Resistive Interfaces

Source Resistance Load

an interface is a divider

This source-resistance-load lesson treats a nonideal source and its load as one ideal resistive divider. The stated 2 ohm source resistance, 6 ohm load, 2 A current, and 12 V load drop are exact only for the DC resistor model. Real interfaces add tolerance, heating, contact resistance, bandwidth limits, parasitic capacitance and inductance, noise, finite precision, and measurement uncertainty.

A real source resistance and a load resistance form an exact voltage divider. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Source and load resistances set one current

The source resistance is 2 ohm and the load is 6 ohm, so the current is 2 amperes.

I=VRs+RL=2 AI = \frac{V}{R_s + R_L} = 2\ \text{A}
Source resistance and loadThe source resistance and load form a divider.16 V2 ohm6 ohmA2 A2 A+-4 V+-12 Voutputload

The two voltage drops close the budget

The source resistor drops 4 volts and the load keeps 12 volts.

4 V+12 V=16 V4\ \text{V} + 12\ \text{V} = 16\ \text{V}
Source resistance and loadKVL checks both displayed voltage drops.16 V2 ohm6 ohmA2 A2 A+-4 V+-12 Voutputload