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  1. #1
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    how to test ic with multimeter

    Any one can shown me how to test the three (3) leged IC LM317T using Multimeter?

    Hope someone could help me as soon as possible.

    Regards,
    Keng Loong

    •   Alt6th December 2005, 11:28

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    lm317t

    Using a multimeter in testing ICs is a very ambiguous issue ..
    In the case of the LM317 I don't think any tests will be conclusive ..
    Regards,
    IanP



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    lm317t pinout

    I'm currently troubleshoot a UPS (Uninterruptible Power Supply), for your information, I already replaced 4pcs of Power MOSFET STP60NF06 to STP60N06. But the UPS is still not working, the problem now is when the AC supply to the UPS, there is an output. Once I swithched off the AC supply, the UPS indicated fail and no AC supply to output socket.

    I'm suspected the LM317T faulty but I don't know how to test this 3 legged IC. Can you please shown me how to test this component?

    Can you please give me more clearer explaination how the IC LM317T work/ operation.

    I hope you can help me out on this.

    Thanks & best regards,
    Keng Loong, Liew


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    ic lm317t

    The LM317T is a series adjustable linear positive voltage regulator. It has an adjust pin an input pin and an output pin. It acts as a variable resistance between the input and the output pin so that the voltage between the output pin and the adjust pin is 1.25V. in order to test it without removing it you can measure the voltage between the output and the adjust pins. If it is less than 1.2V or more than 1.3V then it is not functioning properly. Be carefull because it can shut down if it has overheated or if the output current exceeds its max of 1.5A. Also measure the input voltage the minimum operating input-output voltage is around 2V. Usually such an IC is used with a voltage divider between the output pin the adjust pin and ground in order to get an adjustable voltage and it can be used as a current source. Its pinout is adjust-Vout-Vin looking at it from the front.



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    how to test lm317

    Quote Originally Posted by ptmsl
    The LM317T is a series adjustable linear positive voltage regulator. It has an adjust pin an input pin and an output pin. It acts as a variable resistance between the input and the output pin so that the voltage between the output pin and the adjust pin is 1.25V. in order to test it without removing it you can measure the voltage between the output and the adjust pins. If it is less than 1.2V or more than 1.3V then it is not functioning properly. Be carefull because it can shut down if it has overheated or if the output current exceeds its max of 1.5A. Also measure the input voltage the minimum operating input-output voltage is around 2V. Usually such an IC is used with a voltage divider between the output pin the adjust pin and ground in order to get an adjustable voltage and it can be used as a current source. Its pinout is adjust-Vout-Vin looking at it from the front.
    Thanks for your info, but how to identify which pin is input or output? I'm currently repairing a UPS, just not sure this 1.2V is in AC or DC? How to adjust the input and output of the pin?



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    testing lm317t

    this IC has 3 pins and a heatsink connected to the middle pin too.
    this pin is the output voltage.
    if you look to the ic, the legs towards you, the right one is the input pin.
    you must see a difference of minimum 1.2V between the two pins, otherwise the IC is faulty.
    furthermore, the first test is to see if you have input voltage !
    the 3rd pin stabilizes the reference voltage for proper operation.
    be carefull, because its a floating pwr supply, "seeing" only the differnce between input and output, you may have the surprise to finf very high and dangerous input voltages !



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    lm317 test

    Hi !

    Good idea is to get the LM317T datasheet:

    http://www.national.com/pf/LM/LM317.html

    Take the IC out from the circuit and use a breadboard + 2 resistors (or 1 resistor and a potentiometer) and a variable DC power supply, this turn this possible to be tested with the multester. THe LM317T is not like a TO220 package bipolar transistor that can be checked only with an ohmeter.



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    how to check lm317

    If that's the thing you suspect then take it out and put in a next one. If it works throw the old 317 away. Of course you could end up with two fried 317's if something else is wrong. The only easy way to test these things is in an actual circuit.



    •   Alt6th December 2005, 18:52

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    lm317t transistor

    If this IC LM317T fail/ faulty, is it will still producing voltage at output?

    I understand that LM317T is act as voltage regulator, its just ensure the output voltage produced is stable. Am I right? So possible the IC still produced a voltage at output? Please correct me if I'm wrong.

    Thanks!



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    lm317t test

    Yes it is possible that the LM317 is faulty and still producing voltage at its output. Check the voltage between the left and middle pins (adjust - Vout) looking from the front. If it is more than 1.3V the device is probably faulty. How the LM317 is used depends on the application and the topology of the circuit. If still not sure measure the voltages at all three pins and if possible the current from the middle pin (Vout) and reply so we can guide you further.



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    transistor lm317t

    Below please find the test result that I was done with connected to AC & Battery Supply.

    Test result:-
    Centre Pin & Right Pin
    AC = 5.68V
    DC = 6.15V
    Centre Pin & Left Pin
    AC = 8.55V
    DC = 1.232V

    I wander now in the circuit now is carrying AC or DC voltage, please advice.

    Hope someone can help me to solve my problem.



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    how to test lm-317

    Looks like something is oscilating. Since the DC voltage between Adjust and Out is correct and there is enough DC headroom between input and output, the device is probably working. You must either try looking at the input pin with an osciloscope or search the capacitors around this circuit (voltage regulators can sometimes oscilate if their capacitors are faulty or the feedback loop is broken). By the way is this circuit at the battery charger or the inverter? What is the output voltage from this regulator supposed to be?



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    how to test ic using multimeter

    Thanks for your valuable information.

    The output of the regulator supposed be +24.43VDC but now in my circuit is just giving 6.15VDC. This circuit I think is Invertor cause it's very near to the output circuit. Some more, when I measured on the Battery during UPS switch off, the output of battery is 11.99VDC and when I switched on the UPS, it's was changed to 12.16VDC. That's mean the battery is under charging, right?

    Could you please explained to me more about oscilating process?



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    lm317t pins

    Yes the increase in voltage indicates that the battery is charging but I am concerned that the voltage of 12.16V is very low. Maybe it is not charging but the increase in voltage is caused by the load being disconnected from the battery. Can you connect a multimeter to measure currrent in series with the battery to make sure there is a charging current? If not does the battery voltage increase slowly with time? As for the oscillation the LM317 like most linear regulators is partly an amplifier driving a pass transistor and can self oscillate if the conditions allow it (it becomes unstable and produces an AC component superimposed on the DC output). What is the voltage from the adjust pin to ground?( DC Voltage) What are the values of the resistors between vout-adjust and adjust-ground? Does anything change if you insert a capacitor of around 10uF from vout to ground or from adjust to ground?



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    how to check ic with multimeter

    instead of using multitester, try in-circuit testing. try to power the ciruit if the ic is connected then measure if there is an available voltage at the input side. if there is none, then trace backwards for possible breaks in the circuits. measure the resistances of the input resistors. if there is an input voltage, then try to measure the output voltage. if there is none check the adjust pin of the ic for any possible breaks or open resistances. if all resistors are good and still no output voltage, chances are the ic is defective. also try to see if there series pass transistor connected at the input side of the ic for shorts or open. replace the ic at once. it would be helpful if circuit diagram is at hand. good luck



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    testing lm317

    wht do u want to test in 317??



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    Re: How to Test the IC LM317T Using Multimeter?

    What if you aren't using the LM317T to regulate voltage but rather current? Would you test it in the same way? For example, I configure mine to provide a constant 25 ma output so I don't damage LEDs. So I regulate current, not voltage.

    Would I test it in the same way by connecting the multimeter between the Vadj and Vout pins? But instead of getting the 1.2-1.3v reading, should I be seeing the 25ma I have it configured for?



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