Electronics > Beginners

Switching Reg


Ive got a Maxim MAX630 CMOS DC-DC regulator, wired up deadbug style, that is putting out a little less voltage then I'm putting in it.

Here's the Full Data sheet

I can't get this to work right for the life of me.  I'm putting between 6.6 - 8.2v input, looking for anywhere between 12-15v out (150ma peak).

I'm using -
D1 : 1n5819 schottky
L1: low esr 19r474c 470uh power inductor (1.1A rating)
C1 : 470uf electrolytic in parallel with a 22uf tantalum
Cx: 47pf ceramic
R1: 91k
R2: 10k
Cc: 10nf mlcc
Don't have R3,R4, pin 1,or pin 8 connected

Ive spent the better part of 3 hrs looking over this, and cant find any visible reason it should be working like i want.
 i thought it was maybe the esr on the 470uf, added the 22 in parallel. then CC.  Then considered it could be a dirty power supply. dug another one out.  Then used batteries.

I did have it powered on with R1 & R2 reversed - could i have toasted the comparator op-amp? 
I'm under the opinion that the chip is bad, but the thing is like 8 bucks (and i don't have another handy).
Does anyone see something i missed?

What voltage does it output? I guess it's the input minus the voltage drop over the diode? If so, you will have the same 'output' without the MAX630.
The thing doesn't look very complicated, it should adjust the output so that the voltage on pin 7 equals Vref, 1.3 volts.
If you reversed R1 and R2 it tried to output something like 1.5 volts, you would not kill the comparator but just stop switching completely because your Vout will be above that.
What do you measure on pin 7?
Is the oscillator running? (put the scope on pin 2)
Is it trying to switch? (scope on pin 3)
Did you connect pin 5 and 6 together?

 it was outputting about .3v less then the input. (diode).
yes, pin 5 and 6 are tied together.

I do not have a scope.  Been looking to get one for years, have never been able to do it.

I haven't messed with it too much after finding this, but i was assuming some things and didn't read the whole data sheet.
i was also putting the input to pin 5, but the chip actually does its thing with the output voltage, not the input.

I'm going to fiddle with it some more, but the first impression is that the circut still isn't working :'(

If you don't have a scope you could try a multimeter on AC. You should at least be able to measure some AC on pin 2 and pin 3.
But yes, get a scope...


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