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Mand Labs presents

Circuit Combinations

Electrical Devices

• Consume power to do useful work

• D1, D2, D3: Three different electrical or electronic devices

• Examples: Air Conditioning Unit, Electric Iron, Fan, Refrigerator

• Each device has some resistance

• Each device will draw some current from source

Combining Devices in Series

• Series: Connect all devices back to back (one after the other)

• Current through each device is same

• Total voltage of source is divided among all devices in series

• Vs = V1 + V2 + V3

Combining Devices in Series1. What if, one device is fused or out of order?

Open Circuit Condition

2. What if, one device draws much larger current?

In such cases, if

Maximum Current > Current Rating of any device

Device Breakdown + Open Circuit Condition

Resistors in Series

• Replace devices with resistors

• Requivalent = Total Resistance in the circuit = R1 + R2 + R3

Resistors in Series on BB

• Total Current = Total Voltage/Total Resistance

• I = Vcc/ Requivalent

• Requivalent = R1 + R2 + R3

Current, I, passing through each resistor is same

Equivalent Resistance in Series

Measured Value (= 11.4k Ω) > Theoretical Value (=11.3k Ω ) because of Tolerance

Theoretical Value = R

R = R1 + R2 + R3

= 330 + 1k + 10k

= 11330 Ω

= 11.3k ΩResistances gets added up in series

Connecting LEDs in Series

• Replace devices with LEDs

• +ve leg of 2nd LED is connected to -ve leg of 1st LED and so on

LEDs in series on BB

LEDs are connected one after the other

Combining Devices in Parallel

• Parallel: Connect all devices end to end

• Each device could draw same or different amount of current

• Voltage across each device is same

• Total current from source is divided among all devices

Combining Devices in Parallel

1. What if, one device is fused or out of order?

All other devices work

2. What if, one device draws much larger current?

Depends upon Source Capacity

Resistors in Parallel

• Replace devices with resistors

• 1/Requivalent = 1/R1 + 1/R2 + 1/R3

Resistors in parallel on BB

Voltage across each resistor is same

• Total Current = Total Voltage/Total Resistance

• I = Vcc/ Requivalent

• 1/Requivalent = 1/R1 + 1/R2 + 1/R3

• Current passing through each resistor could be same or different

Theoretical Value = R

1/R =1/R1 + 1/R2 + 1/R3

1/R = 1/330 + 1/1000 + 1/10000

R = 242. 11 Ω

Measured Value (= 250 Ω) > Theoretical Value (=242.1 Ω ) because of Tolerance

Equivalent resistance in parallel

Connecting LEDs in Parallel

• Replace devices with LEDs

• +ve leg of 1st LED is connected to +ve leg of 2nd LED

• -ve leg of 1st LED is connected to -ve leg of 2nd LED

LEDs in parallel on BB

Voltage across each LED is same

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