Current stabilization for TL494

Discussion in 'The Projects Forum' started by Mavlik, Nov 22, 2012.

  1. Mavlik

    Thread Starter New Member

    Nov 19, 2012
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    Power supply for tungsten lamp
    There is need for a regulated power supply for tungsten ribbon lamp
    in the range from 0 to 20A.
    I decided to make supply based on PWM (for TL494).
    (eg, such http://nice.artip.ru/files/pwm-tl4941.gif)
    But do not know how to do this scheme with current stabilization
    (this is important for the lamp).
    Early the lamp was fed from a computer power supply (without adjustment)
    on the channel 5V. In this case, current consumption was about 18A.
    The converter will be fed from the computer PS, but the channel 12B.
    (current can take more than 20A)
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,965
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    You need to make a constant current regulator not a constant voltage regulator, the TL494 is a pwm chip,
    or do you want a voltage regulator with current limit?
     
  3. Mavlik

    Thread Starter New Member

    Nov 19, 2012
    5
    0
    Dodgydave
    Based on TL494 with current stabilization(constant current regulator).
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    The diagram you have wont work,as its using the deadtime pin to regulate.

    To put current limit on a TL494 you need to use pin 16 or pin 1 to detect the increased current through a series resistor in the source load of the mosfet, try a 0.1 ohm resistor so at 20amps thats 2volts across the resistor, so if you put a 1 k pot also across the resistor with the wiper to pin 1, this will serve as the current limit.

    If you look at this diagram of an atx,(the TL494 and KA7500b are the same chip) you will see that pin 16 is used as the current limit, and pin 1 as the voltage control.

    http://www.seekic.com/uploadfile/ic-circuit/201151124854870.gif
     
    Last edited: Nov 23, 2012
  5. Mavlik

    Thread Starter New Member

    Nov 19, 2012
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  6. KrisBlueNZ

    Member

    Oct 17, 2012
    111
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    The circuits you've shown so far actually feed pulses of the full DC voltage into the light bulb, and adjust the duty cycle to give a particular average voltage, and therefore a particular brightness. This is normally fine; I'm just pointing it out.

    You mention current stabilisation without defining what you want. Do you want to operate the bulb at a particular current? Is this to compensate for the effects of aging or ambient temperature or something?

    If you want to regulate the current flowing in the bulb, you need to be able to sense that current. This is a lot more straightforward if the bulb is being driven with DC rather than a PWM voltage. To regulate the bulb current, you have to monitor the bulb current and adjust the regulator output voltage to keep the current at your desired level. The regulator therefore becomes a current regulator instead of a voltage regulator.

    In your case, the current and power are quite high, so I would use a solution that doesn't involve a lot of messing around winding inductors. It should be possible to modify a PC power supply to do what you want. But you have to DEFINE what you want.

    What is the maximum voltage you need to be able to apply across the bulb?

    What is the maximum current you need to be able to supply to the bulb?

    Do you want to regulate the bulb current, rather than the bulb voltage?

    Do you have a PC power supply that you can modify? What are the voltage current ratings on the output rails?
     
  7. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    I dont see the point in the transformer L1/L2 why dont you just put a resistor in the Source leg and monitor the volt drop across it??
     
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