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Latch Circuits
Latch Circuits:  #'s-K      L - 0        P - Z

 

Last Updated: December 07, 2017 02:05 PM

Circuits Designed by Dave Johnson, P.E. :

Press & Hold Latching CircuitA Discover Circuits visitor needed a latch circuit which could operate using a power supply voltage ranging from 3v to 24v.  He wanted to use a tiny pushbutton switch to turn on and off power to a load.  However, he wanted a 2 second delay between the switch activation and the state change of the output . . . Hobby Circuit designed by David Johnson P.E.-June, 2013

Pushbutton Oneshot & LatchThis circuit uses a single IC to convert a noisy pushbutton switch signal into a clean pulse or a sustained push on-push off signal.  It can operate from 3v to 18v. . . Circuit by Dave Johnson P.E.-March, 2002

Pushbutton On-Off Latch CircuitOften you want to turn on and off power to a device with a single pushbutton switch.  The circuit below performs this logic function with just a few parts and can operate from DC supplies between +3v to about 15v.  It uses two inverters within a 74C14 or a CD4069 hex inverter package.  Each press of the button toggles between the two on/off logic states. . . . Hobby Circuit designed by David Johnson P.E.-January, 2010

Super Capacitor makes Low Voltage Latching Relay DriverUsing some small super capacitors, this circuit can latch and unlatch a mechanical relay with 10 amp contacts, from a small 3 volt power source.  By using a latching relay, power can be controlled to a load with a tiny battery . . . Hobby Circuit designed by Dave Johnson P.E.-August, 2006

Switches AC or DC power using a Latching RelayThe 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 . . . Hobby Circuit designed by Dave Johnson P.E.-December, 2009

Touch Activated Battery Powered Latching Relay  -  A client needed a touch activated switch.  The unit needed to be fairly small and wired into the underside of some kitchen cabinets.  When touched, a string of fluorescent or LED lights, mounted under the cabinets, would turn on.  The total light power is less than 100 watts.  The system into two parts.  (1) A relay is mounted inside a plastic junction box and (2) a touch switch module.    Four wires leading from plastic junction box would connect to a second box containing the touch switch module.  The circuit is a simple relay driver powered by a9v battery. . . . Dave Johnson, Lubbock TX-DC Magazine - Issue 20 Nov 2011

Ultra Low Power Latching Relay CircuitThe 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 supplyCircuit Solution by Dave Johnson P.E.-April, 2007

Universal Flasher using a Latching RelayLatching relays are nifty devices.  Most contain two separate coils.  When a voltage is applied to one coil the relay latches in one state and stays in that state until voltage is applied to the unlatch coil.  Since the latching and unlatching pulses only . . . Hobby Circuit designed by David A. Johnson P.E.-October, 2005


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

Power-supply interrupter fights ESD-Induced Device latch-up -  21-Jul-05 EDN-Design Ideas Optoisolator-based circuit protects digital components from ESD __ Circuit Design by Emerson Segura, Lifescale Global Diagnostics Inc, Toronto, ON, Canada

Press & Hold Latching Circuit -  A Discover Circuits visitor needed a latch circuit which could operate using a power supply voltage ranging from 3v to 24v.  He wanted to use a tiny pushbutton switch to turn on and off power to a load.  However, he wanted a 2 second delay between the switch activation and the state change of the output . . . Hobby Circuit designed by David Johnson P.E.-June, 2013

Pushbutton Oneshot & Latch -  This circuit uses a single IC to convert a noisy pushbutton switch signal into a clean pulse or a sustained push on-push off signal.  It can operate from 3v to 18v. . . Circuit by Dave Johnson P.E.-March, 2002

Pushbutton On-Off Latch Circuit -  Often you want to turn on and off power to a device with a single pushbutton switch.  The circuit below performs this logic function with just a few parts and can operate from DC supplies between +3v to about 15v.  It uses two inverters within a 74C14 or a CD4069 hex inverter package.  Each press of the button toggles between the two on/off logic states. . . . Hobby Circuit designed by David Johnson P.E.-January, 2010

Relay: 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 __ Designed by Tony van Roon  VA3AVR

Scalable latch requires no capacitors or clock -  08/19/04  EDN-Design Ideas Circuits that latch one-of-N switches usually use a digital approach.  Such circuits are often useful in human-interface situations, such as audio-mixing consoles, video-feed selection, or current-loop-control redundancy systems.  In __ Circuit Design by Robert Most, Dow Corning S&T Electronics, Midland, MI

Self Latching Relay -  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 __ Designed by Tony van Roon  VA3AVR

Simple Circuit drives latching relays -  02/01/96 EDN-Design Ideas Figure 1 shows a low-parts-count circuit that can drive one- or two-coil latching relays.  Latching relays are useful in sensitive analog designs.  The 74ACT174 hex flip-flop has ample capability to drive the Aromat TQ2E series of latching relays.  Both windings for the TQ2E-L2-5V two-coil relay are on the same magnetic element, so the windings' fields add.  You __ Circuit Design by Roy McCammon, 3M Austin, TX

Simple Circuit Prevents Processor Latch-up -  03/04/99 EDN-Design Ideas -  (contains several designs, scroll to find this one)   The circuit in Figure 1 uses a Dallas Semiconductor DS1820 one-wire digital thermometer in a multipoint temperature-measurement system.  The DS1820 sensor allows distributed temperature measurement and uses only one wire for both data communication and the power supply.  You can easily connect the one-wire interface to a C  (in this example, a PIC16C63) .  The application accommodates as many as 16 DS1820 sensors in a 100m-long network, dubbed MicroLAN by Dallas.   __ Circuit Design by Michal Koby lecki and Wojda Wlodzimierz, MK Design, Warsaw, Poland

Solid-State Relay Saves Battery's Life -  09/01/94 EDN-Design Ideas 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 __ Circuit Design by Tom Gay, Siemens, Regensburg, Germany

Super Capacitor makes Low Voltage Latching Relay Driver -  Using some small super capacitors, this circuit can latch and unlatch a mechanical relay with 10 amp contacts, from a small 3 volt power source.  By using a latching relay, power can be controlled to a load with a tiny battery . . . Hobby Circuit designed by Dave Johnson P.E.-August, 2006

Switches AC or DC power using a 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 . . . Hobby Circuit designed by Dave Johnson P.E.-December, 2009

Tilt Switch -  The output is LOW at start-up due to the capacitor on pin 4.  When the mercury switch closes, the output goes HIGH and remains HIGH until the reset button is pressed.  This circuit is called a LATCH.  __ 555-Timer

Touch Activated Battery Powered Latching Relay  -  A client needed a touch activated switch.  The unit needed to be fairly small and wired into the underside of some kitchen cabinets.  When touched, a string of fluorescent or LED lights, mounted under the cabinets, would turn on.  The total light power is less than 100 watts.  The system into two parts.  (1) A relay is mounted inside a plastic junction box and (2) a touch switch module.    Four wires leading from plastic junction box would connect to a second box containing the touch switch module.  The circuit is a simple relay driver powered by a9v battery. . . . Dave Johnson, Lubbock TX-DC Magazine - Issue 20 Nov 2011

Transistor latch improves on/offry -  11/23/00 EDN-Design Ideas Figure 1 shows an example of on/off circuitry commonly used in battery-operated devices.  The p-channel MOSFET, Q1, serves as a power switch.  When you push the On button, S1, Q1's gate goes low.  Q1 turns on and supplies battery voltage to the DC/DC converter.  Depending on the battery voltage in the device, the DC/DC converter might convert the voltage either up or down __ Circuit Design by Eugene Palatnik, SIMS-BCI, Waukesha, WI

Transistors offer thermal protection for controller -  07/19/01 EDN-Design Ideas When a switch-mode power-supply controller, such as On Semiconductor's NCP1200, operates at a high ambient temperature, you should protect the entire power supply against lethal thermal runaway.  The NCP1200 operates directly from the power mains without an auxiliary winding; therefore, the die in the IC dissipates power (Figure 1)  __ Circuit Design by Christopher Basso, On Semiconductor, Toulouse, France

Turn a Set/Reset Latch Into an Astable/Monostable Multivibrator -  3-Sep-09 EDN-Design Ideas Use latches with either active-high or active-low inputs __ Circuit Design by Luca Bruno, ITIS Hensemberger Monza, Lissone, Italy

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 supplyCircuit Solution by Dave Johnson P.E.-April, 2007

Universal Flasher using a Latching Relay -  Latching relays are nifty devices.  Most contain two separate coils.  When a voltage is applied to one coil the relay latches in one state and stays in that state until voltage is applied to the unlatch coil.  Since the latching and unlatching pulses only . . . Hobby Circuit designed by David A. Johnson P.E.-October, 2005


Latch Circuits:  #'s-K      L - 0        P - Z


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