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TL783 Current Regulator configuration use below 0C

Anthony Cerminara27
Prodigy 60 points
Other Parts Discussed in Thread: TL783

I was considering using the TL783 High Voltage Adjustable regulator in a current source configuration for an application where the temperature range is from -40C to 85C. Figure 17 in the datasheet describes the circuit configuration with R connected between OUT and ADJ. The load current will be set to a range between 11mA to 14mA. The input voltage range is between 110VAC and 220VAC. The load will be switched, however quiescent current will be present to power the regulator. The load is roughly 7.2K ~ it controls an external output. The intention is to keep this point at roughly 110V. So the drop across the current regulator will not exceed 125V. Will this configuration operate at -40C? I have read that operation cannot be guaranteed at this temperature but that may be based on operating conditions. Is there a load in terms of current / voltage where the use below 0C  will cause the device to not turn on?

  • 0
    TI__Mastermind 24485 points

    Hello Anthony,

    Figure 17 shows a curve where the output current is set/limited to a certain value.

     If you want a constant voltage on the output, you have to set up the regulator in a different way.

    Also, if you are trying to get 110V constant output voltage, you are not going to be able to do that with a 110VAC signal through an LDO. If the output is set to 110V, then the LDO will just track the input voltage until it exceeds 110V, and when the AC voltage is negative, you won't have anything at the output. This is not a good part to use in order to get a constant 110V output.

    Ultimately, what are you trying to achieve? Are you trying to keep a constant voltage on the output? What is your external output and what is it controlling?

    Best,
    Michael

  • 0 in reply to Michael J Schultis
    Prodigy 60 points
    Hi Michael. Thanks for your response. I have to clarify a few things that I forgot to mention. First of all, there is a bridge rectifier to rectify the current to DC before reaching the Tl783. Essentially I am driving a solid state relay. The relay has a maximum input voltage of 140V. The maximum operating voltage I intend to run at is 220V. The current source in effect is dropping the excess voltage to keep the SSR happy. We are trying to use this device as a two-wire current limiter. We cannot use the device as a voltage regulator because our load may not always be in the low side. The idea is that the current will pass through the relay input and develop the necessary input voltage at operating current in order to turn on the relay. The remaining voltage will then be dropped across the TL783.
  • 0 in reply to Anthony Cerminara27
    TI__Mastermind 24485 points

    Hello Anthony,

    A bridge rectifier won't supply a DC voltage at the output. Are you implementing other circuitry to get a constant DC voltage?

    Can you please share a schematic or additional details on what you are trying to implement?

    As for your original question about -40C operation. While I don't believe the device will not operate at these temperatures, device operation and the electrical characteristics of the device are not guaranteed.

    Best,
    Michael