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I am trying to find out the value of Ib for 2N2222 transistor.

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sharath_krishna

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I am trying to understand the basics. I am trying to run the motor in uni direction for my robot. what would be the maximum Ic value. some data sheet says Ic sat is 500mA, in other it says peak current for Ic is 800mA. Which one I should consider. And help me out to solve the following problem bjt.png Please find the attachment for the circuit. when Ic = 50mA and Vb = 3.3V find Beta and Rb. I couldn't able to find any relation between Ic and Beta without knowing Ib and Ie.
 

Hi,

IC is given with 50mA ... no need to calculate it.

Klaus

Added:
The values in the datasheet are the max allowed values.
You just need to take care not to cross this limit.

Why 500mA and 800mA?
Maybe one manufacturer's BJT can handle more current than another.
Or the test conditions are different. You need to read the datasheets carefully.
 

I want to know the base resistor value and DC gain beta value when Ic = 50 mA.
 

For a bipolar transistor to turn on well (good saturation), its datasheet says that its base current should be 1/10th its collector current. Beta is not used for a saturated transistor, beta is used for a linear amplifier that is not saturated and has plenty of collector to emitter voltage. The datasheet shows the range of beta at different collector currents.

A transistor used at its maximum allowed current makes a very lossy switch.

You need to find out the maximum current your motor uses.
 

The difference my be that one parameter is maximum saturation current and the other is PEAK current. PEAK implies a limited time
 

Major manufacturers do not make the 2N2222 anymore but Central Semi still make it in the old metal case and Digikey has many of them at a crazy expensive price ($2.23US each). Its datasheet says 800mA continuously maximum but only when it has an obsolete heatsink. All its spec's stop at 500mA.
 

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