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led control transistor

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Zero999:

--- Quote from: yalect on October 01, 2019, 09:55:10 am ---Hi,
I would like to ask you that I found this two circuit, I want to determine which are better and safty for current and load and transistor working
thank you

--- End quote ---
What do you intend to control the transistor with?

This sounds like an X & Y problem.

What are you trying to do?

yalect:
Hi,
I remarked that on all this circuits below, the base of the transistor have to be connected to GND with resistor
we can ignore that resistor by increase resistor of the base?
thank you

Zero999:

--- Quote from: yalect on October 02, 2019, 08:17:39 am ---Hi,
I remarked that on all this circuits below, the base of the transistor have to be connected to GND with resistor
we can ignore that resistor by increase resistor of the base?
thank you

--- End quote ---
It's generally good practise to connect the base to a definite voltage. In reality, the circuit will probably work, without a resistor between the base and emitter, but it makes it more vulnerable to electromagnetic interference. If the wire to the switch is long, it can pick-up stray electromagnetic fields, which can induce a high enough voltage to turn the transistor on. Adding a resistor to pull the base down to ground, reduce the risk of the transistor turning on, due to tiny currents.

Dave:

--- Quote from: Zero999 on October 02, 2019, 09:21:59 am ---It's generally good practise to connect the base to a definite voltage. In reality, the circuit will probably work, without a resistor between the base and emitter, but it makes it more vulnerable to electromagnetic interference. If the wire to the switch is long, it can pick-up stray electromagnetic fields, which can induce a high enough voltage to turn the transistor on. Adding a resistor to pull the base down to ground, reduce the risk of the transistor turning on, due to tiny currents.

--- End quote ---
What you're talking about is usually done for FETs. Resistors between base and emitter are there to turn the transistor off quicker, by helping drain the charge from the base once the control voltage is disconnected.
You'd need a very large EM disturbance to get the transistor conducting sporadically. Darlington pairs, on the other hand, are a different beast.

They can be easily be omitted on circuits like this one.

yalect:
Hi,
What you're talking about is usually done for FETs. Resistors between base and emitter are there to turn the transistor off quicker, by helping drain the charge from the base once the control voltage is disconnected.

thank you
you mean we can ignor that resistor  (base and emitter) for large resistor of the base to limite the current.
greeting

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