Moderator Note: This thread has been split from Calculating Base Resistor for a BJT

I don't see in the diagram the resistor usually connected from Base to Emitter. What's the utility of this further resistor ? Is always necessary or not ?

 

Hello minulescu,

Regarding Beta, in most cases i have seen people using 20 for calculations., however it depends on which transistor (Parameter) you are using.

 

I don't see in the diagram the resistor usually connected from Base to Emitter. What's the utility of this further resistor ? Is always necessary or not ?

You've reopened a 5-1/2 year old thread. If you have a question on something, you should start your own thread.

And no, this circuit doesn't need a resistor from emitter to base. If you supply an example of such an arrangement, someone here will explain it to you.

 

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Regarding Beta, in most cases i have seen people using 20 for calculations., however it depends on which transistor (Parameter) you are using.

If you look at their data sheet, most BJTs are specified at a Beta of 10 for the Vce saturation voltage measurement, so that is why a value of 10 is commonly used when you want the transistor to be fully ON.

Of course you can also use a logic-level MOSFET, which requires no gate current, to control the LEDs.