# How does this simple circuit work (electric shaver)?

#### Alejandro Pérez 1

Joined Jun 8, 2018
2
Hi,

I disassembled a battery-powered shaver but I'm having trouble understanding how it works from a circuit point of view when the machine is operating with the power cable plugged in.

It has a 3-contact point 2-position (on/off) switch (sorry, I don't know its technical name). Here it is:

Here's the schematic I drew in KiCad (no symbol for the switch, I don't think it's available? I would like to know how you'd draw it though...):

So, I know that when the power cable is plugged in, and the switch is off, the battery gets charged through the R1-D1 branch, and that the LED is on.
When the switch is on, the LED gets turned off and the motor spins.

Concerning the case when the power cable is plugged, and switch on, my questions are:
1) Is the battery still getting charged? Why not?
2) Why is the LED off?
3) What is the motor current path? Is it through D2 or is it through D1? What purpose do these diodes serve?

Many thanks,

Alejandro.

#### Irving

Joined Jan 30, 2016
2,524
Welcome to AAC!

As drawn, when ON and external volts<= battery volts +Vf(d2) the battery drives the motor directly.

When ON and external volts > battery volts + Vf(D2) then external supply drives motor through D2 AND charges battery via same route but LED is off as Vf(D2)<<Vf(LED).

Oh, I don't think that type of switch has a specific name...

Last edited:

#### Alejandro Pérez 1

Joined Jun 8, 2018
2
Welcome to AAC!

As drawn, when ON and external volts<= battery volts +Vf(d2) the battery drives the motor directly.

When ON and external volts > battery volts + Vf(D2) then external supply drives motor through D2 AND charges battery via same route but LED is off as Vf(D2)<<Vf(LED).

Oh, I don't think that type of switch has a specific name...
Thank you for both the welcome and the answer.
You solved my problem. Thanks again!