Basic LED Circuit
Led Circuit For Constant Current Regulators
Led Circuit For AC Network
Since LED’s should be operated in the forward direction, reverse voltage protection is required to assure the reverse voltage (Vr) maximum is not exceeded. Inthe folowing picture illustrates the placement of back-to-back silicon diode across the LED, the silicon diode will clamp the voltage across the LED to approximately .6 volts. The picture below shows a different approach that uses two (2) LED’s in parallel which alternately light relative to the device under a forward bias condition.
LED Circuit With Basic Transistor Drive
The picture (a) shows a transistor drive circuit that lights the LED when the transistor is conducting into saturation. And the picture (b) shows a transistor drive circuit that lights the LED when the transistor is not conducting or is considered to be open. The equation below should be used to determine the value of R. Both of the transistor drive circuits shown in picture below can be configured to drive multiple LED’s in series.
Pulsed operation of LED’s can typically be achieved by the transistor drive circuits shown in the picture above. Significantly higher peak LED light output can be realized from large drive current pulses at a low duty cycle. The maximum tolerable limits should not exceed the LED junction temperature above that obtained by operating the lamp at the maximum DC current of LED circuit.