Design Of Ultra-high Voltage Two-Stage Regulator

With the development of modern electronic technology, high performance and low power consumption ICs become more and more popular, so power management ICs are being paid more and more attention.Low dropout regulator has the characteristics of simple structure, convenient for use, low output noise and small area, and is widely applied in many systems.Meanwhile, promoting LED lighting technology due to the world energy crisis is the general trend. To develop this technology, design of the control IC is one of the critical technology of LED lighting.Because LED lighting is always applied in high or ultrahigh voltage system, the control IC is always design in normal low voltage. Usually, a regulator will be used to convert high input voltage to low output voltage and provide enough load current. In this case, startup circuit is need in the regulator, and it will be designed with ultra-high voltage device. So, the startup circuit is not only cost large chip area, but also hard to be controlled accurately. On the other hand, a huge external capacitor, usually in the order of microfarad, is employed to ensure that the ultra-high voltage regulator is stable during all load range. This will increase the costs of the application board. Based on such backgrounds, the design of ultra-high voltage two-stage regulator was proposed, and it solves these problems perfectly.The topology and basic principals of regulator are introduced, the design specifications and the tradeoff between them are considered, and then focus on the transient and frequency response design. This regulator system contains two stages. The first stage is made of a depletion NMOS transistor as the startup circuit of the system due to the threshold voltage is negative. However the first stage can not be cut off when the load is light, hence the second stage is needed. The second stage is designed under normal high voltage to control the output voltage and output current accurately. To make sure the second stage is stable during full load range, it employed current buffer compensation technology and buffer impedance attenuation technology. Besides, the regulator system contains of some other blocks such as current bias circuit, bandgap voltage reference, over temperature protection, and over current protection.This design is based on vanguard international semiconductor,VIS700V 0.5μm process, it provide the special depletion mode NMOS. The design specifications are verified by simulation with the Hspice tool. The designed regulator system has an input voltage range of 8V to 600V, an output voltage of 5V, a maximum load current of 50mA, and a drop voltage of 3V when load is the heaviest. The external capacitor is only 0.1μf. The line regulation and load regulation are both perfect.