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Improved single transistor flyback driver

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Spedy

Fri May 23 2008, 11:32PM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

Cool There are atleast 2 GIANT power-transistor looking thingies in this monitor, but I'm pretty sure which one was driving the flyback. I'll have to do some de-soldering at some point, but it looks like almost all the parts I need are in the monitor or in my junk box...

Antonio

Sat May 24 2008, 12:02AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Look for the part number here, to get the data sheet:

It may be also interesting to have the schematic diagram of the monitor, here:

The two big things are probably a high-voltage transistor and a diode (just what is needed). If you are lucky, there is also a high-voltage mosfet.

Spedy

Sat May 24 2008, 12:13AM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

Got the data sheet off of google. Its a "diffused power semiconductor" from Philips. What are the rating symbols I should be looking for? I see Vcesm, Vceo, ect.. It has an anti-parallel diode and a small resistor from base to emiter..

Look at the philips datasheet.

I also have the perfect capacitor, .47uF 250v. I'm pretty sure its a metal film. I've got plenty of HUGE diodes in that crt set if I need em..

Edit: I have found what LOOKS like a suitable diode but the data sheet results says its a 3-phase rectifier.. would this be ok? It only has 2 leads and I'd expect more on a 3 phase rec. It came from a MO

Double edit: Awesome, Power mosfet. It doesn't have the data sheet, but it's very close to the two results that came up.
SSH6N80. the results were -70 and -90 on the end instead of -80

Antonio

Sat May 24 2008, 01:27AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

This transistor already has a diode in parallel with it.
The important parameters are the maximum voltage (1500 V) and the collector current (8 A). A separated diode for use with a similar transistor should be a fast diode rated also at 1500 V. In monitors it's usual to find one looking as a transistor with 2 pins attached to the same heat sink of the power transistor. Several fast diodes rated at lower voltages, in the conventional axial form, can be found too.

Spedy

Sat May 24 2008, 01:34AM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

Err.. I assume you mean I DON'T need another diode for that one. All I need now are the big fat resistors!

Edit: Is the 4700uF cap absolutely necessary? For some reason I don;t have that value in stock and don;t want to pay the prices at radioshack. I do have a ready-made bank of 4400uF. Would that work?

Weston

Sat May 24 2008, 04:04AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

I think you need .47 uf.

Dr. Dark Current

Sat May 24 2008, 07:02AM

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

The 4700uF cap is for filtering and/or proecting your power supply, so the value is not really critical. if you already have a dc power supply you can probably use 1000uF or less.

quicksilver

Sat May 24 2008, 02:31PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

BELIEVE ME....you may really NEED that cap. (I don't think the value has to right on the money however). If you hunt around enough, you may find a "winner" of a LOPT.

I got one from a huge screen projection TV that blows the doors off anything I have ever used before. Even with the "mini-single transistor" driver I was getting arcs of 3cm and the spray was so violent that the display back into the PS was fouled (bizarre mottled numbering on the digital read-outs).

The cap I used stopped that and arcs went out cleaner and more controllably. It was a 4500 but worked fine.

ALLDATA is great. I discovered that some weeks back when I got several monitors to do at once and wanted to pick the good stuff off fast and not waste time on low voltage material or rectifiers that looked like transistors, etc. This thread is developing some very important issues of a wider range in that the identification of useful materials for any project is occasionally overlooked if one person has access to unique stuff and it's not an "off the shelf item".

)

Spedy

Sat May 24 2008, 04:33PM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

Cool, thanks. Can't wait to get this thing up and running!
(now to chop the filter cap off of my failed SSTC..)
I used to have a ton of 5watt resistors from the same CRT, but the bag disappeared... =/

Dr. Dark Current

Sun May 25 2008, 09:17PM

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

Here is the promised run with a DC flyback

Approx. 40kV. I used: 390R/2W, 10(!)R/6W, 8 pri. turns, 3 feedback turns, 0.56uF cap, KD606 transistor (made by "Tesla", long discontinued, but it's the best transistor for the single transistor driver I ever had...) gets just little warm after short runs.

I'll try to remove some primary turns and set the operating point so I get more kV out with the same power...

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