Junkbox switch for a switcher

Input is going to be 12 volts, sorry.

How about a string of 9 volt batteries?

Or rectify the AC line, with some prudent protections.

You could make a flyback with the big Fairchilds. You could drive it open-loop from a function generator.

Stacking 9 volts would be fun, but it's an expensive way to run a thing if you plan on doing it for any length of time. I don't know if the internal resistance of the string would let me provide say 50 mA.

They used to make big 45 volt alkaline batteries; they looked like the

Directly rectifying the line is scary!

The flyback with the Fairchild seems like a reasonable option.

-Lasse

That's not a flyback; it's a "fryback", a mosfet roaster.

Sure. Google be yer friend, eh?

There used to be 90V "B" batteries for "portable" radios... I can still find mention on the web but none of the links seem to work. ...Jim Thompson

I remember those, for old tube radios. There doesn't seem to be any available anywhere.

Here's some oddballs:

Wouldn't test those with my tongue!

IRF530 is fine:

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:

I always end up putting a bunch of bench supplies in series. (If it's only for a test.)

George H.

Nice. What's an EA-77-188?

Amidon part number, 0.188" (approx. square) center limb ferrite, #77 mix (so, a Fair-Rite product), E shape. Turns give 0.2-0.3T Bmax, and gap gives the desired inductance (add spacers between core halves, or sand down the middle leg).

Most SMPS contain a little transformer that's about the same size, if you don't mind taking one apart and rewinding it. (Hint: superglue is a key disassembly tool...)

Tim

How about a cheap Boost converter module? $12.12 USD

DC-DC-12V-24V input to 100V-250V output @ 70W

The IRF530 is an old inferior part. Someone should tell bitrex his FQP2N60C is generally a fine part, suited for a low-current boost supply, using a simple inductor. An IRF530 has too low a voltage rating for a boost converter.

bitrex may not have a copy of our new book, but Chapter 9 has 109 pages about power supplies, here's a free sample:

For 12V to about 150V at say 25mA, the MOSFET, will be on about D = 1-Vin/Vout = 92% of the time (page 647). The 12V input current will be Iout/(1-D) = 300mA. Yes, the FQP2N60C, with 5-ohm ON resistance, will waste 15% of the power, but hey, it's right there in the junk box. A 220uH inductor with 50kHz switching should work fine.

Thanks, that's sort of what I was hoping for. I think I have some suitable inductors too. I'm not big into winding transformers...

You could tear up a 12v wallwart smps & run it backwards. That'll get you everything you need, parts-wise.

Cheers, James Arthur