Could somebody please tell me what the name of the below circuit is please

[Joshbessant2]

Hi all, does anybody know the name of this circuit and how it operates and the purpose of each component please? any help is much appreciated. Thanks in advance

 

[DPG]

It's a basic transistor switch circuit.

The light dependent resistor (lower left) forms a potential divider with resistor R3 and biases the transistor. At a certain point the voltage will rise to 0.7V (approx) and the transistor will switch on and illuminate the LED. R4 just limits the current to a safe value for the LED.

 

[Joshbessant2]

It's a basic transistor switch circuit.

The light dependent resistor (lower left) forms a potential divider with resistor R3 and biases the transistor. At a certain point the voltage will rise to 0.7V (approx) and the transistor will switch on and illuminate the LED. R4 just limits the current to a safe value for the LED.

Thanks again! haha

 

[DPG]

Thanks again! haha

No problem. It's good to have an understanding of basic building blocks like this. You can then break down more complex circuits and understand them better.

 

[Joshbessant2]

No problem. It's good to have an understanding of basic building blocks like this. You can then break down more complex circuits and understand them better.

I agree, its currently what I'm trying to get my head around. Can I ask what the purpose of R2 is please?

 

[DPG]

I agree, its currently what I'm trying to get my head around. Can I ask what the purpose of R2 is please?

In basic terms it limits the base current. Transistors (even bipolar ones like the BC108 here) only take a tiny amount of base current switch on.

 

[Joshbessant2]

In basic terms it limits the base current. Transistors (even bipolar ones like the BC108 here) only take a tiny amount of base current switch on.

Thank you, you've been a big help!

 

[Pastory]

You know

It's a basic transistor switch circuit.

The light dependent resistor (lower left) forms a potential divider with resistor R3 and biases the transistor. At a certain point the voltage will rise to 0.7V (approx) and the transistor will switch on and illuminate the LED. R4 just limits the current to a safe value for the LED.

You know I have a little bit of a confussion about this circuit, can you show with arrows how current flows during day and during night

 

[DPG]

You know

You know I have a little bit of a confussion about this circuit, can you show with arrows how current flows during day and during night

To be honest you'd be better off googling transistor switch circuits - there will be better explanations than I can type on a phone keypad. Having said that, if you still have any questions I'm sure we can help.