Any improvements, pointers on this simple 5V supply ?

[splaz]

Well this is sort of mostly my own creation, probably just a "eh I could do that with my eyes closed, updside down underwater" sort of thing to most but I'm just proud I'm getting more to this stage. Mostly patched together from past knowledge, a datasheet and a bit of advice. This is meant for digital circuits.

Well basically my reasoning is D1 is for reverse polarity protection, not much of an issue in the application but I have done it before . D2 for back emf, C1 is the main filter cap, C2 is there for decoration. Can't remember, maybe filters off other freqencies or lower ESR or something someone smart mentioned

. C3 is for better transient response according to the datasheet.

Some of the values are a bit "invented". Just what I have on hand really. Just after any feedback, possible improvements, changes etc.

 

[FallenAngel]

Well, C1 is backwards, the 1F electrolytic would be ok.
C2 and C3 1.5 and 0.1 tantalums are ok as well.
You will need to heatsink the 7805 if you're pulling a lot of current though.

 

[splaz]

lol, thought it was right the first time.

Fixed.

Well going by what I have C2 would be a green cap and C3 a polyester box cap.

Any advantage/disadvantage to tantalum as I do have quite a lot 2.2uF lying around ?

I'm giving it a small heatsink as that's all there is space for.

 

[FallenAngel]

I would have actually used a film cap for C2 since it has low ESR and the 2.2uF tantalum after the regulator for filtering.

 

[jarthel]

film cap as C2. also have a read at the 7805 datasheet. there are lots of tips on how to improve PSRR.

 

[Clutz]

Just make sure you over-spec it for voltage. Apparently they can explode rather spectacularly.

 

[Garbz]

I recomend replacing the 7805 with its adjustable brother the lm317. They may look like they have identical specs but the design of the LM317 allows you to bypass the adjustment pin with a 10uf cap dropping the noise floor by a whoping 10-20dB. It will also allow you to make fine adjustments to the output voltage if need be.

 

[FallenAngel]

Wow, I never knew about that great advantage with the LM317! In that case, why not just build Tangent's great little TREAD? It'll only take a another 2 caps + 2 resistors.

 

[Garbz]

Well it wouldn't be designing your own circuit if you were building a tread. But granted it's an almost datasheet implimentation of what I'm talking about. If you must use a 3 terminal regulator the adjustables offer that advantage not only the LM317 but the LM337 and others do too.

Another neat trick is if you starground everything including the regulator at the device to be powered, i.e. run a ground cable from the filter cap to the opamp, and then BACK to the regulator, the regulator can compensate for the impedance of the power cables / traces. It also reduces noise slightly since the ground return current doesn't affect the reugulator's reference point anymore.

 

[splaz]

Well I'll keep that LM317 info in mind for future reference. I doubt I'll ever want to change this from 5V so that feature isn't necesary and I can't really be bothered going to go get a tiny quantity of extra parts just for that, seems like a waste of time imo as all I really want is a simple, stable and fairly clean voltage source for playing around with digital circuits.

Well the datasheet didn't contain much about PSRR to my eyes, although this was just a general 7314/78xxx datasheet.

Only other thing to add from that is a 0.33uF cap, which it said to add if more than 4 inches from input cap or no input cap. Any benefit to adding it anyway ?

Just going out on a limb here if yes is this anser. Film would be best... ?

As to the tantalum, yes over-speced on voltage, 35V is a pretty good ceiling if I do say so myself.

However, showing that I'm still not read to play with the big boys

, would you use it with the 0.1uF film cap or without ?

I'm guessing with, in which case, what side ? Between the regulator and 0.1uF cap or after both ?

 

[splaz]

Well I got impatient so heres my prediction based on the above questions I asked.

Might be going a bit overboard on caps but I have them lying around doing nothing and they are extremely easy to add as this is being built on stripboard so I just insert them in a row.

Not sure if there's any point to the 0.39uF cap, C3. C4 is where I think it goes.