Complementary Variable PWM in LTSpice - Help Needed

Thread Starter

mishra87

Joined Jan 17, 2016
1,034
Hi there,

I am trying to generate the variable PWM in ltspice to drive the two complementary mosfet. By modulating the duty cycle i want to change the output of the converter. My maximum duty cycle is 50%. I want to modulate the duty from e.g. 10% to 50% in ltspice.
I am trying to do it in ltspice but somehow i could not figure out.
Looking for your support guys !
Thanks for help in Advance !
1700135477243.png
1700135495065.png
 

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Thread Starter

mishra87

Joined Jan 17, 2016
1,034
Hi @all
Is there any way to increase the duty here with this approach.
Lets say start with 10% duty and then increase the duty to 50%.
thanks !
1700151269335.png
 

Alec_t

Joined Sep 17, 2013
14,219
Is there any way to increase the duty here with this approach.
You could use the .step d directive to give a series of sims for respective duty cycles.
Params for your pulse sources are evaluated before each sim runs.
If you want to change duty on the fly in one sim you could use behavioral voltage sources.
 

Papabravo

Joined Feb 24, 2006
20,995
Hi...This 1V is not enough to drive the mosfet.
Thanks !
The basic logic elements in LTspice operate with levels from 0 volts to 1 volt. Since this is simulation, you can easily add a gain stage with a behavioral source. I'm surprised that you lack the insight to realize this.
 

Thread Starter

mishra87

Joined Jan 17, 2016
1,034
You could use the .step d directive to give a series of sims for respective duty cycles.
Params for your pulse sources are evaluated before each sim runs.
If you want to change duty on the fly in one sim you could use behavioral voltage sources.
Thanks,
I tried by using .Step param...it changes. ..
I will try behavioral voltage source.

@Papabravo shown here some solutions but somehow I was not able to run it.

We need here some kind of mosfet gate driver for half bridge converter with variable duty e.g 0.1 to 0.5 to change the output voltage.

Hope problem statement is clear.
 

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Papabravo

Joined Feb 24, 2006
20,995
Thanks for sharing the files and your effort.
Somehow i am unable to extract and open the attached file.
There is something wrong with the files.
View attachment 307688

Regards
Here are the files in unencrypted form:

Since you may not have the LTspice Control Library you need to edit the symbol to eliminate the model file field. Then it will look for the explicit subcircuit detailed in the schematic file which you can uncomment and place in your test folder.
 

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Last edited:

eetech00

Joined Jun 8, 2013
3,820
Hi there,

I am trying to generate the variable PWM in ltspice to drive the two complementary mosfet. By modulating the duty cycle i want to change the output of the converter. My maximum duty cycle is 50%. I want to modulate the duty from e.g. 10% to 50% in ltspice.
I am trying to do it in ltspice but somehow i could not figure out.
Looking for your support guys !
Thanks for help in Advance !
View attachment 307680
View attachment 307681
Your circuit needs more than deadtime, it also needs a way to drive the gate of the high side mosfet above the its source voltage to fully turn on.
 

Papabravo

Joined Feb 24, 2006
20,995
Ultimately, your goal is to get something like this:
1700159940234.png
Is this correct?

Blow up view of the bottom plot:
1700160113308.png
Notice the plot of V(n1,n2) which shows the continuously changing duty cycle.
 

Papabravo

Joined Feb 24, 2006
20,995
Without more information I'm going to posit that the circuit given in post #8 does not seem to work very well. It does simulate but it is SLOW, and the output approaches the input voltage after some period of time. Maybe that is the intention.
 
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Papabravo

Joined Feb 24, 2006
20,995
After some additional research, I found the proper switching sequence which does not exactly involve deadtime between complementary signals, but a restriction on duty cycle that ensures that both switches are NOT on at the same time. I have no idea if the values I have chosen are appropriate for any purpose. The simulation is still slow, and I don't have the patience to discover if steady state operation is possible.

1700253163865.png

In the ideal case the output voltage would be:

\( V_o\;=\;V_i \left ( \cfrac{N_S}{N_P} \right)D\;=\;28\text{ Volts}(4.5)(.3)\;=37.8\text{ Volts} \)
 
Last edited:

Thread Starter

mishra87

Joined Jan 17, 2016
1,034
After some additional research, I found the proper switching sequence which does not exactly involve deadtime between complementary signals, but a restriction on duty cycle that ensures that both switches are NOT on at the same time. I have no idea if the values I have chosen are appropriate for any purpose. The simulation is still slow, and I don't have the patience to discover if steady state operation is possible.

View attachment 307825

In the ideal case the output voltage would be:

\( V_o\;=\;V_i \left ( \cfrac{N_S}{N_P} \right)D\;=\;28\text{ Volts}(4.5)(.3)\;=37.8\text{ Volts} \)
Hey,
thanks for you effort and sorry for restarting this thread again, due to some personal reason i could not continue with the thread.
Could you please share ltspice file of this along with sub circuit and assy file.
Thanks again !
 

Thread Starter

mishra87

Joined Jan 17, 2016
1,034
My input voltage is 400Vdc and i want to generate variable output 3V-8V @ 10A current.
Only way to get the variable output is to change the duty of the mosfet to modulate the output voltage.
Please use this circuit attached to add the gate driver.
Thanks in advance !
1702788165231.png
 

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