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DiscoverCircuits.com -- Hobby Corner
"Hobby Circuits for
your Hobby Projects"
Last Updated on:
06/19/2009 02:13:51 PM
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Very Low Voltage
Oscillator Circuit
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.
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| 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.
See schematic below: |
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