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DiscoverCircuits.com -- Hobby Corner
"Hobby Circuits for your
Hobby Projects"
Last Updated on:
06/19/2009 03:15:56 PM
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Reduced Power
Relay Driver
Aug 3, 2008
designed by David A. Johnson, P.E. |
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| Relays
can handle a lot of power. However, for certain power sensitive designs you would
like to reduce the power needed to hold a relay closed. The circuit below performs
such a task. It uses a single CD4093 quad NAND gate. When the “on” logic
input signal is detected, the relay is first pulsed on for about 500ms. This is
sufficient time to insure the relay is fully closed. After that initial pulse the
relay is then driven with a square wave signal, whose duty cycle can be adjusted.
The signal duty cycle can be adjusted from about 10% to 90%. In most cases a 50%
duty cycle will hold the relay closed. This reduces the average DC current
required by the same factor, which means a 4:1 reduction in power. The circuit can
operate over a wide 3v to 15v range. |
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Schematic below to view PDF version of this Circuit |
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