12V to 5V voltage regulator - capacitors required

[DarkYendor]

For a DC-DC conversion, capacitors don't particularly matter. But for AC-DC regulators, the size of the input capacitor is quite significant, and will depend on the max current and delta between Vin and Vout.

Originally Posted by rainwulf

There are 3 pin switch mode regulators that are direct replacements for the 3 pin linear adapters.

Link please? AFAIK, switchmode regulators require big external caps, inductors, dioides and often mosfets - making them significantly more complex, expensive and bigger.

[RobRoySyd]

Originally Posted by DarkYendor

For a DC-DC conversion, capacitors don't particularly matter. But for AC-DC regulators, the size of the input capacitor is quite significant, and will depend on the max current and delta between Vin and Vout.

Why are we talking about AC>DC regulators, the devices in question don't include rectifiers and will probably get all smokey if fed AC. Of course if AC is being rectified then a significant capacitance is required for smoothing and the correct value for that is a separate issue to what the regulator IC(s) require.

With those linear regulators the output cap has a significant effect on stability and transient response. The value isn't critical but some huge electrolytic is going to be pointless and have too much series inductance to be effective. Whatever the manufacturer recommends and as close to the regulator as possible is all that is needed to keep the chip working as it should. Other small caps around the PCB may also help with noise and transient handling. A small cap on the input, again close to the IC may also be required. Both these components have nothing to do with other components that might be required for smoothing of the output of a rectifier.

[2xCPU]

Originally Posted by DarkYendor

Link please? AFAIK, switchmode regulators require big external caps, inductors, dioides and often mosfets - making them significantly more complex, expensive and bigger.

rainwulf was talking about a direct replacement. What he meant by this, is a three pin device that can directly replace a 78xx. Simple.

2.

[Goth]

Personally, I use (on most stuff I design, which is a custom PCB with SMD components) 100 nF ceramic on the input of a LD1117 (which is the most common LDO I use) and a 10 uF ceramic on the output.

I like 10uF 0805 MLCC surface mount ceramics, I use them all the time now as a cheap, non-polarised, compact alternative to tantalum or aluminium electrolytics. They have very low ESR, too.

[rainwulf]

haha, nice articles!!
i love this line:

Trashing the ceramic cap in favour for a big ugly and cheap 100uF elcap entirely cured the problem and left the supply stable and of relatively low noise.

its pretty well the application note for those 3 pin regs.
Short fat wires, smallish crappy caps, and they run like a charm haha

[rainwulf]

Originally Posted by Goth

Personally, I use (on most stuff I design, which is a custom PCB with SMD components) 100 nF ceramic on the input of a LD1117 (which is the most common LDO I use) and a 10 uF ceramic on the output.

I like 10uF 0805 MLCC surface mount ceramics, I use them all the time now as a cheap, non-polarised, compact alternative to tantalum or aluminium electrolytics. They have very low ESR, too.

Just check that low ESR is not actually bad!

[aXis]

Originally Posted by 2xCPU

rainwulf was talking about a direct replacement. What he meant by this, is a three pin device that can directly replace a 78xx. Simple.
2.

Wow! I'll be keeping an eye out for them in the future.

[RSDXzec]

Originally Posted by dakiller

Here are a few links to start you off

http://www.tnt-audio.com/clinica/reg...edance1_e.html
http://www.diyhifi.org/forums/viewtopic.php?f=15&t=471

It is hard to really remember the things that I've read in the past, it has been many years since I did and it all just blurs together across all the sources

that first link is very informative, still taking me a while to take it all in. Haven't looked much through the second one yet.