Frequency of ZVS driver changes through a transformer in LTspice

Thread Starter

icantalktosneks

Joined Apr 23, 2021
25
I was simulating a ZVS driver in LTspice and in the first picture, the frequency is around 80kHz, which can also be calculated by the formula for resonant frequency.
In the second picture, the frequency changes to around 56kHz, even though all i added was the secondary coil for the transformer?
Am i missing something in LTspice, or is my theory wrong?
 

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Thread Starter

icantalktosneks

Joined Apr 23, 2021
25

ronsimpson

Joined Oct 7, 2019
1,475
even though all i added was the secondary coil for the transformer?
You changed more that adding a secondary.
Circuit 1, has L1 and L2 as independent coils.
Circuit 2, has L1 and L2 as a transformer. "K L1 L2 L4 1"
I think the "L4" is not the change you see but "K L1 L2 1" is the change you see.

RonS.
 

ericgibbs

Joined Jan 29, 2010
13,659
hi ican,
The circuit is a self oscillating cross coupled circuit, any changes in L1 and L2 , also L4 values and the overall coupling Constant 'M' will effect and change the frequency of the oscillator.
Also the Load will effect the osc frequency.

L1 & L2 form part of the setting of the time constant [ freq] of the oscillator.
E
 

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Thread Starter

icantalktosneks

Joined Apr 23, 2021
25
hi ican,
The circuit is a self oscillating cross coupled circuit, any changes in L1 and L2 , also L4 values and the overall coupling Constant 'M' will effect and change the frequency of the oscillator.
Also the Load will effect the osc frequency.

L1 & L2 form part of the setting of the time constant [ freq] of the oscillator.
E
Just to be clear, in an actual circuit with a transformer with a center-tapped primary coil, can the frequency of the output voltage at the secondary coil be calculated by the following formula?
1619515210082.png
With L representing the inductance of the primary coil and C representing the capacitance in parallel with the primary coil
 

ericgibbs

Joined Jan 29, 2010
13,659
hi,
Yes, the formula applies, providing that you know the inductances etc, is for fixed inductance & load condition.

What operating frequency do you calculate for just L1 and L2, no L4 secondary.??
Assuming a K coupling factor for L1 and L2 as 1.
E

Update:
Looking at your latest L1/L2 , you are showing no coupling between L1 and L2, how can that be possible if they are wound on the same former.?
That is why you measure around 80kHz
With K = 1 the freq is 56kHz.
 
Last edited:

Thread Starter

icantalktosneks

Joined Apr 23, 2021
25
hi,
Yes, the formula applies, providing that you know the inductances etc, is for fixed inductance & load condition.

What operating frequency do you calculate for just L1 and L2, no L4 secondary.??
Assuming a K coupling factor for L1 and L2 as 1.
E

Update:
Looking at your latest L1/L2 , you are showing no coupling between L1 and L2, how can that be possible if they are wound on the same former.?
That is why you measure around 80kHz
With K = 1 the freq is 56kHz.
Ah i see, ok thank you so much once again
 

Thread Starter

icantalktosneks

Joined Apr 23, 2021
25
hi,
Yes, the formula applies, providing that you know the inductances etc, is for fixed inductance & load condition.

What operating frequency do you calculate for just L1 and L2, no L4 secondary.??
Assuming a K coupling factor for L1 and L2 as 1.
E

Update:
Looking at your latest L1/L2 , you are showing no coupling between L1 and L2, how can that be possible if they are wound on the same former.?
That is why you measure around 80kHz
With K = 1 the freq is 56kHz.
Wait is the spice directive of "K L1 L2 L4 1" correct?
And if how is the value of 56kHz found, specifically, what would the value of L be?
 

Thread Starter

icantalktosneks

Joined Apr 23, 2021
25
hi,
Yes about the extra 4uH.
What are you planning to use the project for.?

E
I am trying to make an EMP generator, and i need a high voltage converter, hence the ZVS driver to step up the voltage from a DC power supply. A spark gap will be placed between its output and a coil to generate the EMP
 
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