Testing the LM555

Discussion in 'General Electronics Chat' started by hp1729, Aug 24, 2016.

  1. hp1729

    Thread Starter Well-Known Member

    Nov 23, 2015
    Design 818 Testing the LM555.PNG
    Ancient but still very popular, the 555 gets a lot of attention in the forum here. "Don't work" is very popular.
    If you are pretty sure of your circuit the next question is, "Is my LM555 bad?" Here is a circuit to test your LM555 and also makes a good lesson in how the LM555 works.
    VCC is not specified so the LED resistors should be selected for about 2 mA. I haven't tried it on the CMOS version yet, but it should work.
    Normally the Control Voltage line has a capacitor to ground. This pin goes to the upper tap of a three resistor voltage divider between VCC and ground. All three resistors are equal. So this line should be at 2/3 of VCC to indicate this pin is healthy.
    Last edited: Aug 24, 2016
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