Output voltage falls at negative temperature (LNK306)

Posted by: Yaumen on 01/27/2014

We made a power supply on LNK306. It has to work in -30 ... +50°C.
At normal conditions (in the room with +25°C) the power supply must have +5V output. For design values of the feedback resistors the output voltage has +4,5V with 0,25V amplitude ripple.
But at -18°C we see to increase the amplitude ripple by output and output voltage falls from +5V to +3,8V.
What's the problem and is there a solution?

Comments

Hi,

What is exactly the output voltage at room temperature at no load and full load conditions? 4.5V?

Hi,

For calculated feedback resistors (2k and 3,9k) we have 4,5V output voltage at full load (about 40-50 mA) and room temperature.

Hi,

Are you going to tune the feedback resistor to get 5V first under room temperature? Then you can check the output voltage under cold temperature, see how worth it will go.

Remember the passive component, like electrolytic capacitor, may have very low value under cold temperature, this will affect your power supply performance too. You could have a check.

I wrote about the 4,5 volts output to check my schematic. Perhaps I erred in it so as calculated values of the resistors from the datasheet does not correspond to the output voltage.
Of course I tuned this resistors for the 5V output but under cold temperature the output voltage fell also.
I thought about the C1 capacitor but I can't check it. I don't know which electrolytic capasitors have better temperature factor. All known for me aluminium electrolytic capasitors have similar characteristics. May be you can help me!?

To make it simple, why not try to use capacitor with bigger value to check if the reason is from the derating of the capacitor value under cold temperature?

Hi,

I can increase the value of the feedback capacitor but only to check under cold temperature. The LNK306 datasheet "speaks": "feedback capacitor's value should be 10 μF to 22 μF". If I'll increase the feedback capacitor to 22 μF to compensate decrease capacitor's value under cold temperature then under high temperature +50 degrees this value may be too big to normal work of the LNK306.

Hi,

I will think the first step is to find out what cause the output voltage drop under the cold temperature. Then you can decide what is the right value to choose.

Let me know if the test is done. Thanks

OK, thank you but this test may take much time. At the moment it's not pretty cold and I have to wait for frost :)