Transistor voltage switch

Other Hardware General Electronics
1

Hi,

I have a 300mA LED load that is powered by 3.7V lipo battery. The way my PCB is made, the load must be connected to ground and the 3.7V needs to be switched based on the Arduino pin state. The LEDS need to be supplied by 3.7V or close to it.

I found a circuit that is similar to my needs but i'm not sure on what to use

Any help is greatly appreciated.

Thanks,
Jeff

2

If you have 3.7V power supply and the LED needs 3.7V then you'll have to use a MOSFET.

A BJT like th 2N2222 needs about a volt to work so the LED would receive less than 3V.

Any MOSFET described as "Logic level" will do.

If the load has to connect to ground then you need a P-channel MOSFET connected "high side".

So... the google search term is: "p-channel logic mosfet"

3

Thanks for your response.

Based on one of the answers from here arduino - Transistor as switch dropping voltage - Electrical Engineering Stack Exchange

If i keep the two 10k resistors and the BC547, then you're saying i can use any mosfet such as http://www.farnell.com/datasheets/190803.pdf ?

Is 10k from the Arduino ok? So when the Arduino pin is HIGH, 3.7V is on the load, otherwise it is zero volts?

Thanks

4

Jeffro_Aus:
If i keep the two 10k resistors and the BC547, then you're saying i can use any mosfet such as http://www.farnell.com/datasheets/190803.pdf ?

Yes.

5

fungus:
Yes.

Those 10k resistors seem a bit big to me though. The MOSFET will switch very slowly.

Replace the resistors with 220 Ohms if you're thinking of using PWM to control the brightness.

6

Those 10k resistors seem a bit big to me though. The MOSFET will switch very slowly.

Replace the resistors with 220 Ohms if you're thinking of using PWM to control the brightness.

I'm only going to have the LEDs either on or off with no other brightness. Would the resistor values matter for different MOSFETS?

7

Jeffro_Aus:
Would the resistor values matter for different MOSFETS?

No.