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led workbench lighting circuit schematic

LED Workbench Lighting

Here is a very useful workbench lighting unit for electronics hobbyists. The portable inspection lamp circuit consists of an on-board voltage regulator and a high-bright 5mm white LED. Any 9 to 18 volt dc rated ac mains adaptor, capable to source about 100 mA of output current can be used to power this portable inspection lamp.

After contruction the led workbench light circuit should be enclosed in a suitable plastic bottle cap as illustrated here. The miniature lens shown is an optional component. In the prototype, plastic made lens lifted from a discarded torch was used!

led bottle cap

The adjustable 3-pin voltage regulator IC1 (LM317L) in TO-92 pack, is here tuned to supply an output of near 4.5 volt dc. This supply is directly fed to the white LED (D2) through the current limiter resistor R3 (51 Ohm). Diode D1 (1N4001) works as an input polarity protection guard and two small electrolytic capacitors (C1 and C2) connected at the input and output pins of IC1 improves the overall stability of the regulator circuit. Use a standard RCA or EP socket as the input terminal J1.

LED workbench lighting lamp circuit schematic

led workbench lighting circuit schematic

9 Comments

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  • krokkenoster

    If you really want to be fancy then make the lower resistor variable and then you can dim the worklight if necessary!

  • Mehrdad

    Do I need a resistor and a voltage regulator if I want to power up 5mm LED from a source of power that voltage can vary, such as a car?

    What is the regulator/resistor would you recommend for powering up 5 LED in series that draws 20mA and 3.5V.

    thanks in advance

    • Author

      Take extreme care while powering high-efficiency white LED(s) from automobile batteries.Dedicated ICs are now available for the purpose,which are basically buck converters.I will try to add such a circuit here as soon as possible.

      Regarding your second question please use the formula for calculation:

      “V In-V LED/I LED(in mA)=R (in Kilo Ohm)”,where V=Volt,I=Current,R=Resistor value.

    • Scott

      Dear Mr Hareendran

      I need to build a small, thin, stand to have a glass sculpture sit upon and be illuminated from below. It needs to run from the mains and I wondered if I might use an old mobile phone charger for this. Electrical work is not a problem but electronics is not something I am familiar with. This circuit of yours is the closest I have found to doing the job I need but can you offer any further advice? The Nokia chargers I have available offer:
      1) 5.3v / 500mA and 2) 3.7v / 355mA
      Thank you in advance for your expertise.

  • Pier Francis

    Hello,

    Since the input is DC you can configure the the lm317 as a current regulator and build the complete circuit with just an lm317 and a resistor. BOM count: 3 including the led. you can use smd for compactness.

    • Author

      I partly agree with you.However,if we configure LM317 as a current regulator as suggested by you,the variable input (9-18V dc) is not possible.Any 9 to 18 volt dc rated ac mains adaptor capable to source about 100 mA of output current can be used to power my prototype.Thanks!

  • vidhyaraj

    i think,can use 7805 IC after removing the 2 resistors.What is the advantage of 317L?

    • T.K.Hareendran

      Sure!
      LM317L is an adjustable voltage regulator so that you can modify the output voltage to a desired value by changing a single resistor(Here R2)| Vout=1.25(1+R2/R1).Always try to keep R1 as 240 Ohm.

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