製品概要Demonstration circuit 1309 features the LT3474-1 36V step-down 1A LED driver. The demonstration circuit is designed to drive a string of 1A LEDs from a high input voltage. The LT3474-1 operates with a 4V to 36V input voltage range and maintains high LED current accuracy from 35mA to 1A. The LT3474-1 can be dimmed with its analog CTRL pin or with a PWM dimming input signal. A few simple modifications can be made to DC1309 in order to add PWM dimming to the circuit.
An external overvoltage protection clamp provides open LED protection and is set to about 24V on DC1309A. The level of the clamp can be changed by replacing the zener diode (D4) with a different zener diode. The LT3474-1 differs from the LT3474 in its output voltage capability. The LT3474 has a 13V clamp that does not allow the use of an LED string of greater than 13V on the output. However, LT3474-1 does not have this clamp and it can power LEDs up to 26V, as long as the external clamp is adjusted correctly.