Trying to figure out the MC34063A buck converter

[Donuts and coffee]

I've been studying the Ti datasheet for the MC34063AP. I want to make a little adapter to go from 12 VDC in to 5 VDC out. On page 15 in the datasheet, they have an example circuit with 25 V in, with 5 V 500mA out.

First question is: will that same example circuit be ok for 12 V_in also? I don't know if it's similar to the 7805 in this regard, in that it doesn't care what the input voltage is, it'll drop it down to 5 V. Or would I have to make a different circuit?

I'm also having trouble figuring out the parameters. Specifically, it says V_in, V_out, I_out, f_min, and V_ripple are set by the user. Second question: how do I know what f_min and V_ripple values to expect?

I do not want higher than 1.5 A output current, so the way I understand it is that I don't need an external switch. 1.5 A should be more than enough for my intended projects. Third question, how do I know what value of components to use? The example only outputs 500 mA.

I've been looking for articles that explain this stuff, and I've found a lot, but they didn't help me. Here's a picture of pages 15 and 16 from the datasheet.

If anyone can help me understand this, I'd appreciate it. Thanks!

 

[KJ6EAD]

The MC34063A is fairly ubiquitous in cheap car USB power supplies so if you just want one that works, there you go. I have it on good authority that this IC is not as efficient as some later models. There have been many prior threads discussing it. Please review them then come back.

https://www.electronicspoint.com/search/15260907/?q=mc34063a&o=date

 

[Donuts and coffee]

The MC34063A is fairly ubiquitous in cheap car USB power supplies so if you just want one that works, there you go. I have it on good authority that this IC is not as efficient as some later models. There have been many prior threads discussing it. Please review them then come back.

https://www.electronicspoint.com/search/15260907/?q=mc34063a&o=date

That's crazy, I searched specifically for MC34063A, as well as MC33063A, and both times the results came up empty.

Thanks for the link

Edit: I see what happened now. I overlooked the "Search in this forum only" checkbox and left it checked. And I correct myself, there was one result for MC34063A with it checked.

 

[kellys_eye]

Plenty of design tools out there if you Google them. Plug in your requirements, out comes the component values! Here's one example.....

http://www.nomad.ee/micros/mc34063a/

 

[Donuts and coffee]

Thanks, kellys_eye . I had found that and played with it, but I still don't know what f_min and V_ripple should be. The datasheet says I should decide what they should be. Sure, it would be convenient to just get this set up and then use it, but I also want to understand this and learn about it. So far, I still haven't found an article that answers my questions.

Edit: I am not as good with analog as I am with digital, because of my computer background, but I would like to improve my skills. I'm open to a solid book recommendation about making reliable, efficient power supplies. I am also finding that there are more efficient chips than the MC34063A. It turns out that I had forgotten that I have a SMD TI 54331. However, I would still like to try out this MC34063A, since it's a DIP that I can quickly and easily try in a DIP-8 socket. I will take the 54331 for a test drive later.

 

[kellys_eye]

f_min is the minimum frequency at which the switching happens and is a compromise between efficiency and inductor design - higher power levels require greater cross-sectional area wire on the inductor which itself limits (potentially) the number of turns you can get on a given ferrite core.

You can get tables that show inductance versus wire guage versus number of turns etc from the micrometals website - using the TO-x range of toroidal inductors can simplify component sourcing and ensure an accurate value component.

V_ripple is just the acceptable amount your circuit (being supplied by the MC34063) can 'work with' - a figure of 10mV would be acceptable for most circuits and is basically set by the filter capacitor at the output - more capacitance = less ripple (at a given current flow).