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LM4040-N-Q1: Referencing shunt voltage reference to positive rail

Jeff Goldberg
Prodigy 10 points
Part Number: LM4040-N-Q1
Other Parts Discussed in Thread: LM4040-N

Tool/software:

I'm currently using a zener diode to create a voltage approximately 2.5 to 3 volts below a positive rail, depending on the zener selected. The rail can vary from 11 to 16 volts so at 16 volts, the shunt current through the Zener is higher than I would like.  

I'd like to replace the zener with a shunt voltage reference, for the sole purpose of being able to reduce the required minimum shunt current...enabling me to increase R1 in the circuit below.  Can I use the LM4040-N in place of the zener as shown, with the cathode connected to the positive rail and anode connected to ground through an appropriately sized current limiting resistor?  All of the applications examples I've seen for shunt references show the current limiting resistor placed between the positive rail and shunt cathode, so I want to be sure I'm not overlooking something.

    

  • 0
    TI__Expert 4560 points

    Hi Jeff,

    As you noted the external series resistor needs to be connected to the cathode in order to properly regulate the current that flows through the shunt resistor and to the load. Therefore you cannot simply replace the zener in circuit as it. However, you could increase the external series resistance at the cathode such that you reduce your shunted current while still maintaining the needed supply current for the load and to power the device.

    Thanks,
    Joshua