6 7-2: Current Dividers with Two Parallel Resistances IT is divided into individual branch currents.Each branch current is inversely proportional to the branch resistance value.For two resistors, R1 and R2, in parallel:Note that this formula can only be used for two branch resistances.The largest current flows in the branch that has the smallest R.
8 7-3: Current Division by Parallel Conductances For any number of parallel branches, IT is divided into currents that are proportional to the conductance of the branches.For a branch having conductance G:I =× ITGGT
10 7-3: Current Division by Parallel Conductances The Siemens (S) unit is the reciprocal of the ohm (Ω)GT = G1 + G2 + G3=GT = 0.8 SI1 = 0.1/0.8 x 40 mA = 5 mAI2 = 0.5/0.8 x 40 mA = 25 mAI3 = 0.2/0.8 x 40 mA = 10 mAKCL check: 5 mA + 25 mA + 10 mA = 40 mA = IT
12 7-4: Series Voltage Divider with Parallel Load Current V1 = 40/60 x 60 V = 40 VV2 = 20/60 x 60 V = 20 VV1 + V2 = VT = 60 V(Applied Voltage)Fig 7-6
13 7-4: Series Voltage Divider with Parallel Load Current The current that passes through all the resistances in the voltage divider is called the bleeder current, IB.Resistance RL has just its load current IL.Resistance R2 has only the bleeder current IB.Resistance R1 hasboth IL and IB.Fig. 7-6
15 7-5: Design of a Loaded Voltage Divider I1 through R1 equals 30 mAI2 through R2 is = 66 mAI3 through R3 is = 120 mAV1 is 18 V to groundV2 is 40 − 18 = 22 VV3 is 100 V (Point D) − 40 = 60 V
16 7-5: Design of a Loaded Voltage Divider R1 = V1/I1 = 18 V/30 mA = 0.6 kΩ = 600 ΩR2 = V2/I2 = 22 V/66 mA = kΩ = 333 ΩR3 = V3/I3 = 60 V/120 mA = 0.5 kΩ = 500 ΩNOTE: When these values are used for R1, R2, and R3 and connected in a voltage divider across a source of 100 V, each load will have the specified voltage at its rated current.