mosfet joule thief

[ztec2002]

has anyone built a joule thief using mosfets instead of bi poler transistors . seems like mosfets are the golden boy of bemf circuits. i would love to build one if anyone has a circuit diagram ?

cheers ztec2002

[Watson]

Yes

has anyone built a joule thief using mosfets instead of bi poler transistors . seems like mosfets are the golden boy of bemf circuits. i would love to build one if anyone has a circuit diagram ?

cheers ztec2002

The MOSFET JT is even simpler than a conventional JT - it does not need the resistor, so you need just a FET, a LED and a coil. Other than that, the circuit is identical. The turns on the feedback winding can be increased to give a more optimum output. You can read more about my experiments with MOSFET JTs here and at the links at the end of the blog.

[nvisser]

Just keep in mind that unlike a bipolar transistor that can switch on with 0.7V, a low side mosfet switch needs at least 10V on the gate with reference to the source to switch properly.

[Slider2732]

Here's a thought Watson, after reading your blog entry.
You say about getting a boost from a button cell to start it up....
Could you use jonnydavro's trick to start the circuit. that of firing a (gas stove) piezo lighter next to the coil ?

[Aaron]

mosfet

The MOSFET JT is even simpler than a conventional JT - it does not need the resistor, so you need just a FET, a LED and a coil. Other than that, the circuit is identical. The turns on the feedback winding can be increased to give a more optimum output. You can read more about my experiments with MOSFET JTs here and at the links at the end of the blog.

If you scope the battery, do you get a spike back to the battery on each
cycle using the mosfet?