Hi,
I am powering a load that consumes about 200mA most of the time but needs short 0.5ms bursts of 2A current at 4V sometimes. I am suing LM2596 module to power the load and 4700uF to take care of the bursts.
Is it ok to connect 4700uF cap on the output of LM2596?
The reason for this question is that many DC/DC onverrtors dont like large capacitances.
Thanks and Regards,
WI
wonderfuliot:
Hi,I am powering a load that consumes about 200mA most of the time but needs short 0.5ms bursts of 2A current at 4V sometimes. I am suing LM2596 module to power the load and 4700uF to take care of the bursts.
Is it ok to connect 4700uF cap on the output of LM2596?
The reason for this question is that many DC/DC onverrtors dont like large capacitances.
Thanks and Regards,
WI
Do you understand why the converters don't like large capacitors? It's because, until the capacitor is 75% charged, it is a short circuit to the converter.
When your short burst, what ever that is, takes place, it discharges the capacitor, which then returns to being a temporary short circuit to the converter.
So, answer your own question. Do you think it would be a good idea to place a large capacitor on the output of a DC/DC converter?
Get a suitable power supply for your project.
Paul
You could put a current limiting resistor between the output of the converter and the capacitor. Chose a resistor that suits the maximum output current assuming a short-circuit presented by the capacitor.
However I believe that module can supply 3A output so, if your peak load is only 2A what's the problem with a direct connection.
Paul_KD7HB:
Get a suitable power supply for your project.
The reference design for the load suggests a DC/DC to convert to a suitable lower voltage and then an LDO right before the load. The high value cap is an attempt to omit the LDO.
jackrae:
You could put a current limiting resistor between the output of the converter and the capacitor. Chose a resistor that suits the maximum output current assuming a short-circuit presented by the capacitor.However I believe that module can supply 3A output so, if your peak load is only 2A what's the problem with a direct connection.
As told above the load needs a better supply stability than what the 2596 can provide hence the extra 4700uF cap.
I like your idea of resistor and theoretically a mere 2.5ohm resistor seems fine, however, do you think an LC would be better instead of RC? And, if yes, then how do I size the values of LC?
To size both L and C for your transient in-rush load you need to exercise some degree of care since you may inadvertently set up instability and overload due to 'ringing' of the LC network. Considering you only want to block the charge in-rush current then a resistor is probably your best (and simplest) option. 4700uF isn't a particularly high value of capacitor and you may well get away with no resistor at all. For it to provide a fast dump into the load you also need to ensure it is of a low ESR (Equivalent Series Resistance) type.
Why not take the 'try it and see' approach rather than anticipating problems that may not exist.
At worst you might only release the magic smoke.
Here's a link to the data sheet http://www.ti.com/lit/ds/symlink/lm2596.pdf
As asked above, what is the problem that the capacitor is supposed to solve, since the LM2596 can supply 3A?
As told above the load needs a better supply stability than what the 2596 can provide hence the extra 4700uF cap.
Post a link to this dubious claim, and the reasoning for using 4700 uF.
are you making supplying power to sim 800 gsm module ??