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TL783: Regulator gets too hot at low load levels

Neil Forcier
Prodigy 30 points
Part Number: TL783

Hello,

I want to use the TL783 in DPak package for a design where I need to convert 48VDC to 5VDC. I chose this regulator because of its high input voltage range. The resistors I selected were R1 = 87ohms and R2 = 260ohms (try to get R1 as close to 82ohms as per datasheet suggestion to reduce min output current). I bread boarded the regulator up to test it with a 330ohm static load. I noticed that I get about 30mA in and out of the regulator with this load level (which ohm's law agrees with). With this setup the regulator gets surprisingly hot, but the datasheet makes no mention of recommendations for heat dissipation. Three questions:

--> Is this heating normal or expected (the regulator is dropping more than 1 watt I guess) and should I worry about it?

-->The end design will have airflow in it, should I do any additional heat sinking? Any recommendations if so?

-->Is there another linear regulator or setup you would recommend?

Thanks in advance for any input.

  • 0
    TI__Guru 55940 points

    Hi Neil,

    Linear regulators are power dissipative devices; therefore, it is normal for the linear regulator to have some heat.  How hot is your regulator?  

    The most common way to estimate the junction temperature of the regulator is to use the junction to ambient thermal resistance.  

    Your application dissipates 1.29W ([Vin - Vout] x Iout).  If we multiply this by 25.3C/W (KTT package), we find that the junction temperature of the TL783 will be ~32.6C above your ambient temperature.  The maximum operating junction temperature for TL783 is 125C; therefore, as long as your ambient temperature is below 92C your application should be okay from a thermal perspective.

    Airflow will certainly help pull heat out of the LDO as would any external heatsinking you may choose to provide; however, the 1.29W dissipated in the TL783 will cause heat.  If you wish to reduce the heat in the TL783 you could reduce the Vin to Vout headroom by using a switcher or even spread the dissipation by placing two regulators in series or even a power resistor placed before the IN pin.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 30 points
    Thanks Ryan, this answer is what I was looking for.