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High voltage pnp's (250 volts)

Started by Hul Tytus April 14, 2020
piglet wrote...
> >On 14/04/2020 2:44 pm, Hul Tytus wrote: >> sci.electronics.design, comp.arch.embedded >> high voltage pnp's (250v) >> >> Anyone know of a good pnp transistor spec'd >> up to 250 volts, a probable current limit of >> 1 amp and designed as a switching device. > > Have you checked if the MJE5731 fits? But a > p-channel MOSFET may work better. These ...
Folks usually use n-channel MOSFETs, with a flying high-side driver. IR (now Infineon), Fairchild (now ON), and ST have good parts in SO8. E.g., FAN7362, $0.70. Some parts include current-limiting. And for higher efficiency, we like to use the half-bridge configuration with both hi and low MOSFETs, and there are loads of driver ICs for that. See AoE x-Chapters Table 3x.5, on page 250. -- Thanks, - Win
On 15/04/2020 2:04 pm, Winfield Hill wrote:
> piglet wrote... >> >> On 14/04/2020 2:44 pm, Hul Tytus wrote: >>> sci.electronics.design, comp.arch.embedded >>> high voltage pnp's (250v) >>> >>> Anyone know of a good pnp transistor spec'd >>> up to 250 volts, a probable current limit of >>> 1 amp and designed as a switching device. >> >> Have you checked if the MJE5731 fits? But a >> p-channel MOSFET may work better. These ... > > Folks usually use n-channel MOSFETs, with a > flying high-side driver. IR (now Infineon), > Fairchild (now ON), and ST have good parts > in SO8. E.g., FAN7362, $0.70. Some parts > include current-limiting. And for higher > efficiency, we like to use the half-bridge > configuration with both hi and low MOSFETs, > and there are loads of driver ICs for that. > See AoE x-Chapters Table 3x.5, on page 250. > >
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
On Tuesday, April 14, 2020 at 5:29:20 PM UTC-4, Hul Tytus wrote:
> I've been ... 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.
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 |<' Q1 AT13 |--+--R1--+-->|--+----| FZT957A x3 | 580 | | |\ '--R2--' | 10K | Cheers, James Arthur
On 15/04/2020 2:16 pm, dagmargoodboat@yahoo.com wrote:
> On Tuesday, April 14, 2020 at 5:29:20 PM UTC-4, Hul Tytus wrote: >> I've been ... 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. > > 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 |<' Q1 > AT13 |--+--R1--+-->|--+----| FZT957A > x3 | 580 | | |\ > '--R2--' | > 10K | > > > Cheers, > James Arthur >
I took AT13 to mean an Atmel AT-Tiny 13? As my earlier reply to Win shows I assumed he was driving the PNP base from 5V levels around ground and the load was at negative HV below ground but your interpretion also makes sense! I wonder if a simple capacitive bootstrap N-ch FET would do? piglet
On Wednesday, April 15, 2020 at 9:26:11 AM UTC-4, piglet wrote:
> On 15/04/2020 2:16 pm, dagmargoodboat@yahoo.com wrote: > > On Tuesday, April 14, 2020 at 5:29:20 PM UTC-4, Hul Tytus wrote: > >> I've been ... 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. > > > > 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) > > C2 +250V > > 3.3nF -+- > > C1 .--||--. | > > 3.3n | | D1 |<' Q1 > > AT13 |--||--+--R1--+-->|--+----| FZT957A > > x3 | 580 | | |\ > > '--R2--' | > > 10K | > > > > > > > > I took AT13 to mean an Atmel AT-Tiny 13?
That makes sense. So maybe the 2nd 3.3nF is a level-shift? I've added it (C1) to the sketch. Looks wayyy too wimpy.
> As my earlier reply to Win shows I assumed he was driving the PNP base > from 5V levels around ground and the load was at negative HV below > ground but your interpretion also makes sense! I wonder if a simple > capacitive bootstrap N-ch FET would do? > > piglet
There are super nice P-FETs that are easy to drive, without a BJT's pesky saturation or storage time. Cheers, James Arthur
On Wednesday, April 15, 2020 at 9:26:11 AM UTC-4, piglet wrote:
> On 15/04/2020 2:16 pm, dagmargoodboat@yahoo.com wrote: > > On Tuesday, April 14, 2020 at 5:29:20 PM UTC-4, Hul Tytus wrote: > >> I've been ... 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. > > > > 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 |<' Q1 > > AT13 |--+--R1--+-->|--+----| FZT957A > > x3 | 580 | | |\ > > '--R2--' | > > 10K | > > > > > > Cheers, > > James Arthur > > > > I took AT13 to mean an Atmel AT-Tiny 13? > > As my earlier reply to Win shows I assumed he was driving the PNP base > from 5V levels around ground and the load was at negative HV below > ground but your interpretion also makes sense! I wonder if a simple > capacitive bootstrap N-ch FET would do? > > piglet
This C2 placement makes more sense -- maybe this is what Hal meant. R2*C2 limits repetition rate. (view in Courier) C2 +250V 3.3nF -+- C1 .------||-----. | 3.3n | D1 | |<' Q1 AT13 |--||--+--R1--+-->|--+----| FZT957A x3 | 580 | | |\ '--R2--' | 10K | Cheers, James Arthur
On Wednesday, April 15, 2020 at 4:29:48 PM UTC+2, dagmarg...@yahoo.com wrote:
> On Wednesday, April 15, 2020 at 9:26:11 AM UTC-4, piglet wrote: > > On 15/04/2020 2:16 pm, dagmargoodboat@yahoo.com wrote: > > > On Tuesday, April 14, 2020 at 5:29:20 PM UTC-4, Hul Tytus wrote: > > >> I've been ... 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. > > > > > > 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 |<' Q1 > > > AT13 |--+--R1--+-->|--+----| FZT957A > > > x3 | 580 | | |\ > > > '--R2--' | > > > 10K | > > > > > > > > > Cheers, > > > James Arthur > > > > > > > I took AT13 to mean an Atmel AT-Tiny 13? > > > > As my earlier reply to Win shows I assumed he was driving the PNP base > > from 5V levels around ground and the load was at negative HV below > > ground but your interpretion also makes sense! I wonder if a simple > > capacitive bootstrap N-ch FET would do? > > > > piglet > > This C2 placement makes more sense -- maybe this is what Hal > meant. R2*C2 limits repetition rate. > > (view in Courier) > C2 +250V > 3.3nF -+- > C1 .------||-----. | > 3.3n | D1 | |<' Q1 > AT13 |--||--+--R1--+-->|--+----| FZT957A > x3 | 580 | | |\ > '--R2--' | > 10K | >
My take on it:
> > (view in Courier)
10K +250V 3.3nF +---------+- .--||--. R2 ^ D1 | 3.3nF | | | | |<' Q1 AT13 |--||----+--R1--+---+--+----| FZT957A x3 | 580 |\ | | R2 and D1 is biasing, like he wrote It has plenty of drive capability
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 <klauskvik@hotmail.com> wrote:
> Hi
> I do not know the AT13, do you have a link?
> About baker clamp:
> https://en.m.wikipedia.org/wiki/Baker_clamp
> It???s used to make sure the npn is never hard on which would cause long storage time when turning off
> Cheers
> Klaus
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 <erichpwagner@hotmail.com> wrote:
> On 14/04/2020 2:44 pm, Hul Tytus wrote: > > sci.electronics.design, comp.arch.embedded > > high voltage pnp's (250v) > > > > Anyone know of a good pnp transistor spec'd up to 250 volts, a probable > > current limit of 1 amp and designed as a switching device. It's to serve as > > the switcher in a variable frequency (pulse width held constant) power supply. > > So far a 2n2907 has been tried, with a 100ma 50 volt limit, with > > impressive results. Zetex (now Diodes Inc) fzt957 & fzt958 with a 1 amp 300 > > volt limit were tried but they were inefective. The 2n2907 showed 47% > > efficiency with a 500ns pulse width; the fzt957 showed 38%. With 4 micro > > second widths, 2n2907 showed 61% & fxt957 showed 32% (). > > Apparantly, the higher collector/emitter voltage implies a greater > > effective restance and higher saturation voltage, which might explain why n > > channel fets with convoluted "high side" drive circuitry are used. I'm hoping > > there are some pnp devices in the relatively low 1 amp and 2 amp range that > > are more useful than the fzt957 units. Any suggestions? > > > > Hul > >
> My go-to jelly bean HV PNP is the MPSA92 but that might struggle above > 500mA. Can you spare some Vce and use one of those in a Sziklai with a > beefier NPN?
> 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
On Wednesday, April 15, 2020 at 11:25:32 AM UTC-4, Hul Tytus 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
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