Electronics > Beginners
Operational Amplifier driving MOSFET
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Ian.M:
That's up to you.  Personally I am somewhat of a perfectionist so would investigate  Hero's improvement, but eventually you need to either scratch-build a prototype on matrix board, put it into service and see how it holds up or take a gamble and skip that step and go straight to laying out a PCB.   If you rarely lay out PCBs, you'll probably want to post PNGs or GIFs of it here for comment (PNGs or GIFs as many users cant handle proprietary PCB design file formats, and not everyone has a Gerber viewer program installed) 
Zero999:

--- Quote from: Ian.M on April 29, 2018, 12:09:44 am ---Errr the O.P's also driving a 12V 20W Halogen bulb, which will have a cold resistance of under one ohm!.   With a >16A turn-on surge, there's no realistic way of getting rid of the MOSFET.     Your buffered LM358 circuit looks nice for isolating the MOSFET gate drive from the hysterisis feedback.   Drive the LED off the comparator stage, sourcing current so it doesn't affect the Vol, and the MOSFET gate off the buffer stage.

--- End quote ---
I agree. This is the problem with not putting everything on the schematic! Although I did read the text, I had forgotten about the halogen lamp, by the time it got to this stage of the thread!

Yes, the MOSFET or relay are unavoidable and the spare op-amp could be used as a buffer for the MOSFET.


I think a comparator with a push-pull output, such as the LMC6762, TSX3702 or LMC7211, would be the ideal solution, but they aren't always available in DIP packages or as cheap and easy to obtain as jellybean parts such as the LM358.
mike_mike:
Thanks for the reply @Ian.M and @Hero999.
I made the top schematic from post 36 (with LM358). I just modified on the old project. It is working.
It is ok to make the layout ?
Ian.M:
Yes, it looks like time to tape it out.
mike_mike:
I attached the layout and the schematic.
The LDR will be connected to the board using wires.
Please have a look and tell me if the schematic and layout are ok.
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