Turing an IC On/Off by a Microcontroller

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hkBattousai

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In my circuit, there will be several ICs (one of them is LM555). These ICs are not required most of the time. Therefore I want to keep them shut off and enable them whenever I need, for power consumption issues.

Does a circuit like in the picture do this job? Is there any improvements you could suggest? What kind of a transistor should I use? Should I add a bleeding resistor as well? If Vcc of the main circuit is 5V, what will be the voltage on the Vcc pin of the IC (i.e.; what will be the voltage drop on the transistor?)?
 
You can use a logic-level type P-channel MOSFET for the switch. Connect the P-MOSFET source terminal to the +5V with the drain terminal being the switch output. The switch will be "on" when the gate voltage is at 0V and "off" when the gate voltage is at 5V.

You don't need any resistors if the control signal goes between 0V (ground) and +5V.
 

Thank you for your reply.

Is there a reason why you are suggesting P-MOSFET, wouldn't it work with an N-MOSFET?
And, can you please suggest me a P-MOSFET for this circuit, for switching 100mA current at most.
 
Hopefully this is just a theoretical example?, it would seem strange to want to switch a 555 using a micro, when the micro could easily replace the 555 entirely.
 
An N-MOSFET would have to be in a source-follower configuration to be used as a switch. So that means you would need a voltage at least 5V higher than the source (or 10V to switch 5V). A P-MOSFET however, is used in a common-source mode so it can be switched by 5V (assuming a logic-level MOSFET).

Digikey, for example, has many P-MOSFETs that would work, such as the Fairchild NDS332P.
 
Nigel Goodwin said:
Hopefully this is just a theoretical example?, it would seem strange to want to switch a 555 using a micro, when the micro could easily replace the 555 entirely.
Click to expand...
Nigel, he stated he wanted to switch several ICs, one of which was a 555.
 
crutschow said:
An N-MOSFET would have to be in a source-follower configuration to be used as a switch. So that means you would need a voltage at least 5V higher than the source (or 10V to switch 5V).
Click to expand...
....provided it is switching Vcc. However, it could be used to switch the Gnd connection of the 555 instead; in which case a 0-5V control signal is ok (if the FET is rated accordingly, i.e. is of the 'logic' type).
 
crutschow said:
Nigel, he stated he wanted to switch several ICs, one of which was a 555.
Click to expand...

Obviously it depends exactly what he's trying to do, but I suspect that many of them (if not all?) could be replaced by software in the micro - and certainly the 555 could.

This is the usual 'problem' where posters ask about their 'solution' rather than ask about their 'application' - I may be completely wrong, but mostly in these cases it turns out that the posters solution wasn't a very good one.
 

I was planning to drive a buzzer by 555. The code is very complicated, all timers are used and so I didn't want to make the code more complicated.
 
the code for a buzzer is pretty straight forward, if you use a buzzer with integrated driver all you need to do is apply a voltage, pretty much in the way you are doing to the 555 timer
 
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