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TL783: constant current circuit using TL783.

park sanghyun
Prodigy 10 points
Part Number: TL783
Other Parts Discussed in Thread: LM317, LM317HV

I want to implement a constant current circuit using TL783.

Currently, I am using LM317 as shown below and using 36V 120mA. However, I want to change the input voltage to 48V and the output voltage to be approximately 48V.

If I implement the circuit below from the TL783's datasheet, the TL783 input voltage is 48V and R is about 4.23ohm,

the voltage applied to the load is 48V - Vref (1.27V) = about 46.73V. Is it correct that the I is 300mA?

  • 0
    TI__Mastermind 32795 points

    Hi Park,

    Can you provide any additional details on the application? What is the system this is going into (is it automotive?) and what will the current sources be powering? Do you have any other key requirements (such as noise)?

    To answer your specific question: yes, the output current is 300mA when R = 4.23 ohms.  The load voltage will be 48V - Vdropout - Vref = 48V - (Figure 10) - 1.27.  Figure 10 is heavily dependent on the temperature but this is an old linear regulator and so your dropout voltage is high.  I don't think this solution will work well for you.

    You can also use the LM317HV in place of the original LM317.  The LM317HV can withstand up to 60V from Vin to Vout.

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    Prodigy 10 points

    Thank you for your quick response.
    This circuit is used for high current LED in industrial equipment. (SMT) I am looking for a regulator to charge the capacitor of CE5.

    The input voltage of LM317 is given by Switching regulator. (Currently, I am converting 24V -> 36V and applying it).
    I need to increase the voltage from 36V to about 48V, so I am looking for a new part.

    I didn't think of the dropout voltage, thank you. As you said, TL783 is not suitable.

    I am currently using LM317AEMP (Package: SOT-223). The LM317HV you recommended doesn't seem to fit our package criteria. Can you recommend a product with a similar package to LM317AEMP?
    Input Voltage : 24~48V
    Output voltage : 48V ~
    Output Current : 200mA ~

  • 0 in reply to park sanghyun
    TI__Mastermind 32795 points

    Hi Park,

    I don't see anything in our portfolio that is a drop in replacement for the LM317AEMP and also meets your requirements. However, this LDO may still work for you.  The 40V abs max placed on the LM317AEMP is the differential voltage from Vin to Vout, it is not Vin to GND or anything like that.  This is because this LDO uses a floating reference based topology and has no actual GND pin.  If your Vin is 48V, will your Vout ever go lower than 8V?  If the answer is no, then you can still use the LM317AEMP in your design.

    Thanks,

    Stephen