#1900

Episode 1900
Seems like 1/2 of a 3 terminal regulator. 1.5 terminal?
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[@mikesradiorepair]

Still made and a fairly common transistor in my world. I ordered a stick of 100 a month or so ago to restock. Think the ones I ordered were Texas Instruments brand from DigiKey.

[@misterhat5823]

TI bought National. They'd be branded TI if recently made.

[@MinceWalsh]

I remember being introduced to the LM395 in a Popular Electronics magazine article. In that article it was described if you did not need protection but needed gain, you could substitute a three transistor Darlington configuration.

[@scottsmith5048]

Mouser has the LM395T in stock, TO-220-3 package.

[@jsdutky]

So does DigiKey, and they list the part as "Active". DigiKey wants $3.67 in quantity 1-44, $2.91 for quantity 45-134. You can get down as low as $1.72 for quantity 5040.

[@rkirke1]

Whoa! Having a few of them back as a kid experimenting with electronics would have avoided a lot of magic smoke releases!

[@lunalangton5776]

Heh - would it? Or would it release the magic smoke somewhere else in your circuit? Sometimes the power transistor failing is good news. Now I'm not saying you should intentionally use them as a fuse, but...

[@SeanBZA]

They do die, reverse voltage, trying to push too much base current, or high voltage spikes will kill them, plus running at thermal limit for a long time will definitely result in the various diffusion's going all the way through the die, and shorting it out.

[@SeanBZA]

@@jim9930 Yes that old version of SOA protection could malfunction, and also would oscillate at high temperature, switching the device on and off as the die cycles. That leads to die detach from the heat spreader, and some real nasty things.

[@TomLeg]

Texas Instruments ... $1.373 in 1K lots - You KNOW you need them!

[@nathanschenk8886]

Take a look at the LP395. It’s a similar part in a TO-92 package. Very handy part when you need a bulletproof output for the end user to connect things to.

[@mikebond6328]

Especially when you are the end user.

[@mikebond6328]

You in general. Not you specifically.

[@Manf-ft6zk]

3:46 in the bullet points of the datasheet it says 3µA typical base current. So the transfer function is voltage to current without to much base current. The input current is rather low as the main device is a darlington driven via additional input transistor.

[@akm3726]

That's why the data sheet quotes transconductance.

[@TranscendentBen]

I recall seeing this in a (surely NS) databook a few short decades ago, maybe 1980, and thinking they would get a lot of use. This video is the first I've heard of the part since then. I'm surprise they're still made.

[@uni-byte]

They have them in stock at Digi-Key. Gain is extremely high. You can typically get 2A out with 3uA of base current. That's about 667,000. Edit: But then again, not really. Almost looks like a non-differential op-amp, whatever that is.

[@williamogilvie6909]

There are "Smart FETs" 4 terminal devices that have a MOSFET inside, with lots of protection circuitry. Makes relays obsolete.

[@ChrisDreher]

My friend and I tested some bullet-proof transistors once. I miss my friend and am facing 10-20 years.

[@jj74qformerlyjailbreak3]

The Democrats thought they had a Bullet proof plan when they started supporting the Transistors

[@zexusdexus4193]

Mouser has them in stock.

[@pault6533]

Does it read NPN transistor on one of those little transistor testers? Curve tracer?

[@silverXnoise]

I would think so. You can see the collector characteristic curve chart in the data sheet @2:45 - I think that’s more or less what you’d see on a curve tracer.

[@centheiatrust9153]

The small signal graph on the last page will tell you what the HFE is. About one megahertz.

[@jacobsoby3910]

LoL - I was expecting an individual component test circuit. There's a full end-user power supply demo.

[@pault6533]

When I saw the title I expected more tesla coil zapping was going to occur.

[@SeanBZA]

Still around, still current, and they are not totally bullet proof though. Yes you do get higher power more improved versions, there are plenty of protected mosfets that incorporate both current limit, overvoltage clamping, SOA protection and even have a fault output, to indicate the device is very unhappy and has turned itself off. But they are mostly used as automotive drivers, either high side or low side, and are generally not run as linear devices. You even get some with a current sense output, which uses a portion of the devices to allow use of a lower power shunt. 9 pin TO220 package. Think some even come complete with level shifters and high side charge pumps built in as well.

[@misterhat5823]

This thing is 40 years old. Back then transistors failed if you looked at them crosseyed. It would have been considered "bullet proof" compared to those.

[@robinbrowne5419]

Please settle the debates. Put it on the curve tracer. Although I guess that is really getting sidetracked from fixing the Wavetek.

[@farhadsaberi]

LM395T, digikey has 1232 quantity available. TO-220 package.

[@ivolol]

Given it's almost a darlington, the hFE is probably gonna be in the high hundreds

[@bobkozlarekwa2sqq59]

Why not measure the HFE?

[@misterhat5823]

Because of the way the input stage works.

[@kenzingzong6704]

I wonder how glitchy it would sound being used for fun (if it can?) as a class A or A/B audio amplifier? Love mystery parts like this. Think I saw one once in a PSU and didn't know its function. I'm sure the hfe is low but this begs the question.. have they made modern versions of this with higher speed? What other uses can it fit into?

[@kenzingzong6704]

@@jim9930 Well of course. I've worked with the LM3886 and it's a wonderful IC for HIFI audio but my idea was to push the LM395 into audio amplification service just to see how nasty it would be as an experiment, not as an actual practical use.

[@bayareapianist]

I tought your problem wasn't the ps. Last time we saw the PS was being cobared.

[@IMSAIGuy]

I had only tested the PS out of the box, unloaded. Once in the box the voltages went to zero. you should always test your PS loaded to make sure it can handle the current.

[@lizardkeeper100]

Digikey has lm395 in stock and says they are still active so I assume that means they still make them.

[@KeritechElectronics]

TME has 250 or so LM395 in stock.

[@jazzjohn2]

It lists 3 uA as base current. So hfe would be at least 1A/3uA.

[@misterhat5823]

Not really. That's actually current coming out of the "base."

[@mnoxman]

Apparently a lot of "old skewel" electronics is going the way of the dodo. 80% of my digikey searches say "Obsolete" or send me to "Central Semi" to buy 2000 of them.

[@misterhat5823]

Mouser sells a lot of Central Semi parts by the piece.

[@googlem7]

Is the unijunction transistor to sense over voltage that triggers and shunts the control circuit of the lm395 to inhibit it?

[@opera5714]

Do they still make these? I have a large bag of TO-3 I've had for years and never use one. Design a circuit right and you don't need one.

[@andymouse]

TO-3 is a package, are you saying you have a bag of these devices?

[@opera5714]

@@andymouse yes, in TO-3 package

[@andymouse]

@@opera5714Thank you ! :)

[@bob_mosavo]

Thanks 👍

[@isoslow]

500 ns switch time?? That's bad!!

[@nickcaruso]

put one in one of those universal device testers and see what it says!

[@williamogilvie6909]

Today people use protected MOSFets. Same idea, better device.

[@campa_d]

What is the purpose of CR4?

[@TesserId]

New on me.

[@zachariavallickad7264]

ft?

[@andymouse]

@@jim9930 Even the datasheet says they can be damaged with an excessive Collector to emitter voltage .

[@andymouse]

@@jim9930 :)