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How much capacity for these regulators ?

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JanJansen:
Hi, my project have a 9 volt wall adapter input, then a 5 volt regulator ( 7805 ), then a LDO 3,3v regulator ( LD33V ),
the 3,3v section takes 100mA, on the 5 volt and 9 volt there is almost no difference, most power goes to the 3,3v regulator.

What capacitance would you use for the 9 volt wall adapter in, and then for the 5 volt out, and for the 3,3v out ?, does it all need the same value ?
Ofcourse i have extra 100n & 330n ceramics as needed.

thank you

nctnico:
Regarding the LDO it would be careful. Some need capacitors with a minimal ESR value and ceramics may have an ESR which is too low so the LDO will start to oscillate. An easy fix is to use a small resistor like 0.47 Ohm in series with a several uF ceramic capacitor.

JanJansen:
That is a half ohm ?, i do have 1 ohm resistors.
So from the 5v to the LDO a 1 ohm resistor and a big ceramic, not the regular 100n as in the datasheet ?

capt bullshot:
Look up the datasheet for the LD33 which output capacitor to use. Sometimes these are critical, I guess a 10uF tantalum will work fine.
For the 7805's output capacitor, nearly anything will do the job. I'd suppose a 10uF electrolytic, or if space is at a premium a 100n ceramic. This also acts as the input cap for the LD33, but in general the input capacitor isn't critical.
For the 9V input, I'd use an electrolytic in the 10uF ... 100uF range.

chemelec:
Why use a LDR Regulator from the 5 volts?
If you need both voltages, Just use a 5 Volt and 3V3 one, Both connected to the 9 Volt battery.

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