LED light chain circuit diagram

Application: Electro-sensitive protective equipment (ESPE) ¨ Light curtain LED driver ¨ Light barrier LED driver

LED light chain circuit diagram iC-NT device is an LED pulse driver for LED light barrier applications, especially LED light chain circuitries. The device, which is controlled by a shift register logic, features an adjustable LED current sink with a set range of 0.4..1A (at room temperature).

For chain circuitries with several transmitters in operation, the internal set of three flipflops enables a secure beam and data shift control, free of race conditions. The decrease in LED efficiency with a rise in temperature is almost compensated by a positive temperature coefficient of the current sink. In order to generate steep light pulses, the LED switch off is actively supported by the discharge of its junction capacitance. The duration of this LED short-circuiting is controlled by a monoflop. In the event of a quick follow-up light pulse, a monoflop reset is performed automatically to protect against cross currents.

The driver stage for the LED output prepares for a light pulse when DIN reads a high signal; synchronized with the CLK leading edge, the first flipflop transfers the DIN data to Q1 and powers up the LED sink. Since the chain is loaded with just one single high bit and DIN is given by the output DOUT of the previous device, input DIN now reads low at the falling edge of CLK. The LED current sink stops the power, at the same time as an internal data shift from Q1 to Q2 occurs. The LED pulse is well-defined by the time difference between two leading edges of the clock signal CLK. The second falling edge of CLK triggers the third flipflop and activates the next device in the chain via DOUT if enabled by SHEN.

Since only one device is activated at a time, several iC-NT drivers may share one resistor, RSET, to define the LED current value.