TL431LI: Is it aviliabile for placing a Diode between pin REF and cathode? Urgent!

Hi Gordon, 

I dont believe the current setup in the schematic will work.  D2 will prevent current from flowing into the REF pin.  The TL431LI requires some current (0.2uA) to operate.  According what you have described, VM4 is the power supply correct? Placing D1 will prevent the TL431 to operate because the minimum current flowing into the cathode needs to be 1mA.

Ben

Hi Ben,

I may not descirbe it clearly. The power supply on the left of TL431, so you can ignore the D1 above picture, and VM4 is voltage meter. if there is a dioed leakage current >0.4uA(refer to Iref through D2), whether the circuit will achieve normal work? 

Hi Gordon,

The diode leakage from D2 is not a "controlled" current and may vary over temperature and voltage.  The uncontrolled current may cause the TL431 to not work as expected.  Is there a reason for the D1 diode?  The pin consumes very little current (0.2uA typ).

Ben 

Hi Ben,

You refer to D2 in your last question? Actully, I have the same confusion about D2. My customer want to use D2 to reduce Iref for lower power loss.But I thought it will be effective if replace D2 with a 10k or other sizes resistance. 

My customer want to regulator the series super capacitors with TL431LI. And customer does not want the TL431LI to consume too much power when super capacitors discharges.

Hi Ben,

From above dicusstion, does it mean that connecting a resistance or short between Cathode and REF, the REF pin always takes 200-400nA? And could you gvie a selcetion about the resistance if i place a resistance between Cathode and REF?

Hi Gordan,

No problem! Glad to be of help!

Ben