# Base Emitter Resistor Calculation

1. ## Base Emitter Resistor Calculation

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.

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2. ## Re: Base Emitter Resistor Calculation

you didnt specify the collector(load) current.

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3. ## Re: Base Emitter Resistor Calculation

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

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4. ## Re: Base Emitter Resistor Calculation

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?

5. ## Re: Base Emitter Resistor Calculation

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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