How to wire circuit DC Motor with LED

Question

I'm trying to learn a bit more about forward voltage and Ohm's law but I'm not sure how to wire this circuit.

I have:

• One 4.5 DC motor (Operating Volts: 1.5- 4.5V, Nominal Volts: 4.5V, Current (no load): 0.25A)

• Three 5mm LEDs (IF Typical (mA)20, IF Max Continuous (mA)50, VF Typical (V)2.1) -

• One 3 - 12VDC Switchmode Plugpack (Output voltage: 3, 4.5, 5, 6, 7.5, 9, Output current: 1000mA (max))

Do I use the power at 4.5V and run the motor and the LEDs in parallel?

Do I need resistors on the LEDs?

Answer 1

You can connect DC Motor and LED in parallel with the resistor in series with LED. LED can draw current about 24 mA (4.5 V - 2.1 V)/ (100 Ohms). If resistor is not placed in series with it, The LED will eventually get over heated and gets destroyed. use a fly back diode in parallel with motor if it is unidirectional. If Power is set to 4.5 V, then using a 100 ohm resistor with LED is recommended.

^{simulate this circuit – Schematic created using CircuitLab}

LED do not have a datasheet, so assuming typical Vf for calculation.

Answer 2

You should wire things like this:

^{simulate this circuit – Schematic created using CircuitLab}

You require a current limiting resistor in series with each LED, to limit the current in that LED to 20 mA. The motor will draw whatever current it requires - no need for a current limiting resistor for it, as long as you don't feed it more than its rated voltage.