Voltage regulator 7905 capacitors.

[Rajinder]

Hi,
I am using 7905 regulator and would like to ask the capacitors that are required. The data sheet says 0.33uF across input and 100nF across the output.
I have seen 10uF across input and output too.
My question is should the 10uF be electrolytic, tantalum or ceramic. Low ESR type?
I would like to justify my selection. So would appreciate help.
Best regards,
Rajinder

 

[shrtrnd]

What is the application?
Typically voltage regulator circuits are non-critical and electrolytics are fine.
Your circuit determines the need for specialized composition capacitors.
Are you working at high frequency, high temperature, or other specialized applications?

 

[Arouse1973]

Most modern regulators can run just fine without capacitors on the output. If you do put one on the output try not to use too high a value and not low ESR types like Tants and ceramics. These can cause the regulator to oscillate, if you have to use low ESR caps then a small value series resistor can be used to prevent oscillations.
Edit. Its important to choose the right capacitor for the regulator.

Thanks
Adam

 

[Rajinder]

Most modern regulators can run just fine without capacitors on the output. If you do put one on the output try not to use too high a value and not low ESR types like Tants and ceramics. These can cause the regulator to oscillate, if you have to use low ESR caps then a small value series resistor can be used to prevent oscillations.

Thanks
Adam

Hi Adam,
Thanks for your reply. I always have been told that 10uF + 100nF at the input, the 10uF should be low ESR. The same at the output. Alot of engineers have told me to use tantalum and not aluminium capacitors for the 10uF.
I am not sure 100%, so need to really understand why we select one and not the other.
I would be grateful if you could explain in a bit more detail please. Especially why low ESR is not recommended for the output cap.
Best regards,
Rajinder

 

[Arouse1973]

I have seen myself a standard 7805 produce a nice saw tooth waveform with a Tant on the output. The purpose of the capacitor to allow the error amplifer to react to transients. But you cause a transient yourself by having too large a capacitor on the output. LDO regulators however are different and need lowish ESR, but not ceramic capacitors. The reason is the 78 and 79 series have npn transistors as the output transistors and can operate with no output capacitor.
Adam