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Registered Member #952
Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388
I'm finally building my first halfbridge SSTC (hehee still no mains power; it's going to run from a flyback converter and a cap), and I have a simple question. As the coil will be quite small, perhaps 45mmx100mm, the driver circuitry needs to be pretty small too.
So, the gate drive part is going to be borrowed from Steve Ward's Mini SSTC schematic. On Steve's page it says:
Its also possible to completely eliminate the 74HC14 and feed the antenna directly to the UCC37321/2 gate driver inputs, but this might not work as reliably for some people, so experiment at your own risk.
Ok, so I have successfully done this with one gate drive chip but has anyone tried it with two GD chips like in Steve's schematic? I bet there are quite many people who have replicated Steve's Mini SSTC but has anyone tried removing the 74HC14?
I don't myself see any problem on it. The GD chips have high impedance inputs so they are also very sensitive and can be easily driven from the antenna feedback.
Registered Member #1153
Joined: Mon Dec 03 2007, 07:27PM
Location: Croatia
Posts: 213
Hey from where you stole the flyback idea!
Aynway i did experiment many many times with feeding the antenna signal directly to UCC by just shorting the 1 and 4 pin in socket of 74HC chips. And then sometimes i built the circuits without the 74HC chip and it didn't work (fets with UCC died often).
I was looking for nights and nights why half of circuits works extremly good, and other half just dies. Basically only difference was that half of circuits was made with 74HC originally and then bypassed and second not working half without 74HC. Then i found what makes it 100 % reliable, altrough i still dont know exactly why.
I understood if i was clamping the antenna signal to 5 V and feeding it to UCC-s it worked perfectly. If i clamped it to 12 V it worked bad.
Here is a photo, i ran this coil so hard my connection points on FETS melted. Never had any problem with reliability. The circuit shows that 74 HC is installed but i just removed it and put a jumper on 1 and 4 pin.
Registered Member #580
Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410
Its also possible to completely eliminate the 74HC14 and feed the antenna directly to the UCC37321/2 gate driver inputs, but this might not work as reliably for some people, so experiment at your own risk.
Registered Member #952
Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388
Ok, so I will just use 74HC14 to get the coil running more reliably. Could it be possible to use just one 74HC14 inverter gate instead of two in series, and reverse the primary phasing? I would like to do this to minimize the delay.
Registered Member #1200
Joined: Mon Dec 31 2007, 01:43PM
Location: Kaohsiung, Taiwan
Posts: 27
Dr. 2N3055 wrote ...
Ok, so I will just use 74HC14 to get the coil running more reliably. Could it be possible to use just one 74HC14 inverter gate instead of two in series, and reverse the primary phasing? I would like to do this to minimize the delay.
I think it will work. I've done something similar to your concept and it works very well.
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
My coil was running with that, the only reason of the second 74hc14 gate is the inversion of the signal on the second driver. Here I made one Class E SSTC with one TC4429 and a mosfet, the TC4429 was the input clamped to 12V, it works like the 74hc14 on the input. For Half-Bridge I never tested without the 74hc14.
Registered Member #952
Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388
So if you use a UCC37321/22 pair (inverting/noninverting), there's absolutely no need for the second 74HC14 gate. The primary phasing just has to be reversed.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Dr. 2N3055 wrote ...
So if you use a UCC37321/22 pair (inverting/noninverting), there's absolutely no need for the second 74HC14 gate. The primary phasing just has to be reversed.
I have a feeling it might not work with just single gate. Yes, you can reverse primary, but the starting pulse will have negative feedback so I think there will be nothing to kick the coil intooscillation. I might be wrong though.
If someone did not understand me well here is what I mean: 1) the antenna feedback must be right polarity 2)the starting pulse must have positive feedback. Only if these 2 things are right the coil catches feedback.
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An antenna feedback question
