust the duty cycle on the fly to keep the current within reasonable limits. This is more or less demonstrated in the first video, just before the end.
I have abused this bridge a lot with things like transformers going into saturation, glitched pulses because of EMF, heat etc.. and so far I haven't managed to kill a mosfet.
I got a monster 10kw variac that I'm going to use to gradually test this bridge up to off-line voltage....in a couple of weeks.
Right now the bridge was powered by a 250w trafo with the output at about 70V dc
Edit: The PWM IC is UC3843, not a SG
More edits: Alex, forget about what the PWM IC can output, use gate driver ICs or NPN+PNP buffers (totem poles). Don't drive big mosfets (or gate drive transformers) directly from PWM ICs no mater what they are, the all don't have the drive power to turn on-off a power mosfet fast enough.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
In case anyone wants to duplicate the SG3525-based bridge circuit that Marko linked to, the pin designation that looks like a "3" at first glance, is actually pin "9", I believe.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
jpsmith123 wrote ...
In case anyone wants to duplicate the SG3525-based bridge circuit that Marko linked to, the pin designation that looks like a "3" at first glance, is actually pin "9", I believe.
Hm, looked at the schematic again, and I don't see anything that looks like 3 .. so the pin with 10nf cap and 10k resistor on it is indeed the pin 9 :)
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Daedronus wrote ...
A zvs is not controllable. on,off, not much else. To control a resonant SMPS you have to control the input, so you actually have 2 SMPS. A full bridge can be made to adjust the duty cycle on the fly to keep the current within reasonable limits. This is more or less demonstrated in the first video, just before the end.
I have abused this bridge a lot with things like transformers going into saturation, glitched pulses because of EMF, heat etc.. and so far I haven't managed to kill a mosfet.
I got a monster 10kw variac that I'm going to use to gradually test this bridge up to off-line voltage....in a couple of weeks.
Right now the bridge was powered by a 250w trafo with the output at about 70V dc
Edit: The PWM IC is UC3843, not a SG
More edits: Alex, forget about what the PWM IC can output, use gate driver ICs or NPN+PNP buffers (totem poles). Don't drive big mosfets (or gate drive transformers) directly from PWM ICs no mater what they are, the all don't have the drive power to turn on-off a power mosfet fast enough.
Hmm I was going to make a start on this circuit over the week-end so I will keep the idea of using a totem pole and gate drive IC in mind if things start to heat up too much (ie the MOSFET's).
Are there any particular gate drive IC's that you recommend? and are the 2n3094 and 2n3096 complementary NPN and PNP pair good for this sort of thing?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Alex1M6 wrote ...
Are there any particular gate drive IC's that you recommend? and are the 2n3094 and 2n3096 complementary NPN and PNP pair good for this sort of thing?
Thanks.
I like the FAN7382 dual gate driver. (because with one part i can drive lo-lo or lo-hi pairs on different boards.)
(I disagree with the previous oppinions on the PWM chips not driving mosfets. its true i would not trust the 8038, 555, tl494, or similar tradional ones, but the more modern ones like the UC3526, and UC28023/UC28025 can easily drive pretty hefty gates with no problems. And this is true of other makers, not just TI.)
EDIT: the UC3843, based on SGS, TI and fairchild datasheets does look pretty weak on tranistor drive, so for this IC id use a gate driver or IC.
EDIT: the SG3525 also looks a wee bit weak in current for gate drive.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Unmagnified, it looks like a sloppy "3". Since pin 3 is not shown as it is not used, and since many here are not familiar with that IC, I thought it best to clarify it before someone builds it that way.
Dr. Pork wrote ...
jpsmith123 wrote ...
In case anyone wants to duplicate the SG3525-based bridge circuit that Marko linked to, the pin designation that looks like a "3" at first glance, is actually pin "9", I believe.
Hm, looked at the schematic again, and I don't see anything that looks like 3 .. so the pin with 10nf cap and 10k resistor on it is indeed the pin 9 :)
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Full bridge flyback transformer driver
