Jelly bean N FETS

Fairchild is one source, but they are generic and very common in designs for offshore manufacturing if you don't need a very high Vceo. TO-92 like the 2N7000. The "D" beta bin is only marginally more expensive.

Best regards, Spehro Pefhany

I just had one of those high-current SOT-23 suckers quit on a digital photo frame... took out the switching power supply adapter too. It was the switching element in LED backlight power supply. Wonder what the most rugged SOT-23 MOSFET is that I can buy from Digikey.

Best regards, Spehro Pefhany

I wondered who would spoy that!

martin

The 138 looks quite nice, thanks

martin

You'd have to put target numbers to the definition of "rugged". But mind that something will then have to drive its largish Cgs.

But they didn't say "enbrighten" :-)

I remember that Perry Rhodan (Sci-Fi books) had a serious influence on language in Germany when I was a kid.

Good point-- the Taiwan-designed PWM chip (BIT3251) is really rather wimpy-- 50 ohms output impedance (typical, no limits given), probably running at 5V, and it operates at a fairly high frequency (330kHz). No idea what the dead part is/was other than it's obviously an n-channel SOT-23 MOSFET.

Suggestions? If 20V is enough, I like the looks of the Zetex ZXMN2F30FHTA 4.9A, 0.045 ohms at 4.5V and only 4.8nC total gate charge. Best regards, Spehro Pefhany

I was curious on just what a tiny NTS4001 could take so I did some test. Here is the test setup I did on the breadboard.

There is about three inches of 22AWG between the TLC555 output and the NTS4001 gate.

I ran Vcc between 2.5VDC to 6VDC, Vcc equals Vgs. I have no way to adjust the ambient temp accurately but its about 25 degrees C. The NTS4001 is mounted on one of my homemade proto adapters. L=0.75 cm X

This is a non magnified view (scope capture) showing CH1= Vgs and CH2=VDS. The pulse length is 112mS. Vcc = 6VDC, IDS = 0.4A, VDS= 272mV. This was consistent even over 10 one shots at about ten second intervals.

The rest of the scope captures are higher resolution zooms of VDS. Magnified view 6VDC.

For Vcc = 3VDC,VDS= 0.228mV,Ids= 0.18A

For Vcc= 2.5Vdc , Vds= 292mV,Ids=0.147A

Not to shabby for a FET I paid 0.05 cents for (During one of there sales). Newark raised the price a bit to ten cents but still worth the money. As with most single and dual mosfets and bipolars I find Newark consistently is cheaper then Digikey most times significantly.

Whoops made a boo-boo the dimensions are L=0.75cm x W=0.6cm

It's a perfectly cromulent word.

Tim

exxxcellent

martin

Thanks mucho for that, I don't really use Digikey, since I'm based in spain, only use Digikey for some eurounobtainium stuff like panasonic jog wheels

martin

No problem :)

I started reading that series in the early '70s. ACE had english translations, & I had every book they translated. His mutants would have fit right into the newsgroup, although most had better manners than our current crop of mutants. :(

I usually go by whatever Digikey has, preferably a five-digit qty of stocked parts. Got to throw it on Spice to see what the switching losses will be with a 50ohm driver. At 330kHz probably not a pretty picture.

If you are going to use an external current limiting resistor, what the hell difference does it make if your fet has a few ohms of Rds unless you can't heat sink a watt and a half or so for a few milliseconds (and you really didn't specify duty cycle)? There really are only a couple of choices ... heat sink the fet or heat sink the cl resistor. Me? I'd look at a SMD variant of the 2N7000 and see what the peak pulse current/power capability is.

Jim

-- "It is the mark of an educated mind to be able to entertain a thought without accepting it." --Aristotle

Looks like he wants to do short pulses of defined brightness. Then the Rdson does matter. At low duty cycle it won't blow up.