Monostable Multivibrator operation for constant excitation voltage

Rajat Phate

Other Parts Discussed in Thread: LM555, SN74LVC1G123

Hello,

I have been trying to get the above mentioned output when triggered by a digital output signal from microcontroller. The output will be controlling an electromagnet with resistance of about 25 Ohm. The trigger pulse will activate and deactivate the electromagnet as commanded by the trigger signal. I have explored monostable multivibrator option using LM555 Timer IC. But the IC requires a short trigger pulse, not continuous voltage signal. Is there any other possible way to achieve the logic.

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 243220 points

What happens when the trigger signal is 0 V? Is the desired output 0 V?

Logic cannot handle currents more than a few milliamperes. Do you already have a circuit to drive the electromagnet, and can you show its schematic, especially how it is controlled?

0 Ron Michallick over 4 years ago

TI__Guru*** 140026 points

Rajat,

The data sheet's mono-stable circuit can provide a high output for 200ms.

A resistor, capacitor, and diode can be added to pulse the trigger low to start the timer. After that the input can remain high indefinitely or go back low.

0 Rajat Phate over 4 years ago in reply to Clemens Ladisch

Prodigy 60 points

Hi Clemens,

Yes right, When the trigger signal is 0V, the desired output will be 0V.

The logic will just control the switching power circuit which will provide the required power for the load. Although the switching circuit is not the finalized, I have added a schematic for reference.

0 Rajat Phate over 4 years ago in reply to Ron Michallick

Prodigy 60 points

Thanks Ronald,

I will give it a try for sure and get back to you soon.

0 Clemens Ladisch over 4 years ago in reply to Rajat Phate

Guru 243220 points

The 74xx123 monostable multivibrator is edge controlled; see the application report Designing with the SN74LVC1G123 Monostable Multivibrator (SLVA720). (Use the B input to always get a 200 ms pulse, or the CLR input if the output should be reset if the trigger is shorter than 200 ms.)

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Monostable Multivibrator operation for constant excitation voltage