Those mini tesla coils were always interesting to me, as they can be battery powered while still producing voltages well into the 10kV range, which lights up fluorescent bulbs and destroys electronics. Most of the designs I found were based on the slayer exciter, but this one caught my attention, as it clearly didn't feature all the components normally found in a slayer exciter coil.
Does this circuit work like the slayer exciter and can it be further improved?
At first sight this also can be an oscillator which outputs to the resonant circuit. In that sense it's not different than Slayer Exciter.
I do not say, that it cannot work, but I have some doubts. If it does not start to oscillate (for ex. wrong coil directions) the mosfet can easily get hot and destroyed due high Id and the Vds =20...40V DC. At least some current limiting should exist to prevent it
If it starts to oscillate, the gate insulation can get overvoltage. If this can induce the needed few volts peak-to.peak to the gate, there's nothing preventing it to be few times more, which can be too much.
This circuit shouldn't be impossible to simulate. Coarse equations for the inductances should be easy to find. The capacitance in the secondary coil is tricky to estimate. It's easiest to build one and add the parts that prevent the overheating and blowing the gate with overvoltage. That is to use current limited power supply and add a couple of zener diodes between the gate and source of the mosfet.
This is the circuit improved as user287001 says. The MOSFET type Slayer Exciter has the problem that natural start is difficult. It is necessary to give a pulse for starting from the outside.
I've built variants of this. It works up until the supply voltage approaches max gate-source voltage. Any higher will break your mosfet. This is typically around 20V for power mosfets, but don't go higher than 16-18V due to voltage spikes from the coil feedback.
You can separate the power supply for the gate and drain circuits, and then you can keep the gate below 18V and the drain can go a little higher.
However, due to resonance, the drain voltage swings can easily exceed the drain-source maximums too. I burned out a few IRF640s which has a 200V max drain-source, but I was inputting only 24-26V. Then I simulated it in LTSpice and the voltage peaks hit almost 300V for that input.
I suggest learning to use LTSpice or another simulation tool and play around with different topologies if you want to go higher in voltage. If you just want a small slayer exciter that's quite a bit better than the BJT equivalent, use a power mosfet and stay below the gate-source voltage max.
I think the bias resistor of 50 Ohm is a little low, you should start higher and monitor current flowing thrue the circuit as you lower the source to gate resistance, while at the same time looking if it starts to oscillate. If it draws current and does not oscillate you should check your connexions, if the primary coil is connected in the right direction for instance. Also play a little with the coupling of the primary, meaning the height of it, how close it is wound to the secondary. Find it's optimal circumstances before going full power. That saves you a few trips to the electronics store to buy new Mosfets.
