Today we are going to quickly examine a very simple yet useful part – the Intersil ICL7660 CMOS voltage converter.

This is the part you have been looking for when you needed -5V and you’re not running off a multi-tap transformer. For example, some old-school TTL electronics projects need +/-5VDC power rails. Or if you are using the ICL7107 analogue to digital/3.5-digit display driver IC .

But first of all, let’s say hello:

To do so with the ICl7660 is very simple, you only need two 10uF electrolytic capacitors!

Firstly, how does it work? A very simple definition would be: the 7660 charges one capacitor, then the other – an oscillator controls the charging cycles between C1 and C2 and inverts the polarity, allowing the capacitors to discharge at an inverted voltage (negative instead of positive).

For a more detailed explanation, have a loot at the data sheet. Furthermore, if the oscillation frequency interferes with other parts of your circuit, you can boost the oscillation rate with the use of a NAND gate, from an external logic IC (4011, etc.)

However due to the oscillations, there is a ripple in the supplied -5V. I only wish I had an oscilloscope to show you this, perhaps next month. In the meanwhile, there is an explanation of this in the data sheet.

At this stage, let’s have a quick look at an example circuit, from the data sheet – figure 13A.

And here it is in real life. The circuit on the breadboard to the right is a simple 12VAC > 5VDC converter, with the 7660 on the left breadboard.

So there you have it  – a very easy and cheap way to get yourself -5 volts DC. Some information from this review obtained from Intersil website and the ICL7660 data sheet. You can order ICL7660 in both through-hole and surface-mount from PMD Way, with free delivery worldwide.

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