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Old 18th December 2008, 09:41 AM   #1
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Lightbulb Peak Current in SMPS

I am working at SMPS , using gate drive transformer.

But the design i have does not include any diodes at the outputs of the gate drive transformer secondary, between G and S.

I am unable to determine IF those diodes are responsible for burning my Mosfets so quick!

What Zener values I should use, and can those help?

Schematic is below, please watch the part ZNR1, in the schematic. is it there for PEAK CURRENT protection? instead of the ZENERS?


Thanks All
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Old 19th December 2008, 04:16 AM   #2
dtproff is offline dtproff  United States
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A good gate drive example is here http://www.onsemi.com/pub_link/Collateral/AND8257-D.PDF

see page 4
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Old 28th December 2008, 07:50 AM   #3
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Default dtproff

dtproff


many thanks for your link, I started to read more about the power supplies around, and i found that the A-and-T-Labs power supply, will NOT work as the design shows, since driving those heavy mosfets needs attention.

Driving them Directly from the GDT is useless, putiing that ciruit in place will make things much , much better,


Thanks
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Old 28th December 2008, 11:47 PM   #4
Eva is offline Eva  Spain
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The A-and-T-Labs power supply is a bit of a scam, but the website continues in place and they are probably selling some from time to time. I think this was already discussed in some thread one or two years ago.

Are there at least 5mm of creepage between the mains live primary side and the isolated output side on the PCB?
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Old 2nd January 2009, 02:16 PM   #5
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Quote:
Originally posted by Eva
The A-and-T-Labs power supply is a bit of a scam, but the website continues in place and they are probably selling some from time to time. I think this was already discussed in some thread one or two years ago.

Are there at least 5mm of creepage between the mains live primary side and the isolated output side on the PCB?
No, it dosn't have that. It's quite scary, take a look:
http://www.a-and-t-labs.com/K6_Sw_Am...k6pwr-comp.pdf
http://www.a-and-t-labs.com/K6_Sw_Am...k6pwr-sold.pdf
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Old 2nd January 2009, 06:07 PM   #6
dtproff is offline dtproff  United States
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Yuck...

I don't think I would want to plug this in to anything I want to keep.

Tony
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Old 3rd January 2009, 03:14 AM   #7
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You don't need diodes on the output of the gate drivers. You just can't violate the max gate voltage. Gates are rated for +/-20V or +/-30V. What does the FET current look like? Drain voltage?
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