Question

How to calculate power in an electronic circuit?

Answer 1

Calculating power in an electronic circuit involves using one of two formulas, depending on whether the circuit is purely resistive or contains reactive components like capacitors and inductors. The formulas are as follows:

Power in a purely resistive circuit:
In a circuit containing only resistors (no capacitors or inductors), you can calculate power using Ohm's law and the formula for power (P):

P = V^2 / R

Where:
P = Power in Watts (W)
V = Voltage across the resistor in Volts (V)
R = Resistance of the resistor in Ohms (Ω)

Power in a circuit with reactive components:
In a circuit with reactive components (capacitors or inductors) or a combination of resistors, capacitors, and inductors, you'll need to consider both the active power (real power) and the reactive power. The total power, also known as apparent power (S), is the combination of both:

S = Vrms * Irms

Where:
S = Apparent power in Volt-Amperes (VA)
Vrms = Root Mean Square (RMS) voltage across the circuit in Volts
Irms = RMS current flowing through the circuit in Amperes

Now, to find the active power (P) in Watts, you can use the power factor (PF) of the circuit:

P = S * PF

Where:
PF = Power Factor (a dimensionless value between 0 and 1)

The power factor is the cosine of the angle (phi) between the voltage and current waveforms and represents the efficiency of power usage in the circuit. For purely resistive circuits, the power factor is 1 (cosine of 0 degrees), indicating that all the power is used effectively. However, in circuits with reactive elements, the power factor is usually less than 1 due to energy losses caused by phase differences between voltage and current.

In summary, to calculate power in an electronic circuit:

For purely resistive circuits, use P = V^2 / R.
For circuits with reactive elements, calculate the apparent power S = Vrms * Irms and then multiply it by the power factor (P = S * PF) to get the active power.