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Turning a 7805 on/off with a Push to Make Switch


MPapps
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Hi All,

I am trying to design a circuit to do the following:

Use a Momentary Push To Make Switch to toggle the input of a 7805 on/off

The 7805 is supplied by regulated 12v so i need a circuit that switches its output between 0v and 12v using a Momentary Switch.

I was hoping to find a design or at least a starting point somewhere but have had no luck so far.

Any Suggestions / ideas would be great.

Thanks  :)

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Hi MPapps,
1) Your circuit doesn't need base-emitter resistors because the output from a Cmos inverter goes to the supply voltage.
2) Your circuit doesn't need the NPN transistor because Cmos inverters can operate fine from the 12V supply and can drive the PNP transistor.
3) The 2N3703 transistor has a very wide range of current gain. Its lowest gain could be only 30. A 2N4401 transistor has a minimum current gain much higher, 100 at a collector current of 150mA.

Try it like this:
Corrected

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Looking at the datasheet do i not need a transistor with a higher current rating as my Voltage Reg could be drawing as much a 1A?

You forgot to say how much is its load current.

A 7805 voltage regulator IC has a max operating current of only 8mA. It regulates very well with a load current up to 1A but can supply up to 1.5A with a small drop in regulation. Most of them limit the current at 2.2A.

The max current for a little 2N4403 transistor is 600mA but the 10k base resistor in my circuit limits it current to about 150mA. The CD4069 cannot drive a resistance lower than about 10k.
Use a darlington PNP transistor for higher current.
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I must admit i'm a little confused by what you said

I said:
1) The max current for a little 2N4403 is only 600mA.
2) The 10k base resistor for the 2N4403 limits its current to only about 150mA.
3) The CD4069 cannot drive a resistance lower than about 10k.
4) Use a darlington PNP transistor for higher current.

You don't understand what?
Do you know a TIP125 power darlington PNP transistor?
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ok thanks, what modifications would i have to make to run off 13.4v?

The CD4069 IC has a max operating voltage of 18V and the TIP125 darlington transistor has a max operating voltage of 60V so they are fine with only 13.4V.
If your 7805 regulator has a current of 1A then it will try to dissipate 7.7W and it will probably get too hot and shut down unless it has a pretty big heatsink.
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