High voltage pnp's (250 volts)

[Winfield Hill]

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

 

[piglet]

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 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

 

[piglet]

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 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 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

 

[Hul Tytus]

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

 

[Hul Tytus]

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

 

[Klaus Kragelund]

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

 

[piglet]

On 15/04/2020 4:50 pm, Hul Tytus wrote:

James - I should have used ATTINY13 (Atmel's AVR series microcontroller in an
8 pin package) rather than AT13. The output, with 3 (cmos) pin's wired together,
is, by spec, +/- 75ma. To alter your schematic a bit, the base of the fzt957
is connected to the emiter through a 10k resister and a diode. It's connected
to the ATTINY13's output with 1 3300pf cap directly and another 3300pf cap in
series with a 580 ohm resistor.
Along the lines you suggest, checking with a more powerful driver might
provide some insight. I'm hoping though to find a more effective pnp device,
probably one designed as a switcher.
That's a nice looking drawing you made, truely an artist.

Hul

OK Hul, so is this your circuit?

(view in Courier)
+250V

--+----+-------+-
C1 3.3nF | | |
.--||-------. 10k R2 - D1 |
| | | ^ |<' Q1
AT13 |--+--R1---||--+------+----+-----| FZT957A
x3 | 580 C2 3.3nF |\
|
|


(Adapted from Klaus and James previous ascii art).

If this is now the correct circuit my observation is there is nothing to
limit the peak base current except the mcu port drivers?

piglet

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

 

[Hul Tytus]

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

dagmargoodboat@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)
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

 

[Hul Tytus]

James - I should have used ATTINY13 (Atmel's AVR series microcontroller in an
8 pin package) rather than AT13. The output, with 3 (cmos) pin's wired together,
is, by spec, +/- 75ma. To alter your schematic a bit, the base of the fzt957
is connected to the emiter through a 10k resister and a diode. It's connected
to the ATTINY13's output with 1 3300pf cap directly and another 3300pf cap in
series with a 580 ohm resistor.
Along the lines you suggest, checking with a more powerful driver might
provide some insight. I'm hoping though to find a more effective pnp device,
probably one designed as a switcher.
That's a nice looking drawing you made, truely an artist.

Hul

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

 

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

 

On Wednesday, April 15, 2020 at 12:17:43 PM UTC-4, piglet wrote:

On 15/04/2020 4:50 pm, Hul Tytus wrote:
James - I should have used ATTINY13 (Atmel's AVR series microcontroller in an
8 pin package) rather than AT13. The output, with 3 (cmos) pin's wired together,
is, by spec, +/- 75ma. To alter your schematic a bit, the base of the fzt957
is connected to the emiter through a 10k resister and a diode. It's connected
to the ATTINY13's output with 1 3300pf cap directly and another 3300pf cap in
series with a 580 ohm resistor.
Along the lines you suggest, checking with a more powerful driver might
provide some insight. I'm hoping though to find a more effective pnp device,
probably one designed as a switcher.
That's a nice looking drawing you made, truely an artist.

Hul


OK Hul, so is this your circuit?

(view in Courier)
+250V
--+----+-------+-
C1 3.3nF | | |
.--||-------. 10k R2 - D1 |
| | | | ^ |<' Q1
AT13 |--+--R1---||--+------+----+-----| FZT957A
x3 | 580 C2 3.3nF |\
|
|


(Adapted from Klaus and James previous ascii art).

If this is now the correct circuit my observation is there is nothing to
limit the peak base current except the mcu port drivers?

piglet

I think you've gotten it piglet. And yes, the uC port pins are the
peak current limiters, and given the FZT957's dismal switching, we
know it's not getting enough.

Cheers,
James Arthur

 

On Wednesday, April 15, 2020 at 11:59:06 AM UTC-4, Hul Tytus wrote:

dagmargoodboat@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)
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.


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

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

https://www.infineon.com/dgdl/Infineon-BSP317P-DS-v02_04-en.pdf?fileId=db3a30433b47825b013b604df1d959f2

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

 

[Hul Tytus]

Thanks - I'll take a look.

Hul

dagmargoodboat@yahoo.com wrote:

On Wednesday, April 15, 2020 at 11:59:06 AM UTC-4, Hul Tytus wrote:

dagmargoodboat@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)
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.


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

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

https://www.infineon.com/dgdl/Infineon-BSP317P-DS-v02_04-en.pdf?fileId=db3a30433b47825b013b604df1d959f2

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

 

[Hul Tytus]

The schematic you drew is as intended. The current from the at13 to the base via the
2 caps & 1 resistor is limited by all the components mentioned in this sentence.

Hul

piglet <erichpwagner@hotmail.com> wrote:

On 15/04/2020 4:50 pm, Hul Tytus wrote:
James - I should have used ATTINY13 (Atmel's AVR series microcontroller in an
8 pin package) rather than AT13. The output, with 3 (cmos) pin's wired together,
is, by spec, +/- 75ma. To alter your schematic a bit, the base of the fzt957
is connected to the emiter through a 10k resister and a diode. It's connected
to the ATTINY13's output with 1 3300pf cap directly and another 3300pf cap in
series with a 580 ohm resistor.
Along the lines you suggest, checking with a more powerful driver might
provide some insight. I'm hoping though to find a more effective pnp device,
probably one designed as a switcher.
That's a nice looking drawing you made, truely an artist.

Hul

OK Hul, so is this your circuit?

(view in Courier)
+250V

--+----+-------+-
C1 3.3nF | | |
.--||-------. 10k R2 - D1 |
| | | ^ |<' Q1
AT13 |--+--R1---||--+------+----+-----| FZT957A
x3 | 580 C2 3.3nF |\
|
|

(Adapted from Klaus and James previous ascii art).

If this is now the correct circuit my observation is there is nothing to
limit the peak base current except the mcu port drivers?

piglet

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

 

[Winfield Hill]

piglet wrote...

On 15/04/2020, Winfield Hill wrote:
piglet wrote...
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?

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.


--
Thanks,
- Win

 

[Winfield Hill]

Klaus Kragelund wrote...

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

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.


--
Thanks,
- Win

 

[Klaus Kragelund]

On Wednesday, April 15, 2020 at 11:06:54 PM UTC+2, Winfield Hill wrote:

piglet wrote...

On 15/04/2020, Winfield Hill wrote:
piglet wrote...
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?

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