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inverter theory - how can I bring the inveter to resonance ?

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anotherbrick

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inverter theory - how can I bring the inverter to resonance ?

hello dear forum,

this below circuit is the schematic of an ultrasonic inverter

ultrasonic5.JPG

I want bring the circuit to resonance by playing with the value of inductance between output transformer and the piezo element

my question is ;

if I display the current and voltage at the 220 VAC input with the osciloscope - can I get an info if the circuit is at the resonance or capacitive or inductive behaviour ?

better said - if the circuit is capacitive or inductive for example would I see an out of phase scope display of input current and voltage ?

similarly , if the circuit is at the resonance is the line current and voltage in phase ?

thank you
 

Re: inverter theory - how can I bring the inverter to resonance ?

anotherbrick said:
can I get an info if the circuit is at the resonance or capacitive or inductive behaviour ?
Click to expand...

It's possible to do this, with the help of a sense resistor. That is how to detect the moment when current changes direction.

The sense resistor develops a voltage when current goes through it.
The op amp detects zero crossings. It detects the resonant frequency automatically, and drives the half-bridge at that frequency.



We might wonder if it works if we take voltage across the inductor or capacitor? However this does not give us switching signals at the correct point in the cycle.
 

The sense resistor could be in the ground side of the load (Tx) which would make it easier to use (the signal therefrom)...

- - - Updated - - -

For a set driving frequency, varying the o/p L will only get you so far, as, you need to match the effective load of the transducer (at full power) to the impedance of the circuit driving it, ideally aiming for a Q of about 2-3, i.e. the driving impedance being lower than the piezo load at full power, and still having inductive drive, i.e. operating just about true resonance, this gives best performance. Zo = SQRT(L/C) Z piezo needs to be ~2-3 times this to avoid too heavily loading the ckt.
 

Hi,

if I display the current and voltage at the 220 VAC input with the osciloscope - can I get an info if the circuit is at the resonance or capacitive or inductive behaviour ?
Click to expand...

No. Not at the 220V AC input side.

Klaus
 

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