Design Of The High Performance Relaxation Oscillator Applied To LED Constant Current Driver

Nowadays, LED constant current driver is one of the hottest globe research aspects. The performance of LED constant current driver is deadly determined by its oscillator on-chip. The relaxation oscillator that has advantages of low cost, low dissipation and which duty cycle that strictly maintains 50% is always selected for the oscillator on-chip in existing products. On the other hand, this oscillator also has disadvantages of high voltage dependency, high temperature dependency and high dependence of process error.In this dissertation, a design of high performance relaxation oscillator applied to LED constant current driver will be discussed based on their principles. This dissertation particularly points out the origin of voltage and temperature dependency and the effects brought by process error, whereas the disadvantages of existing products. New methods have been put forward that use bandgap and mixed resistance to reduce temperature dependency of charge current, use LDO to eliminate voltage dependency of charge bias voltage, use the principle of microelectronics and solid state electronics and art of layout to compensate charge current which has been affected by process error. Meanwhile the designs of the circuits concerned have been introduced, especially for mixed resistance and process error compensation circuit. And then the solution of match problems has been given.Finally the relaxation oscillator designed has been simulated, the results indicate temperature dependency has been reduced to 600ppm/℃and voltage dependency has been limited to 0.08%/V, maxim error is under 20%, the typical dynamic dissipation is only 455μW. The performance of relaxation oscillator designed achieves the target and exceeds existing products.