High voltage pnp's (250 volts)

Need more info--pulse width and schematic in particular.

Cheers

Phil Hobbs

Suggest using a MOSFET, good choices all the way to 600V.

Phil - you might read the message again.

Hul

Phil Hobbs wrote:

Mouser returns about one result meeting the spec:

Looks like a very nice part and has a high current gain (unusual for HV PNPs I think) but at $1 in singles, not cheap.

oops, you already found that one, didn't read carefully :)

What about the 2N5415 apparently you can still get 'em:

Or to meet the 250 volts the 2N5416 but gosh it's 9 bucks.

This is dirt cheap :

You need to drive the base either hard negative to shut it off fast or use a baker clamp type method

Cheers

Klaus

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BTW: your Q is all over the place, like mad woman's breakfast.

.... Phil

I'll take a look. Thanks

Hul

bitrex wrote:

If you look at a power stage with less than 0.5A or so, a BJT has lower conduction loss for the same price vs a FET

Problem is they are a lot more sensitive to overvoltage, secondary breakdown and are a pain to drive (or so one would think)

Even though beta is small and base currents seems excessive, they are only multiplied with base voltage, so ends up with low base drive, conduction loss wise

Klaus - what's the "baker clamp" method? I've been woking along the line you suggest: first driving the transistor from 3 pal'd AT13 outputs through 3300 pf parrallel with 3300pf in series w/580 ohms along with a diode & 10k resistor to maintain bias. On the scope that appears pretty good with just a hint of curvature in fall time when measured at the AT13 output. With just one output, the curvature is quite noticable.

Hul

snipped-for-privacy@gmail.com wrote:

Hi

I do not know the AT13, do you have a link?

About baker clamp:

It?s used to make sure the npn is never hard on which would cause l ong storage time when turning off

Cheers

Klaus

By the way the baker clamp is difficult to tune robustly for low VCE

If you know your load you can do intelligent trimming, but that is even more flaky

Last I looked at it there is tons of papers and patents on these techniques

I see a reference to a 500 ns pulse width--is that a design requirement?

Still no schematic. I'd be interested to see it, whether or not I could contribute. Your call.

Cheers

Phil Hobbs

Any favourite references?

Cheers

Phil Hobbs

There is a lot of IEEE papers, but you need access to get those, and the wording is hidden, so cannot just search for "baker" clamp

This app note is ok:

Some of the better patents:

My go-to jelly bean HV PNP is the MPSA92 but that might struggle above

Have you checked if the MJE5731 fits? But a p-channel MOSFET may work better. These may help: IRFR9214; FQT2P25; FQP9P25.

More details of your circuit should help us find an answer.

piglet

APT27 is also extremely cheap, 0.5A:

Beta is ok up to 200mA