# Amplifier circuit, need some help on high freq and low input voltage

#### kriddaliim

Jan 28, 2015
2
Hello,

I'm troubled with amplifier circuit. My purpose is to create a circuit for driving a coil in my "wireless power transmission" project. So, may I have your ideas or recommendation on amplifier circuit that be suitable with conditions below :
1. Be proper with Sine wave
2. Input voltage is about 1 Vp-p and 1-3 MHz of frequency
3. Need to have output voltage about 10 Vp-p on 10 ohm (with 400 mA at least)

#### Arouse1973

Dec 18, 2013
5,178
Wireless power is quite a complicated subject to get right. I know! You need to supply the details of your coils, size and shape, value of inductance and turns, wire used and series resistance. Also the distance you are hoping to be able to transfer this amount of power.

#### kriddaliim

Jan 28, 2015
2

A waveform generator (AD9850), it generates 1 Vp-p of sine wave. I design its frequency about 3.56 MHz. Its purpose is standing for "resonance" with receiver circuit. The waveform generator is connected with amplifier circuit (it is my big trouble). The amplifier, I chose "class E amplifier" (MOSFET, IRF510) and tried the experiment on last week. Its result was not good because a small signal that carry out to the transmitter coil.

By the way, the properties of the transmitter and receiver coil will be shown below :

transmitter coil
conductor size = SWG24 (0.559 mm of diameter)
inductive = 37 uH (L-equivalent for matching in class E is about 33.9 uH)
Using frequency = 1-4 MHz (for finding resonance)

conductor size = AWG40 (0.0799 mm of diameter)
inductive = 4 uH
Added capacitor = 850 pF (for matching between transmitter coil)

However, everything looks OK except "amplifier circuit" because it amplifies the signal from waveform generator very very low !!! in the class E system. I am not sure which FET in the circuit is correct or not. On the other hand, if you have an experience or idea how to amplify the signal (up to 10 Vp-p with 10 ohm load), please help share and I am looking forward to discussing with you. ^^!

POP

#### Arouse1973

Dec 18, 2013
5,178
Hi POP, before we go into looking at the coils which can become quite a task. You will not get very good results from a sine wave with this circuit. You need to use a square wave, I have found a square wave or PWM to be much better in terms of power transfer. This is because the square wave has a higher V/s than a sine wave, this is what is important in WPT.

A better circuit would be a push-pull amplifier and your coil set up as a series tuned circuit. This way energy is transferred all the time. You could look at NPC technology where you make a sine wave shape out of switching in square waves at different times. This is how some of the modern inverters work now.

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