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Registered Member #1200
Joined: Mon Dec 31 2007, 01:43PM
Location: Kaohsiung, Taiwan
Posts: 27
I finally build the Mini SSTC. first, I try to input 50Vdc to the halfbridge(IRFP264*2 38A peak current) and it starts to oscillate successfully. I think that means my bridge is switching the power properly. I try to input 110Vdc and result in the death of my rectifier and FETs(all pin shorted together without any visible damage). It may caused by the over current since my rectifier is only rated at 8A. But I still want to listen you guys opinions.
I did have some 25A rectifiers, I just never thought the primary will draw so much currents so I didn't use them.
Well, another question: What will happened if I input the power to bridge without any load and driving signal(I never did this, just out of curiosity)
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
It seems to me that the rectifier died after the FETS, because 8A means at least 50A in pulse mode. But next rather use your 25A bridge...The break out point is a good hint; make it sharp and at least 3cm long. I also recommend you to use TVS for protecting the transistors. BTW: when you used 50V did you checked the performance using a fluorescent lamp placed close to the top load? If not, than this the way how to set your coil (frequency, number of primary turns...)
I just checked the picture you posted - it looks like your transistors have no heat sinks - no wonder you destroyed them
Registered Member #1200
Joined: Mon Dec 31 2007, 01:43PM
Location: Kaohsiung, Taiwan
Posts: 27
Thanks for you guys' reply.
Well, I did use a sharp breakout point almost 15cm long and when operating at 50vdc there are near 4.5cm discharges without interrupter and the FETs are only a little warm after 1min.
My primary is 5 turns direct on secondary.(When operating at 50vdc, it draw 4.xA from the power supply)
I was using a small secondary which resonates at 6xxkhz.(The new resonator is still under varnishing )
As for the heat sink, I removed them with the dead FETs.
Also, I am still wondering what will happened if I input the power to half bridge without any load and driving signals.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Also, I am still wondering what will happened if I input the power to half bridge without any load and driving signals.
Shouldnt do any harm as long as the GDT is in place to keep the gate voltage down to 0V. There will be some transient current to charge up whatever capacitors you have across the power supply, but the MOSFETs shouldnt draw any power.
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Problem with Steve's Mini SSTC
