Capacitor of the lnk304 input is getting too hot
Hello,
I have used the LNK304 to make a small power 24V power supply from the 230VAC (European) grid.
I am using a small RF module (XBee) through a 3v3 linear regulator and the problem is that the electrolytic capacitor 4.7uF/400V that is in the entry of the LNK304 is too hot and there is no ventilation!
I believe that it is because of the RF current spikes that the module may be requesting.
The RF module is not that powerfull, so i think that the LNK304 circuit of the datasheet should be able to drive it.
Specs:
Supply Voltage 2.1 - 3.6VDC
Transmit Current 35 mA/45 mA boost mode @ 3.3VDC
Receive Current 38 mA / 40 mA boost mode @ 3.3VDC
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I tried to use the a full-wave rectifier instead of the half of the example of the datasheet to reduce the ripple but it is still very hot.
I tried to rise the 1mH inductor of the low-voltage side to 4, 5 and 6mH but it is still warm.
I can't make the capacitors bigger because of the space requirements.
Do you have any idea of how to solve the problem?
The original circuit i am using is attached to this post. I'm out of ideas now.
By the way. I need the 24V to drive some relays, but i am not using them right now and they will be turned on just for a few seconds, so i believe it will not be an issue.
Best regards,
Nuno
Comments
Hello,
I have measured the ripple in the capacitors and that is about 4V
But the capacitor i'm using can hold just some mA.
That may be the problem, but i dont know what kind of capacitor should i use then.
Does it have to withstand 4V of ripple??? It seems too much!
Thanks and regards.
Hi,
I am not sure what exactly is the cause of heating since the power level is quite low.
I suggest you try putting low ESR capacitors and verify performance. If this brings down the temperature of the capacitors, you will not need additional design changes.
Please note that 10 to 20 degree rise in capacitor temperature may not be objectionable unless it is a problem for meeting life time requirements.
Regards
PI-Sarek
I do not understand your issues with your RF module. By looking at your schematic, if input caps are getting hot is because: 1 they may be in reverse polarity. 2 The voltage applied to the caps is over the rated voltage of the capacitor. 3 The ripple current the capacitor in handling exceeds its specs. May be your situation is a combination of too much ripple and not enough ventilation. You my try a high ripple capacitor. Digi-key handless high ripple capacitors.