No announcement yet.

Circuit Design for a simple LED

  • Time
  • Show
Clear All
new posts

  • #16
    A quick simulation of your circuit shows that grounding or floating the Switch node does not turn on/off the LED.
    Click image for larger version

Name:	image.png
Views:	10
Size:	8.0 KB
ID:	22401Click image for larger version

Name:	image.png
Views:	8
Size:	7.8 KB
ID:	22402
    Furthermore, the 555 node is being pulled to a voltage of ~500mV in the simulation. I would be cautious with any circuit configuration that can drive the 555 nodes to any voltage other than ground while the device is powered off, as this can cause damage to the device. Remember, just because the 555 timer is powered off does not mean that it is no longer in the circuit!​


    • #17
      As I stated, the switch signal in the simulation I created needs to high in order to switch on, NOT to Gnd.
      If you want it to switch on when connected to Gnd, you have to use PNP or 2x NPN to invert (not darlington).

      I do not think that the 8nA going to a switched on 555 timer would be a problem. In your simulation nothing is connected there. So if you still want to reduce the voltage, you could add a 100k pull-down on the 555 port too.