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3.3V 300mA power supply

Posted by: enkavak on 07/16/2009


Is it possible to remove the inductor and one of the capacitors at the input of the circuit and adding only a bridge to the input? What should be Cin capacitor value for the new circuit.

3.3V 300mA will be the specs.


Submitted by Paul Lacey on 07/16/2009


Yes, it is possible to replace the half-wave rectifier with a full-wave bridge. This will allow you to use a smaller input capacitor to maintain the same minimum DC Bus voltage. Our software tool PIxls will assist you in calculating the new capacitor value needed to maintain the same minimum DC Bus voltage as seen in your original design. The PI Expert design software can be downloaded here:

Please note that Cin1, Lin1 and Cin2 provide an input pi filter to suppress differential mode EMI. Removing this filter will most likely require you to compensate the design by adding a different form a EMI filtering. (Such as an x-capacitor across the AC input terminals, an input common mode choke, a series input inductor, etc.) Also don't forget to include a fuse or fuseable resistor in your final design for increased safety.

Submitted by enkavak on 07/17/2009


Then, I'll not remove the L(in) inductor. However there is no exact value give for the L(in). There is a range 0.05A-0.3A for the inductor. How will I choose it considering the output current.

Besides, I tried to use PIExpert for the design but there is no output capacitor value in the spread sheet output. What will the value of the output capacitor?

I'll use a Full-wave brige at the input. and I changed the output specs to 4.5V and 300mA

Submitted by enkavak on 07/17/2009


In addition to e-mail above, Is a must to use an electrolitic capacitor at the input. Could it be a Metallized polyester film capacitors like the attached file or any other ?