White Led Driver Circuit In The Current Regulation Circuit Design

With the development of hand-held devices which have several white LEDs as their backlights, the white LED boost converter is in largely demand. The backlights are required to be as bright as need and the degree of the brightness should be expediently adjustable. The degree of brightness of the LED is direct ratio of its current. The current regulator designed in this dissertation can regulate the degree of brightness of the white LED by regulating the current of LED.The current regulator can work in two modes which are movie mode and strobe mode. User can set needed current by changing the value of outside resistors in each mode. In movie mode, the LED current is regulated at 100 times the current user-selected, and maintains constant; in strobe mode, the momentary LED current is equal to 1000 times the current user-selected.The current regulator is divided into two parts that are voltage control circuit and current control circuit. The voltage control circuit boosts the input voltage to needed level to supply the LED current and level off the LED current in movie mode. The current circuit is composed of three subcircuits: the user- selectable current source, 1x or 10x current amplify circuit and the 100-times current amplify circuit. The user-selectable current source converts the value of the resistor set by user to corresponding current, 1x or 10x current amplify circuit copies the user-selected current in movie mode and amplifies it into 10 times in strobe mode. The 100x current amplify circuit regulate the LED current at 100 times the current output by lx or 10x current amplify circuit. To design the lx or 10x current amplify circuit, a low voltage emitter follower augmented current mirror, which has precision amplificatory, is brought forward.Every composing cell, module circuit and the entire circuit designed in this dissertation are simulated by Hspice. The simulation reports show that they are all good in performance. Under typical work condition, the maximum error of the current adjusting of the current regulator is 0.7% in movie mode, and 1% in strobe mode.