Relay Circuits, Page 2 O-Z

Relay Circuits, Page 2
Relays: #'s - N O-Z
Last Updated on: Friday, March 12, 2010 12:07 PM

Circuits Designed by Dave Johnson, P.E. :

NEW On/Off Switch with Latching Relay
The circuit below switches AC or DC power to a load using an ultra low power 3v latching relay with two coils. The relay can handle about 10 amps of current, up to 250vac. Each time the small pushbutton is pressed, the circuit either latches the relay contacts closed or unlatch them open. The 3v powered circuit uses a single 74HC14. This device contains six Schmitt trigger inverters in the one 14 pin package. Two inverters form a flip/flop circuit. Each time the pushbutton is pressed, the circuit changes state and stays in that state until the button is pressed again. With each state change, a 25ms latching or unlatching pulse is produced and is routed to the correct relay coil. The coil resistance is about 45 ohms so about 70ma of current is drawn from the 3v battery for each relay pulse. The average power is so low that the circuit can operate for many years on one set of batteries. I would suggest using two AA or AAA alkaline cells.

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.

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.

THROUGH GLASS PUSHBUTTON SWITCH
This simple technique allows a mechanical pushbutton switch assembly to activate a reed type relay through a pane of thick glass. Pushing the button moves a magnet near the reed relay, closing the relay contacts.

Ultra Low Power Latching Relay Circuit
The circuit below takes advantage of some inexpensive small super capacitors. The circuit pumps 6 volt pulses into the separate 5 volt latching and unlatching relay coils. A short 25ms pulse is all that is needed to flip the relay states. A third super capacitor is used to supply a higher peak current than a small lithium cell might otherwise be able to supply.

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

One oscillator drives multiple solid-state relays - (Design Ideas - EDN, 03/16/2006) A conventional electromechanical relay often makes sense for switching large amounts of load current on and off and when proportional control of the load’s current or voltage is unnecessary. (circuit added 9/06)

Parallel port relay interface - (electronic circuit added 4/05)

PC Securely Controls Relay - 11/23/95 EDN-Design Ideas / (added 6/06)

Photo Electric Street Light - (electronic circuit added 10/05)

Pi Newood Derby Finish Line using a Computer: Scores times and places. - (electronic circuit added 10/05)

Pinewood Derby Finish Line Lights - (electronic circuit added 10/05)

Pinewood Derby Finish Line Using a Computer - Scores times and places. - (circuit diagram added 6/07)

Power on Time Delay Relay Circuit - (circuit / schematic design added 6/06)

Power-Off Time Delay Relay Circuit - (electronic circuit added 4/05)

Power-on sequencing using TL431 in comparator mode - TL431 as a comparator. Delay timers. Power-on sequencers. TL431 without feedback can be considered as an NPN or N-MOS device with high transconductance and precise 2.5V turn-on voltage. Tube heads beware: the upper (+supply) pin on TL431 is cathode, lower (-supply) - anode... it's another world. ….(design added 07/07)

Pulse relay Reduced Power Relay - This circuit will convert a standard relay to a pulse relay; pressing the button will switch it on and pressing it again will switch it off. For this purpose you need a relay with 2 sets of contacts: one is used for the circuit and the other is available for an outside circuit. … (added 9/07)

Reduced Power Relay Driver - 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. ….(designed by David A. Johnson)

Relay card - relay card interface circuit - german text (added 05/08)

Relay Circuits use Reverse hysteresis - 05/08/97 EDN-Design Ideas / (added 3/03)

Relay Delay - (electronic design added 2/-76)

Relay driver saves substantial power - (07/02/98 EDN-Design Ideas / (added 6/06) It is common practice to operate relays and solenoids at a reduced holding power once the mechanical actuation takes place. Relays are usually specified to pull in within 3 msec at 80% of the rated voltage and to release at 30% of the rated voltage. The circuit in Figure 1 drives as many as eight 12V (Ž120V coil) power relays, ....

Relay Toggle Circuit - This toggle circuit operates by using a couple 555 timers wired as inverters. Pins 2 and 6 are the threshold and trigger inputs to the first timer and pin 5 is the output. The output at pin 5 will.... (added 05/06/07)

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 and Push Button - (electronic circuit added 10/05)

Relay Toggle Circuit using a Single Transistor and Push Button - (electronic circuit added 10/05)

Relays eliminate high-voltage noise - (Design Ideas - EDN, 09/13/2007) A simple relay circuit cancels noise in the actuator stage of a scanning electron microscope. (electronic design idea added 9/2008)

Relays: Automatic Turn-off - (circuit added 9/04)

Relays: Delayed Turn-on - (circuit added 9/04)

Relays: Long Duration - (circuit added 9/04)

Relays: Long Duration--1 min to 20 hrs - (circuit added 9/04)

Relays: Long Duration--1 to 100 min - (circuit added 9/04)

Relays: Self Latching - (circuit added 9/04)

Relays: Sound Activated - (circuit added 9/04)

Relays: Transistor Boosted - (circuit added 9/04)

Relays-12 Sec to 90 min - (circuit / schematic added 2/06)

Remote Control turns Battery on and Off - 09/12/97 EDN-Design Ideas / (added 3/03)

RF Sensing relay driver - (circuit added 6/07)

SCR phase control yields solid state switch - 03/15/01 EDN-Design Ideas / (added 11/05) SCRs (silicon-controlled rectifiers) / PDF contains multiple circuits scroll to find the one of interest, or thyristors, have higher current and voltage ratings, lower conduction losses, and more robustness than triacs. For these reasons, SCRs are better suited to high-power applications....

Simple Circuit Drives Latching Relays - 02/01/96 EDN-Design Ideas / (added 3/03)

Simple Solenoid Driver Reduces Power and Cost - (07/18/96 EDN-Design Ideas / (added 3/03)

Smartcard-controlled Relay - From a designer's perspective, there are no "good" or "bad" circuits. This article will show how to transform a "pirate" smart card (cheaply available almost everywhere nowadays , as consequence of digital TV piracy plague) into a legal and pacific electronic key application. Opposite to popular belief, most TV smartcards are not clones of the original and trusted ones. Instead, they often are minature versions of general purpose microcontrollers - well known to the electronics enthusiasts - like PICs from Microchip or AVR from Atmel. (added 05/06)

Soft-Start Circuit For Power Amps - Although the soft start circuit can be added to any sized transformer, the winding resistance of 300VA and smaller transformers is generally sufficient to prevent a massive surge current. Use of a soft start circuit is definitely recommended for 500VA and larger transformers....(electronic design added 10/06)

Solenoid Driver Reduces Power and Cost - (07/18/96 EDN-Design Ideas / (added 3/03)

Solenoid Starter - (electronic schematic / circuit added 4/02)

Solenoid trip circuit Works at Battery's end of life - (07/08/04 EDN Design Ideas / (added 1/05) This Design Idea involves a low-power motion-detector circuit that operates from battery power for extended times. Part of the design includes a solenoid-operated trip mechanism that triggers whenever it detects motion. The drive circuit for the solenoid in the original design worked fine as long as the battery was fresh but failed as the battery got into the middle of its life, even though suf...

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. Published in Electronic Design, Dec 2, 1996. ….(designed by David A. Johnson)

Solid State Relay Saves Battery's Life - 09/01/94 EDN-Design Ideas / (added 2/05) The circuit in Fig 1 uses a low-resistance p-channel FET, Q4, to disconnect a load from the battery when the battery's voltage drops below a certain value. After you disconnect the circuit, it remains off until you remove and replace the battery.

Solidstate Remote Control Switch - Circuit / schematic (added 02/05)

Solid-State Tesla Coil, #1 - (circuit / schematic added 2/06)

Solid-State Tesla Coil, #2 - (circuit / schematic added 2/06)

Square Tesla Coil - (circuit / schematic added 2/06)

Switch Intelligently Controls Current - 03/30/00 EDN-Design Ideas / (added 5/02) This circuit can intelligently control ac or dc current when connected in series with a load

Telephone in Use Relay Circuit - (circuit / schematic design added 6/06)

Through Glass Push Button Switch - This simple technique allows a mechanical pushbutton switch assembly to activate a reed type relay through a pane of thick glass. Pushing the button moves a magnet near the reed relay, closing the relay contacts. ….(designed by David A. Johnson)

Time Delay Relay (Aaron Cake) - (electronic schematic / circuit added 08/08/08)

Time Delay Relay II (Aaron Cake) - (circuit added 08/08/08)

Time delay relay reduces inrush Current - 03/(07/02 EDN Design Ideas / (added 10/03) A transformer switching onto a line can sometimes cause a circuit breaker to trip or a fuse to blow. This phenomenon occurs even if the transformer presents no load, such as when the secondary is open. The problem arises because of the heavy magnetizing inrush current... .

Time delay relay uses proximity control - 03/15/01 EDN-Design Ideas / (added 11/05)

Time Delay Relay-2 - ….(circuit design added 03/08)

Transformer Driver Controls BiDirectional Switch - (07/17/97 EDN-Design Ideas / (added 3/03) -You can use a transformer-driver IC to simply control a MOSFET on/off switch

Two Lead Solid State Breaker Resets itself - 03/30/95 EDN-Design Ideas / (added 03/03/03) Simple dc circuit breaker can protect a power supply from the ever-present screwdriver or even isolate a satellites dual power system from a short circuit in one subsystem

Two Simple Relay Based Motorcycle Alarms - These are two - easy to build - relay-based alarms. You can use them to protect your motorcycle - but they have many more applications. If you use relays with 6-volt coils - they'll protect your "Classic Bike". Both alarms are very small. The completed boards occupy about half a cubic-inch - 8 cc. The standby current is zero - so they won't drain your battery.

Ultra Low Power Latching Relay Circuit - The circuit below takes advantage of some inexpensive small super capacitors. The circuit pumps 6 volt pulses into the separate 5 volt latching and unlatching relay coils. A short 25ms pulse is all that is needed to flip the relay states. A third super capacitor is used to supply a higher peak current than a small lithium cell might otherwise be able to supply. ….(designed by David A. Johnson)

Universal Flasher Using a Latching Relay - This circuit is powered by a 9v battery and controls any AC to DC load through a set of relay contacts, rated at 10 amps. To conserve power, the circuit uses a latching relay. A variable frequency oscillator controls the flashing speed from 0.2Hz to 2Hz. A pair of pulse generators first latch the contacts closed then unlatches them open. The power consumption is so low that a 9v battery will last for several months. Posted ….(designed by David A. Johnson)

Water Activated Relay - The circuit uses a 555 timer wired as an astable oscillator and powered by the emitter current of the BC109C. Under dry conditions, the transistor will have no bias current and be fully off. However as the probes get wet the transistor will conduct and sounding the alarm. An On/Off switch is provided and remember to use a non-reactive metal....(design added 8/03)

Relays: #'s - N O-Z