DC1827A

DC1827A demonstration circuit features a 110V LED controller with spread spectrum frequency modulation - the LT®3795. Unlike most boosts, the circuit disconnects the output to protect against shorts or other fault conditions when the input voltage exceeds the output. The input voltage range for normal operation is from 8V to 60V. OVLO becomes active for inputs above 63V and the maximum input voltage is 110V. The LED current is 400mA and the switching frequency is 250KHz. The efficiency is 92% when the input is 12V and the LED voltage is at 87V which is the maximum LED voltage. Spread spectrum switching is available to simplify ;conducted emissions compliance. There is a 6.8nF capacitor from the RAMP pin to ground to set the rate at which frequency modulation occurs, but resistor R20 shorting the RAMP pin capacitor must be removed to activate spread spectrum.

• 400mA LED current (ILED) at RS2 = 0.62ohm
• 4A input current limit at RS3 = 0.015ohm
• Designed to be easily reconfigured to buck mode, buck-boost mode and SEPIC topologies
• Demo circuit uses ceramic input and output capacitors