ICL7660, another useful little IC.

With this review, I’d like to continue introducing readers to all sorts of useful electronic components. Reviews like this don’t come along very often, but I hope they can be useful too.
Anyway, as always, the rest is after the jump.

Many radio hobbyists occasionally run into situations where they need to generate both positive and negative voltages. The positive rail is usually available already, but the negative one often has to be generated separately.
I’ll get into the theory and practical details a little later. For now, as always, here’s the standard introduction.

I bought these ICs for $2.7 per ten-pack; the seller has since lowered the price.
I haven’t seen them for less than 50 cents apiece here, so paying half as much is still a saving.

The ICs arrived in a bundle with some other components I’ve covered before. They were in their own little bag, with the name written by hand.


The IC itself is nothing unusual; it comes in a standard SOIC-8 package. It doesn’t look like a counterfeit.


As everyone knows, electronic components are the kind of thing you can’t test until you hook them up to a few other parts.
First, here are the datasheets for this IC and its equivalents. Some datasheets cover application examples in more detail, but they may all come in handy.
ICL7660
LMC7660
MAX1044

This IC is one type of converter.
But it has no transformers, inductors, or anything like that; it converts voltage using a switched capacitor.
A better-known IC of this type is the MAX232, but it’s considerably more complex: it not only converts voltage, but also boosts it, generating +10 V and -10 V from 5 V for the RS232 interface.
In some applications, though, it’s overkill and requires more external components.

The ICL7660 is primarily intended to invert the polarity of a 1.5–10 V input, producing 1.5–10 V with negative polarity.
The IC’s internal circuitry:
As the schematic shows, it contains an oscillator and four switches that alternately connect the capacitor to the power input and then to the output.


Specifications:
Supply voltage — 1.5–10 V (1.5–12 V for versions without the letter A in the part number)
Quiescent current — 80–170 µA
Switching frequency — 10 kHz
Efficiency — 98%
No-load efficiency — 99.9%

Basic connection circuit in voltage-inverter mode:


The IC can be used in many ways: as a simple step-up converter, as a voltage inverter, or in a cascaded configuration to increase the voltage.
All these configurations are described in the datasheet and in a Russian-language description of the IC, which I’ll include in the supplementary materials for this review.

I came across this principle in Radio magazine many years ago. It described a mains power supply using switched capacitors: during charging, they were connected to the mains and charged in series; during discharge, they discharged into the load, but were switched into a parallel configuration. The circuit seemed to be connected to the mains, but apparently had no galvanic connection to it.
I wanted to include that article, but couldn’t find it. I remember liking the originality of the design.


Finally, I checked the current draw with the output shorted.
Along the way, I also managed to accidentally test reverse polarity—I noticed it by the smell. I disconnected it, let it cool down, then switched it back on. Everything worked just as before. No magic smoke escaped :)


Since I had an op-amp running in addition to the load resistors, the readings did of course drift, but judging by the current draw with and without the resistors, the efficiency is still pretty good.

In summary, these ICs are perfectly suitable for use. The price may not be the best, although when I bought them I tried to find the best deal on a lot with a small number of ICs. Still, it was better than buying locally. The seller is perfectly decent, although I wasn't happy with one type of IC I got from him (see flashlight mod).

Although at first glance the circuit seems completely unnecessary and pointless, I actually plan to use it in one of my upcoming reviews, so I'm posting all the necessary documentation here. That way I won't have to go back and revisit this step later.
Additional materials, datasheets, PCB layout, schematic — download.

Thanks to everyone who read this. I hope the information was useful.