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What's the simplest ballast to maintain 25mA-rms @ 98Vrms?

  1. Jun 15, 2009 #1
    I have a circuit containing ACST6-7S AC switch. That power switch is used to put out 98Vrms, which drives another circuit (Circuit B). The problem is, the power switch needs to have 25mA-rms throughput in order to stay 'turned on'.

    The simplest solution is to just put a ~4k resistor in parallel with circuit B. However, this solution is not optimum because it will always be dissipating an extra ~3W of heat.

    What I'd really like is something which only draws extra current as needed. Circuit B will at times draw well over an amp. Another limitation is size - the solution, when manufactured, would have to fit in the palm of one's hand.
  2. jcsd
  3. Jun 15, 2009 #2


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    Would there be any way to use a voltage regulator that has a internal thermal overload?
  4. Jun 16, 2009 #3


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    You could do it inductively. Not sure what your power source is and why it is important to not dissipate the 2.5 watts. Are you just trying to keep power consumption down to be 'green'? Or is there battery life compromised here? Would like to know a bit more.
  5. Jun 16, 2009 #4


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    I calculated that a 0.68 uF capacitor would have about the right reactance at 60 Hz, but I don't know if the AC switch would appreciate a reactive load like that.

    In a device that usually uses about 100 watts, 3 watts of standby power doesn't seem too bad.
    Last edited: Jun 17, 2009
  6. Jun 18, 2009 #5
    I want to keep power dissipation to a minimum because the application is very heat-sensitive. I did try a reactive load of 1.1uF...the AC Switch didn't blow up, and didn't get too hot, but the LEDs would be on for about one second, then off for about one second, and repeat this cycle.
  7. Jun 18, 2009 #6


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    Not sure I understand.

    The AC switch is controlling power to the circuit B, but when the AC switch is turned off you still want current to flow through it, but you don't want this current to flow normally?

    And if you put a capacitor in parallel with Circuit B, some LEDs flash? Which LEDs would these be?

    Maybe you could explain a bit more or put up a circuit.
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