DC/DC converter question

[mastevano]

Hi,

I have a question regarding the output voltage calculations of a DC to DC boost converter. I understand how to calcuate the output if the input is a pure DC signal.

In my application, I'll be using a diode bridge rectifier to convert my AC voltage to DC. This is the waveform that will be the input to my boost converter.

What input voltage should I use? Do I take the average or the rms of the signal after the bridge rectifier?

 

[VVV]

The control loop will adjust the duty-cycle for you and maintain the output voltage constant, so the output voltage will be set not by the input voltage but by the divider and reference. The duty-cycle will change according to the INSTANTANEOUS input voltage, keeping the output constant.
To get an idea of where the average duty-cycle will be, just use the average input voltage. The maximum duty-cycle will correspond to the minimum instantaneous voltage and the minimum duty-cycle will occur for the maximum instantaneous input.
But to calculate the transistor current always use the minimum instantaneous voltage, for a worst-case scenario.

 

[IanP]

I assume that you are using smoothing capacitor between the bridge and your boost converter, so your input unregulated voltage will be roughly 1.4 * AC (rms) voltage before the bridge, and that value (-x% ripple) you can use in transistor calculations ..
Regards,
IanP