Voltage Divider Bias: 4 Resistors, Base/Emitter, Collector, Stabilization?

[smart_worker]

why do we need 4 resistors?we are applying voltage across base emitter junction.Why do we need a resistor for collector side.One more thing how does the resistor across emitter provides stabilization?

 

[UltrafastPED]

A picture helps ...

 

[berkeman]

why do we need 4 resistors?we are applying voltage across base emitter junction.Why do we need a resistor for collector side.One more thing how does the resistor across emitter provides stabilization?

Please do some reading on your own first, and then if you have specific questions about that reading, you can ask them here. We prefer that you do some research/reading on your own before asking questions here.

Start with the intro article at wikipedia: http://en.wikipedia.org/wiki/Bipolar_transistor_biasing

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[sophiecentaur]

why do we need 4 resistors?we are applying voltage across base emitter junction.Why do we need a resistor for collector side.One more thing how does the resistor across emitter provides stabilization?

This question is too vague for a definitive answer but I could say that you do not 'need' a collector resistor. The point is, though, that the transistor is an Amplifier, which controls the current through the collector by the signal on the base. If we are talking common emitter mode, then the collector current flows through a Load (to fulfil the purpose of it being an amplifier). That load does not have to be a resistor. It can be a loudspeaker, lamp, motor etc. etc. For analysing how the common emitter amplifier works basically, it's usual to use a Resistor because the calculations are more straightforward and you can just look at the voltage variation at the collector.

An emitter resistor provides feedback - but you need to read up some basic theory about amplifiers - as already suggested - and then about feedback (more advanced).

 

[sardar]

Voltage divider bias is a commonly used method for biasing a transistor circuit. It involves using a series of resistors to divide the input voltage and provide a stable bias voltage to the base of the transistor. The four resistors in this setup serve specific purposes and are essential for the proper functioning of the circuit.

The first two resistors, connected in series, act as a voltage divider, dividing the input voltage and providing a smaller voltage at the base-emitter junction. This voltage is used to bias the transistor and control the amount of current flowing through it.

The third resistor, connected between the collector and the supply voltage, acts as a load resistor. It helps to stabilize the collector voltage and prevents it from fluctuating due to changes in the circuit.

The fourth resistor, connected between the emitter and ground, provides stabilization by creating negative feedback in the circuit. This helps to regulate the current flowing through the transistor and ensures that it remains constant, even when there are variations in the input voltage or temperature.

Overall, the four resistors work together to provide a stable bias voltage and current to the transistor, allowing it to function properly and accurately amplify the input signal. Without these resistors, the transistor would not be able to operate reliably and could potentially be damaged.