Hi there!
I´m facing the following problem: I have dozens of Panasonic FC 680µF/16V.... Tested them in my PC-Soundcard(12V/-12V filtering, after regulators at the DAC(WM8770) and at the opamp´s) With them I got really fantastic results with the "unreal" RMAA-test...
I don´t give much about this test (SNR improved by 4dB?? THD+N also...) BUT: It also does sound fantastic!
So, the Problem: you know, all datasheets tell us to use "small" caps after regulator, ~<10µF, to keep the dynamic stabilisation...
Do you think there´s a problem when putting them after regulators (7812/7912/TL413)
I plan to build another TDA1541A DAC with plenty of them, as I have them
My approach is: [100nF 0812] || [680µF FC] at all decoupling points.... and ~10 of them paralleled at every rail in the PSU
P.S.: Are they better than OS-CON in analog systems? OS-CON´s made the sound really harsh...
Regards,
max weissi
I´m facing the following problem: I have dozens of Panasonic FC 680µF/16V.... Tested them in my PC-Soundcard(12V/-12V filtering, after regulators at the DAC(WM8770) and at the opamp´s) With them I got really fantastic results with the "unreal" RMAA-test...
I don´t give much about this test (SNR improved by 4dB?? THD+N also...) BUT: It also does sound fantastic!
So, the Problem: you know, all datasheets tell us to use "small" caps after regulator, ~<10µF, to keep the dynamic stabilisation...
Do you think there´s a problem when putting them after regulators (7812/7912/TL413)
I plan to build another TDA1541A DAC with plenty of them, as I have them
My approach is: [100nF 0812] || [680µF FC] at all decoupling points.... and ~10 of them paralleled at every rail in the PSUP.S.: Are they better than OS-CON in analog systems? OS-CON´s made the sound really harsh...
Regards,
max weissi
I read some app´notes from ONsemi.....
So, it primary depends on the output stage of the regulator... In the case of 78xx, and 317 it´s a NPN transistor that should be unconditionaly stable - no matter what type of cap is used....
LDO´s require more investigation for choosing the right capacitor, because they typicaly work in a more unstable area of the output stage (therefore typical a PNP).
So, it primary depends on the output stage of the regulator... In the case of 78xx, and 317 it´s a NPN transistor that should be unconditionaly stable - no matter what type of cap is used....
LDO´s require more investigation for choosing the right capacitor, because they typicaly work in a more unstable area of the output stage (therefore typical a PNP).
Caps on Regulator Output
The regulaors don't like to see a lot of capacitance on their outputs or they can oscillate because of the inductance of their outputs. You can put a small value resistor, like 1 ohm (how much current is flowing?) between the regulator output and a giant cap and you won't have any problems.
The regulaors don't like to see a lot of capacitance on their outputs or they can oscillate because of the inductance of their outputs. You can put a small value resistor, like 1 ohm (how much current is flowing?) between the regulator output and a giant cap and you won't have any problems.
All of those 3-terminal jobs have a feedback loop, and just throwing any old cap......especially with low ESR is asking for problems. It affects phase margin, and can easily make an oscillator. As you have found out.
Those of you with access to a spectrum analyzer.....here's what you do.
Look at the noise vs frequency with several different value and types of caps. You will see how the noise will peak at some frequency if you pick the wrong one.
If you don' t have an analyzer, but do have a 'scope and a square wave source.............drive the output with the square wave, and see if it rings. If it rings a lot, you have stabilty problems
Jocko
Those of you with access to a spectrum analyzer.....here's what you do.
Look at the noise vs frequency with several different value and types of caps. You will see how the noise will peak at some frequency if you pick the wrong one.
If you don' t have an analyzer, but do have a 'scope and a square wave source.............drive the output with the square wave, and see if it rings. If it rings a lot, you have stabilty problems
Jocko
Well, I do have access to something that has a FFT function... But it might bre that it hasn´t enough bandwith for really serious measurements....
http://www.rapid-tech.com.au/dl708e.htm
But that thing looks quite prominent to someone (actually, this was one of a reason why I choosed my actual occupation, hehe, beside the metcal´s and the microscopes for soldering SMD...)
http://www.rapid-tech.com.au/dl708e.htm
But that thing looks quite prominent to someone (actually, this was one of a reason why I choosed my actual occupation, hehe, beside the metcal´s and the microscopes for soldering SMD...)
So what values are we talking here? Is a low esr 1000uf Not a good thing behind a regulator? Or are even smaller values causing trouble?
I have build my ps, for my cd pro2 mechanism, using this schematic, using lm317t`s for regulators.
I don`t have acces to a scope, so I have to just build it correct, if anyone have advise on the caps behind the regulator, plz share it!
I have build my ps, for my cd pro2 mechanism, using this schematic, using lm317t`s for regulators.
I don`t have acces to a scope, so I have to just build it correct, if anyone have advise on the caps behind the regulator, plz share it!
Hi!
I refered to a size of ~680µF, no big difference to 1000µ as this values *are* much higher than suggested in datasheets....
As much as I can say this time, standard regulator should not face any troubles with that high values, in terms of oscillation....
For some app´s and under certain conditions, the power-on delay time might be to long....
As sayed before, this does not apply to LDO´s, they are (as far as I know now...) more sensitive for output capacitance....
But I don´t use LDO´s, so why should I care....
Also, be sure that the input voltage is in any circumstance higher than the output voltage (in the case you power down) as regulators don´t like that *g* - a 1N4001 helps... see the datasheets...
I refered to a size of ~680µF, no big difference to 1000µ as this values *are* much higher than suggested in datasheets....
As much as I can say this time, standard regulator should not face any troubles with that high values, in terms of oscillation....
For some app´s and under certain conditions, the power-on delay time might be to long....
As sayed before, this does not apply to LDO´s, they are (as far as I know now...) more sensitive for output capacitance....
But I don´t use LDO´s, so why should I care....
Also, be sure that the input voltage is in any circumstance higher than the output voltage (in the case you power down) as regulators don´t like that *g* - a 1N4001 helps... see the datasheets...
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