1 Reply Latest reply on May 30, 2020 6:56 PM by kkazem

    Isolate Sections of a Circuit


      I am using a latch circuit to power a 7805 and some other IC's,  currently the bypass caps on the IC's and 7805 are causing errors in my latch circuit.  How would I isolate my latch circuit from the 7805 and other IC's?  Would I use some sort of opamp buffer or unigain amplifier?  I am not sure what word I am looking for here but buffer sounds about right.  

        • Re: Isolate Sections of a Circuit

          It's hard to answer your question since your drawing (jpg file) doesn't show what the NPN really does. What kind of power control are you trying to do here? This is what I've figured out:

          1. Before SW is closed, Pch-G and Nch-D are pulled-up high, all else is off.

          2. When SW closed, Pch-G goes low, turning on Pch FET with Pch-S near 12V.This also turns on Nch-G, which effectively latches Nch FET on.

          3. I only see the 7805-INPUT(???), but not the output. What is the 7805 for if you don't use the output? 7805 is not a shunt regulator, it's a series regulator and it also needs the ground connection to work, which is not shown.

          4. The NPN-B connection is not shown, so what is driving it (if anything)?


          That's all the analysis that can be done. Your other IC grounds are also missing in the diagram. It's important when you're asking for help on circuits to show complete schematics in terms of all the IC pin connections that are used (including grounds, VCC, inputs, outputs). Unconnected pins need not be shown. But in your case, the 7805 input and output and ground pins (that's all there are in a 7805) are not shown. I can't tell if your 7805 pin to switched VCC is actually an input, but I'm assuming it is. But if it is, no 7805 output is shown.


          Please clean-up your circuit and ask this again.