BJT behaviour at ridiculously low current levels

On Thu, 26 May 2022 07:51:28 +0200, Piotr Wyderski
<bombald@protonmail.com> wrote:

>jlarkin@highlandsniptechnology.com wrote:
>
>> Had a part in mind? If it's enhancement mode, it will need something
>> to bias it up.
>> 
>> We do have the LND150s in stock, SOT23 package.
>
>Mouser has this IXTA1N170DHV. More expensive that LND150, but I am not 
>sure if a safety circuit is the best place for savings and IIRC your 
>business is of the high-added-value/low volume profile anyway. Just 
>saying, it's your decision.

The 1400v supply is low current and doesn't store lethal energy, but
someone could damage parts by poking around while there's still
voltage. The linear discharge with blinker helps with that, and is
cool too. Sometimes we do things just because they are cool.

>
>I use the IXTA08N100D2HV for the same purpose (have a blinker too, and a 
>buzzer specifically tuned to emulate a fighter jet warning system: 
>https://youtu.be/fd50GtnXR7Y?t=1145, just couldn't resist), but my cap 
>voltage is under 900V, 650V typical.
>
>	Best regards, Piotr

That is an interesting part, but Mouser has four for $20 each. That's
another factor these days, availability and price.

We also use DN2530, a 300 v depl fet in SOT89. It good for discharging
bigger caps.

In a couple of boxes with gigantic caps, we used a depletion fet + LED
indicator and a discharge resistor + pushbutton inside, so our techs
are warned and didn't have to wait minutes to poke around.



-- 

Anybody can count to one.

- Robert Widlar

jlarkin@highlandsniptechnology.com wrote:

> The 1400v supply is low current and doesn't store lethal energy

Oh, in that case never mind. My comment was entirely safety-driven.

> Sometimes we do things just because they are cool.

So do I. :)

> We also use DN2530, a 300 v depl fet in SOT89. It good for discharging
> bigger caps.

I use it as a resettable fuse. The short-circit current is limited and 
the part just stops being hot when the short-circuit is removed. The 
carbon-based PTCs wear off.

	Best regards, Piotr

On Thu, 26 May 2022 18:06:43 +0200, Piotr Wyderski
<bombald@protonmail.com> wrote:

>jlarkin@highlandsniptechnology.com wrote:
>
>> The 1400v supply is low current and doesn't store lethal energy
>
>Oh, in that case never mind. My comment was entirely safety-driven.
>
>> Sometimes we do things just because they are cool.
>
>So do I. :)
>
>> We also use DN2530, a 300 v depl fet in SOT89. It good for discharging
>> bigger caps.
>
>I use it as a resettable fuse. The short-circit current is limited and 
>the part just stops being hot when the short-circuit is removed. The 
>carbon-based PTCs wear off.
>
>	Best regards, Piotr
>

Ixys makes a self-protecting SSR, CPC1540. Off leakage is picoamps.

If you drive the input full-time, it becomes a fuse. 



-- 

Anybody can count to one.

- Robert Widlar