Joule Thief Circuits: Illuminating LED with 1.5V DC

A Joule Thief is a simple electronic circuit which can convert a low DC voltage into a higher voltage. We can make this circuit using a transistor, an inductor and a few other components.

The interesting thing about this circuit is that we can use a single 1.5V battery to light up a white or blue LED which normally needs around 3V or more.

There are many ways of making a Joule Thief circuit. We can use different transistors, different types of inductors and even modify the circuit for operating multiple LEDs.

So in this article let us look at six different Joule Thief circuit ideas. Each circuit has a different purpose, and you can select the one which suits your requirement. You can also visit the individual articles to see the complete circuit diagrams and working details.

Different Types of Joule Thief Circuits

Joule Thief Circuit Which Can Illuminate Any 3.3V LED or Higher

A normal 1.5V battery cannot directly light up a white or blue LED which needs around 3.3V. But we can use a Joule Thief circuit to increase the voltage and operate such LEDs. This design explains one such arrangement which can be useful for experimenting with different types of higher-voltage LEDs using a low voltage battery.

Read the complete circuit here:

Can We Power a Joule Thief Circuit With a Small DC Motor?

Normally we use a battery for powering a Joule Thief circuit. But can we use a small DC motor for this purpose? Yes, a DC motor can also generate electricity when we rotate its shaft from an external source. This experiment explains how we can use this generated electricity for running a Joule Thief circuit. The output will depend on the motor speed and how much voltage and current it can produce.

Read the complete circuit here:

Joule Thief Circuit Using a Single-Winding Inductor

Most ordinary Joule Thief circuits use two winding sections for getting the required feedback. But in this design we try a different type of inductor arrangement using a single winding with a suitable connection. This is an interesting experiment for understanding how we can use different coil arrangements in a Joule Thief circuit.

Read the complete circuit here:

Illuminating Four 1-Watt LEDs With a 1.5V Cell Using Joule Thief Circuit

Here we have an interesting experiment where we try to operate four 1-watt LEDs using just a 1.5V cell. The Joule Thief circuit is modified for driving multiple high-power LEDs from a low voltage supply. But we must remember that four 1-watt LEDs need considerable power, so the actual brightness will depend on how much current the battery and circuit can supply.

Read the complete circuit here:

Joule Thief Circuit Using 2N3055 Power Transistor

This Joule Thief circuit uses a 2N3055 power transistor instead of an ordinary small signal transistor. The idea here is to experiment with a bigger power transistor for the switching operation. However, the actual output power will depend on the battery, inductor and the way the complete circuit is designed.

Read the complete circuit here:

8X Overunity Circuit Using Joule Thief

This is a different type of Joule Thief experiment which uses an additional resonant arrangement. The original experiment describes a claim of getting around 8 times more output compared to the input. However, this overunity claim has not been independently proved. We must measure the actual input and output power properly before accepting such a result.

Still, the circuit can be interesting for experimenting with resonant switching and modified Joule Thief arrangements.

Read the complete circuit here:

Comparison of the Different Joule Thief Designs

The following table will help us understand the main purpose of each circuit. So you can quickly select the design which you want to experiment with.

How to Select the Right Joule Thief Circuit?

Before selecting a Joule Thief circuit, we must first decide what we want to do with it.

If you just want to light up a small white or blue LED using a single 1.5V cell, then a basic Joule Thief circuit may be enough.

But if you want to operate multiple LEDs or high-power LEDs, then we must check the total output power and the required LED current.

The battery is also very important. A small battery may provide enough voltage to start the circuit, but it may not provide enough current for operating a bigger load.

The inductor is another important part. Its core material, number of turns, wire thickness and winding arrangement can change the output voltage and current.

So, we should always select the complete circuit according to the load requirement. We should not select a circuit just because it is producing a very high voltage.

What You Should Know Before Building a Joule Thief

Before building any Joule Thief circuit, let us understand a few important points.

1. A higher output voltage does not mean that we are getting higher output power. When the voltage increases, the available output current generally becomes lower.
2. The battery still supplies all the energy required by the circuit. A Joule Thief can use a low battery voltage, but it cannot produce unlimited energy.
3. High-power LEDs need proper current control and heat dissipation. Just because an LED is glowing does not mean that it is working safely.
4. The transistor must be selected according to the required switching current and voltage. If the current becomes too high, then the transistor may overheat and get damaged.
5. The inductor winding and feedback connections must be correct. Otherwise, the circuit may not oscillate properly or may give an unexpected output.
6. We should measure the actual output voltage and current with suitable measuring instruments while the circuit is connected to its intended load.

Conclusion

Joule Thief circuits are interesting electronic projects which help us understand how a low DC voltage can be converted into higher voltage pulses using a transistor and an inductor.

We can experiment with different transistors, coil arrangements, LED loads and switching methods to make different types of Joule Thief circuits.

The six designs explained above give us several interesting ideas to try. You can visit the individual articles to see their complete circuit diagrams, component details and working explanations.

So select the circuit according to your requirement, check the component ratings and then start your experiment carefully.

Reference: https://en.wikipedia.org/wiki/Joule_thief