BJT Biasing

# BJT Biasing - Simple BJT DC Bias Circuits Bob York BJT DC...

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©B ob Y o rk Simple BJT DC Bias Circuits

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©B obY o rk Back to TOC BJT DC Biasing V out I c R c Biasing circuits and load-lines similar to FET circuits. Consider the design of the circuit to set a certain Q-point: V ce 10V 6V 200 20mA c R  BJT current gain: 100 +10 V Design goal: 20mA out c V I Now find the base resistance R b that will give this current (KVL): V ce 10 I c 6 20mA 40mA 200 A c b I I  To get a 4V drop across the collector resistor @ 20mA requires a resistor value I b 10mA 30mA I b 400 μ A 300 μ A 200 μ A 100 μ A 0 μ A 50mA R b +10 V 0.7 V V b 0.7V 0 bb b VI R  b b b V R I +6 V 47 k 200 100 If we use the same supply voltage for V b (+10V) then 10 0.7 47k 200 A b R 
©B obY o rk Back to TOC Base-Current Bias Network + V cc In some BJT resistive bias circuits it may help to make use of Thevenin equivalent circuits for the base-current bias network: R c I b R b1 I c V out R b2 Replace this side by Thevenin equivalent + V cc R c I b I c V out V th 12 th b b R RR 2 b th cc bb R VV R R R th Then currents/voltages can be found easily as in previous slide 0.7V 0 th b th VI R  out cc c c I R cb II

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## This note was uploaded on 03/17/2010 for the course ECE 2B taught by Professor York during the Winter '07 term at UCSB.

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BJT Biasing - Simple BJT DC Bias Circuits Bob York BJT DC...

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