With the acceleration of urban construction, leisure squares and green parks, as the highlights of the city, represent the desire of urbanites to return to nature. Water represents spirituality, water features and fountains are an integral part of leisure plazas and green parks, and the demand for underwater lights is considerable. At present, color underwater lights are generally traditional PAR lights, and various colors are required to add filter light, which greatly reduces the luminous efficiency. It can be seen from the comparison that in the red, green and blue underwater lights, the total luminous flux of the traditional lamps is 1~2 times that of the LED underwater lights. The packaging technology of the LEDs determines the direction of the light source is very strong, and the LED volume is very Small, able to match optical lenses of various angles, these characteristics determine that traditional underwater lights consume 13 times more power than LED underwater lights. It can be seen that the energy saving effect of the LED underwater light is quite remarkable. In addition, the spectral distribution of LED determines that its color purity and saturation are unmatched by traditional PAR lamps, so it has a strong competitive advantage.
For example, the LT3474 and LT3475 are high-voltage, high-current, single-channel and dual-channel buck LED converters with wide PWM dimming ratios that can drive one or more LEDs with currents up to 1A and 1.5A. Each LED achieves a brightness of 80 lumens to 120 lumens (this value will be higher when LEDs with higher output are available). These dedicated LED drivers feature an onboard high-voltage NPN power switch and internal sense resistors designed to maximize board space, reduce component count, and simplify design.
With its high-end sense resistors, the LT3474 and LT3475 are capable of driving grounded LEDs, which is an important advantage in many systems. Current mode control and a precise reference voltage optimize loop dynamic performance to achieve a well-regulated, low ripple constant LED current. The thermally enhanced bare pad package maintains a low junction temperature during high power operation in a stress environment. A PWM pin uses the dimming MOSFET gate signal to increase the dimming ratio of the converter by maintaining a constant output capacitor voltage and controlling the loop state during PWM dimming off time. The shutdown and external analog current regulation pins provide a simple interface for greater LED light and current control flexibility in any system.
Single Channel Step-Down 1A LED Driver
The LT3474 buck converter 1ALED driver shown in Figure 1 has features that make it suitable for automotive applications (and other battery-powered applications) or industrial applications where board space is limited, high voltages and high ambient temperatures are present. The circuit uses a high-end integrated 100mΩ sense resistor (for true LED current sensing and regulation) compared to an inefficient method that uses a constant voltage and an energy-consuming bias resistor to bias the LED. Its performance is superior. The 4V to 36V input voltage range makes it ideal for use with protection circuits that have minimal (or no) input transients in automotive, industrial, and aerospace applications. In these applications, long cables from the battery can cause very high High input spikes.
Figure 1 LT3474 high voltage step-down LED driver can regulate 1A current
In one LED and two LED applications, the boost NPN power switch achieves high efficiency (Figure 2). A boost diode is integrated to further reduce the number of components. Driving the shutdown pin to ground will turn off the LED and bring the brightness of the LED from 400:1 TrueColorPWM? Dimming and an external MOSFET driver are controlled using an analog 25:1 (or filtered PWM) signal on the VADJ pin. The switching frequency can be set from 200kHz to 2MHz with an external resistor, which optimizes the application for maximum efficiency or minimum component size.
Figure 2. The LT3474 buck converter can efficiently drive single or multiple LEDs.
The maximum output voltage of the LT3474 is clamped at 13.8V, which prevents the LED on the LT3474 output from opening. Short-circuit protection makes the LT3474 the last feature to be a "bulletproof" converter in all kinds of LED fault conditions. Dual channel step-down 1.5A LED driver.
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