How to Calculate Collector-emitter Voltage in Transistor Circuits

Understanding how to calculate the collector-emitter voltage (V_CE) is essential for analyzing transistor circuits. This voltage indicates the operation state of the transistor and helps in designing and troubleshooting electronic devices.

Basic Concept of V_CE

The collector-emitter voltage is the voltage difference between the collector and emitter terminals of a bipolar junction transistor (BJT). It is a key parameter that determines whether the transistor is in cutoff, active, or saturation mode.

Calculating V_CE in a Circuit

To calculate V_CE, identify the supply voltage and the voltages across other components connected to the collector and emitter. Use Kirchhoff’s Voltage Law (KVL) to sum voltages around the circuit loop.

For example, in a simple common-emitter configuration:

• Determine the collector voltage (V_C) by subtracting the voltage drop across the collector resistor from the supply voltage.
• Find the emitter voltage (V_E) by measuring or calculating the voltage across the emitter resistor.
• Calculate V_CE as V_C minus V_E.

Example Calculation

Suppose the supply voltage (V_CC) is 12V, the collector resistor (R_C) is 2kΩ, and the collector current (I_C) is 1mA. The collector voltage (V_C) is:

V_C = V_CC – I_C × R_C = 12V – (0.001A × 2000Ω) = 12V – 2V = 10V.

If the emitter resistor (R_E) is 1kΩ and the emitter current (I_E) is approximately 1mA, then the emitter voltage (V_E) is:

V_E = I_E × R_E = 0.001A × 1000Ω = 1V.

Finally, the collector-emitter voltage (V_CE) is:

V_CE = V_C – V_E = 10V – 1V = 9V.