I need advice, selecting a capacitor to protect the StepDown voltage regulator "Pololu 5V, 600mA Step-Down Voltage Regulator D36V6F5.
I’m going to run some 5V electronics at a 24V source.
I chose D36V6F5 for regulate voltage.
I want to protect the D36V6F5 against the voltage peek at switching on the DC 24V power.
What are the requirements for the capacitor (voltage, capacity)?
HI.
For the capacitor, between 33-100uF and rated for at least 50V should be fine. Your email to us also asked about adding a diode between your supply and regulator. That is generally not needed; is there a specific reason you want to add it?
-Claire
Thank You for the recommendation of a capacity. Is the 50V required, for You expect such high peak voltage or is it just because not going below the limit accepted for the D36V6F5?
The diode is wanted to protect the regulator against wrong polarity external 24V power; a multiple people will use it in different arangements and in case someone makes a mistake attaching the assembly.
Using 50V is to get a nice margin above your 24V supply. If your supply is not very noisy and you have no other reason to expect spikes, you could probably get away with a 35V electrolytic capacitor, though I don’t expect them to be much cheaper or smaller.
Using a diode between your supply and the input of the regulator can protect against reverse polarity and should not be too wasteful for low current draws. I recommend getting a diode with as low a forward voltage drop as possible (generally a Schottky diode) and making sure it can handle the current draw you expect.
-Claire
Thank, You @Claire 
Regarding selection of a Shottky diode:
The expected current taken from the regulator at the 5V lower side will not be much above 0.1 Amp. So due to the high efficiency of the regulator, I presume the current of the external power at 24V will be appoximately also circa 0.1Amp.
Was my assumption for the selection of the Schottky diode correct ?
You can use the formula P_{out} = P_{in} × eff to calculate the maximum input current. Since the regulator is a step-down though, it will be lower than the output current, so 0.1A should be enough. The specifications you listed sound reasonable.
-Claire
