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#731 ICL7660

About the ICL7660 CMOS Voltage Converter, and testing its use to convert a +5V supply to a ±5V supply.

Build

Notes

The ICL7660 is a CMOS charge-pump voltage converter IC designed to invert, double, or divide a positive input voltage, enabling efficient generation of negative or doubled outputs from a single positive supply.

It operates across a wide input voltage range of 1.5V to 10V (or 12V for the ICL7660A variant) and requires only two external capacitors for basic operation, making it ideal for low-current applications such as battery-powered devices, op-amp power supplies, and dynamic RAM systems. By leveraging a built-in oscillator (typically 10kHz) to alternate charge transfer between capacitors, it achieves high power efficiency (up to 98%) and open-circuit voltage conversion efficiency of 99.9%.

The IC is commonly used to generate negative rails (e.g., -5V from +5V) for analog circuits, LCD biasing, or data acquisition systems, though its output current is limited to 20–40mA depending on configuration. While simple to implement, it may introduce voltage ripple due to its switching mechanism, a trade-off for its compact design and minimal component requirements. Available in DIP-8 or SOIC-8 packages, the ICL7660 remains a cost-effective solution for applications needing dual or inverted voltages without complex circuitry.

NOTE: the ICL7660 is now officially end-of-life, although it is still widely available.

icl7660

The ICL7660 datasheet provides details of a range of possible circuits, including:

  • Simple Negative Voltage Converter
  • Positive Voltage Doubling
  • Combined Negative Voltage Conversion and Positive Supply Doubling
  • Voltage Splitting
  • Regulated Negative Voltage Supply

Further information and other applications are covered in AN051 Principals and Applications of the ICL7660 and ICL7660A CMOS Voltage Converter

Circuit Design

The most basic and common use of the ICL7660 is to convert a +5V supply to a ±5V supply.

A few key points about using the ICL7660:

  • The LV pin may be tied to GROUND to bypass the internal series regulator and improve low voltage operation when V+ <3.5V.
  • The charge pump operates at a nominal 10kHz. The OSC pin can be used to alter the frequency to suite the application:
    • lower the frequency with a capacitor between OSC and V+, and a corresponding increase in the value of C1 and C2
    • increase the frequency with an external clock source

bb

schematic

Testing the +V and -V rails with multimeters. No load, and it pretty perfectly mirrors the voltage:

ICL7660_bb_test1a

Demonstration - Driving a Dual-supply OpAmp

As a simple demonstration, I’ve added an UA741 op-amp powered from the dual ±5V rails, configured as a square wave oscillator, similar to LEAP#039 Astable Opamp Oscillators.

With R1=10kΩ and R2=10kΩ, ß=0.5 so the expected frequency of oscillation is 455.1Hz

bb_build

We are recording 465Hz, which is nicely close to the prediction. Note: component values matter, especially for C3 ceramic capacitor which can be far from nominal value.

In the scope trace:

  • CH1 (Yellow) - OSC_OUT
  • CH2 (Blue) - capacitor C3 charge
  • CH3 (Red) - tracking V+
  • CH4 (Green) - tracking V-

scope_796

Credits and References

About LEAP#731 PowerICL7660

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

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About LEAP

LEAP is my personal collection of electronics projects - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting.

Projects are often inspired by things found wild on the net, or ideas from the many great electronics podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know or send a pull-request.

NOTE: For a while I included various scale modelling projects here too, but I've now split them off into a new repository: check out LittleModelArt if you are looking for these projects.

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