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    Closed: Re: Driving 140x 3W LEDs

    I assume that 700mA is the maximum allowed current for your LEDs.
    Then what about the range of reference voltage of the LM317 (1.3V max) and the tolerance of the 1.8 ohm resistor (minus 5%= 1.71...
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    Closed: Re: Driving 140x 3W LEDs

    Without seeing the datasheet for the UV LEDs, I wonder if the 700mA is the absolute maximum allowed current if they have perfect cooling? How will you cool them? With a spray of Liquid Nitrogen? Then...
  3. Closed: Re: Testing LI Batteries with the help of a device

    Your link is in a foreign language.
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    Closed: Re: Astable Multivibrator not switching

    I posted my simulations on the other forum:
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    Closed: Re: Astable Multivibrator not switching

    1) R5 and R6 should be replaced with wires.
    2) R2 and R3 are calculated to cause the transistors to saturate, not to be a linear amplifier, then hFE is not used. Make R2 and R3 about 10 times the...
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    Closed: Re: Driving 140x 3W LEDs

    Some of the very cheap LEDs will be shorted and with your simple circuit using a resistor to limit the current then the current will be too high and cause the good LEDs in series to quickly burn out....
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    Closed: Re: Driving 140x 3W LEDs

    I do not know how you can mount 4 LEDs to the 12W heatsink you found. A glue that passes heat?

    Since the LEDs are cheap Chinese no-name-brand then their forward voltage are not binned. Then some...
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    Closed: Re: Driving 140x 3W LEDs

    How will you cool each LED? 3W is a lot of heat in that tiny LED. Since it is Chinese no-name-brand then a suitable heatsink might be difficult to find.
  9. Closed: Re: Problem with Logitech Audio PCB (No Sound Output)

    It is possible that damage to the circuit caused by the screwdriver buzzer and installing one or two ICs backwards caused the full DC supply voltage to be applied to the loudspeakers, destroying...
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    Closed: Re: BJT V(ce) ON in common emitter mode

    Don't you trust the datasheets? They guarantee that ANY transistor that has an hFE high enough to pass will saturate at the spec'd low saturation voltage. Then the base current MUST be 1/10th the...
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    Closed: Re: BJT V(ce) ON in common emitter mode

    No. The op is using the transistor as a common-emitter saturated switch and does not know that hFE is not used for a saturated transistor.
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    Closed: Re: BJT V(ce) ON in common emitter mode

    Of course you can have a common-emitter transistor saturate with its Vce much less than its Vbe. it is called "saturation".

    - - - Updated - - -


    The input transistor of a darlington transistor...
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    Closed: Re: BJT V(ce) ON in common emitter mode

    hFE is measured when the transistor is linear with plenty of Vce voltage and not saturated.
    Your transistor is a saturated switch and like most little transistors its datasheet says it saturates...
  14. Closed: Re: Problem with Logitech Audio PCB (No Sound Output)

    Your 18.22V power supply voltage is too high for those ICs.
  15. Closed: Re: Problem with Logitech Audio PCB (No Sound Output)

    The datasheet for the CD6282CS says its absolute maximum allowed power supply voltage is 15V or 16V so your 18V might blow them up.
    I did not see your photos because Imgur is still asleep.
    Why are...
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    Closed: Re: Power Amplifier Design

    When you said Power Amplifier Design I thought it would drive an 8 ohms speaker.
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    Closed: Re: Forward voltage of blue 3 mm led

    3.7V is the "storage voltage" when the Lithium Ion battery cell is half discharged or half-charged. You are lucky that the blue LED did not instantly burn out. A wall power supply that is only 3.6V...
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    Closed: Re: Forward voltage of blue 3 mm led

    What is the voltage of the 18650 battery cell while it is lighting the LED?
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    Closed: Re: Forward voltage of blue 3 mm led

    The forward voltage of a little blue LED is about from 2.6V to 3.6V at 20mA. Each one will have a different forward voltage, but most will "typically" be 2.8V.
    An 18650 Lithium Ion cell is 4.2V when...
  20. Closed: Re: Problem with Logitech Audio PCB (No Sound Output)

    When the IC was damaged by being connected backwards then maybe it damaged a part of the power supply. Measure the power supply voltage to see if it is normal or bad.
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    [SOLVED]Closed: Re: 12 vdc led running very hot

    It is NOT a 12V LED, It is an LED with a resistor that is designed for a 9V power supply voltage. It is overloaded when powered from 12V. At 9V then the small resistor and LED will not get too hot....
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    Closed: Re: Isolate R37 from Equation

    R37 is a very important part of the circuit since it and R42 set the input voltage of the opamp, then since the opamp has a gain of 1 the output voltage of the opamp is also set to be the same as the...
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    [SOLVED]Closed: Re: dc current gain variations

    A transistor in operation heats or cools which affects its hFE.
    A transistor in operation has a variable current which also affects its hFE.
    Design a transistor circuit with enough base current so...
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    Closed: Re: Rebuild low end computer speakers

    Many stereo sound systems are made with a ported woofer called a "sub-woofer" and two satellite speakers. Some of them sound pretty good. A midrange speaker is not needed if the tweeter can do it....
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    Closed: Re: Rebuild low end computer speakers

    The cheap little speakers have a single driver that is only 3.5" in diameter so it produces no bass and a very uneven high end. Each speaker amplifier is only 3.5W so the loudness is only a little...
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