High voltage pnp's (250 volts)

[Klaus Kragelund]

On Wednesday, April 15, 2020 at 11:33:48 PM UTC+2, Winfield Hill wrote:

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.

Oh, maybe I am guessing. But using a BJT seems like he is cost driven

It's true that a HV PNP will cost more than the NPN. The drive method dictates a PNP.

If he shifts to NPN, he needs the gatedriver, or use an old style transformer based driver, but then the price of the high side switch (NPN) is very low, contrasted by high cost for the transformer

On the other hand, a 0.5A DP350 PNP is almost as cheap, looking it up

https://www.diodes.com/assets/Datasheets/ds30624.pdf

That brings the levelshift idea and PNP down to very low cost

Cheers

Klaus

 

On Wednesday, April 15, 2020 at 11:50:47 AM UTC-4, 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.

With an oscilloscope you can easily tell where the problem is.
If the leading edge is slow, the PNP isn't getting turned on hard
enough.
If the PNP isn't fully on, d.c. drive.
If the falling edge is a ramp, you're not turning it off hard enough.

It's not the transistor that's giving you trouble. It's the drive.

Cheers,
James Arthur

 

[Hul Tytus]

The FZT957's poor performance turns out to be caused by the device itself.
Looking through it's datasheet again, I saw the, previously unseen, typical
rise & fall time spec: 109ns and 2500ns...

Hul


Hul Tytus <ht@panix.com> wrote:

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

 

[Winfield Hill]

Hul Tytus wrote...

The FZT957's poor performance turns out to be caused by the
device itself. Looking through it's datasheet again, I saw
the, previously unseen, typical rise & fall time spec:
109ns and 2500ns...

Hul, an amp at 250V implies quite a bit of power. I trust
you're not creating an inefficient design, saving 50 cents
in parts cost during manufacture, but costing the user $3
in extra electricity used over its operating lifetime?


--
Thanks,
- Win

 

On Thursday, April 16, 2020 at 9:37:19 AM UTC-4, Hul Tytus wrote:

The FZT957's poor performance turns out to be caused by the device itself.
Looking through it's datasheet again, I saw the, previously unseen, typical
rise & fall time spec: 109ns and 2500ns...

Hul

But those times are a result of the manufacturer's test setup,
not the way we use the devices in real life. Those test fixtures
often drive the device with 0..10V through a weenie resistor,
with no speed-up cap.

In this case, the t.off is spec'd at i.b=-50mA, that's why it's
so slow. You should be pulling hundreds of mA out of the base
to turn the FZT957 off *hard*.

You're going to find, looking around, that the FZT957 is not some
poorly-designed geometry that's 1/10th as good as it should be .
It's a low-saturation device optimized for switching power supplies.

But you'll find that making efficient 250V x 500ns x 1A pulses with
a bipolar transistor -- or even a FET -- takes a bit of doing.

Cheers,
James Arthur

 

[Klaus Kragelund]

On Thursday, April 16, 2020 at 4:12:19 PM UTC+2, Winfield Hill wrote:

Hul Tytus wrote...

The FZT957's poor performance turns out to be caused by the
device itself. Looking through it's datasheet again, I saw
the, previously unseen, typical rise & fall time spec:
109ns and 2500ns...

Hul, an amp at 250V implies quite a bit of power. I trust
you're not creating an inefficient design, saving 50 cents
in parts cost during manufacture, but costing the user $3
in extra electricity used over its operating lifetime?

Well, that is an issue I have heard before for sure

You need to be competitive, so always doing designs with lowest possible loss is not an option

Cheers

Klaus

 

[Winfield Hill]

Klaus Kragelund wrote...

Winfield Hill wrote:

Hul, an amp at 250V implies quite a bit of power. I trust
you're not creating an inefficient design, saving 50 cents
in parts cost during manufacture, but costing the user $3
in extra electricity used over its operating lifetime?

Well, that is an issue I have heard before for sure.

You need to be competitive, so always doing designs with
lowest possible loss is not an option.

It's one thing to be competitive, it's another to be eeking
out every last cent for profit. Klaus, you have a history
of designing for low manufacturing cost, but also for high
efficiency, higher than most of us manage when we're trying.


--
Thanks,
- Win

 

[Hul Tytus]

Phil - placed an order today for the mje15035. Thanks for the suggestion.

Hul

Phil Allison <pallison49@gmail.com> wrote:

Hul Tytus wrote:

=====================

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?

** The MJE15035 is gonna be hard to beat.

https://www.onsemi.com/pub/Collateral/MJE15034-D.PDF

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

> .... Phil

 

[Winfield Hill]

Hul Tytus wrote...

Phil - placed an order today for the mje15035. Thanks for the suggestion.

Phil Allison:

** The MJE15035 is gonna be hard to beat.
https://www.onsemi.com/pub/Collateral/MJE15034-D.PDF

I have always thought of the MJE15034 and MJE15035
transistors as linear amplifier parts, rather than
switching transistors. It'll be interesting to
see how they work out for you. Let us know.


--
Thanks,
- Win

 

[Phil Allison]

Winfield Hill Nit Picks Me Again:

===================================

Phil - placed an order today for the mje15035. Thanks for the suggestion.

Phil Allison:

** The MJE15035 is gonna be hard to beat.

https://www.onsemi.com/pub/Collateral/MJE15034-D.PDF


I have always thought of the MJE15034 and MJE15035
transistors as linear amplifier parts, rather than
switching transistors.

** Same goes for most of the parts suggested here.

It'll be interesting to
see how they work out for you.

** Which is totally irrelevant to the doubt raised.

With near constant Hfe of 200 up to 1A, typical Ft of 80Mhz plus Vce sat of 0.2V at 1A falling to and 50mV at 100mA - you never know, it might just work out OK ?

Want another fight over mS v ms ?

Can you spell the word " pedant " aloud please ?


...... Phil

 

[Klaus Kragelund]

On Friday, April 17, 2020 at 10:08:23 AM UTC+2, Winfield Hill wrote:

Klaus Kragelund wrote...

Winfield Hill wrote:

Hul, an amp at 250V implies quite a bit of power. I trust
you're not creating an inefficient design, saving 50 cents
in parts cost during manufacture, but costing the user $3
in extra electricity used over its operating lifetime?

Well, that is an issue I have heard before for sure.

You need to be competitive, so always doing designs with
lowest possible loss is not an option.

It's one thing to be competitive, it's another to be eeking
out every last cent for profit. Klaus, you have a history
of designing for low manufacturing cost, but also for high
efficiency, higher than most of us manage when we're trying.

Correct, many power supplies or motor drives can be made with a higher efficiency, just spending a little more time

Problem about it is that the competitors, often the Chinese manufacturers, only think about minimum cost, and that is what the customer looks for first. Trying to explain full lifetime cost is a battle lost forhand in most cases

Some years ago the adapter supplies would need to comply to level 6 (>90%) efficiency. All the big players placed their efficiency close to that mark to squeeze last cost out of the product.

Even today many regions allow Level 5 power supplies, which only has about 88% efficiency. In this case US regulations demand level 6, which is more strict than level 5 (maybe Trump sees this and pulls it back to level 5)

https://slpower.com/data/collateral/PW153KB_DS.pdf

Graph of converter efficiencies:

https://r7knmqt3qn1hbgxc30yrat1a-wpengine.netdna-ssl.com/wp-content/uploads/2016/02/Power-supply-Efficiency-versus-Output-plot-1.jpg

Cheers

Klaus