Are These Two BJT Circuits Equivalent?

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SUMMARY

The discussion confirms that the two BJT circuits in question are equivalent, as both configurations connect to ground. The presence of the bottom left resistor influences the base bias current, which is determined by the upper left resistor and the supply voltage when the bottom resistor is absent. In contrast, with the bottom left resistor present, a resistor divider effect stabilizes the base bias current against temperature variations. The emitter current is defined as the sum of the base and collector currents in both configurations.

PREREQUISITES
  • Understanding of BJT (Bipolar Junction Transistor) operation
  • Knowledge of circuit grounding techniques
  • Familiarity with resistor divider circuits
  • Basic principles of current flow in electronic circuits
NEXT STEPS
  • Study BJT biasing techniques and their impact on circuit performance
  • Learn about resistor divider circuits and their applications in biasing
  • Explore temperature effects on transistor characteristics and bias stability
  • Investigate the role of emitter, base, and collector currents in BJT circuits
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Electronics students, circuit designers, and engineers interested in understanding BJT configurations and their implications on circuit behavior.

Air
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I've got these two BJT circuits. I want to know if the result are the same. Are both circuits below same? Can the bottom left resistor be grounded and be same as the second circuit.

http://img21.imageshack.us/img21/2886/bjtt.jpg
 
Last edited by a moderator:
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Air said:
I've got these two BJT circuits. I want to know if the result are the same. Are both circuits below same? Can the bottom left resistor be grounded and be same as the second circuit.

http://img21.imageshack.us/img21/2886/bjtt.jpg
[/URL]

Yes, they both go to ground, so the circuit can be drawn either way.
 
Last edited by a moderator:
Thank you.

Also, if the bottom left resistor branch didn't exist, then the current in the emitter would just be the current in the collector plus the current in the emitter?
 
Air said:
Thank you.

Also, if the bottom left resistor branch didn't exist, then the current in the emitter would just be the current in the collector plus the current in the emitter?

Not exactly, and I think you made s small typo anyway. The emitter current in this configuration is always the base+collector currents.

If the lower left resistor is not there, then the base bias current is set by the upper left resistor and the supply voltage (Vs-Vb/R = Ibias). With the lower left resistor there, the bias is set more by a resistor divider effect, and will be a bit less temperature sensitive in terms of the base bias current versus temperature (Quiz Question -- whi?).
 

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