Part Review – Intersil ICL7660
Today we are going to quickly examine a very simple yet useful part – the Intersil ICL7660 CMOS voltage converter. Huh? 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 (as used in my bbboost project).
But first of all, let’s say hello:
To do so with the ICl7660 is very simple, you only need two 10uF electrolytic capacitors! Honestly, I couldn’t believe my luck when I discovered this part, that is why I am writing about it today.
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.
So there you have it - a very easy and cheap way to get yourself -5 volts DC.
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