Hold-current-limiter


Posted on Apr 18, 2012

In many applications, a solenoid driver must first briefly supply a large amount of pull-in cnrrent, which quickly actuates the solenoid. Thereafter, the driver must supply a much lower holding cnrrent to avoid burning the solenoid out. To avoid using the customary, cumbersome, large capacitors or power-wasting resistors, you can use the switch technique.


Hold-current-limiter
Click here to download the full size of the above Circuit.

As long as the input to the circuit is low, diode Dl holds Ql off; a low input also prevents the op-amp circuit from oscillating. When the input reaches 24 V, Ql switches on and pulls in the solenoid. Concurrently, D4 is back-biased, and Cl begins charging up. When Cl charges up, the op-amp circuit begins to oscillate, switching Ql on and off. The time constant defined by Rl and Cl determines the length of the period during which the solenoid receives full power. R3 and C2 set the oscillator"s frequency, and R2 sets the oscillator"s duty cycle. The hold cnrrent is directly proportional to the duty cycle. For the components shown, the full-power period is 300 ms, the oscillator"s frequency is 3kHz, and its duty cycle is 50%.




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Digital clock with thermometer and hygrometer
RF probes
Flood-alarm-or-temperature-monitor
DIY Binary Clock with Arduino
commodore 64c
high side current measurements
11W Stereo/22W Mono Power Amp Using TDA1519C
Antenna selector circuit diagram electronic project
Storage Battery Exerciser
a simple Astable Multivibrator with the help of a circuit diagram
The equivalent circuit and a local oscillator



Top