Anyone know of some small (e.g., SOT-23, SC70, etc.) open collector output driver that can sink, say, 100mA, can stand off, say, 32V, and is controlled by a logic level (5V or 3.3V CMOS) input?
The ideal is to take the slightly wimpy outputs from a microcontroller and directly drive a small 28V relay coil, power up some 15V op-amps, etc... and I'm looking for a better solution than a handful of FET/BJTs and resistors.
"Digital transistor" (BJT with bias resistors built in).
Best regards, Spehro Pefhany
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Well, I'd prefer high side drive (the situation I'm thinking of is to power up some high-power amps that require 110mA at 28V, and I'd rather have 28V moving around a little rather than "ground"), and the (P channel enhancement mode MOSFET) 30V Vds parts I'm using only allow an 8V Vgs. So there's already one 'FET and 2 resistors (to limit Vgs). Then, I end up with an N channel FET driving the resistor going to the gate of the P channel FET since the microcontroller can't stand off 28V. Thus: 2 FETs, 2 resistors. At that point, I'd prefer to have a single part solution -- adds a little reliability, and -- at least in small quantities -- could actually end up being cheaper (say, $0.25 vs. $0.50).
Given that you can get complete microcontrollers in SOT23-6 packages these days, it's surprising sometimes just what _isn't_ available!
I'll look into the BJT packages with built-in bias resistors...
Isn't the ULN-2003A, 7 channel darlington available in the required SMD package?
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Excuse me, but exactly what scale is your mindset? I'm just confused by your terms... when I saw your post I was expecting to see at least a hundred volts! 28V is swatting gnats, even for SOT devices.
I suppose 2.9W is "high power" compared to like... a wristwatch... but gee...
Tim (whose mindset is in the medium power, i.e., 10kW range)
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It's the mindset of "low power" is, say, 6V or less (typically 3.3V or 2.5V) and many microwatts to a few handful. "High power" is >6V and hundreds of milliwatts to watts.
I'd love to buy a bunch of the single gate logic ICs (e.g., NC7SZ38) in higher voltages (their maximum is ~6V); alas, I've never seen such things.
Yeah, I took a power electronics class in college some years ago where "low voltage" transistors were the ones rated 600V or less!
Ok, didn't know that you wanted high-side. You had said sink, not source...
$0.50? How 'bout this: BSS123 after your gate, two resistors to rail, BSS84 up top? Ok, considering your 110mA the BSS84 is a wee bit marginal here but you should be able to find a p-channel that does 300mA or so for maybe a penny more.
That scenario would cost around $0.10 in production. If you'd spring for a fifth part (base resistor) you could use a BJT and shave a little over a penny off of this. If power efficiency isn't a concern and you also use a BJT up top you could get the whole chebang done for $0.06 or so.
As Graham suggested, look at the ULN series. IIRC there are some high-side versions, maybe even in TSSOP.
For Tim it seems he'd only consider parts high power if the road has to be blocked and they have to be hoisted up and lowered in through the roof using a massive crane. Anything that doesn't have a crane hook is wimpy.
Probably they could have sold a lot more of these if the marketeers would have coined a catchy name. 'Digisistor', 'Logistor' or something like that.
I haven't seen them used much, maybe for cost reasons. Imagine somebody trying to repair a board, thinking it was a normal transistor. Click .... kablouie.
Back in the late 60s, a friend was designing SCRs for GE. Big ones. Their primary customer was another division of GE - the one that made diesel electric locomotives.
What sort of control electronics are used in modern locomotives?
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