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Universal driver

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vasil

Sun Mar 19 2006, 07:21PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

After reading the high voltage threads, I wanted to build a kind of universal driver for flybacks and ignition coil too. As usually, it is structured around an astable chip. I found the schema on a german site. The power is much lower than in a ZVS driver, but still is a nice toy to play with...

http://www.geocities.com/romtcb/universaldriver.html

Enjoy

vasil

Marko

Sun Mar 19 2006, 07:42PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I think its very good idea to replace bipolar transistor gate drive with driver IC or power transistors in darlington, in my flyback driver

I had problems with overheating of gate drivers, for mosfet that was actually BDT driver!

On low duty cycles it works nice but f I go for 50% and more they overheat and blow in couple of minutes.

Dr. Dark Current

Sun Mar 19 2006, 09:40PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

meh, nothing new under the sun

Actually, if well designed, these flyback topology (single power switch) drivers work very efficiently at low powers. (yes, flybacks got their name from the topology they are being driven with, not the driver from the transformer).

Marko

Sun Mar 19 2006, 10:11PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

For now it works too good (5cm spark with only 50W) and it can stand a lot more than current 28V.
I fried foolishly some HV transistors, overvolting B-E with bad BDT so I cant make it running at 300V as I intended.

Now I use my own BDT with protection diodes and even without them it doesnt generate more than 2V in kickback.

As I said most of problems are with driver, gatedrive of mosfet suffers great stresses and I cant help it for now

Dr. Dark Current

Sun Mar 19 2006, 10:18PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

For me, a 494 driving directly a power mosfet gate with a help of pull-up resistor works well. (crappy 8kvac flyback, 30kV out with 20W in, drives a big plasma globe really nicely).
In that schematic posted by Vasil, there's a cap. across the transistor which I have found really helps keeping it cool.

Simon

Sun Mar 19 2006, 11:04PM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

My universal driver is far simpler. It's an MJ10012 driven directly from a tunable 555.

Of course, to get the most out of a transformer, the all-rounder approach won't work but having a driver for trying out any transformer you have is handy.

Marko

Sun Mar 19 2006, 11:12PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

My universal driver is far simpler. It's an MJ10012 driven directly from a tunable 555.

Im wondering how don't you fry NE555, bipolar transistors need lots more current than it can give.
At least small darlington would help.

For real power base drive transformer must be used, it lowers greatly needed drive current, drives base on low voltage/high current for minimum dissipation and helps in isolation if circuit operaes at high voltages...

Sulaiman

Mon Mar 20 2006, 11:27AM

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

I LIKE the 555 with a MOSFET or IGBT, very reliable/dependable.
I also use HOT BJTs for very high voltages. (with a buffer/driver)
I never find the driving to be a problem,
it's the inductance snubbing that bugs me
and for this the easiest/safest is to use an avalanche-rated switch/IGBT etc.
Since your BUP307 is avalanch rated - no problem (except heat)
Others should be aware that a non-avalanche rated device may die in this circuit
as there's no other proper snubbing.

The capacitor across the transistor will 'snub' the spikes
but it would be better with 10 to 100 ohms in series
as it is discharged directly into the transistor each time the transistor turns on
giving unneccessary current spikes.

vasil

Mon Mar 20 2006, 01:01PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

The resistor would not slow down the voltage droping across the drain- source?
I can try though...

Dr. Dark Current

Mon Mar 20 2006, 01:06PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I found that without the cap, the driver would draw 2-3x the power when not drawing an arc, as opposed to with the capacitor and properly tuned frequency, the "idle" power is much lower, but the output voltage is higher and arcs are a bit hotter. (and the fet stays cooler as mentioned); maybe the cap resonates with the flyback primary???

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