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  1. #1
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    Lamp Test Circuit with some other indications.

    Hi everyone,

    Please let me know that I builds a circuit of Lamp Test and indications of 5 pressure sensors and 3 indication connected to 3 SPST switches. SW2 is lamp test button,

    Problem is, when I energize this circuit on real in Vero board the 5 LED's D13 to D17 were slightly glow.

    What is the problem with these D13 to D17 LED?

    Can anyone interested to tell me?

    Click image for larger version. 

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    IMRAN

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  2. #2
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    Re: Lamp Test Circuit with some other indications.

    You don’t tell us switch positions or component values or what that “volt meter” is, but I suspect you’ve got some leakage through your diodes, or something wired wrong.


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    Re: Lamp Test Circuit with some other indications.

    Why don't you wire all 8 LEDs the same way?
    SW1 controls D1, D5 and D9, not D13-D17?


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    Re: Lamp Test Circuit with some other indications.

    I’m not even sure WHAT this circuit does. Just a whole bunch of diodes.


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    Re: Lamp Test Circuit with some other indications.

    SW1 is common signal for D1,D5 and D9 and below 5 LEDs will get separate signals from pressure sensors.
    D1,D5 and D9 negative connected with SPST switches SW3,4,5.

    But I faced some leakage current on original circuit in 5 LED's.
    Where it comes from?

    - - - Updated - - -

    It is Lamp Test circuit simple but all LED will glow by Lamp Test Switch SW2 and D1,D5,D9 also glow with input signal and negative comes with SPST SW3,SW4,SW5.

    And below 5 LED's are separate signal LED's but problem is, they were glow slightly when apply +ve voltage at SW1 on original circuit on Vero board?
    IMRAN



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    Re: Lamp Test Circuit with some other indications.

    Looks like a device for killing LEDs to me. I assume they all have series resistors.
    Maybe you are seeing leakage through reverse-biased LEDs because of the relatively high voltage exceeding their PIV.
    For lamp testing, the more conventional way is to enable all the drivers simultaneously rather than provide a completely current source to each lamp.
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    Re: Lamp Test Circuit with some other indications.

    Brother all LED's have internal current limiting resistors in natural circuit.
    And all LED's have 24VDC.
    IMRAN



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    Re: Lamp Test Circuit with some other indications.

    Hi,

    Without knowing
    * the complete circuit
    * LED type
    * switch type
    * diode type
    * flux type and your soldering skills
    All we can do is guessing

    To cure the symptom you may connect a 10k resistor in parallel to each (glowing) LED.

    Klaus
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    Re: Lamp Test Circuit with some other indications.

    I don't recognize reverse biased LEDs in the circuit, assuming the diodes are regular silicon diodes with low leakage. Similarly they won't "glow".

    I suspect a wiring error.


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    Re: Lamp Test Circuit with some other indications.

    I agree FvM but I couldn't think of any other path that would allow only a small current to flow. The series diodes, assuming they are normal Si types should block reverse current anyway but the two supply solution to testing the LEDs is unconventional to say the least.

    Brian.
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    Re: Lamp Test Circuit with some other indications.

    I have China make LED attached herewith.

    They are 24V and no polarity mention.I tested with DC supply of 24V and they glow on both polarities.

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  12. #12
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    Re: Lamp Test Circuit with some other indications.

    The ONLY possible current path is through reverse biased diodes. Either you've got something wired wrong, or those diodes are leaking.


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    Re: Lamp Test Circuit with some other indications.

    I checked all wiring, it is OK but I used diodes 1N5819.
    You are saying is right diodes are leaky.
    Please recommend me good diode for my lamp test circuit or recommend me good lamp test circuit
    IMRAN



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    Re: Lamp Test Circuit with some other indications.

    Those are Schottky diodes. If you had actually gone to the trouble of reading the data sheet, you’d see that they have 1ma of reverse leakage current, enough to make an led glow. There’s no reason for you to use a schottky in your application; a standard rectifier diode like a 1N4001 or 1N4148 should work. Check your current ratings.


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    Re: Lamp Test Circuit with some other indications.

    Yes you alright sir I got it.
    Please recommend me more diode other than 1N4001 or 1N4148 with negligible reverse current.
    IMRAN



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    Re: Lamp Test Circuit with some other indications.

    Quote Originally Posted by imranahmed View Post
    Yes you alright sir I got it.
    Please recommend me more diode other than 1N4001 or 1N4148 with negligible reverse current.
    There are thousands of diodes that would work. The two I recommended are extremely common; cheap and plentiful. What’s wrong with those? If you don’t like those, then just search for ones that meet your voltage, current and leakage requirements.



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