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Relay Circuits, Page 4a
Relay Circuits:  #'s - B        C - H        I - O        P - S        T - Z
Last Updated on:
Wednesday, July 16, 2014 06:35 AM


Circuits Designed by Dave Johnson, P.E. :
  • Reduced Power Relay Driver  Aug 3, 2008
    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.

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Relay Toggle Circuit Using a 555 Timer -  This is probably the best toggle circuit.  (circuit diagram added 6/07)
Relay Toggle Circuit using a MOSFET  & Push Button -  ....
Relay Toggle Circuit using a Single Transistor & Push Button -  ....
Relays and Renewable Energy -  Find out more about relays and their uses in renewable energy applications…. [REUK - Renewable Energy UK website]
Relays eliminate High-Voltage noise -  13-Sep-07 Issue of EDN  A simple relay circuit cancels noise in the actuator stage of a scanning electron microscope.... [Design Idea by Jui-I Tsai, Woei-Wu Pai, Feng-Chang Hsu, Po-Jui Chen, Ching-Cheng Teng, and Tai-Shan Liao, National Applied Research Laboratories, Hsinchu, Taiwan]
Relays: Automatic Turn-off -  The above circuit is similar to the "Delayed Turn-on" type but now configured as an automatic turn-off type. The diagram shows how the circuit function can be reversed so that the relay turns on when power is applied but turns off again automatically…. [Tony van Roon's circuit]
Relays: Delayed Turn-on -  This circuit is a delayed turn-on relay driver and can produce time delays for up to several minutes with reasonable accuracy. The 14001 (or 4001) CMOS gate here is configured as a simple digital inverter. Its output is fed to the base of a regular 2N3906 (PNP) transistor, Q1, at the junction …. [Tony van Roon's circuit]

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Relays: Long Duration -  This is an accurate long-duration time delay driver, switchable between 1 and 10 minutes or 10 to 100 minutes and whose function does not depend on electrolytic capacitors. Film dielectric caps have been selected. IC1 is configured as a free-running astable multivibrator which frequency is divided down by IC2, a 14020 (or 4020) CMOS 14-stage,…. [Tony van Roon's circuit]
Relays: Long Duration--1 min to 20 hrs -  Shows a 'long-range timer relay' switching circuit which spans 1 minute to 20 hours in three ranges using a three-step, two-deck mechanical rotary switch… [Tony van Roon's circuit]
Relays: Long Duration--1 to 100 min -  This circuit shows a pair of CMOS NOR gates which form a push-button-activated one-shot multivibrator relay-switching circuit that provides delays up to several minutes with resonable accuracy.  The relay turns on as soon as the START switch S1 is closed. However, it turns off again after a preset delay of about 0.5 seconds per microFarad (uF) of the value of capacitor C2.  The two CMOS gates are configured as a manually-triggered monostable multivibrator whose output is fed to the relay through R4 and transistor Q1.... [Tony van Roon's circuit]
Relays: Self Latching -  This relay driver is Self-Latching which means that once it activates it will remain in that state until S1 is pressed and momentarily disrupts power to the latch.…. [Tony van Roon's circuit]
Relays: Transistor Boosted -  This relay driver boosts the input impedance with a regular 2N3904 transistor (or equivalent). Very common driver. It can drive a variety of relays, including a reed-relay, and is non-latching.
Transistor Q1 is a simple common-emitter amplifier that increases the effective sensitivity of the 12 volt relay coil about a 100 times…. [Tony van Roon's circuit]
Relays-12 Sec to 90 min -  Schematic and notes only, no circuit description provided…. [Tony van Roon's circuit]
Relays-Dark Activated -  This circuit switches a relay at dark via a Light Dependent Resistor or LDR for short. The applications are numerous.  In my application, it switches on a light with an older type movement sensor and is mounted on the top corner of my workshop with the LDR facing upwards.  The Dark Activated Relay prevents that the light is triggered during daylight hours.  But, it can also be used to switch led-beacon lights for your driveway, or whatever.... [Tony van Roon's circuit]
Relays-Long Duration--1 to 100 min -  This circuit shows a pair of CMOS NOR gates which form a push-button-activated one-shot multivibrator relay-switching circuit that provides delays up to several minutes with resonable accuracy.  The relay turns on as soon as the START switch S1 is closed. However, it turns off again after a preset delay of about 0.5 seconds per microFarad (uF) of the value of capacitor C2.  The two CMOS gates are configured as a manually-triggered monostable multivibrator whose output is fed to the relay through R4 and transistor Q1.... [Tony van Roon's circuit]
Relays-Sound Activated, #1 -  This relay remains dormant until the op-amp activates upon sound via the electret-microphone. I only tested the 2-wire type. The input stage is a regular off-the-shelf 741 operational amplifier and connected as a non-inverting follower audio amplifier.… [Tony van Roon's circuit]
Relays-Sound Activated, #2 -  This relay remains dormant until the op-amp activates upon sound via the electret-microphone. Only tested with the 2-wire type.  The input stage is a regular off-the-shelf 741 operational amplifier and connected as a non-inverting follower audio amplifier.... [Tony van Roon's circuit]
Remote Control turns Battery on & Off -  09/12/97 EDN-Design Ideas.... EDN is migrating links. This link is not verified.  Search the "title" + EDN for new link.
RF Sensing relay driver -  (circuit added 6/07)

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