A hybrid-type Single Inductor Boost/Buck Inverting Flyback(SIBBIF) DC-DC Converter is presented. To increase the converter efficiency, a flying capacitor as well as an inductor is adopted as another energy transfer medium together with multi-level gate driver (MLGD). Besides, to enhance load transient response, hybrid fast transient control (HFTC) is adopted. The proposed chip is implemented in a 0.5-μm power BCD process and operates at 1.25 MHz with a max efficiency of 87.1% at an output power of 600 mW.
I. IntroductionIn Active Matrix Organic Light Emitting Diode (AMOLED) displays, positive and negative supply voltages are generally required [1]. Thus, several Single-Inductor Bipolar-Output (SIBO) converters have been introduced [2], [3]. However, [2] is too complicated to design an inductor current sensing circuit for current mode control and cannot operate as buck converter for supply voltage(5V) from a Universal Serial Bus(USB) port. And [3] is a commercialized version of a SIBO converter, which is simpler than that of the aforementioned converter; it utilizes combining two separate operation modes, a boost mode and an inverting flyback mode. However, this converter has poor efficiency owing to its large inductor peak current and does not have buck operation either. Therefore, Single-Inductor Boost/Buck Inverting Flyback converter with the method of efficiency enhancement is presented in this paper. Fig. 1 shows the comparison of the proposed SIBBIF converter using inductor L and flying capacitor CF as hybrid energy transfer media (HETM) and previous SIBO converter [3]. The previous SIBO converter transfers energy to VOP and VON simultaneously during II. However, this is an inefficient type of energy transfer since the input VIN is isolated from the energy delivering path during II as in a flyback operation. Furthermore, the peak current level of the inductor becomes large due to the extremely steep slope of discharging inductor current through VON -VOP/L during II. In comparison, since the proposed SIBBIF converter maintains VIN and ensures a low amount of voltage variation across CF during the charging/discharging intervals through the use of a proper capacitance value, the overall discharging inductor current slope can be gentler than that of previous SIBO converter [3]. Thus, the peak inductor current of the proposed method is lower than that seen in a previous method under the same output power as shown in Fig. 1. This decreases the rms current and enhances the efficiency. Besides, the charge is delivered sequentially not concurrently in the new SIBBIF converter as shown in Fig. 1. This indicates that the transferring path is not isolated from the input during the (2) period of the boost operation, unlike the previous SIBO converter [3]. Thus, energy can be delivered efficiently. Buck operation: SIBBIF converter operates as boost mode for VOP normally. However, when VIN of 5V from USB port is connected, buck operation is performed automatically. Even though IL is still charging in phase (2) period of bu...
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