LED Driver Circuit With Self-Adaptive Current To Temperature

LED as a new era of green lighting light source is more and more popular and widely used in many fields because using it will not pollute the environment, and energy consumption is less than other lighting, and it itself has a long life,. Therefore, the required amount of driver chip is becoming more and more. But the use of the chip has a large extent influenced by temperature and the forward current. In order to protect the chip in the driver circuit, over-temperature protection circuit needs to be added. At normal temperatures, the circuit is working properly. When the temperature exceeds the allowable maximum junction temperature, the drive circuit will stop working due to the addition of over-temperature protection circuit. This approach will reduce the power consumption of the chip, and prevent driver circuit from burning out at the same time.Two measures were taken to protect LED driver chips. One is that power is cut off as soon as possible until the system cool down before restarting the driver chip, the other is that the current directly is reduced when the chip is over-temperature to reduce thermal power consumption, inhibit the rise of temperature. But they are not suitable for high-power continuous illumination. Then the thermal hysteresis shutoff protection circuit with the Schmidt characteristics is designed to control the whole circuit temperature, and avoid thermal oscillation. Then an LED driver circuit with self-adaptive current to temperature is designed which needs the MOS transistor's turned on or off to control. When the temperature reaches a certain value, PTAT current is applied to the whole circuit. At this time the overall current in the circuit will be reduced so that the automatic adjustment of the drive current to achieve. It will achieve uninterrupted lighting because its change was not perceived by human eyes in the circumstances.Finally,in order to prevent sudden changes in the external voltage, over-voltage protection circuit is also designed to protection circuit in a safe state.The structure block diagram of the driver chip and main design parameters of the index are given, and elaborated the principle of adaptive current with temperature regulating function. Then according to the indicator of performance determined, each sub-module within the circuit design and simulation analysis are completed through the circuit design software of Cadence. Finally, the whole chip simulation and verification were conducted to examine the matching between the design and the requirements of specification.The Spectre simulation results show that the variances of driving current are lessthan 1.1% and 0.28% respectively when the supply voltage was changed by ±10% or ambient temperature was varied in the range of 0~83 ?.From 83 ? to 103 ?, the maximum adjustable amplitude of driving current is 93 mA, which the visual lighting of human changes less than 3%, and LED luminous flux maximum is reduced by 25%.Its change was not perceived by human eyes in the circumstances. When the temperature rose to 106?, the output circuit would be turned off and wouldn't be restarted until the temperature dropped to 69?. Meanwhile, effective regulation of the drive current will be better achieved and circuit's energy will be reduced.