Valley Current Mode Pulse Train Controlled Switching Converter

With the development of power electronics technology and the wide use of portable electronic equipment, the requirement on the performances of switching power supply (SPS) becomes more and more important. Problems like slow transient response and complicated control circuit in traditional Pulse Width Modulation (PWM) control technique impede the improvement of SPS seriously. In such case, Pulse train (PT) control technique was proposed to improve the performance of switching converter. PT control is a new kind of fixed frequency control technique for the converters oprating in discontinuous conduction mode (DCM). Different from the tranditional voltage and current control technique, PT control regulates the output voltage through the presence and absence of preset power control pulses, instead of adjusting the duty ratio cycle by cycle as in pulse width modulation (PWM) technique. Advantages in PT control technique, such as no need for compensation circuit, small number components in control circuit and fast transient response, make it successful in many application requiring high reliability.When PT controlled switching converter operating in discontinuous conduction mode (DCM), the energy from the input power source is completely delivered to the load in each swiching cycle, which means the variation of energy stored in the inductor is zero for each swiching cycle. However, when PT controlled switching converter operating in continuous conduction mode (CCM), in each switching cycle, the input energy may be higher or lower than the energy required by the load, which leads to the variation of energy stored in inductor is not zero, making low-frequency oscillation occur in such case. Although larger equivalent series resistance (ESR) of output capacitor can effectively inhibit the low-frequency oscillation phenomenon, however, larger ESR increases switching ripple of output voltage.To inhibit such low-frequency oscillation phenomenon exists in traditional PT controlled CCM switching converter, valley current mode pulse train (VCM-PT) control technique is proposed and studied in this paper. It can be proven that the variation of energy stored in the inductor of VCM-PT controlled CCM converter always be zero in one switching cycle, thus VCM-PT control technique can effectively inhibit the low-frequency oscillation. Computer simulation and experiment validate the theoretical results.Finally, in order to expand the load range of VCM-PT controlled switching converters, the multi-valley current mode pulse train (MVC-PT) control technique is prsposed in this paper. The principle and control strategy of VCM-PT control are studied with a Boost converter operating in CCM as an example. Simulation results verify the theoretical analysis and the feasibility of the controller design.