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Circuits designed by David Johnson, P.E.
Last Updated on:
Thursday, March 22, 2012 06:39 AM
Master Category List
- Dave's Circuits
Text & Graphics
Copyright © David A. Johnson, PE - ALL Rights Reserved.
LINKING to Dave's circuits is permitted but DO NOT COPY to your WEB SITE server! |
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Solid State Relay (SSR) Circuits |
- CHARGE COUPLED
BI-DIRECTIONAL POWER MOSFET RELAY
The circuit uses an inexpensive C-MOS inverter package and a few small
capacitors to drive two power MOS transistors from a 12v to 15v supply. Since
the coupling capacitor values used to drive the FETs are small, the leakage
current from the power line into the control circuit is a tiny 4uA. Only about
1.5mA of DC is needed to turn on and off 400 watts of AC or DC power to a
load.
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- Solid State Relay
Requires Ultra Low Control Current
Most solid state relays require at least 5ma and often more input control current,
to fully turn on the device. But such current levels often force battery powered
circuits to use excessively large batteries. The relay hobby circuit shown below
demands only 50uA of input current. This about 100 times lower than that needed by
a typical optically isolated solid state relays. The circuit uses a combination of
a high current triac and a very sensitive low current SCR, to control up to 600 watts of
power to a load, while providing full isolation and transient protection.
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SOLID STATE RELAY
REQUIRES ONLY 50uA DRIVE CURRENT
This circuit demands a control current that is 100 times smaller than that needed by a
typical optically isolated solid state relays. It is ideal for battery powered systems.
Using a combination of a high current triac and a very sensitive low current SCR, the
circuit can control about 600 watts of power to load while providing full isolation and
transient protection.
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