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DiscoverCircuits.com
-- Hobby Corner
Last Updated on:
07/10/2008 08:39:48 PM
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Very Low Voltage Oscillator
designed by David A. Johnson, P.E. |
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February 8, 2007 |
| OK, you may not ever need an oscillator to function using a power supply voltage below one volt, but if you ever do need one,
here is one way to do it. Getting any electronic circuit to operate below one volt is a real challenge. Typical silicon bipolar transistors don’t work below 0.7 volts. Some old
germanium transistors do work down at low voltages but those are hard to find and are usually offered only in large packages. |
| Why operate below one volt? Many energy harvesting systems generate low voltages. Fuel cells, vibration transducers,
thermoelectric devices, RF detectors and photovoltaic cells all will typically produce low voltages. A single solar cell will only produce 0.5 volts. This is well below any
practical voltage, so some type of DC to DC converter would be needed, to boost the voltage to some reasonable level to perhaps charge a battery. At the heart of any DC to DC converter
is an oscillator. If you can’t run an oscillator with the available voltage, you will never be able to boost that voltage to a higher one. |
| I gave some thought about the various ways one could design a low voltage oscillator. After doing some research, I decided to
try some new zero threshold voltage n-channel FETs from Advanced Linear Devices (www.aldinc.com). These devices come two transistors in an 8 pin package, with a common source connection.
I wired up one of their devices as a classic two transistor astable multivibrator circuit. By carefully picking the component values, the circuit operates from about 0.16 volts to over
0.6 volts. The circuit below generates a nice square wave signal with a frequency of about 300Hz. A higher frequency is possible by changing the two 0.01uF caps to smaller values. |
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