Alternative 9V regulator

[Mark Hammer]

I was throwing together a "power brick" thing with regulated outputs yesterday.  While poring through the parts drawer of regulators, I realized I had these Toshiba TA78L009 3-pin regulators that were about 50% taller than the typical NatsSem LM78L09 type.  The latter is spec'd at 100ma, which is why whenever you see the specs on power bricks, they will often have some number of 9VDC outputs at 100ma; because that's what the smaller TO-92 style can do.

The Toshiba ones are in what is essentially a taller TO-92 package, and are spec'd to deliver up to 150ma each.  The extra 50ma capacity is not a huge leap, but for those wondering how to safely address power for one or two digital pedals, without having to step up to the larger package with the heatsink, this can be convenient in providing enough additional capacity.  I was able to stick a quartet of them in a fairly small space on a piece of perf.

I used up all the ones I had, so I'm keeping my eyes peeled for more of them.  Worst case scenario, I'll use the LM78L09s I have, but these Toshiba ones look like a very good alternative.

[R.G.]

Interesting. I didn't know about those.

If you can't find them, this may help - the 78Lxx package is about the same price as the 78xx in the TO-220. The TO-220 is not all that much more PCB space, and can dissipate about five times the power without a heat sink. Of course, they have a 500ma or 1A nominal overcurrent limit. I've done some things where I used the TO-220 and then externally limited the current with a two-transistor current clamp before the regulator. 'Course that takes another volt or two of input voltage to keep it in regulation, and adds some more parts. In payment for that, you get any current limit you want to dial in with a resistor.

Another thing to think of is the two protection diodes that all three terminal regulators need. To date, I've only found two commercial power supply designs (other than mine  ) that put these diodes in; therefore, they're subject to sudden-death-syndrome if you short the input voltage. Put in those diodes.

[Mark Hammer]

The Toshiba ones are also handy if one is powering a digital or hybrid pedal using on-board down-regulation, where an external 9vdc supply is dropped to 5vdc.  You're right that the TO-220 package is not huge, but its somewhat larger size and bigger footprint can introduce some awkwardness in layout; not a make-or-brake thing but a nuisance that is potentially avoidable if all you need is a little more juice-control.  The Toshiba unit has the identical footprint to a TO-92.

And thanks for the reminder.  I'll have to stick in those diodes later tonight.  Best not to tempt fate, eh?

[Kesh]

You can get a little more out of the 78Lxx by soldering it as close to the PCB as possible. A little less than 100mW more.

[R.G.]

You can get a little more out of the 78Lxx by soldering it as close to the PCB as possible. A little less than 100mW more.

That is right. The actual specs on the 78Lxx devices say that their overcurrent operates at a minimum of 100ma, typically 150ma, at least last time I did a detailed walk through the specs. But overheat will get you when you least expect it. Putting it down very near the PCB gets the metal leads near bigger metal surfaces on the PCB.

There are a few alternates too. You can epoxy a flag of aluminum or copper to the flat face of the to-92 to get a little more heat out of the package, or solder a flag of copper to the center leg to get heat out more directly there.

But TO-220s are easier to make.

@Mark: I've done this with the TO-220: put the 220 in last, and with the leads as long as possible, but bend the leads at a 90 degree angle so the body lays over the top of some of the circuitry like a shed roof. Saves some height anyway.

[armdnrdy]

I've had to bend over the top heat sink portion of a TO-220 voltage regulator to make it fit in an enclosure! (after I bent the leads 90 degrees as you were saying)

Sometimes....whatever it takes!

[Kesh]

There are a few alternates too. You can epoxy a flag of aluminum or copper to the flat face of the to-92 to get a little more heat out of the package, or solder a flag of copper to the center leg to get heat out more directly there.

there are also ready made to-92 heat sinks available.



36 C per watt

[armdnrdy]

That thing is huge!

Just in time for the season. A Christmas ornament!