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Latch Circuits
Latch Circuits:  #-C      D-O      P-Z
Last Updated on: Saturday, August 22, 2015 05:47 AM


Circuits Designed by Dave Johnson, P.E. :
  • Low Voltage Latch Circuit -  A Discover Circuits visitor wanted a simple on/off latch circuit which can turn on and off power to a small motor. The kicker was that he wanted to power the circuit and the motor from a single 1. 2v NiMH battery cell. Texas Instruments comes to the rescue with their family of low voltage single gate ICs. Specifically the SN74AUP1Q14 Schmitt trigger inverter will operate down to 0. 8v and lower. When used with a good NPN transistor, the circuit below works quite nicely . . . [Circuit by David A. Johnson P.E.,  03/01/13]

  • 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 . . . [Circuit by Dave Johnson P.E.,  08/13/06]

  • 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.  . . . [Circuit by Dave Johnson P.E.,  01/09/10]

  • On/Off Latch Circuit with 2 Second Delay -  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 . . . [Circuit by David A. Johnson P.E.,  06/30/13]

  • 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 . . . [Circuit by Dave Johnson P.E.,  12/24/09]

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

Drive a single coil latching relay without an H-bridge circuit -  03/05/09  EDN Design Idea   Drive current in both directions to cut power consumption. . .  [by Carlos Cossio, Santander, Spain]

Drive latching relays -  02/01/96  EDN Design Idea   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 . . .  [by Roy McCammon, 3M Austin, TX]

Drive Single-Coil Latching Relays -  11/13/08  EDN Design Idea   Five driver circuits operate single-coil latching relays. . .  [by Alfredo H Saab and Tina Alikahi, Maxim Integrated Products, Sunnyvale, CA]

Electronic Relay Latching Circuit -  I've spent a lot of time thinking about how I want to wire my conversion. The electrical system will consist of a combination of 12 volt DC, 24 volt DC, and 110 volt AC. It's important that the system provide the greatest functionality, but have a simple interface. It must be easy to install and relatively inexpensive to build. The system can't be overly complicated and must be easy to maintain. . . .  [Copyright 2001-2010 Craig Shepard]

Fault-latch circuit protects switchers -  02/19/04  EDN Design Idea   Many power-supply designers like to have a regulator latch off in the event of an overcurrent situation or other fault condition. Yet, many PWM controllers do not internally support this latch-off function. Most do, however, have a. . .  [by Craig Varga, National Semiconductor, Phoenix, AZ]

Inverting latches make simple VCO -  06/19/97 EDN Design Idea   The output frequency of the simple VCO in Figure 1, which is synthesized from inverting latch stages, is tunable to an integer multiple of the input frequency by selecting which output phases feed back to the input multiplexer. The circuit has worked successfully in on-chip clock multiplication in ASICs. The number of latch stages that you can cascade in a real-world design limits the multiplication factor. However, this circuit is practical for applications that require low size, cost, and power consumption but that don't require output frequencies in the hundreds of megahertz. . .  [by Ed Nielson, VLSI Technology, Sophia Antipolis, France]

Latch -  This circuit is a LATCH and remains ACTIVE when the push-button has been pressed for an INSTANT and released. . . .  [Designer's name is not given}

Latch Switch -  In this circuit a non-locking push switch is used to activate a load. The load remains switched on until power is removed from the circuit. . . .  [Circuit by Andy Collison]

Latches Solenoid at a Distance -  10/14/00 EDN Design Idea   The circuit in Figure 1 controls low-cost, latching solenoid valves over long distances. For example, it can control one valve 1 km away using two wires and a 12V supply. The circuit provides 700 mA at 12V for the 20 msec. . .  [by J Pelegri and D Ramirez, University of Valencia, Spain]

Latching Continuity Tester -  A continuity tester is a must on every service bench for testing cables, pcboards, switches, motors, plugs, jacks, relays, and many other kinds of components. But there are times when a simple continuity test (Tony van Roon's or your multi-meter) doesn't tell the whole story. For example, vibration-induced problems in automobile wiring can be extremely difficult to. . .  [Tony van Roon's circuit]

Latching Continuity Tester 1 -  This Latching Continuity Tester can help you locate those difficult-to-find intermittent short and opens that other testers always seem to miss. It has been part of my workbench for many years and performs superb. I have solved many intermittend problem with this highly flexible unit. . .  [by IQ Technologies Industry, unless otherwise noted online]

Latching light detector is frugal with power and parts -  09/26/02  EDN Design Idea   This idea demonstrates three uses for the humble LED. The circuit in Figure 1a forms a simple light detector that latches and turns on an LED when the ambient light exceeds a preset limit determined by potentiometer P1. LED D1 is. . .  [by Anthony Smith, Scitech, Biddenham, Bedfordshire, UK]

Latching power switch uses momentary pushbutton -  01/20/14    EDN Design Idea   This could be the cheapest way yet to convert a momentary switch into an on-off power controller - Low-current, momentary action pushbutton switches, such as PCB-mount 'tactile' types, are cheap, and available in an abundance of different styles. Latching types, on the other hand, are often larger, more expensive, and available only in a relatively limited range of styles. . .  [by Anthony Smith]

Latching power switch uses momentary-action pushbutton -  10/28/04  EDN Design Idea   Most inexpensive pushbutton switches, particularly pc-board-mounting and membrane types, have momentary action. Latching types are often larger and relatively expensive, and they frequently are unavailable in the style you'd like t. . .  [by Anthony Smith, Scitech, Biddenham, Bedfordshire, UK]

Latching Regulator Prevents Deep Discharge -  03/16/95 EDN Design Idea   To avoid a deep discharge that can shorten or destroy a rechargeable battery's life, you need to remove the load at the point of complete discharge. Because a battery's terminal voltage recovers after load removal, you can't. . .  [by Doug Vargha, Maxim Integrated Products, Sunnyvale, CA]

Latching relay driver -  Schematic only, no circuit description. . .  [Designer's name not given]

Latching Relays -  Find out about latching relays and their uses. . . .  [REUK-Renewable Energy UK website]

Latching Switch -  In this circuit a non-locking push switch is used to activate a load. The load remains switched on until power is removed from the circuit. . . .  [Circuit by Andy Collison]

Low Voltage Latch Circuit -  A Discover Circuits visitor wanted a simple on/off latch circuit which can turn on and off power to a small motor. The kicker was that he wanted to power the circuit and the motor from a single 1. 2v NiMH battery cell. Texas Instruments comes to the rescue with their family of low voltage single gate ICs. Specifically the SN74AUP1Q14 Schmitt trigger inverter will operate down to 0. 8v and lower. When used with a good NPN transistor, the circuit below works quite nicely . . . [Circuit by David A. Johnson P.E.,  03/01/13]

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 . . . [Circuit by Dave Johnson P.E.,  08/13/06]

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.  . . . [Circuit by Dave Johnson P.E.,  01/09/10]

On/Off Latch Circuit with 2 Second Delay -  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 . . . [Circuit by David A. Johnson P.E.,  06/30/13]

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 . . . [Circuit by Dave Johnson P.E.,  12/24/09]

One-button lock provides high security -  03/04/99 EDN Design Idea (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. . .  [by Michal Kobylecki and Wojda Wlodzimierz, MK Design, Warsaw, Poland]


Latch Circuits:   #-C      D-O      P-Z


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