LM2917-N: LM2917MX-8/NOPB

Hi Santhosh,

Santhosh Poojary said:

Whether can we make use of LM2917MX-8/NOPB for the application of PWM signal (where Duty cycle will be varying) to voltage conversion?

The LM2917 is a frequency to voltage converter (Vout ∝ fin) which it does not do PWM to voltage converter. 

I think that you want to do PWM signal to voltage converter. 

For fixed Duty of PWM signal, this is fairly straight forward, where Vout = Duty * Vin (amplitude of PWM) --> Use RC filter.  

For variable duty PWM signal, this is a bit tricky, which it depends what you want. You can accomplish with the following technique:

1. Use RC filter, but this is a rough average technique.

2. User integrator to calculate average voltage for any given time. This method gives you precise average, but you need to reset the integrator periodically (try to avoid the op amp saturation), and you would need to have know PWM frequency or duty cycle figure. 

The third way is to integrate the PWM input numerically. 

Please let us know what you are trying to do. There are pros and cons in each methods. RC LPF will be the easiest method, but errors may be large depending on how you configure your filter.  

Best,

Raymond

Hi Raymond,

Thanks for the valuable Suggestions. 

I'm looking for the variable duty cycle PWM (where frequency will be constant but On and Off time will be varying in nature and signal Amplitude is also constant) to Voltage conversion. So could you please suggest any simple IC/solution which can support for this application.

Thanks & Regards,

Santhosh