Study On Emulated Current-Mode Control Methods Of Switching Mode Power Supply

Switching dc-dc converters realize their output voltage regulation by adjusting the turn on time of switch devices. In some special cases when very short on-times are needed, traditional control method of switching converters can not operate well due to error caused by spike signal. Thus new control methods are need for such applications.In this paper, Emulated current-mode (ECM) control method is a new type of switching power supply control technology. Being different from the traditional peak current-mode control method, the objective of ECM is to create a signal that accurately represents the current through the buck switcher without actually making a direct measurement. This control method could prevent leading edge spike from tripping PWM comparator. The emulated switch current can be broken down into two parts, a pedestal and a ramp. Without actually making a direct measurement, the emulated current signal is free of noise interference of leading edge spike. Another advantage of this new control method is giving full play to the ability of traditional peak current-mode control. The switch converters using emulated current-mode control method has attracted widespread concern in the industry field. National Semiconductor Corporation has developed the corresponding chips and applied to the design of switching power supply products successfully.In this paper, voltage-mode control and current-mode control methods of switching power supply are briefly introduced. Based on this, the emulated current-mode control method of switching power supply is studied in detail and compared with peak current-mode control. Finally the analytical results are verified by simulation. The controller is easy to realize. Simulation results indicate that leading edge spike has no impact on emulated current-mode controller which works well without extra filtering circuit.