• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 62 subscribers
  • Views 5843 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TL783 high voltage input

Konstantinos Vasileris100221
Prodigy 130 points
Other Parts Discussed in Thread: TL783, TIP150

Hello. I need a linear regulator that can source 50mA -70mA max @ 9 Volts with an input voltage up to 350 Volts. I have seen inside the TL783 datasheet and it has a note for higher voltage than 125Volt. Can it be modified for 350Volt operation? i can understand that the series pass transistor has to handle the voltage. Basically the circuit will be the power supply for a couple of comparators that they sense the voltage (from the same line that the TL738 will be powered) and some optocouplers

  • 0
    TI__Guru**** 167616 points

    Kontantinos,

    Yes, this circuit works at higher voltages, but change components to support higher NPN voltage, resistor and zener power.
    Be sure to calculate power rating and heat sinking for all components.

    As an alternative, consider the LNK304. This is not a Texas Instruments device (use Google).

    Regards,
    Ron Michallick

     

  • 0 in reply to Ron Michallick
    Prodigy 130 points

    Hello Ron

    some questions about the circuit, why the zener diode is between output of the regulator and base of darlington and not between base of NPN and GND? If i want an output of 5 volts should i use a 6.2 zener? what about Vbe 8 volts of tip150?

    Finally for my case how can i calculate the power dissipation of the part? Vin-Vout* I consumption?

  • 0 in reply to Konstantinos Vasileris100221
    TI__Guru**** 167616 points

    Konstantinos,

    When the input is less than 125V, the VCE of the NPN transistor is about 2V. So the TL783 see almost all of the voltage drop (and power dissipation).
    When the input is greater than 125V, the 120V Zener will shunt current to the 5V output, the TL783 Vin will remain constant and the NPN transistor drops all the excess voltage. However, the Zener current increases the minimum load requirement.

    Moving the Zener anode to ground will also protect the TL783 and the Zener will turn on 5V earlier and the Zener current flows to ground instead of the load. So the current  is "wasted", but it does not add the the minimum load requirement.

    The two resistors on the ADJ pin set the output voltage. The Zener sets the maximum TL783 voltage drop and can be as low as 25V or high as 120V.

     The power is as you calculated.

    Regards,
    Ron Michallick