dumb regulator question

[pinkjimiphoton]

i've been messing around with some ddl circuits lately, and have smoked a few chips by accident... and was thinking since these run at 5 volts, would it be wise to use maybe an 8 volt regulator for circuits like this so they don't get surges that pop the chips? i don't think i'm asking this right lol..

but i figure an 8v regulator with the usual 9v supply and i shouldn't have to worry so much using smaller caps in the circuit etc...  i'm a little leery about using small 16v or 10v caps with a 9v supply... i like to have about twice the b+ handling but really am getting into crowding big things into little boxes lately, so been experimenting with alternate ways of wiring in electros... under the board, or laying down over other stuff to give me more room.

just a thought... would there be any benefit in this kind of situation, or do i need a cup of coffee?

i do need coffee, just got up... 5 pm. musician hours. egad.

[tonight, we ride]

Maybe I'm misunderstanding something, but if the chips run at 5V is there a reason to use an 8V regulator instead of a 5V? What is the Maximum VCC listed for the chips??

[pinkjimiphoton]

the chips melt if they go above 5 volts. i've had a couple 78l05's put out a fraction more and roast 'em.

i had seen someone else ask recently about using a 9v regulator to protect a 9v circuit, but its my understanding that the reg needs a volt or two higher than its output to function correctly.

most 9v pedals run fine on 5,6 volts, so i figured an 8v regulator may help protect more sensitive stuff on the board. too little sleep, too little coffee...lol

[EBK]

So, are you thinking about protecting a 5V regulator by putting an 8V regulator first?  Drink some coffee, please, before answering that.   

[pinkjimiphoton]

yes. this is why i need coffee. lol

i kinda think i meant using like an 8v reg right across the power supply jack so its regulated before it hits anything.

but yah i guess i was thinking of protecting a 5v reg with an 8v reg. lol

[anotherjim]

Regulators don't put out higher voltage unless they are miswired. Less voltage during power up or down, but never more.

I think the issue is the 5v chip is connected to other circuits powered by a higher voltage, usually indirectly via resistors or capacitors. If power goes on-off quickly enough, a cap can act like a charge pump and maybe exceed the input voltage limits of the 5v chip. If that happens, it can damage the chip, or if you're lucky, only put it in "latch up". Latch up can be recovered either by leaving it switched off for long enough so the overvoltage charge bleeds off naturally, or by shorting all the chip pins together (put it on metal foil). A PT2399 can , in my experience, hang on to the excess charge for a long time and might not actually be smoked.

Probably the best way to protect the chip is to fit overvoltage clamp protection diodes on any pin connection leading to a higher voltage circuit.

In a single supply that -15v connection for the lower diode will be ground. The Upper diode must connect to the +supply of the device it is protecting.
Schottky diodes are preferred to limit the overvoltage to 0.3v and act fast.

If the connection is via resistance or direct, you only need the upper diode, A cap can have a charge pump action delivering excess positive AND/OR negative voltage. Without a cap, the excess can only be positive since both circuits share the 0v connection and can't drive it negative.

For the PT2399, don't fit too much capacitance on pin2 for the reference supply. When power goes off, you don't want pin2 (normally 2.5v) to stay higher than pin1 when the 5v supply drops off.

[pinkjimiphoton]

thanks jim~

its actually an em5 clone i had the issue with, with an m65831 chip. the clock chips cooked on me a couple times, and in each case the regulator was reading really weird stuff, one 6.3 v, the second one 1.4 or something. weird.

i was wondering if it may be a cap doing it... so even more, thanks for the explanation. i gotta re-read this once i'm fully awake... man, hippy getting old...lol... gigging these days is really kickin my ass

[Mark Hammer]

Maybe what is requiredis not so much voltage regulation - which you seem to have enough of - but current limiting.  Maybe there needs to be some series-resistance feeding the V+ pin on whatever the chips involved are.

[pinkjimiphoton]

could be, sir mark! remember, i'm a monkey with a breadboard, and am just barely understanding most of the easiest stuff.

just seems to me a cheap easy way to protect stuff and keep the voltage constant would be to drop pretty much whatever down a volt or so and run it with a regulator at a normal 9v. 1 or 2v shouldn't make much of a difference, especially with fuzzes