Can someone test this circuit for me please

Discussion in 'General Electronics Chat' started by ArakelTheDragon, Oct 28, 2018.

  1. ArakelTheDragon

    Thread Starter Well-Known Member

    Nov 18, 2016
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    Hello! Can someone please test this circuit and tell me the results. Theoretically it should work and its with minimum components. I do not get along with my simulator later (Orcad).

    The idea is simple: when the 5VDC source is connected, that switches the PMOS transistor off and the 9VDC battery power soucrce. When the 5VDC is disconnected, the resistor on the PMOS gate grounds it and the transistor should conduct, connecting the load to the 9VDC battery.
     
  2. OBW0549

    Distinguished Member

    Mar 2, 2015
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    Even without testing the circuit, it seems to me it cannot work as described: the MOSFET's gate and drain are connected together, along with the +5V supply, the 1 kΩ resistor and the load resistor. As I see it, the circuit isn't going to do anything at all.
     
  3. danadak

    Distinguished Member

    Mar 10, 2018
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  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Are you making the same mistake I made recently in a thread like this? The mosfet is a P not a N.
     
  5. OBW0549

    Distinguished Member

    Mar 2, 2015
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    No mistake; the MOSFET is clearly a P-channel device, and the drain, gate, load resistor and 1 kΩ gate pulldown resistor are all connected together and connected directly to +5V.
     
    shortbus likes this.
  6. crutschow

    Expert

    Mar 14, 2008
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    Why not?
    Try the free LTspice.
     
  7. MisterBill2

    Distinguished Member

    Jan 23, 2018
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    With that wired in short circuit there is not much chance of the circuit functioning, no matter what kind of transistor is used. And if the short circuit were removed the circuit would be quite inefficient at best. It appears that the intent is to have a 9 volt battery connect when the 5 volt mains powered source fails. It would be more effective to use 3 cells, 1.5 volts each, and when the 5 volts failed the 4.5 supply would feed through a simple shottckey diode.
    And I believe that this is reallky a continuation of a different thread.
     
  8. ArakelTheDragon

    Thread Starter Well-Known Member

    Nov 18, 2016
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    its because I am using Orcad 9.2. And I have some problems with getting it work properly on "Windows 7". I prefer not to install Orcad 16 or later, as its not good and is even detected as a virus.

    I tried LTSpice once, but its different and I had a hard time finding how to do things, in OrCad at least I know the things by now.

    I will revise the circuit and post the new one, as soon as I can. Thanks for the replies.
     
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