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This amazing little circuit is one that I have used in many projects for teaching alternative energy and circuit theory. It also introduces us to Inductors (Measured in Henrys (H)) which are basically coils of wire around a ferrite core which ‘induce’ a magnetic field (you may wish to research Inductors further).
The circuit works via a magnetic field which is created around the Inductor due to current passing through it. This current causes the Transistors to switch off resulting in power to the Inductor being cut off. As a result of this, the magnetic field is converted into electrical energy which is sent through the LED as a pulse.
When the pulse ends and the magnetic field stops , the transistors turn back on again which recreate the magnetic field – This happens rapidly enough to provide a seemingly constant voltage.
Build and test the circuit (Fig 1 and Fig 2) and see if you can measure the frequency spikes generated by the Joule Thief!
The circuit works via a magnetic field which is created around the Inductor due to current passing through it. This current causes the Transistors to switch off resulting in power to the Inductor being cut off. As a result of this, the magnetic field is converted into electrical energy which is sent through the LED as a pulse.
When the pulse ends and the magnetic field stops , the transistors turn back on again which recreate the magnetic field – This happens rapidly enough to provide a seemingly constant voltage.
Build and test the circuit (Fig 1 and Fig 2) and see if you can measure the frequency spikes generated by the Joule Thief!
In addition to a Prototype board (Breadboard), wire for connections and a power source, you will need the following components to build this circuit:
1 x 10KΩ Fixed Resistor1 x 220Ω Fixed Resistor1 x 220pF Capacitor2 x BC 548B Transistors1 x LED1 x 100µH Inductor1 x Solar Motor and Propeller
1 x 10KΩ Fixed Resistor1 x 220Ω Fixed Resistor1 x 220pF Capacitor2 x BC 548B Transistors1 x LED1 x 100µH Inductor1 x Solar Motor and Propeller
Fig 1
Fig 2
I have used a small DC Solar Motor to provide the input voltage to the circuit – this has allowed me to attach a propeller which when spinning the motor shaft gives a small input voltage (perhaps you could measure this).
You can replace the motor with a seemingly run out battery or cell which will provide a constant voltage. I have used a propeller connected to the motor as it gives a glowing effect to the LED’s when wind pushes the propeller around.
This gives an interesting effect when used in project work (Fig 3 and https://sites.google.com/sheffield.ac.uk/diamond-electronics/project-ideas/glow-light ).
You can replace the motor with a seemingly run out battery or cell which will provide a constant voltage. I have used a propeller connected to the motor as it gives a glowing effect to the LED’s when wind pushes the propeller around.
This gives an interesting effect when used in project work (Fig 3 and https://sites.google.com/sheffield.ac.uk/diamond-electronics/project-ideas/glow-light ).
Joule Thief.mp4
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