Abstract: LED is a new type of semiconductor solid-state light source with significant advantages of low power consumption, long life and environmental protection. The PT4115 is used for LED constant current driving, and an LED spotlight driving system with intelligent dimming control is designed. Based on the input voltage range of the PT4115, a power adapter based on TOP249Y is designed. The results show that the system can effectively realize the intelligent control of the lamp, improve the power efficiency and save energy.
0 Preface
LED lighting is the mainstream of global energy conservation, and high-power LED lighting is the mainstream trend of the world's lighting system. High-power LED features high brightness, energy saving, safety and stability, saving 60% ~ 70% compared with traditional light sources.
The traditional sound and light control delay controller can realize the control of the lamp well. When the light is dark or at night, it can effectively realize that "the person comes to light, the person goes to the light to turn off", but because the switch is used A mechanical controller such as a relay, so it is more likely to be damaged due to frequent switching in places with a large flow of people.
According to the existing high-power LED spotlight products on the market, intelligent lighting systems can be designed for use in corridors, stairs, classrooms and other places.
The system is powered by a 24 V / 3 A switching power supply, and the lower stage can distribute multiple LED intelligent lighting modules (see Figure 1). The controller adopts AT89C2051, and the constant current drive adopts PT4115 chip. The lighting and brightness of the lamp are realized and changed by dimming.
The DIM terminal of the PT4115 chip can be adjusted by PWM dimming from 0 to 100%. According to this feature, an intelligent dimming module integrating sound control, light control and time control is designed. Its functions are:
(1) When there is light (natural light), the light does not illuminate with or without sound.
(2) When there is no light (natural light), if someone produces a sound, the controller first determines the time period. If the sky is completely dark (defined as the first time period), the LED emits 100% brightness. In the remaining time period, the sky is still brighter, and the controller can output a 50% duty cycle square wave to make the LED emit 50% brightness, which can further save power and improve power efficiency.
Figure 1 LED intelligent drive system block diagram
1 PT4115 based constant current drive
1. 1 Introduction to PT4115 chip
PT4115 is a continuous inductor current conduction mode buck constant current source for driving one or more series LEDs. PT4115 input voltage range is 6 V ~ 30 V, output current is adjustable, up to 1. 2A Depending on the input voltage and external components, the PT4115 can drive up to tens of watts of LEDs. The PT4115 has a built-in power switch that uses high-side current sampling to set the average LED current and accepts analog dimming and a wide range through the D IM pin. PWM dimming. When the voltage of D IM is lower than 0.3 V, the power switch is turned off, and the PT4115 enters a standby state of extremely low operating current.
1. 2 LED spotlight drive circuit
When V IN is powered up, the initial current of the inductor ( L ) and current sense resistor ( RS ) is zero and the LED output current is also zero (see Figure 2). At this time, the internal power switch is turned on and the potential of SW is low. Current flows from V IN to ground through inductor (L), current sense resistor (RS), LED, and internal power switch. The slope of current rise is determined by V IN , inductor (L ), and LED drop, producing a voltage across RS. Poor VCSN, when (V IN-VCSN ) 》 115 mV, the internal power switch is turned off, and the current flows through the inductor (L), current sampling resistor (RS), LED and Schottky diode (D) with another slope; When (V IN-VCSN ) is 85mV, the power switch is turned back on, so that the average current on the LED is IOUT = (0. 085+ 0. 015) /2 ? RS = 0. 1 /R S. If the dimming function is not used, the DIM pin can be left floating and the set maximum current can be output.
Figure 2 LED spotlight drive circuit
2 Top249Y based 72W switching power adapter design
2. 1 Transformer design
High-frequency transformer design should pay attention to: 1) In the design of high-frequency transformer, the magnetic induction in the core should not be saturated at the maximum output power, so as to avoid distortion in large signals. 2) During the transient process, the leakage inductance and distributed capacitance of the high-frequency chain will cause surge current and spike voltage and pulse top oscillation, which will increase the loss and cause damage to the switch tube in severe cases. At the same time, when the number of turns of the output winding is large and the number of layers is large, the influence of the distributed capacitance should be considered, and reducing the distributed capacitance is beneficial to suppress the interference of the high-frequency signal on the load. It is difficult to reduce the distributed capacitance and leakage inductance at the same time for the same high-frequency transformer. The proper capacitance and inductance should be ensured according to different working requirements.
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