Base Emitter Resistor Calculation

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abhishek.2138

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I want to use MMBTA2222A as switch. Its hfe = 40 (min.), Vcc = 5V, Base input voltage is 14V. Series base resistor value i have calculated,

But how to calculate the value of base to emitter resistor.
Please help..
 

you didnt specify the collector(load) current.
 

Hi,

An internet search about "base resistor calculator online" gives a lot of hits.
Usually they come with description.
Read it first to avoid wrong input.
Especially with hfe - you won't use the value "40".

Klaus
 

Hi,

One way of seeing things: It's part of a resistive voltage divider. How much or how little do you want to attenuate the base voltage?
 

The B-E shunt resistor is responsible (or partly so)
for turnoff speed as a saturated switch. Do you
care about LH risetime at the collector node? If so,
characterize or find data for max temp, max "on"
base drive, min Vce(sat) switching w.r.t. the base
network impedance.
 
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