chip for converting positive to negative like the ICL7660A - Page 1
Forum section: electronics / projects

author: dentaku
author_rank: Frequent Contributor
timestamp: July 26, 2015, 02:20:22 am
content: I was looking at a little power supply from an old Brother fax machine and one of the pins puts out -10V and it's powered from a 16V DV power brick.At first I thought it was weird but then I saw that on the bottom of the board there's a tiny uSOIC ALPHA AS7660S chip that takes the -10V from the KA7810 regulator and creates a negative voltage out of it.QUESTION: What other chips do people use for doing stuff like this? Maybe something more modern butstill available as DIP?I see that the ICL7660A is pretty much the same chip as this ALPHA and TI has their version of it that only goes to -10V instead of -12V like the others I've mentioned.It looks like a handy device to have.

author: vindoline
author_rank: Unknown
timestamp: July 26, 2015, 02:48:52 am
content: I like the LT1054. It's good up to 16V input and is available in DIP.

author: dom0
author_rank: Super Contributor
timestamp: July 26, 2015, 07:59:27 am
content: 555Or a few transistors.

author: ajb
author_rank: Super Contributor
timestamp: July 26, 2015, 12:53:33 pm
content: The ICL7660A is acharge pumpcontroller, many manufacturers have similar parts with various capabilities as you've seen. Be aware that some of them have trouble starting under load and so some applications require an esternal schottky diode across the output.A charge pump is fundamentally a square wave generator plus a couple of diodes, so if you don't need much current, you can create a charge pump from a spare PWM output from an MCU plus a couple of external diodes and caps. This is handy for LCD bias voltage, for instance. The drive strength of the MCU's IO pins will be a limiting factor in the amount of current such a charge pump can provide, but you could add a couple of transistors to improve this if you wanted. You could also use a 555, as mentioned, and you can even daisy chain pump stages to create higher, lower, or bipolar voltage output options.More generally, if you need more current, you can configure a standard buck converter as an inverter--what would normally be the output node gets tied to ground, and what would normally be ground becomes the negative output. Note that in this configuration the converter sees the full potential between the positive input and the negative output as its supply voltage, so watch the switch voltage rating, and any control/status signals will need to be referenced to the negative output rather than ground.

author: jeroen74
author_rank: Frequent Contributor
timestamp: July 26, 2015, 05:11:54 pm
content: I used a MAX868 once, it's a regulated inverter.Only available in uMAX or die form though.

author: dentaku
author_rank: Frequent Contributor
timestamp: July 26, 2015, 06:51:15 pm
content: Quote from: vindoline on July 26, 2015, 02:48:52 amHmmm... That one looks interesting.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 26, 2015, 07:08:38 pm
content: The charge pumps produce quite some noise, especially if they have to deliver more than a mA. For more mower often a switched mode inverter is better. They also provide a regulated voltage, so less drop if loaded.