Tracking Resonance Frequency

[AAOAA]

Hello,

I am working in my thesis on optimization of resonance DC/DC converter, the input voltage is 10V and the output voltage is 5KV (voltage multiplier is used), almost no current at the output.

The working principle is based on the resonance of the transformer. Somehow, when I increase or decrease the output voltage the resonance frequency is shifted, does anyone have an idea on how can I track the resonance and switch according to the new frequency.

Regards,
AAOAA

 

[KlausST]

Hi,

Around resonance frequency there is a large change in phase shift. Maybe you can track with the help of phase shift.

Klaus

 

[chuckey]

I do not understand what you are doing. If you change the output voltage - how? the oscillations re-adjust in frequency to maintain the 180 degrees phase shift. So why would you want to track the frequency? Just take a sample of the AC at some point and use that to lock what ever it is you want to lock.
Frank

 

[D.A.(Tony)Stewart]

If you reverse engineer the drum HV bias generators used in large laser printers you will find they use a step up transformer in a resonant oscillator mode. Thus no EMI is generated with the sine wave output. No bridge multipliers are needed, just rectify with a string of 500V rated 1/4W resistors for DC voltage feedback. PWM control is used to generate the reference voltage to regulate the HVDC output by modulating the primary bias current of a differential driver.

Regulation of drum voltages to 1% are possible with controlled ramp rates and outputs can swing from -5kV to 15kV with precise control.

 

[AAOAA]

Basically, The output voltage will be changed by duty cycle, anyway the project will run over a wide range of temperature, so any deviation in resonance frequency will drop the output voltage, what I am seeking here is a regulation of the output voltage, and specially locking the resonance frequency, since the resonance has the least power dissipation

I do not understand what you are doing. If you change the output voltage - how?

 

[chuckey]

" since the resonance has the least power dissipation ". So either you stabilise the resonance frequency by using capacitors whose temperature coefficients off set the transformer temperature coefficient. Or the better way is to use the resonance frequency of the transformer as the carrier frequency for your PWM. Which means generating the reset for a sawtooth generator. So a tiny capacitor from the output ( 1PF?) to another cap to earth (1000PF?) will give you and applying this to the base of a transistor should give you a sharp pulse.
Frank