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Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Hi all, I was working on my DRSSTC, since I stoped long time ago.
I re-assembled all my Zarc Building ( ) because I was planning to buy a few IRG4PC50U for increasing performance (I found IRG4PC50U for about R$15, that is something near US$8 each, expensive but its the lower price that I have ever found here)
I turned on, but without a secondary coil, only with a metal piece on the middle (for absorv energy and dont blow my mosfets up), made a CT with 1:20 cascaded with 1:48, so 1:960~ and used 10 1k Resistors in parallel to current shunt (100R total)... Retified with 1n4148 and smooth with a 2uF cap in parallel with a 1k resistor.
Hooked up a GOOD dmm on the output of the CT (the retified one) and put it to measure voltage.
When I turned on, smokes come from the metal piece (induction heating), something about 4A from the mains (127Vac) but all working good. I was measuring mosfets temperature, and with a 30ºC ambient temperature, the mosfet only rised to 40ºC... Ok, for a ressoant circuit with a 94nF cap and a 18uH, I expected more than 50A on the primary circuit... But my DMM measured 0.94V only.
With my calculations, 0,94V + 1,2V (Diode Bridge Dropout) = 2.14V with a 100R resistor, that means 21,4mA 21,4mA * 960 = 20,544A That with max duty and max settings. 150VDC on the bridge.
(Video: ) Ok, I think it was correct, but today when I hooked up my IGBT's (IRG4PC50U with UF5408 in anti-parallel to protect them), my DRSSTC worked fine, but I got a little higher (1,5V at max, so 25A), but I was having 70cm sparks to the air with a 300V on the bus, at a lower duty. Even at max settings, I didnt got more than 2V on the CT output.
Is I measuring something wrong? I didnt think that 70cm sparks do only 25A on the bridge. The IGBT got to 42ºC too. All is working fine, without problems, but now 8A from mains (doubled 127VAC, so ~300VDC bus)
I am making a few more resistors arrays, to decrease the shunt resistor to 10R, to get a higher voltage and more precision.
Registered Member #2115
Joined: Fri May 08 2009, 01:17PM
Location: Singapore
Posts: 46
I thought its because the current waveform is pulsed high frequency at low duty cycle, so the dmm may be measuring the average voltage but not the peak voltage.
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DRSSTC Driver working, but wrong corrent at feedback?
