#### martin de jong

- Jun 19, 2017

- 11

- Joined
- Jun 19, 2017

- Messages
- 11

Ive designed a circuit that should efficiently make a 10 Watt 3000V DC signal, but when I connect the output to my Delon voltage doubler, or even to a simple rectifier circuit instead of just a (1Meg) resistor, the Royer circuit stops oscillating at its intended frequency (of about 70 KHz), and suddenly switches over to a much higher frequency (about seven times or 500 KHz), which brings down efficiency greatly to about 15% from about 80% when I simply load it with a resistor.

The strange thing is that I cannot simulate the problem, the circuit below shows the LTSpice simulation of my circuit, but it always simulates oscillating at the lower frequency with good efficiency.

I'm starting to become desperate for a solution, or a theory why the royer oscillates at the higher frequency if the load resistance becomes less than say 100 Meg Ohm, without any load it works, but the moment I load it even slightly the strange effect happens, and efficiency goes down the drain.

Note my real circuit under test now doesn't use the PWM regulator, and I simply put something like 3 or 4 Volt between M3d and Vin, so the PWM circuit doesn't affect the royer.

Current theory is that the transformer somehow becomes saturated, but I don't know how that could happen, the Transformer used is rated 14 Watt, so I'm not using it out of specs. also for the frequency to become seven times higher as it does, the inductance (or capacitance)in the LC loop should become the square lower or 7 x 7 = 49 times lower. The royer still generates a sinusoidal signal when it oscillates at 500 KHz, so I believe its still resonating, only with a 47 times lower LC.

Can anyone shine some light on this problem? Why does the way I load the output coil of the Royer matter for the frequency the royer oscillates? In the simulator I can "tweak" the frequency a bit, but it goes only slightly down, not massively up.

The strange thing is that I cannot simulate the problem, the circuit below shows the LTSpice simulation of my circuit, but it always simulates oscillating at the lower frequency with good efficiency.

I'm starting to become desperate for a solution, or a theory why the royer oscillates at the higher frequency if the load resistance becomes less than say 100 Meg Ohm, without any load it works, but the moment I load it even slightly the strange effect happens, and efficiency goes down the drain.

Note my real circuit under test now doesn't use the PWM regulator, and I simply put something like 3 or 4 Volt between M3d and Vin, so the PWM circuit doesn't affect the royer.

Current theory is that the transformer somehow becomes saturated, but I don't know how that could happen, the Transformer used is rated 14 Watt, so I'm not using it out of specs. also for the frequency to become seven times higher as it does, the inductance (or capacitance)in the LC loop should become the square lower or 7 x 7 = 49 times lower. The royer still generates a sinusoidal signal when it oscillates at 500 KHz, so I believe its still resonating, only with a 47 times lower LC.

Can anyone shine some light on this problem? Why does the way I load the output coil of the Royer matter for the frequency the royer oscillates? In the simulator I can "tweak" the frequency a bit, but it goes only slightly down, not massively up.

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