Linear's LT3956 is an 80V input 80V output constant current constant voltage DC/DC converter ideal for driving high current high brightness LEDs (HBLED). 3000:1 true color PWM dimming, input voltage from 4.5V to 80V, Output voltage up to 80V, integrated 3.3V/80V switch, adjustable frequency from 100kHz to 1MHz, can drive LED in boost, buck, buck-boost, SEPIC or flyback mode, mainly used for high power LED, battery Charger and precision current-limiting voltage regulator. This article describes the main features of the LT3956, block diagram, and a variety of application circuits, including efficiency 95% 25W WLED automotive headlight driver circuit diagram, rise-and-down mode LED driver circuit diagram, ultra-capacitor charging Circuit diagram, and buck mode 90W LED driver circuit diagram, etc.
80VIN, 80VOUT Constant-Current, Constant-Voltage Converter
The LT®3956 is a DC/DC converter designed to operate as a constant-current source and constant-voltage regulator. It is ideally suited for driving high current LEDs. It features an internal low side N-channel power MOSFET rated for 84V at 3.3A and driven from an internal regulated 7.15V supply. The fixed frequency, current-mode architecture results in stable operation over a wide range of supply and output voltages. A ground referenced voltage FB pin serves as the input for several LED protection features, And also makes it possible for the converter to operate as a constant-voltage source. A frequency adjust pin allows the user to program the frequency from 100kHz to 1MHz to optimize efficiency, performance or external component size.
The LT3956 senses output current at the high side of the LED string. High side current sensing is the most flexible scheme for driving LEDs, allowing boost, buck mode or buck-boost mode configuration. The PWM input provides LED dimming ratios of up to 3000 :1, and the CTRL input provides additional analog dimming capability.
Main features of LT3956:
3000:1 True Color PWMTM Dimming
Wide Input Voltage Range: 4.5V to 80V
Output Voltage Up to 80V
Internal 3.3A/84V Switch
Constant-Current and Constant-Voltage Regulation
250mV High Side Current Sense
Drives LEDs in Boost, Buck Mode, Buck-Boost Mode, SEPIC or Flyback Topology
Adjustable Frequency: 100kHz to 1MHz
Open LED Protection
Programmable Undervoltage Lockout with Hysteresis
Constant-Voltage Loop Status Pin
PWM Disconnect Switch Driver
CTRL Pin Adjusts High Side Current Sense Threshold
Low Shutdown Current: <1μA
Programmable Soft-Start
Available in the 36-Lead (5mm × 6mm) QFN Package
LT3956 application:
High Power LED
Battery Charger
Accurate Current Limited Voltage Regulator
Figure 1. Block diagram of the LT3956
Figure 2. LT3956 efficiency 95% 25W WLED car headlight drive circuit diagram
Figure 3. LT3956 liter-buck mode LED driver circuit diagram
Figure 4. LT3956 large capacitor charging circuit diagram
Figure 5. LT3956 Efficiency 90% 20W SPEIC LED Driver Circuit Diagram
Figure 6. LT3956 Buck Mode 90W LED Driver Circuit Diagram
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