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Very low thresold/depletion power TO-220 MOSFET?

Hi all,

The only missing link in a design I'm doing is a swith that must be able to operate at very low voltages (1V or less if possible), have minimal losses, available through mouser/digikey/etc, and be through-hole (TO-220, say) for breadboard prototyping. I've been out of the field for some time so I don't know what's available. Here are the specs:

rON max @ 500mA : 100mOhms Vgs(th) : as small as possible, less than 1V Vgs(ON): less than 1V Imax, power, etc : should be able to handle 500mA when ON.

frequency is irrelevant. The switch is going to be turned on or off every few seconds at the fastest. Relays don't cut it because the circuit is going to be constantly shaking!

Bipolar darlingtons (I would need them because I also don't have much power available to turn the switch ON/OFF) seem to be out of the question since their Vce(sat) is 1V or more, translating to an rON of about 2 ohms. Their Vbe(on) is also not that great.

I found this Vishay P-channel MOSFET (SUP/SUB15P01-52) which comes close, and that I *could* use at the cost of 2 more transistors and resistors in the design. Unfortunately there seems to be no N-channel equivalents. From what I see there are no IGBTs that cut it due to Vce(sat).

Strictly speaking the switch should be 'on' by default, but I couldn't find any depletion mode MOSFETs that would satisfy the Ron and through-hole specs, that's why I am look for very low threshold enhancement mode transistors.

Are the specs hopeless, or does anybody know of something useable?

Best,

- Cesar

Reply to
cesar.crusius
Loading thread data ...

** The ZTX1049A meets your spec.

formatting link

Vce sat = 30mV @ 0.5 amp (= 60 mOhms)

This with Ib a mere 10 mA and Vbe about 0.8 volts.

Tiny TO92 pack.

Cheap.

........ Phil

Reply to
Phil Allison

I'd look at the Supertex web site. They make depletion mode N channel MOSFETs. Can you make something like that work?

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kensmith@rahul.net   forging knowledge
Reply to
Ken Smith

I looked at those, but the minimum ron I could find was 330mOhms. Too much!

- Cesar

Reply to
cesar.crusius

That's a very interesting transistor, thanks! The gain is almost where I want it but it should be doable. Printing datasheet now...

- Cesar

Reply to
cesar.crusius

** Please ALTER your settings on Google Groups so that QUOTED text becomes visible.

It is VERY bad etiquette to post on usenet with no visible hint as to whom or which words to you are addressing.

....... Phil

Reply to
Phil Allison

Thanks. I've been around the net for some time and know it, so I ALSO AVOID SCREAMING. I always make sure the default behavior on my mail/news/etc applications is to quote the post.

To tell you the truth I also found the google groups behavior very annoying but saw no way of changing it. If you can point me to where in the settings I can change to quoted default I'd do it immediately, but there doesn't seem to be a way.

Being annoyed myself, though, I searched some and now I know how to do it: It turns out that on Google groups the only way to quote the article is *not* to click on "reply", but instead to click on "show options" and then on the "reply" that shows after that. Go figure. At least I know how to do it now though.

- Cesar

Reply to
Cesar Crusius

"Cesar Crusius"

** Good one.

Now I can give explicate advice to others in the same boat.

( SS Google ? )

.......... Phil

Reply to
Phil Allison

Thanks for that useful factoid. Sometimes I can't get my usenet provider's system to cooperate, or it has lost an article, etc., and I have to use Google -- so that's a great usage hint you've figured out and given us!

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 Thanks,
    - Win
Reply to
Winfield Hill

I just bumped into some solid state relays that may just be the ticket. The PS710B-1A from NEC has almost the specs I want. NEC has some "on by default" relays but not with low resistance. I shall search some more...

- Cesar

Reply to
Cesar Crusius

Those are made with 60V depletion-mode FETs. Sadly, there's not a lot of choice with such beasts. When I found the PS710 and saved its datasheet, a few months ago, I saved it as "ps710A_0.1-ohm-SSR.pdf" adding the low-Ron description to the part number, which I rarely do.

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 Thanks,
    - Win
Reply to
Winfield Hill

Yep. Sadly, there seems to be nothing I can use. I was reviewing the circuit requirements and it turns out nothing that is not normally closed would be ideal, as now it seems I actually need the switch closed at about 0.2V. Depletion mode FETs are rare enough, and when you get them Ron is too high. I kind of threw in the towel and started searching for normal relays - those one can easily get normally closed, but alas, they require way too much current to turn on (off). The search continues, but I may need to bump up that voltage somehow...

- Cesar

Reply to
Cesar Crusius

Since you're not switching that often, perhaps you could use a small boost regulator to generate the gate bias you need.

Cheers,

Phil Hobbs

Reply to
Phil Hobbs

Maybe a latching relay? What are you working on?

Actually, before leaving depletion-mode FETs behind, did you consider low-Ron JFETs. While meant for signal low-resistance switching, they can work great in power applications. For example, the J105 at 3 ohms max, perhaps 1.5 ohms typical, in a tiny package. Maybe a bunch in parallel?

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 Thanks,
    - Win
Reply to
Winfield Hill

Don't forget "View as Tree". ;-)

Cheers! Rich

Reply to
Rich Grise, but drunk

In article , Winfield Hill wrote: [....]

Take a look at Interfet for JFETs with low RDS(on) values. They make some parts that are interesting.

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kensmith@rahul.net   forging knowledge
Reply to
Ken Smith

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