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resistors' value in transistor circuit

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Advanced Member level 4
Jul 27, 2007
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U need attension to hefe (DC gain cuurent) to design your circuit to terminate resistor value. Note Ic max (collector current max) to design a limited current.
example .For designing transistor as switch which Ic =100 mA. You calculate Rc to limit Ic curent. after chosing Rc(Resistor on collector) => Ib(current on base)= Ic/(hfe*k) .(K= safety factor , usually chosing k=4). and base on Ib you can terminate Rb(resistor on base).

As you say, and get from datasheet, I have these parameters
Ic Collector Current 500 mA (ok, this is Icmax value)
hFE* DC Current Gain for 2N1613
................Ic = 500 mA......Vce = 10 V........hFE(typical) = 55
Do I need Vce for calculation ?

hi, smile . Transistor usually use as two function in three region operation of it.

When it i used as swicth, It work in two region : ( saturated region , and break down region).when it is saturated Vce≈ 0, and Ic =VCC/( Rc+Re ) while (Ic ≥hfe*Ib).on this case you must note Ic on datasheet to note that it must be more than Ic which u need to design
when it in break region it is considered no current through Collector and Vce ≈ Vcc ( U need to notice Vce on datasheet must be more than Vcc in order to avoid destroying C -E junction)
Ic =500ma on datasheet is the max current that CE junction can tolarate. Simliar to Vce that is the max voltage drop on CE junction. When U design , you can also choose Ic < Ic max =500ma , and Vce <Vce max

when it is working on linear region. it works as amplifying signal device . The signal on Base will amplify with gain =hfe on Colletor
According to your Bias . You Transistor can either Work in two above function
note that hfe can change when temperature change.
Ic , Vce on datasheet are the max factor which transistor can tolerate

Thanks so much !!!

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