Generating two frequencies using a voltage controlled oscillator

Thread Starter

SiCEngineer

Joined May 22, 2019
220
I am trying to use PLECS to generate one of two switching frequencies using a voltage controlled oscillator and an external control signal which has values of 0 or 1. When the signal is 0, I want to generate a low frequency, and when the signal rises to 1 I want to generate a higher frequency.

In an implementation in PLECS (shown) I generate the low frequency fine, but don't understand how I can generate the high frequency. This is because even when the control input changes from 0 to 1 the frequency of the carrier stays at the low frequency and does not change.

Any advice appreciated on how to do this. Waveforms are also attached which show the issue. It makes sense to me that when the signal is 0, the low frequency should be output, and when a 1 the higher frequency. However I think I misunderstand how the VCO is working (?)
 

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Thread Starter

SiCEngineer

Joined May 22, 2019
220
EDIT: I have figured out how to do it in PLECS. However if anyone has any advice on how I could implement such a switching frequency control in practice that would also be appreciated.
 

AnalogKid

Joined Aug 1, 2013
8,534
What are the two frequencies? There are many different ways to do what you have described so far. Rather than have us waste our time suggesting things that will not work well in your application, please give us a more complete picture of the requirements.

For example - if the two frequencies are harmonically related, such as 1 kHz and 10 kHz, then a single oscillator and some digital circuits will work. If the two freqs are 50 MHz and 60 MHz, then something else is needed.

ak
 

Thread Starter

SiCEngineer

Joined May 22, 2019
220
What are the two frequencies? There are many different ways to do what you have described so far. Rather than have us waste our time suggesting things that will not work well in your application, please give us a more complete picture of the requirements.

For example - if the two frequencies are harmonically related, such as 1 kHz and 10 kHz, then a single oscillator and some digital circuits will work. If the two freqs are 50 MHz and 60 MHz, then something else is needed.

ak
A very good point AK, thank you. Well, it is for a resonant converter. I am unsure of the maximum and minimum frequencies yet, but for example it could be 100kHz and 500kHz, or something like this. Although it could also be 120kHz, and 655kHz... it depends on the resonant tank and which frequencies deliver the correct amount of power needed.

I would be interested to hear your suggestions.
 
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