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Topic: Wireless power LED (Read 385 times) previous topic - next topic

tjones9163

Oct 17, 2019, 03:31 am Last Edit: Oct 17, 2019, 03:40 am by tjones9163
Hello, i have this circuit from here that the transmitting side creates a high oscillating magnetic field the induces current into the receiving side and lights an LED. I want to learn exactly how this works and i will have a pic of the cicuit below.

According to the website "1.5v conventionally flow through the top coil on the transmitting side through R1 to the base of the NPN transistor, through the emitter to ground. Which turns on the transistor The transistor then discharges the inductor as the emitter is connected with the ground. That is what creates the oscillating field."

My question is when the circuit is first powered, the top 17-turn coil builds up a magnetic field and once current flows through it and goes through the resistor, transistor to ground. Is the magnetic field built up in the top coil what discharges through the bottom coil through the collector and emitter to the ground?

So first, the coil goes from the 1.5v in the upward direction and goes through the base, then downward from the magnetic field built in the top coil and it goes through the bottom coil, collector the emitter to the ground? Up and down.

jremington

#1
Oct 17, 2019, 03:38 am Last Edit: Oct 17, 2019, 03:40 am by jremington
Quote
what discharges through the bottom coil
The magnetic field and induced current.

Charging an inductor via current flow creates a magnetic field, which when collapsing, induces a current flow in the inductor. This is covered in introductory physics textbooks.

tjones9163

The magnetic field and induced current.

Charging an inductor via current flow creates a magnetic field, which when collapsing, induces a current flow in the inductor. This is covered in introductory physics textbooks.
I do understand that, i have the image up now. So when the top coil discharges, current flows from the top coil, through the bottom coil, through the collector, through the emitter to the ground? In that direction?

jremington

#3
Oct 17, 2019, 05:23 am Last Edit: Oct 17, 2019, 06:05 am by jremington
Look up "blocking oscillator".

This simple circuit is somewhat complicated to analyze because the base-emitter junction will break down due to high reverse voltages, and allow reverse current to flow. To avoid eventual destruction of the transistor, add a diode to protect the base-emitter junction as shown below. L2 current shown, for a guess at the inductance values.


tjones9163

Look up "blocking oscillator".

This simple circuit is somewhat complicated to analyze because the base-emitter junction will break down due to high reverse voltages, and allow reverse current to flow. To avoid eventual destruction of the transistor, add a diode to protect the base-emitter junction as shown below. L2 current shown, for a guess at the inductance values.


Thank you for the response and that does make sense that you would need a diode. I also looked up blocking oscillator and i feel that i have a better understanding.
I like to also like to visually see what the circuit is doing. Was i correct in saying
"current goes through L1(charging), then through the resistor and through the base to ground and when it reaches ground L1 discharges, flowing through L2, then the collector, then through the emitter to ground.

herbschwarz

Some call that type of circuit a Joule Thief.
I'm told that there is a very good explanation
at https://www.youtube.com/watch?v=0GVLnyTdqkg.

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