Low voltage at gate of ZVS driver / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

Low voltage at gate of ZVS driver

1 2 next

Move Thread

LAN_403

Travalon

Fri Oct 26 2018, 07:46AM

Registered Member #61835 Joined: Wed Oct 11 2017, 02:00AM
Location:
Posts: 5

Hi all. First time posting but lurking for a good time before this.
I appreciate any input.

I have successfully built a center tapped zvs driver and it worked well until I overloaded it. Rather than fix it I decided to go with a tapless design for greater flexibility. However I am having issues getting good chokes. I went with this design because of my choke issue. I built it twice and get the same results. I only get 3.4 to 3.7 volts on the gate. I have removed the zener diodes as well as the 10k resistor and it has no effect on the voltage. I have probed with a meter and found no shorts. I have found corresponding voltages that suggest a voltage divider. It doesn't matter if i apply 12 or 24 volts. The gate stays at around 3.7 volts. However, if I disconnect the fast diodes, the voltage jumps back up to where it should be. Can anyone explain to me what is causing this. Thanks in advance.

K3568 mosfett x 2
(500v, 12 amp/48 amp pulsed, + - 30 Vgss, 40watt )
12v zener x 2
10k resistor 1/4w x 2
470 ohm resistor 3 watt x 2
Uf3003 or 1n4007 diodes (waiting on UF4007 in the mail.)
70mh choke x 1
.88uf x 2 or .44uf x 2 split center tapped capacitor bank

On a side note, any sources of good toroids for inductors or GDTs would be greatly appreciated.

Edit: I fixed the backwards zener.

1540536747 61835 FT0 Modified Zvs Oscillator

866rectifier

Fri Oct 26 2018, 09:02PM

Registered Member #64743 Joined: Sat Sept 08 2018, 07:41PM
Location: Canada
Posts: 9

Um, I don't think that circuit works, because the tuning capacitors are in-series with DC power.
How much current can you put into the transformer when C1, C2 are limiting it?

For ZVS with no transformer center-tap, I find the circuits using two chokes:
sch from http://www.kiblerelectronics.com/bob/app_notes/note11/note11.html#section%201

1540587657 64743 FT183130 Schematic1 Zvs Driver

Travalon

Sun Oct 28 2018, 01:23PM

Registered Member #61835 Joined: Wed Oct 11 2017, 02:00AM
Location:
Posts: 5

Thank you 866rectifier. I was so happy to find a schematic that didn't use 2 chokes I failed to inspect it thoroughly. It seems there's no way for the charged caps to discharge through the coil. I'm pretty new to all this so not too sure of that statement.

Travalon

Tue Oct 30 2018, 09:29AM

Registered Member #61835 Joined: Wed Oct 11 2017, 02:00AM
Location:
Posts: 5

So I got it to start oscillating by splitting the caps and adding a couple of 1n4007 diodes and jumper wires. Its dirty but works. I'm still getting low gate voltages though a bit higher now. About 5v. This translates into a weak magnetic field at the coil as I'm only getting around 5v at the caps. If I can get the gate voltage up I think it should work well. Then I can work on making it compact and pretty.

1540891508 61835 FT183130 20181029 093332

flyrod

Wed Nov 07 2018, 09:55PM

Registered Member #61905 Joined: Sun Nov 12 2017, 03:27AM
Location:
Posts: 23

What do you mean when you say that it works? It seems to me those diodes would just bypass the work coil. If you want to run without a center tap and a single inductor, then I think you need two windings on the inductor (in opposite directions like a common mode choke I think).

You could temporarily go back to the center tap version to test what you had working before. The coil and capacitors carry a lot of current. If you put the caps closer to the coil and straight across in parallel with it (no jumper wires), it should work better.

Travalon

Sat Nov 10 2018, 04:08PM

Registered Member #61835 Joined: Wed Oct 11 2017, 02:00AM
Location:
Posts: 5

866rectifier pointed out there was no way for the caps to discharge into the coil. So I split the caps and added a diode (to direct which way to discharge) as well as a path to discharge into the coil. But I didn't get the desired results. So I reverted to the center tapped design and it works as well. The issue with both I believe is the low voltage at the gate. It should be at 12v at least since I am using a 12v zone. Tried with an 18v too. If I remove the diodes that bridge the gates and the drain the voltage jumps up to where it should be. I have tried different diodes and they all have the same effect. Got me stumped.

flyrod

Sat Nov 10 2018, 04:19PM

Registered Member #61905 Joined: Sun Nov 12 2017, 03:27AM
Location:
Posts: 23

Travalon wrote ...
The issue with both I believe is the low voltage at the gate.

If the circuit is working, the voltage at the gate will be some form of AC signal. How are you measuring it? If you are just probing the pin with a volt meter while the circuit is running, then you'll probably get some value between 12 and 0 volts.

Again, how are you determining whether or not the circuit is "working"? Because I don't think the version you posted a picture of with the inductor connected to two diodes will.

On a whim, I stuck one of these circuits together and used a common mode choke on the input. It seemed to work fine, but I'm not sure it could handle much power without saturating the choke. So my point is, you can use a single inductor with two windings if you don't want to center tap the work coil.

Travalon

Sat Nov 17 2018, 12:36AM

Registered Member #61835 Joined: Wed Oct 11 2017, 02:00AM
Location:
Posts: 5

Appreciate it fly rod. Ordered a couple toriods. Hope they work out. All the ones I see on commercial drivers are the yellow/white variant. However, all mine of the same give me low mh readings without a ton of turns. Any advice on the best Toroids to use and where to get them?

flyrod

Tue Nov 20 2018, 11:57PM

Registered Member #61905 Joined: Sun Nov 12 2017, 03:27AM
Location:
Posts: 23

There are a bunch of different toroids on fleabay. You can get some yellow/white chineze ones for pretty cheap. I don't think they're very critical for experimenting. Iron powder doesn't saturate easily, and as I mentioned I even tried a common mode choke pulled from an old television and it worked fine. Something random out of an old PC power supply would probably work too. After the common mode choke, I tried a single iron powder toroid wound with two windings and it handled 600w fine.

What are you trying to do?

Sulaiman

Wed Nov 21 2018, 10:15AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Ferrite without an air gap is a poor choice for a power inductor as the core will saturate easily,
for experimenting, in order of fool-proof-ness;

air-core coil
... needs a relatively large coil of a lot of copper, but cannot saturate
The most efficient use of copper for an air-core coil is a Brooks coil

(don't get too pedantic about the coil dimension ratios, just something close to the ratios is ok)

ferrite core with an air gap
... the longer the air gap the lower the inductance and higher current handling
The simplest is to use a ferrite rod, I like gapped E cores as it is easy to wind the bobbin.

Air core coils interact with each other so physical placement and alignment can be critical, but not so much in the case of a zvs oscillator.
Ferrite rod inductors are even more likely to interact with each other.
Gapped E-cores and powdered iron cores have only minimal interactions.

powdered iron core
... good for commercial designs but tedious to wind
Iron powder cores saturate at higher flux densities than ferrites so use less core + copper.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob