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Voltage regulator with Vin up to 40 V DC

Discussion in 'General Electronics Discussion' started by Dkuriloff, Jan 18, 2010.

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  1. Dkuriloff


    Jan 18, 2010
    Hi all:

    I have a circuit that needs ~ 35 volts DC (unregulated) @ 8 AMPS to drive a flyback primary coil and a oscillator controller circuit using a UC3844 that requires 18 volts regulated + DC @ 500ma. My stepdown 8 amp transformer gives ~27 volts from the 120 v mains and after full bridge rectification and filtering I get 37-38V (no load). I want to use the same transformer for both parts of the circuit. It is center tapped. I can use an LM7818 and a few series diodes to drop the input DC voltage from the transformer to below 35Vin (max for the LM 7818) or an adjustable voltage regulator like the L200.

    I thought the the L200 would be a more versatile solution since I could eliminate the voltage dropping diodes. Any thoughts?

    What are the differences between the L200, L200C, L200CV, L200CH?

    Where can I purchase just 10 pieces without the shipping costing more than the parts?

    Is there another more available adjustable voltage regulator that can tolerate 38-40 volts DC in (rectified AC, filtered DC) and output 15-18 volts at ~ 500 ma??

    Here is the circuit:

    Thanks for the help
  2. Resqueline


    Jul 31, 2009
    The UC3844 requires at least 17.5V to assure turn-on. Too bad that excludes using the center tap as a (reliable) power supply for it.
    There is an LM317HV that can stand up to 60V Input-Output Voltage Differential & 1.5A.
    The datasheet for the L200 says it can stand 40V (& 60V for 10ms) but also gives an example of how to allow for continous input voltages above 56V. It also says that the operating junction temperature for L200C is -25 to 150 °C, & for L200 it is -55 to 150 °C.
    The T stands for TO-3, but I'm unable to find the meaning of the H & V.

    Have you tried ebay? China & Hong-Kong based companies often have "free" shipping.
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