The circuit below illustrates powering a LED (or two) from the 120 volt AC line using a capacitor to drop the voltage and a small resistor to limit the inrush current. Since the capacitor must pass ...

This circuit uses low-voltage AC to drive a string of 50 or so bi-color LEDs (two LEDs connected in inverse parallel). Power to the LEDs is controlled by the Triac and the two optocouplers which have ...

Fig 1. This voltage regulator circuit (a) uses green LEDs as both the stabilization elements and as the voltage indicators at the front-panel switch (b). Fig 2. The addition of resistor R4 to the ...