EET Survey of Electronics Chapter 13 - Parallel Circuits

Parallel Circuit Connection n The voltage source is seen across each component in parallel n Each branch has a load current which is independent of the currents of those loads in parallel with it.

Parameters n Current - the total current is the sum of all branch currents n Voltage - The voltage is the same for each component in parallel n Resistance - the TOTAL resistance is lower than the smallest resistance in the set – each parallel load adds another path for current – resistance is inversely proportional to current

Parameters n Power Dissipation - Total power is the sum of power dissipated in each load – Each power is the product of branch current and the source voltage – P T = P 1 + P 2 n or – P T = I T x V T

Solving Parallel Circuits n As with series circuits, take the process one step at a time n I T = I 1 + I 2 + I 3 … n V T = V 1 = V 2 = V 3 … n R T = R 1 x R 2 /(R 1 + R 2 ) {for two loads} n R T = 1/ ( 1/R 1 + 1/R 2 + 1/R 3 …) n P T = P 1 + P 2 + P 3 …

n Example 13-1 Find all unknown values of V, I, R, and P

Example 13-1 Voltage Current ResistancePower R1 R2 Total 12V 0.5A 2 A 2.5 A 24  6  4.8  6 W 24 W 30 W

Example 13-2 n Find all unknown V, I, R, and P

Example 13-2 Voltage Current ResistancePower R1 R2 Total 120V 2 mA 4 mA 3 mA 60 k  30 k  40 k  0.24W 0.48W 0.36W 120V R3 9 mA 13.3 k  1.08W

Example 13-3 n Find all unknown values of V, I, R, and P It =5.5A

Example 13-3 Voltage Current ResistancePower R1 R2 Total 24 V 3 A 1.5 A 1 A 8  16  24  72W 36W 24W 24 V R3 5.5 A 4.36  132W

Troubleshooting n Troubleshooting for opens/shorts – use a table of ‘expected’ values. – compare measurements to predictions

Assignment n Ch13: 1-4 n Read Chapter 14 – Series/Parallel Circuits