Mosfet Hartley Oscillator.

[Lightium]

I am having trouble designing a Hartley oscillator using Mosfet's because Mosfet's a new to me still. All I know is that Q/I= switching time. I had to change the extension on the file, EOL won't take an sp3 file?

 

[Lightium]

Thanks Tony Stewart.

 

[rjenkinsgb]

Have you tried the re-arrangement I suggested in post #11?

 

[Lightium]

I am gonna back away from this today. I refreshed my knowledge on MOSFET's with this video. https://www.microtype.io/designing-power-mosfet-circuits/

And read up on the Hartely osc. There must be something about MOSFET's I am not getting.

 

[Lightium]

Have you tried the re-arrangement I suggested in post #11?

I'll try that this morning.

 

[Lightium]

So I figured out that:
L1+((N2*flux1)/I1) / L2+((N1*flux2)/I2) = gain

I'll see how this plays out when I get back to my desk.

 

[Lightium]

So from the equation if the tank circuit is symmetrical gain will be 1. If L1 is higher then L2, then gain will be > positive 1.

 

[Lightium]

The mosfet model I am useing is just a replacer until I can get the exact one in a week from now.

 

[Tony Stewart]

The key variable for MOSFETs is the OFF threshold Vgs(th)=Vt @100uA and the ON resistance RdsOn at Vgs >> 2Vt in between controlled by (Vgs-Vt)^2.

Here I bias each transistor with some threshold just using a DC battery then sweep with adjustable AC to compare how they differ yet similar. https://tinyurl.com/2la4ml22 for voltage controlled quadratic current.

I plotted all the input and output voltages, currents and power dissipation. To choose this input DC bias, this can be done by a large series R for a load and connect input to output. But then if you know the characteristic equations, you don't need to do this.

Any questions?

 

[Lightium]

My latest Hartley is this one. And I can't get sustained oscillations.

 

[Tony Stewart]

Of course with Vgs=0Vdc it won't oscillate.

 

[Tony Stewart]

Define what you expect on the output exactly with impedance at 75kHz?, then what is needed on Vgs to get that. Your gate bias and excess of inductors are problems.

 

[Lightium]

I should be getting 3 volts on the bias connection, but I am not.

 

[Lightium]

I am getting close, I can feel it. lol

 

[Lightium]

I finally got this MOSFET to oscillate. Had to add 50 ohms on the output.