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Project Notes

#165 Power2662Inverter

Test a negative 5V power supply using the LM2662 Switched Capacitor Voltage Converter

Notes

The LM2662 is a single-chip CMOS charge pump voltage converter:

  • 1.5V to 5.5V positive voltage input
  • up to 200 mA of output current
  • operating efficiency greater than 90% at most loads

There are three basic application topologies:

  • voltage inverter (Vout = - Vin)
  • voltage divider (Vout = 1/2 Vin)
  • voltage doubler (Vout = 2 Vin)

This circuit is a basic test of the voltage inverter configuration, with a few simplifications:

  • 5V regulated input voltage
  • frequency control is left open, so operates at 20kHz (as opposed to 150kHz)
  • I’m using 47µF electrolytic capacitors since they are what I have on hand. The datasheet recommends low-ESR ceramic or tantalum for better performance.

I have some LM2662MX chips in SOP-8 packaging, so I mounted one on an adapter module for easy breadboarding.

The circuit includes a simple LED/resistor fixed load.

Some Measurements

Item Value Notes
Vin 4.97V from LM7805 regulator powered by 9V battery
Vout -4.96V with no load
Vout -4.83V with LED/resistor load

Here’s Vin (CH1) and Vout (CH2) DC-coupled on a scope, with load attached:

vin vout

Zooming in on Vout (CH1) AC-coupled to see the ripple:

vout ripple

I’m seeing 200-400mV dropouts every few seconds as captured above. I’m not sure of the source or if that is particularly normal. The electrolytic capacitors may play a role, so I might measure that again if/when I can get my hands on some sufficiently large low-ESR ceramic capacitors.

As it is, it seems the inverted voltage output would need further filtering/smoothing and perhaps regulation for applications requiring a good clean negative voltage supply.

Construction

NB: Fritzing diagrams use the LM2662 Switched Capacitor Voltage Converter - DIP8 module custom part

Breadboard

The Schematic

The Build

Credits and References

About LEAP#165 Power
Project Source on GitHub Return to the LEAP Catalog

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

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 (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.