Franki N. K. Poon

A novel high frequency current-driven synchronous rectifier applicable to most switching topologies

A novel current-driven synchronous rectifier is presented in this paper. With the help of a current sensing energy recovery circuit, the proposed current-driven synchronous rectifier can operate at high switching frequency with high efficiency. Compared with those voltage-driven synchronous rectification solutions, this current-driven synchronous rectifier has several outstanding characteristics. It can be easily applied to most switching topologies like an ideal diode. Constant gate drive voltage can be obtained regardless of line and load fluctuation. This makes it desirable in high input range application. Power converters designed with this synchronous rectifier are also capable of being connected in parallel without taking the risk of reverse power sinking. Their principle of operation is given in the paper. A series of experiments verify the analysis and demonstrate the merits.

A Single Phase Voltage Regulator Module (VRM) With Stepping Inductance for Fast Transient Response

A single-phase fast transient converter topology with stepping inductance is proposed. The stepping inductance method is implemented by replacing the conventional inductor in a buck converter by two inductors connecting in series. One has large inductance and the other has small inductance. The inductor with small inductance will take over the output inductor during transient load change and speed up dynamic response. In steady state, the large inductance takes over and keeps a substantially small ripple current and minimizes root mean square loss. It is a low cost method applicable to converters with an output inductor. A hardware prototype of a 1.5-V dc-dc buck converter put under a 100-A transient load change has been experimented upon to demonstrate the merit of this approach. It also serves as a voltage regulator module and powers up a modern PC computer system

Two methods to drive synchronous rectifiers during dead time in forward topologies

Conventional self-driven synchronous rectification forward topology cannot provide drive voltage for freewheeling synchronous rectifier (SR) when transformer magnetic reset process is over and zero voltage appears across the transformer windings. This causes SR body diode turn on and deteriorates the performance of synchronous rectification. In this paper, two SR drive mechanisms, gate charge retention drive and energy recovery current drive are presented. Both mechanisms can solve this body diode turn on problem. The current driven method also provides constant drive voltage and allows parallel operation. Two 250 kHz, 48 V input 5 V/10 A output DC-DC modules are designed using these two methods. 92% efficiency is achieved at full load for both modules.

Practical solutions to the design of current-driven synchronous rectifier with energy recovery from current sensing

A current-driven synchronous rectifier with current sensing energy recovery has been proved to be suitable for almost all high frequency switching topologies. The synchronous rectifier can be driven on and off automatically according to the current direction. In fact it can be taken as an active diode with very low power dissipation. Some theoretical analysis and experimental results have been shown in the previous work. This paper presents an extended analysis to some practical considerations when applying this current-driven synchronous rectifier in switching power converter design.

A constant power battery charger circuit with inherent soft switching and PFC

A battery charger circuit is proposed which operates as a constant power source by means of discontinuous operation of the two half bridge dividing capacitors. Its input characteristic is resistive and input harmonic current content can meet international regulation. Soft switching is also accomplished by paralleling two diodes across two dividing capacitors. A 12 V 65 W prototype was built to demonstrate the merit of this topology.

General impedance synthesizer using minimal configuration of switching converters

A general impedance synthesizer using a minimum number of switching converters is studied in this paper. We begin with showing that any impedance can be synthesized by a circuit consisting of only two simple power converters, one storage element (e.g., capacitor), and one dissipative element (e.g., resistor) or power source. The implementation of such a circuit for synthesizing any desired impedance can be performed by: (i) programming the input current given the input voltage such that the desired impedance function is achieved; and (ii) controlling the amount of power dissipation (generation) in the dissipative element (source) so as to match the required active power of the impedance to be synthesized. Then, the instantaneous power will automatically be balanced by the storage element. Such impedance synthesizers find a lot of applications in power electronics. For instance, a resistance synthesizer can be used for power factor correction (PFC), a programmable capacitor or inductor synthesizer (comprising of small high-frequency converters) can be used for control applications.

General impedance synthesis using simple switching converters

A general impedance synthesizer using a minimum number of switching converters is studied in this paper. We begin with showing that any impedance can be synthesized by a circuit consisting of only two simple power converters, one storage element (e.g., capacitor), and one dissipative element (e.g., resistor) or power source. The implementation of such a circuit for synthesizing any desired impedance can be performed by (i) programming the input current given the input voltage such that the desired impedance function is achieved; (ii) controlling the amount of power dissipation (generation) in the dissipative element (source) so as to match the required active power of the impedance to be synthesized. Then, the instantaneous power will automatically be balanced by the storage element. Such impedance synthesizers find a lot of applications in power electronics. For instance, a resistance synthesizer can be used for power factor correction (PFC), a programmable capacitor or inductor synthesizer (comprising of small high-frequency converters) can be used for control applications.

Input ripple current cancellation technique resulting in less differential mode noise current

Switching current generated from the main switch in a switching converter injects a substantial amount of ripple current at the input side of the converter. The ripple current is undesirable, as it becomes an EMI noise source. Differential mode current traditionally need bulky and costly filtering components to suppress the first several harmonics down to an acceptable level. An alternative way to reduce the ripple, by means of nullification technique, is proposed. Both active and passive nullification approach are discussed in this paper. This technique results in smaller components size and reduced cost.

Synthesis of impedance using switching converters

A general impedance synthesizer using a minimum number of switching converters is studied in this paper. We begin with showing that any impedance can be synthesized by a circuit consisting of only two simple power converters, one storage element (e.g., capacitor), and one dissipative element (e.g., resistor) or power source. The implementation of such a circuit for synthesizing any desired impedance can be performed by (i) programming the input current given the input voltage such that the desired impedance function is achieved; (ii) controlling the amount of power dissipation (generation) in the dissipative element (source) so as to match the required active power of the impedance observed at the input terminals of the given electrical to be synthesized. Then, the instantaneous power will automatically be balanced by the storage element. Such impedance synthesizers find a lot of applications in power electronics. For instance, a resistance synthesizer can be used for power factor correction (PFC), a programmable capacitor or inductor synthesizer (comprising of small high-frequency converters) can be used for control applications.