High voltage pnp's (250 volts)

Thanks Win, I get the impression from the OP description that his load is at 250V below ground and that is why he went for PNP? He also said it was fixed pulses so perhaps he could use an NPN or Nch FET either transformer or capacitively coupled?

piglet

I'm having trouble understanding exactly what that looks like, but it sounds way too wimpy to drive a FZT957. Turning it on and off quickly will take a short hefty burst, hundreds of mA at least.

Here's my best guess at your drive (I don't know what an AT13 is).

(view in Courier) +250V 3.3nF -+- .--||--. | | | D1 |

There are super nice P-FETs that are easy to drive, without a BJT's pesky saturation or storage time.

Cheers, James Arthur

x3 | 580 | | |\ '--R2--' | 10K |

Cheers, James Arthur

My take on it:

The AT13 refers to Atmel's (now Microchip's) ATTINY13. It's a small 8 pin 1k flash microcontroller of the AVR group. Thanks for the reference to the Baker clamp.

Hul

Klaus Kragelund wrote:

The mpsa92 didn't fit. I'm guessing due to insufficient current gain and probably designed to 100ma and spec'd for 500.

The mje devices you mentioned are next on the list, thanks.

Hul

piglet wrote:

Your FZT957 is a fine device, you just have to drive it harder.

'Scoping the collector waveform would tell you a lot about where it's wanting.

Cheers, James Arthur

James - I should have used ATTINY13 (Atmel's AVR series microcontroller in an

Hul

snipped-for-privacy@yahoo.com wrote:

James - about your "super nice p channel fets". Know of any 250volt versions that can be driven by 5 volts ("logic level")? That would be an attractive direction.

Hul

snipped-for-privacy@yahoo.com wrote:

OK Hul, so is this your circuit?

(view in Courier) +250V

--+----+-------+- C1 3.3nF | | | .--||-------. 10k R2 - D1 | | | | ^ |> but it sounds way too wimpy to drive a FZT957. Turning it on and

"Logic level" cuts down the candidates. At Digikey, there's only one (!).

We don't know enough about your duty cycle and such to know if the BSP317 (or two or three in parallel, if you'd rather) will fit your needs, though.

Cheers, James Arthur

The schematic you drew is as intended. The current from the at13 to the base via the

Hul

piglet wrote:

Thanks - I'll take a look.

Hul

snipped-for-privacy@yahoo.com wrote:

Dunno, there's a +250V rail in one drawing. An SO8 package FAN7362 driver would work well with any of dozens of 400V n-channel MOSFETs, like a 1-ohm 70-watt DPak STD7NK40Z, for $1.

Gatedrivers can be had for below 0.2 USD at volume

But the OP is going for a cheaper solution. The level shift cap solution is about 10 times cheaper

The levelshift idea is more susceptable to noise, voltage dips and surges on the 250V rail

Cheers

Klaus

He's going for a $0.02 solution? A p-channel part will more than wipe out that savings, compared to n-channel. Maybe not compared to bipolar, but I'd check what LCSC and the Pacific rim has to offer.