Design Of Current Self-adaptive LED Driver Circuit With Over-temperature Protection

LED(Light Emitting Diode)has a series of advantages,such as fast response,good anti-vibration capability,low power consumption,long service life,many types of colors,and green environmental protection,etc.With the deeper research and the rapid development of technology,LED emission efficiency will gradually increase,and will completely replace the traditional light source.The LED market is quite broad.However,the LED does not use the commercial power as a conventional light source.It must have a dedicated drive circuit,so the quality of the drive circuit affects the function of the entire circuit.The driver circuit is designed in this thesis has a shutdown function when the driver chip exceeds a certain temperature,and has a hysteresis effect.A voltage adaptive circuit is also designed which can make that the driver circuit has a certain ability to suppress the temperature rise.The specific design principle is as follows:(1)In order to make the circuit more stable,a second-order temperature compensation is performed on the voltage source circuit.The compensation current which decrease with the temperature is obtained in the low temperature compensation stages while the compensation current which increase with the temperature is obtained in the high temperature compensation stage.The two currents flow into the reference core circuit so that a voltage is gotten with a smaller temperature drift coefficient.The temperature drift coefficient obtained by the second-order compensation is smaller,making the subsequent circuit more stable and reliable.(2)The hysteresis thermal-shutdown circuit's principle is that the voltage which increase with the temperature is compared with the reference voltage.The output of the comparison is connected to the LED driving circuit after the three-stage inverter,to control the LED driving circuit's on and off.When the chip temperature exceeds the maximum temperature setting point,the LED driver circuit is turned off,making the LED failed to work.When the temperature drops to the temperature hysteresis point,the circuit is turned back on and then the LED circuit works normally.(3)The temperature self-adaptive circuit's principle is that the adaptive voltage generated by adaptive current acts on the LED driving circuit.When the temperature is higher than the adaptive temperature and lower than the shutdown temperature,the adaptive circuit works making the LED current decreases gradually with the adaptive voltage decreases.Using the same power supply voltage,the power will be reduced,and then can suppress the temperature rise.Based on 0.5?m standard CMOS technology,the circuit is simulated by Cadence Spectre.The result shows that the temperature coefficient of reference output voltage is 2.62x10-6/? in-50?+125 ? after compensation,and the power supply rejection ratio can reach up to 88 dB at the low frequency.The LED driver circuit current outputs 350mA in 0?64.2? and its changeable range is under 0.285%.The variation range of temperature self-adaptive current is 85mA when the temperature changes from 64.2 ? to 108?.The signal for hysteresis thermal-shutdown would be high level and the output circuit would turn off when the temperature rises up to 110?.The circuit wouldn't restart until the temperature down to 60?.