Common Emitter Configuration
| Transistors can be made to amplify, detect, or to oscillate in much the same manner as vacuum-tubes. Shown in the drawings below, is a comparison between a triode vacuum-tube and a PNP transistor; where the transistor |
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| Triode Vacuum Tube | PNP Transistor | |||
| base is comparable to the tube grid, the transistor emitter is comparable to the tube cathode, and the transistor collector is comparable to the tube plate. |
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| Transistor Formulas | Transistor Symbols | |||||
| Input resistance, |  |
= | Current gain common base | |||
 |
Ae (Av) | = | Voltage gain | |||
| Current Gain, | Ai | = | Current gain | |||
 (with Vc constant) |
Ap | = | Power gain | |||
| Voltage Gain, | B | = | Current gain common emitter | |||
 (with Ic constant) |
Ib | = | Base current | |||
| Ic | = | Collector current | ||||
| Output Resistance, | Ie | = | Emitter current | |||
 |
Ii | = | Input current | |||
| Pi | = | Input power | ||||
| Power Gain, | Po | = | Output power | |||
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Ri | = | Input resistance | |||
| Ro | = | Output resistance | ||||
| The current gain of the common base | Vb | = | Base voltage | |||
| configuration is alpha, where | ||||||
 (with Vc constant) |
Vc | = | Collector voltage | |||
| Vi | = | Input voltage | ||||
| The current gain of the common emitter is beta, where |
A direct realtionship exists between the alpha and beta of a transistor. |
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 (with Vc constant) |
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