Protecting a Max1044 question

[therecordingart]

I'm playing around with the Max1044, and I want to protect it just in case a 12v or 18v supply is plugged into it. Is a zener regulator sufficient or should I go with a 7809?

[midwayfair]

I'm playing around with the Max1044, and I want to protect it just in case a 12v or 18v supply is plugged into it. Is a zener regulator sufficient or should I go with a 7809?

If you have room on your layout, go with the 7809 -- you KNOW it'll do the job every time, all the time. I've been using a zener, though, in the little portable one I have for breadboarding. That has an LT1044, so it's a little extra safe.

[Govmnt_Lacky]

The problem with using a 7809 is that you need to have a minimum input of ~11.5V tin order to get a 9V output 

If you put +9V into a 7809, you ARE NOT going to get +9V out of it.

[therecordingart]

The problem with using a 7809 is that you need to have a minimum input of ~11.5V tin order to get a 9V output 

If you put +9V into a 7809, you ARE NOT going to get +9V out of it.

True. I'll have to see how much of a voltage drop I'll see. I don't need exactly 18v out of the charge pump, but I need more than 9v. It is going to power a gain stage that needs more headroom than a 9v supply can provide.

[R.G.]

Put in an LT1054.

Unless your raw DC supply to the MAX1044 is current limited, you can't just hang a zener across it and have everything live. If the zener can't conduct the full current available from the raw supply when it exceeds the zener voltage, then the zener burns out and either shorts and frys the raw supply (if it can be fried by overcurrent) or the zener opens, and then the raw supply kills the MAX1044.

The LT1054 will survive up to 15V. Then it has the same issues as the MAX1044.

If you're playing around, use an LT1054 and don't plug in an 18V supply. If you're not just playing around and want to design a supply that's capable of living through an 18V supply into a device intended for 9V, you have other problems.

[therecordingart]

Thank you!

[midwayfair]

The problem with using a 7809 is that you need to have a minimum input of ~11.5V tin order to get a 9V output 

If you put +9V into a 7809, you ARE NOT going to get +9V out of it.

Ah, crap, I forgot about that. I'm so used to using the 7805 where the voltage drop isn't relevant.