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Latch Circuits, Page 2
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Last Updated on: Thursday, October 30, 2014 09:22 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...
    ...
  • 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.
  • 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.  The logic output is connected to a PMV65XP p-channel FET from Philips. This component should be able to handle 2 amps of current.  The inputs of any unused devices within the IC package should be connected to either V+ or ground.
  • On/Off Latch Circuit update
    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 tiny parts and can operate from DC supplies between +2v and 5v.  It uses two inverters within a 6 pin SN74LVC2G14 device from Texas Instruments.  Each press of the button toggles between the two on/off logic states.  The logic output is connected to a PMV65XP p-channel FET from Philips. This component should be able to handle 2 amps of current. 
  • 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.  The delay would prevent accidental activation of the circuit from a quick push button switch closure. The circuit below performs this function.  A dual Schmitt trigger inverter IC and a single flip/flop IC form the heart of the circuit.  The A1A section performs the 2 second delay function....
  • 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.

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

Drive a single coil latching relay without an H-bridge circuit -  5-Mar-09 Issue of EDN  Drive current in both directions to cut power consumption..... [Design Idea by Carlos Cossio, Santander, Spain]
Fault-latch circuit protects switchers -  19-Feb-04 Issue of EDN  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..... [Design Idea by Craig Varga, National Semiconductor, Phoenix, AZ]
Inverting Latches Make Simple VCO -  06/19/97 EDN-Design Ideas..... EDN is migrating links. This link is not verified.  Search the "title" EDN for new link.
Latch -  This circuit is a LATCH and remains ACTIVE when the push-button has been pressed for an INSTANT and released.
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]
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.....;(electronic design added 5/09)
Latching light detector is frugal with power and parts -  26-Sep-02 Issue of EDN 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 both the indicator and the light detector. All junction diodes exhibit some degree of photosensitivity..... [Design Idea by Anthony Smith, Scitech, Biddenham, Bedfordshire, UK]
Latching power switch uses momentary-action pushbutton -  28-Oct-04 Issue of EDN  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 to use. You can thus have a problem if you need a small, inexpensive on/off switch for latching power to a load..... [Design Idea by Anthony Smith, Scitech, Biddenham, Bedfordshire, UK]
Latching Regulator Prevents Deep Discharge -  03/16/95 EDN-Design Ideas…. EDN is migrating links. This link is not verified.  Search the "title" + "EDN" for new link.
Latching relay driver -  Schematic only, no circuit description
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...[Designed by David A. Johnson]
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.…. [Designed by David A. Johnson]
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.  The logic output is connected to a PMV65XP p-channel FET from Philips. This component should be able to handle 2 amps of current.  The inputs of any unused devices within the IC package should be connected to either V+ or ground. [Designed by David A. Johnson]
On/Off Latch Circuit Update -  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 tiny parts and can operate from DC supplies between +2v and 5v.  It uses two inverters within a 6 pin SN74LVC2G14 device from Texas Instruments.  Each press of the button toggles between the two on/off logic states.  The logic output is connected to a PMV65XP p-channel FET from Philips. This component should be able to handle 2 amps of current.   [Designed by David A. Johnson]
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.  The delay would prevent accidental activation of the circuit from a quick push button switch closure. The circuit below performs this function.  A dual Schmitt trigger inverter IC and a single flip/flop IC form the heart of the circuit.  The A1A section performs the 2 second delay function....[Designed by David A. Johnson] June 30, 2013
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..... [Designed by David A. Johnson]

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


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