Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

External signal to trigger a PFET once only???

External signal to trigger a PFET once only???

External signal to trigger a PFET once only???

I have a PFET in series with the high side of a Battery. I have an external signal that will come in and go anywhere from 0 - 60V. I want that signal at ~2V to turn on the MOSFET. I will use an NPN transistor most likely here. Now for the ugly piece. Once the PFET connects the battery to the circuit I don't want any other edge of the external signal to turn off the NPN. That is to say the external trigger signal 'could' drop below 2V due to a loading surge thus toggling the NPN to shut off. Basically I want to latch the rising edge of the external signal at 2V and bootstrap my battery on and never have to worry about any more edges from the external signal.

Any ideas on how to do this???


RE: External signal to trigger a PFET once only???

An SCR will also act as the thyristor mentioned above.
on the SCR gate, it you put a voltage there above the trigger level, DC current will flow thru the SCR, and will continue to do so even if the gate voltage goes back to zero.

your big problem is that this trigger voltage is between zero and 60 volts, which would probably blow out the gate in the SCR. So you probably need some sort of series resistor/shunt zener diode to translate the 0-60V range to maybe 0-4V. THEN apply it to the scr gate.

flip flops will do this also, but once again, the 60 V will blow the digital gate up.
you could make your OWN discrete transistor flip flop that could work on 60 V signals.

you could set up a relay to latch once it is energized. You would need a push button switch to de-latch it.

You could use various solid state relays, who use an optoelectric device to take the input control voltage, and then output a switched high current signal. there probably are latching solid state relays....

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close