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LM2576 Voltage regulator

I've looked at the LM317 linear voltage regulator in this blog, but at the same time wondered about the efficiency and ease of use of a switching voltage regulator. The linear regulator has the most stable output, but the switching regulator is the most efficient. When I eventually get around to building a power supply unit, I am thinking that a combination of the two makes the most sense.

For example you could bring the voltage down from something like a laptop power supply (31V DC) to just a couple of volts above the required voltage, and then regulate the final target with a linear regulator to the required (smooth) output.

Most switching regulators that I have purchased seemed to be based on the LM2576 IC - a strange looking 5 legged beast that arrived awhile back, but hasn't been pressed into service yet...until now.

The LM2576 IC is "monolithic" which means to say the internal structure has a circuit which has most of the components so very few external components are required to make the circuit work as intended.

Block diagram of the IC from the datasheet

The datasheet and many online resources suggest the following circuit:

So with that in mind I wired up a prototype for testing. It was also an opportunity to test some simple voltage indicators that I had purchased which will hopefully be used in the final PSU design (e.g. monitoring the output of the switching and linear regulators).

I didn't have any 2000uF capacitors in a suitable voltage (e.g. 25V or greater - but now I have ordered 50V 2200uF), so I paralleled a couple of 1000uF units instead (note that paralleled capacitors add capacitance, the opposite of resistor addition).

I also could not fit the 1N5822 into the holes of the breadboard (!), so I used a 1N5819 Schottky diode which should be good to 40V and 1A, as opposed to the 40V 3A recommended.

It works great! Now I just need to put it onto a PCB and wrap it up in a suitable box.