I have some basic questions about 7805 based power supply circuits. The circuit design is very simple, and not terribly difficult to understand. Looking at the datasheets, there are decoupling capacitors on both the input and output side of the regulator...and that's about it. What I do not totally understand is how to select those capacitors, not the values but the type. In TI's data sheet, for example, they explicitly specify a 0.1uF ceramic capacitor should be used on the output. However for the input side they only specify that it should be .22uF, but not any particular type. I have also seen data sheets that do not specify the type to be used for either the input nor the output.
How do you determine the right type of capacitor for the application? Does it matter at all? I'm mostly confused by this because in photos of boards people have made I have seen electrolytic capacitors used almost universally and I assume there is a reason for this. Those types of caps are also used on the output which is the only place I have seen a datasheet specific specifically what type to use. Even then, they called for the use of a ceramic capacitor, so why does everyone seem to use an electrolytic?
I also have a question regarding the use of the protection diode called in the application notes. Again, it is not difficult to see how this works, but when to apply it is not obvious to me. They talk about usage in instances when the load on the other side is capacitive, but I'm not sure how to determine this. In my current application I'm looking at using the supply to drive a small MCU like an ATTiny85 and maybe a small two line LCD display. Is that a capacitive load? How do you determine this?
Full disclosure, if my questions seem exceedingly basic, I'm a software engineer by training and whatever EE material I learned is now 20 years old and unpracticed. I'm approaching this completely as a hobbyist at this point with maybe a slightly stronger background in some of the fundamentals
Thanks in advance.
How do you determine the right type of capacitor for the application? Does it matter at all? I'm mostly confused by this because in photos of boards people have made I have seen electrolytic capacitors used almost universally and I assume there is a reason for this. Those types of caps are also used on the output which is the only place I have seen a datasheet specific specifically what type to use. Even then, they called for the use of a ceramic capacitor, so why does everyone seem to use an electrolytic?
I also have a question regarding the use of the protection diode called in the application notes. Again, it is not difficult to see how this works, but when to apply it is not obvious to me. They talk about usage in instances when the load on the other side is capacitive, but I'm not sure how to determine this. In my current application I'm looking at using the supply to drive a small MCU like an ATTiny85 and maybe a small two line LCD display. Is that a capacitive load? How do you determine this?
Full disclosure, if my questions seem exceedingly basic, I'm a software engineer by training and whatever EE material I learned is now 20 years old and unpracticed. I'm approaching this completely as a hobbyist at this point with maybe a slightly stronger background in some of the fundamentals
Thanks in advance.