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Detecting the resonant frequency of a LC circuit?


AnD
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Hi everyone!
I need your helps .
I have a project of induction heating. And I want to detect or sensing the resonant frequency of a LC circuit. This LC circuit is configurated as a parallel resonant, it includes two branks: one is L and other is C and they is parallel.
I have an idea is: using a phase dectector or phase comparator to determine the order of phase/frequency of the current signal and the voltage signal of the circuit.
Then I get a error signal of phase to put it to a PI regulator. The regulating voltage of the regulator is used as a input of VCO (Voltage Controlled Oscillator) and regulated the output frequency (fosc). The fosc is used to switchs two MOSFET transistor that is configulated of Half-Bridge form. And the frequency of current and voltage of LC circuit is controlled until achieve the resonant frequency of circuit.
I want to know this method is right? And are there the other methods?
Help me!
Thank you very much!

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Like a Phase Locked Loop chip?

http://www.uoguelph.ca/~antoon/gadgets/pll/pll.html

;D

Thank for your reply!
I think that it is similar that, but phase of the voltage signal as a reference signal and phase of the current signal is a other input of PLL. In my project, I need to lock of phase between two signals - one is voltage and other is current.  Note that: the voltage is total voltage of LC circuit and the current is total current of LC circuit.
Thank you again!
Best regard.
A&D-HUT (AutoLab - Hanoi University of Techonology - Vietnam).
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Hi AnD,
You can use a CD4046 or 74HC4046 as a phase locked loop and it will give frequency control and indication of when the LC circuit's total voltage and total current are in phase by using the IC's phase detector II. The phase of the current is sensed by a low value resustor in series with the LC circuit and its AC volatge that corresponds to the current can be amplified if it is too small for the phase detector.

What frequency?
The ICs above have max operating frequencies of about 1.8MHz and 18MHz. ;D

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Hi AnD,
You can use a CD4046 or 74HC4046 as a phase locked loop and it will give frequency control and indication of when the LC circuit's total voltage and total current are in phase by using the IC's phase detector II. The phase of the current is sensed by a low value resustor in series with the LC circuit and its AC volatge that corresponds to the current can be amplified if it is too small for the phase detector.

What frequency?
The ICs above have max operating frequencies of about 1.8MHz and 18MHz. ;D


Thanks audioguru!
Your solution is great! I think so. If using the CD4046's phase detector II, we can lock up phase of two signal at 0 degree, and at the same time, the operating frequency of VCO is similar to the resonant frequency of LC circuit.  I need lock up at range of frequency of about 100kHz, is it OK?
Best regard.
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