Hi there,
I have purchased a Pololu step down regulator (D36V6F5) to be part of a circuit to convert a 24VAC power supply to 5VDC (I am building a watering controller that needs 24VAC to switch the solenoid and uses 5VDC to power an ESP32 for the smarts). I need to determine the specification for a bridge rectifier to go in front of it and was hoping for some advice on maximum input ripple voltage and therefore capacitor values.
On the face of it, I could have a ripple voltage of around 27V (a high of say 32V after diode voltage loss, to a low of 5.2V) and keep within the design boundaries of the buck converter (so a 50V capacitor of around 370uF – assuming regulator efficiency of 70%, an average input current of around 0.5A, and a mains frequency of 50 Hz (Australia)). However, I can’t help but think that it may not be able to cope with that level of ripple or have inherent inefficiencies. Alternatively, I could put a bigger capacitor on the front and keep ripple to a minimum, but this may be overkill, depending on the design of the buck converter (so a 1,300uF capacitor by my dodgy calcs would keep ripple to 1V).
Any advice on where the sweet spot for input ripple voltage from someone who has some knowledge of the D36V6F5 design (and probably much better electronics knowledge than me!) would be most appreciated. I also assume that I don’t need to add a small ceramic to high frequency smoothing as that would be in the regulator already, but please correct me if I’m wrong.
Thanks,
Ed