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Project Notes

#165 Power2662Inverter

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


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.


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


The Schematic

The Build

Credits and References

About LEAP#165 Power
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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!).

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