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Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Hi all, I have found some mosfets here (K2049 ones) and I resolved to make a good SSTC.
I search for some time on the internet schematics of SSTC's and one friend mine have maded one long time ago.
The basic schematic is here:
I have followed a part of the schematic. I made some changes, and I used MJE13007 as the IRF950. I made some changes too on the driver, because I have 2 NPN BJT, my driver has one inverted output (totaly 2 outputs, one invert from other) with perfect Square Wave.
My Schematics is there : (The Q1(C) is 12V)
Ok steps I have made:
First I test the Low Side Circuit, I plugged all, and for test I put one 20W speaker on place of GDT Primary, Turn On, and All is working, the Speaker is Jumping (Too much :P, if some time more, its burn out).
Second I Plug the GDT Primary on the Low Side. And on one out of GDT I Put the Speaker again. But now the sound is very low, and the Speaker doesnt Jump as before, Too Low, I think 1V max. What I did make wrong?
The Primary of GDT have 2 Turns of Wire 14, and Secondaries have 6 Turns Each, of the same wire.
I am not the biggest expert but ... only 2 turns on the primary of the gate drive transformer ?? Isn't it saturating therefor not able to transer enough energi to te speaker/gates ?
Registered Member #180
Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187
Yeah, like they said you need more turns, this depends on your GDT material and also the frequency your running at. A good starting spot (for most SSTC anyways) would be around 12-16 turns or so. This site has alot of great info on GDT so have a read through Link.
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Thx all! Now it works, Now its 18 Turns of wire com PC Network cable, 2 pairs twisted it self.
Totally I have 4 wires, Some places I see the proportion needs to be 1:1:1 other I see 1:2:2. What is the correct?
I made 2 pairs, because if I want a 1:1:1 I use only one pair more one wire (three wires total), for 1:2:2 I get one pair together (As paralel) and other 2 wires I get to the exit (The wires in Paralel get half resistance and the secondaries get double of voltage :D).
Now with 18 Turns, of wire, if I put the speaker on the exit of the toroid, I get the same effect if its on the place of primary.
I was see to an error on my circuit (not in the schematics, on the monted version), I have made some mistakes, I putted the Capacitor one pin to the Source of Mosfet 1, and other to the ground, and the Primary as on the middle of Two mosfets (Source of Mosfet 1, and Drain of Mosfet 2). I am correcting now, I hope it works :)
If you use 1:2:2 then you will have a step-up transformer and when you feed it with 12v you will have 24 at the end. This will be more than the maximum gate-source voltage therefore damaging your MOSFETs. People use 1:2:2 when they want faster switching and less heat but that is dangerous for the devices (i have seen to use it when they are driving IGBTs). . Sorry about my english i am from Bulgaria
Edit: I am sorry didn't see at the first that it is a half bridge
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
You'll need a 1:2:2 ratio if you use the driver you posted above. This is because the voltage is halved when using a totem pole/ half-bridge. Remember that the 12V has to swing an equal amount negative too, meaning +/- 6V, 12Vp-p (pv-p?). Using a 1:1:1 ratio and 24V would be best.
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Help, problems on SSTC - Low Side -> High Side
