I have changed out the old LM7805 regulator and replaced it with a mini360 buck converter. I solder the mini buck converter on my PCB and wire my components on the board.
My question is:
Do i need, or is it recomended to use an capacitor before or after the buck converter in a circuit?
Usually my input feed is 9V and output is between 3.3 to 5V. The load is arround 50mA to around 500mA. Mayby a little more, but not more than 1 amp.
There are two parts to this question.
For the capacitors at the converter you should consult the manufacturer datasheet. These usually contain recommended values/formulas or tables for external components needed to achieve a certain characteristic e.g. minimum ripple (which depends on your application). Have a look at a couple of datasheets from a good analog supplier like TI or IFX, they are quite informative with good explanations.
For the rest of your design you need to look at the requirements of the components and the connections between them. If your converter for instance is connected via a long wire the current is limited by that wire. So, if your component needs a fast rising current you might need add a capacitor after the wire close to your component. There are also recommendations for these bypass capacitors in datasheets.
In some cases you will see multiple capacitors with different values in parallel. The reason is that different capacitor materials have different frequency response. So, a larger but slower capacitor will provide the power needed for slower changes while a smaller, faster capacitor provides the power for faster changes.
If you have bought a board with a complete buck converter on it then I would expect the board to come with the correct capacitors fitted. However, there is no such thing as too much capacitance across a DC power supply, so if in doubt add some capacitors.
Actually there is such a thing as too much capacitance across a switch-mode supply output - this will
cause it to cutout immediately on power-up, and then continue to do so. Most switch mode chips monitor
for excessive current and protect themselves.
Go with what's provided, if you need less ripple use a subsequent linear regulator that's a volt or two lower.
MarkT:
Actually there is such a thing as too much capacitance across a switch-mode supply output - this will
cause it to cutout immediately on power-up, and then continue to do so. Most switch mode chips monitor
for excessive current and protect themselves.
Hmmm, makes sense. I've never had this problem.