DP 2-3 Resistors are given a power rating. For example, resistors are available with ratings of 1/8 W, 1/4 W, 1/2 W, and 1 W. A 1/2-W resistor is able to safely dissipate 1/2 W of power, indefinitely. Resistors with larger power ratings are more expensive and bulkier than resistors with lower power ratings. Good engineering practice requires that resistor power ratings be specified to be as large as, but not larger than, necessary.

Consider the circuit shown in Figure DP 2-3. The values of the resistances are R₁ = 1000 Ω,

R₂ = 2000 Ω, and R₃ =4000 Ω. The value of the current source current is i_s =30 mA. Specify the power rating for each resistor.

Figure DP 2-3

Since current is constant in a series resistor use the following for calculating Power

So the power for each resistor

R₁ (1000 Ω) should be a 1 W Resistor

R₂ (2000 Ω) should be a 2 W Resistor

R₃ (4000 Ω) should be a 4 W Resistor

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This page last updated on December 29, 2018