PSU with *simple* Short-Circuit Protection... no more blown 317/337 regulators!

Photo of new PSU-2448mk2 Power Supply Kit

Has (3) on-board fuses with LED indicators.
If all (3) LED lamps are lit up, everything is good. All systems go.



Now, we intentionally create a short circuit by shorting the +48V voltage rail to Ground. 
Poof! Fuse blows, and LED lamp for the +48V fuse is OFF - meaning, there was a short circuit somewhere and this fuse needs replacement.



Remove the short-circuit we created during this demo, and replace the fuse with a brand new one.
Voila! LED is lit up again - meaning, our +48V line is working again.




NOTE: We didn't damage the voltage regulator, didn't have to desolder it, or  replace it with a new one. We just pop-out the old fuse and replace it with a new fuse. 

Cost of fuse = $0.10
Time to fix = 2 seconds
Peace of mind knowing that you won't have to desolder a 3-pin device and solder it again, and risk damaging your PCB while you fight to get the old voltage regulator out....  Priceless! 

The LED behind the glass fuse is one of those things that makes you ask, "Why diddn't we see that all over the place before this?"

Nice work!

Smart, I saw a similar design on aRhodes preamp yesterday to ease troubleshooting should a transistor fail... 

that looks great..... you dont have any trouble with heat of the regs with sinks that size?

boji said:

The LED behind the glass fuse is one of those things that makes you ask, "Why diddn't we see that all over the place before this?"

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True. But they should be green ;D
In my book red is always "failed"

I did a console PS design a couple decades ago where I used  bi-color LEDs to indicate PS/fuse status.

Green for PS rail voltage good- fuse good, red for fuse open but power supply rail voltage still good, and dark or no LED, for no PS rail voltage.

This was useful for troubleshooting, since if the PS was bad. the customer wasn't going to fix it by replacing the fuse. If all voltages go away at the same time, you know to check the mains fuse or line cord.

JR

Properly applied 317/337 regulators won't fail from output shorts. And fuses usually don't protect transistors, rather the other way around...

Samuel

Samuel Groner said:

Properly applied 317/337 regulators won't fail from output shorts. And fuses usually don't protect transistors, rather the other way around...

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During my testing, I accidentally used a higher rating fuse, and when I shorted the +48Volts, the LED lamp just turned OFF.  I remove the temporary short, the LED turned back ON.  It didn't blew the fuse.

So the Vregulators continued working even with my intentional short-circuit.

But once in a while, I'll get reports from customers saying they accidentally shorted their PSU and only replacing the regulators fixes their problem.  This should take care of that issue.

True. But they should be green Grin

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Yeah I know. I'm out of Green LEDs!  But good idea!

How hot do the heatsinks get under full load?  Kind of close to the Al electros.

The trafos I use are 800+mA, so they don't even approach the 1.5Amp rating of the Vregs.  They don't get hot. They may get warm if you have a heavier load, but you can still touch it and not get burned hot. Used with my preamps (i.e. IC chips), they barely get warm.

There is a good clearance between the heatsinks and caps. 

Looks great, Owel!
What is the voltage of the power transformer secondary?
I have a bunch around so may not need to buy one.
Also, how many Ma does the 48volt output supply?
This is a pretty good price for a small regulated supply.
Definitely interested.

I'll get reports from customers saying they accidentally shorted their PSU and only replacing the regulators fixes their problem.

Click to expand...

This is on the +48 V rail, right?

Samuel

Lm317/337 are not made to withstand the 50+ volts across them when their output is shorted to ground. I've seen several audiophools projects using them on B+ rails at 300V+. It's all very fine when everything works according to plan (smooth ramp-up of both input and output voltage), but as soon as anything goes wrong, the whole thing goes down.
I would not use anything else than a TL783 on 48V reg. Even the 317HV does offer enough safety in case of elevated mains voltage.
Good design practice is making sure the equipment works or is easily repairable even in degraded operation.

abbey road d enfer said:

Lm317/337 are not made to withstand the 50+ volts across them when their output is shorted to ground.

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...and it's questionable whether a fuse will be sufficient protection in such situations.

JDB.

Samuel Groner said:

I'll get reports from customers saying they accidentally shorted their PSU and only replacing the regulators fixes their problem.

Click to expand...

This is on the +48 V rail, right?

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Not always. Some of them short the V+ or V- rail. 

abbey road d enfer said:

Lm317/337 are not made to withstand the 50+ volts across them when their output is shorted to ground. I've seen several audiophools projects using them on B+ rails at 300V+. It's all very fine when everything works according to plan (smooth ramp-up of both input and output voltage), but as soon as anything goes wrong, the whole thing goes down.
I would not use anything else than a TL783 on 48V reg. Even the 317HV does offer enough safety in case of elevated mains voltage.
Good design practice is making sure the equipment works or is easily repairable even in degraded operation.

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A 317 on a 300V B+????  Man, they're brave.

I'm using the HV version for my +48 and V+ rails. 

Unfortunately, there is no HV version for a 337. (Someone correct me if I'm wrong).

Mike Cleaver said:

Looks great, Owel!
What is the voltage of the power transformer secondary?
I have a bunch around so may not need to buy one.
Also, how many Ma does the 48volt output supply?
This is a pretty good price for a small regulated supply.
Definitely interested.

Click to expand...

Transformer I use is spec at 18+18 @ full load (30VA).

Also, how many Ma does the 48volt output supply?

Click to expand...

The regulators on the +48V line are max. rated 1.5Amps.
But I'm only using an 800+mA power transformer. 
Enough to power 4 channels preamp on a 1u rack with plenty spare power left.

owel said:

Transformer I use is spec at 18+18 @ full load (30VA).

Click to expand...

For 24V out?

JD 'considering the name of the PSU' B.

owel said:

A 317 on a 300V B+????  Man, they're brave.

Click to expand...

Audiophools are not brave, they are dangerous.

lm317/337 have current limiter and thermal protection, so if their Vin does not exceeded never their Vin max then it's impossible destroy them with a short circuit if there is a fuse to protect them, even if this fuse has a big i2t factor.
With the short circuit the LM317/337's current limiter becames active because the fuse keeps more time then the current limiter to became active to make the Iout to zero. The LM317/337 limiter gets the Vout near to zero so the LM317's  Vin-Vout = Vin until the fuse gets to zero the Iout.
Since the Iout_max time becames very low for the fuse action then LM317/337 has zero damage.

The problem there is when there's a circuit with an LM317 with its Vin that's superior to 40V (or 60V for the HV version), even if there is a very fast fuse to protect the LM317 from a short circuit.
Infact, after this short circuit the LM317's  Vin-Vout goes over its max value ammitted (over 40V) , even there is the fuse.