A use for 7660s (instead of MAX1044s)

[cd]

Nothing new here, but I haven't seen this posted in a while, and it came up for me today.   I was assembling some circuits which needed +/-9V power, and ran out of MAX1044s - but I do have lots of 7660s.  As anyone who has used a 7660 knows, it's a PITA since the oscillator runs in the audio range and you can clearly, clearly hear it in your circuit.  The MAX1044 is the preferred chip in this case since it has a function where the oscillator can be pushed out of the audio range (the 7660 does not have it).  So it's usually preferable (and ten times easier) to just use a MAX1044.

Anyway, I have to order all my MAX1044s through the mail, which is another PITA.  So I cobbled together an external oscillator (in the MHz range) using a 555 and ran the 7660 off that - bingo, +/-9V power from a 7660 and no whine!  Here's the 555 oscillator circuit:

http://www.interq.or.jp/japan/se-inoue/e_ckt5_1.htm

To get the oscillator in the MHz range, change the two resistors to 470ohms.  If you poke around that website some more you'll find the formula for figuring out the frequency of the oscillator.  Use whatever RC combinations you have in your parts box to get the right frequency (100KHz minimum to be safe).  The output of the 555 (pin 3) goes into pin 7 of the 7660 through a 1k resistor.  Then setup the 7660 as usual (see www.geofex.com in the circuit sweepings section).

If you're like me, you can easily get 7660s and 555s dirt cheap locally - for me, it's around 75 cents each (plus whatever caps/resistors you need - 10 cents worth).  A MAX1044 costs $1.70 at Digikey (my source) plus waiting around time & shipping.   So the MAX1044 is still an overall better deal if you have them on hand (no extra components required, just plug in and go) but if you already have the parts (& time, and board space) there's always that 2nd option.

[Ansil]

good to know man. thanks.

[mikeb]

You little ripper! Thanks! 1044s are expensive here in Australia whereas 7660s I can buy over the counter.

Thank you.

Mike

[lightningfingers]

Maxim will give you free 1044s and 7555s :wink:

[smoguzbenjamin]

Maxim will give you free 1044s and 7555s :wink:

They give you two free MAX1044s

[mikeb]

I've already got a bunch of samples .... I'm talking about for 'normal' use.

Mike