Hi Everybody I am using the uPSD of ST. It is a new controller with core of the Intel 8032. Does anyone know how the PWM port gives a linear output? The PWM port is connected to RC network and the capacitor is not a linear device. Thanks Kobi
Assume you are talking about smooth output. If there is no load no capasitor is required. The higher is load the bigger capasitor you need.
I am not a hardware engineer, but I will have a go at answering you question anyway. The RC network is a low-pass filter and it will convert a PWM ratio to a voltage. You need to match the charactersitics of the low-pass filter to the characteristics of the PWM. Essentially, provided the time constant of the RC filter is very large compared with the period of the PWM, all be well. The smaller the RC time constant, the more PWM ripple will get through to the output. If the PWM ratio changes only slightly, then you will be working on a small part of the C's charge/discharge curve and the response will be approximatly linear. However, that is probably not what you want. If the PWM ratio changes very slowly compared with the RC time constant, all will be well. If the PWM ratio changes quickly, the response of the low-pass filter will be non-linear. You can fix this either by using some sort of feedback or by calculating the PWM ratio required for the required response - tricky but it works.