Power Input Sensor?

Discussion in 'General Electronics Chat' started by prometei, Nov 27, 2008.

  1. prometei

    Thread Starter Well-Known Member

    Apr 13, 2008
    53
    0
    Hi ever1

    I did not know how to name this topic 'cause I don't even know what the thing that I'm looking for is called.

    Pretty much every modern device that can run of battery or mains/outside power has a circuit built in that automatically switches off the battery if mains/outside power is hooked up, for example if you listen to a Walkman on batteries and hook up a power adapter, the Walkman will automatically switch to the adapter power and at the same time disconnect the battery part of the circuit. How is this mechanism/circuit called? Anyone have a simple schematic for it?

    thanks
     
  2. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    In the example you give (A walkman) many times the power switching is built into the power socket connector. There is a normally closed contact inside the connector that routes the internal battery voltage to the rest of the device. When you plug in the external power plug, it opens those internal contacts and lets external power route to the device. So in those cases the power switching is built into the power connector on the device.
     
  3. prometei

    Thread Starter Well-Known Member

    Apr 13, 2008
    53
    0
    I c. I've looked at some of external power plugs that I have and I've found one that has switching contacts. Pretty simple, and I thought there is a special circuit for that :). Thanks for your help

    p.s. just curious, is it possible to do the same but electronically not mechanically?
     
  4. mindmapper

    Active Member

    Aug 17, 2008
    34
    0
    Another solution to solve this, is by using diods. Each power supply is connected to the anode of a diod. Without external power, the current pass from the battery into the diod and out on the diods catode and into the device. Plugging in the external power plug the current pass through the diod connected to the external supply. Both catodes are connected to each other and to the device. If the external voltage is a little higher than the voltage from the battery the diode connected to the battery will be in reverse and can not pass any current.

    In this case the power switching is done by biasing the diods in forward or reverse direction. A typical example of using diods as switches.
     
  5. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    Yes, there are special IC chips available that can handle this kind of switching as well as the charging of built-in rechargeable batteries if used. However you would have to review their data sheets to see how they operate and would be applied to any specific application.

    Also this kinds of battery management can also turn off the device when the internal battery is supplying the power and it's voltage reaches a predetermined minimum amount to protect the battery from damage from over discharging.
     
Loading...