Practical Electronics/Bipolar Transistors/NPN Transistor/Transistor circuit


 * [[Image:Transistor_amplifier_blocked_emitor.svg|250px]]


 * $$\frac{v_o}{v_i} = (\frac{R_2}{R_2+R_3}) (\frac{R_4}{R_3})$$

Electronics switch
When $$R_3=R_4$$, Transistor operates as Electronics switch
 * $$\frac{v_o}{v_i} = \frac{R_2}{R_2+R_3} $$
 * $$\frac{v_o}{v_i} = 0 $$ . $$R_2=0$$
 * $$\frac{v_o}{v_i} = 1 $$ . $$R_1=0$$

Electronics amplifier
When $$R_1=0$$, Transistor operates as Electronics amplifier
 * $$\frac{v_o}{v_i} = A $$ .  $$R_4=A R_3$$
 * $$v_o = A v_i $$

Transistor's Rectifier
A PNP Transistor only allows half of a negative cycle of a voltage or signal wave to pass and grounds any positive cycle of a voltage or signal wave.