Voltage Regulator ID

This is the 5V regulator in a little power supply I hacked together in the mid 90s for a TTL logic class (please don’t look at the solder joints…). I want to ID it exactly so I know what its specs are. Searching DigiKey gets me close, but seemingly not exact. It looked most likely up to 35V input, rated for either 1A or 1.5A. Google can find pictures with LM340T5 and 7805 labels, but not with 8830 beside the logo so I’m not confident in my guesses about the specs.

Bonus question: what would be the closest match in a 3.3V regulator? I’d like to put it back into service, and with the standard now being 3.3V instead of 5V I’d like to have either option. Lucky for me, thirty years ago all I had was a dpdt switch, so it’s ready for a second regulator.

Welcome to the DigiKey tech forum. Based on the part markings it looks like you have DigKey part LM340T-5.0/NOPB-ND which the datasheet page 23 of 36 shows a marking of LM340T5 7805 P+ . The 8830 is more than likely a date code. Take a look at DigiKey part LM1086CT-3.3/NOPB-ND as a possible option for a 3.3v regulator.

HI @Trurl ,
In addition to Steve’s suggestion for 3.3V, you could amaze your friends with using a modern drop-in DCDC converter, which (usually) wastes less energy than an LDO.

Cheers, heke

A note on the LM1086, above, is that it has a different pin-out than the LM340T5 (a.k.a. 7805), and it requires specific output capacitor types and values to ensure stability. So make sure you check the datasheet for details.

The MIC2940A-3.3WT is a 3.3V output linear regulator with the same pin-out as the LM340T series. For stability, it requires an output capacitor of at least 10uF of either tantalum or aluminum electrolytic type with an ESR of 5 Ohms or less (most of the decent quality ones are).

The switching type regulator that @heke mentioned is also a very nice option, especially if your input voltage is more than a few volts higher than your output voltage, as this type efficiently converts from higher voltage to lower voltage with about 85% efficiency. For comparison, a linear regulator outputting 3.3V from a 9V input will be operating at less than 37% efficiency.

Ah. I didn’t even think of a date code. Makes sense. I’m going to put a note inside the case so I can find the specs in the future.

Good idea, now I feel old that it didn’t occur to me that by now there would be tiny switching supplies. But I would need to find more friends that would be amazed about electronic devices. :smiley:

I have to say this is an extremely helpful forum. Thanks very much to all of you.

Apparently when I put that together back in the lower Jurassic I didn’t know anything about regulators and filter capacitors–it’s a bare regulator soldered (badly) to the switch and banana socket terminals. It worked OK for TTL logic, and the data sheet appears to say it’s usable without filtering, but there wasn’t much going on in those circuits anyway. I figured I’d better fix that even for the existing regulator since I’m putting it back into service to play with controllers, and it would be nice if they didn’t periodically reset and otherwise express their displeasure with the ignorance of the power supply maker. :smiley: That was another reason I wanted to ID the existing part, to see what filtering it likes.

I think I’ll get one of the switching supplies for the 3.3V mode. With it and a couple more capacitors, I’ll have to put it all on an actual breadboard instead of just attached to the wires like the existing student-style horror. I’ll turn it into a minor project for my son’s education, he wants to build combat robots (who didn’t when they were fifteen?) and needs to start acquiring electronics knowledge.