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The LED lighting industry is rapidly evolving, gradually replacing traditional lighting solutions across various applications. As this transition accelerates, the power demands of LED drivers are increasing. Maintaining high current detection accuracy becomes more challenging as the current increases, especially when efficiency is not compromised. To meet these demands, LED drivers must ensure accurate current sensing while efficiently delivering current to multiple independent LED loads, supporting parallel connections and precise current averaging.
Some high-power LEDs have unique mechanical and electrical characteristics, where the positive terminal is electrically connected to the thermally conductive rear housing. In a conventional buck-regulated LED driver, thermal management typically involves cooling the chassis. However, this configuration presents an electromechanical challenge because the rear housing must be both thermally conductive and electrically isolated from the chassis if there's a voltage difference. Since LED manufacturers are often constrained by existing production processes, the driver itself must address these design challenges effectively.
One solution is to use a four-switch positive buck-boost LED driver, although this approach increases system complexity and cost. Alternatively, the negative output buck-boost topology uses only one set of switching MOSFETs, allowing the positive terminal to be directly connected to the heat sink. This eliminates the need for additional isolation components on the heat sink, simplifying the mechanical design significantly.
To support high-performance requirements, the LT3744 can be configured as either a synchronous buck or a negative output buck-boost controller, capable of driving LED loads with continuous currents exceeding 20A. The device accepts input voltages ranging from 3.3V to 36V. When used as a buck converter, it regulates LED current from 0V up to the supply voltage range. As a negative output buck-boost converter, it accurately controls LED current over an output voltage range from 0V to 20V.
The LT3744 offers impressive analog current regulation accuracy of 3% across the full scale, and even at 1/20 scale, the accuracy remains better than ±30%. It features three independent analog and digital control inputs, along with three compensation and gate drive outputs, making it suitable for a wide range of LED configurations. By separating inductor current sensing from LED current sensing, the LT3744 can easily be configured as a buck or negative output buck-boost controller. All input signals are referenced to board ground, eliminating the need for complex level shifters and simplifying system design.
In a negative output buck-boost configuration, the total forward voltage of the LED string can exceed the input supply voltage, enabling the driving of high-voltage LED strings using a low-voltage power source. Additionally, the LT3744 can be paralleled to handle large LED pulse or DC load currents, improving power density and component thermal management.
High Accuracy Current Detection
The LT3744 includes a high-accuracy current-regulated error amplifier that supports precise analog dimming down to 1/20 of the total current control range. This feature is essential in applications where the digital PWM dimming range is limited or where a very wide dimming range is required. For example, with a 100Hz PWM dimming frequency and a 1MHz switching frequency, the LT3744 can achieve a 1250:1 PWM dimming ratio, which can be extended to 25,000:1 when combined with 20:1 analog dimming.
Figure 1 illustrates the production consistency of the LT3744’s offset voltage as a function of temperature when the analog control input is 0V. The typical number of devices tested is 380. With the low offset of the error amplifier, the control loop achieves a typical accuracy of ±10% with 1/20 scale analog dimming. Figure 2 shows the distribution of the regulated voltage across multiple LED current sense pins when the control input is 1.5V. The full-scale accuracy is better than ±3%, equivalent to ±1.8mV at a 60mV full-scale regulation level.
Figure 1: The typical offset voltage of the LED current-regulating amplifier in the LT3744 is ±300μV with VCTRL = 0V.
NUMBER OF UNITS: number of devices
380 TYPICAL UNITS: typically 380 devices
REGULATED VLED_ISP – VLED_ISN VOLTAGE: Stable VLED_ISP – VLED_ISN voltage
Figure 2: The typical accuracy of the LED current regulation loop is ±1.7% at full scale current and VCTRL = 1.5V.
Flicker-Free Performance
One of the most critical performance metrics for LED drivers is the speed at which the LED current recovers during PWM dimming. In the initial switching cycles after the PWM turn-on signal rises, the driver’s performance has a significant impact on the final product quality. The LT3744 employs proprietary PWM, compensation, and clock synchronization techniques to deliver flicker-free performance, even when driving LEDs at 20A.
Figure 3 shows the LED current recovery over a 5-minute period when a 20V current is supplied to a red LED with a 12V power source. The switching frequency is 550kHz, the inductor is 1μH, the PWM dimming frequency is 100Hz, and the turn-on time is 10μs (1000:1 dimming ratio). The graph shows approximately 30,000 dimming cycles with no jitter in the switching waveform, and each recovery cycle is consistent.
Figure 3: LT3744 provides flicker-free LED dimming.
10V/DIV: 10V per division
5-MINUTE PERSISTENCE: lasts 5 minutes
KW3-Multi Circuit Micro Switch
Features
â—† Variety of lerers
â—† Multi circuit function
◆ Contact gap ≥ 3mm, suit of power tools
✿ Material
Made of high quality plastic and metal, rust resistance and corrosion resistance, durable enough for you to hanging items, So the product appearance is exquisite, perfect workmanship.
✿ Rating
You can meet the different RATING daily needs. Please pay attention to the model of the switch before purchase, to ensure that you purchase the same as you need.
✿ Vairous Sizes
Actuator Action is momentary and Actuator Type is long straight hinge lever. Switch Body Size as shown in the picture.So different sizes can meet all your daily different needs.
✿ Wide Application
Home appliance: micro oven, electric cooker, washing machine, electric heater, warmer, water fountain and so on.
Commercial appliance: Vending machine, electric toy, electric tools, duplicating machine and so on.
Machinery: Transport machinery, printing machinery, textile machinery and so on.
Multifunctional Mini Switch,Mini Micro Switch,Multi Circuit Micro Switch,Multi Circuit Function Switch
Ningbo Jialin Electronics Co.,Ltd , https://www.donghai-switch.com