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decoder/counter 7 segment/circuit

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cybertalk1

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hello all i have a problem how do i find the hfe (min) of a transistor

my led is total 24 each has a resister 10 ohm 1/4watt

480ma total current

mps2222 is the transistor type but i can't calculat RL of my leds array

please help
 
From the datasheet: https://www.electro-tech-online.com/custompdfs/2011/08/MPS2222-DPDF.pdf hfe is about 50 at 500 mA.

Before we get our underwear in knots, Vce (Sat) at 500 mA means 50 mA of base current. Can you supply that.

What is Vf of the LED
What is If (assume 20 mA)?
What is the supply voltage to the LED?

Rled should be <= (Vs-Vce(sat)-Vf)/20 mA

With Ib, you have to take into account Vbe.

If you wanted to saturate the transistor and the applied voltage was 5V, Rb would have to be ~ (5-Vbe)/50 mA; 50 mA = 50 e-3 Amps
 
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