Vrms and rectified current sense full-bridge synchronous-rectification integrated with PFC

• US 20070058402A1
• Filed: 09/12/2005
• Published: 03/15/2007
• Est. Priority Date: 09/12/2005
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Inventors: Shekhawat, Sampat, Huh, Dong-Young, Randall, Ronald
• Granted Patent: US 7,269,038 B2
• Time in Patent Office: Days
• US Class Current: 363/89
• CPC Class Codes: H02M 1/0085 Partially controlled bridges
• CPC Class Codes: H02M 1/42 Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
• CPC Class Codes: H02M 7/219 in a bridge configuration
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y02P 80/10 Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier

Abstract

A synchronous full bridge rectifier is controlled to provide a power factor near unity. The full bridge rectifiers are transistors each with a controlling input. The AC input signal and currents within the circuit are sensed and sent to a controller. In response, the controller output control signals to turn on/off the rectifying MOSFETS on a timely basis to form a power factor of near one with respect to the AC input signal. The full wave rectifier is made of N-channel MOSFET'"'"'s, some with fast body diodes. The MOSFET'"'"'s are rectifiers and PFC control elements. The result is a one stage synchronous rectifier with PFC. A solid state precision analog differential amplifier senses the AC line waveform and high frequency current transformers sense the currents. The controller accepts the inputs of the amplifier and the sensed currents and outputs control signals that turn on and off the four MOSFET'"'"'s. The timing of turning on/off is arranged so that the current drawn from the AC source is sinusoidal and matches the phase of the sinusoidal AC source.

Claims

1. A synchronous full bridge rectification circuit having an AC input and a DC output, the circuit comprising:

a boost inductor with a first node coupled to the AC signal;

a full bridge rectifier circuit functionally connected between a second node of the boost inductor and the DC output, the full wave rectifier circuit comprising at least two controllable switches;

means for sensing current in the DC output and in the charging paths of the boost inductor on both half cycles of the AC input; and

a controller arranged to receive the AC signal, the sensed currents, and the DC output, wherein the controller outputs signals to control the at least two controllable switches in a manner where the PF of the synchronous full bridge rectifier approaches unity with respect to the AC source.

2. The circuit of claim 1 wherein the at least two controllable switching devices comprise:

a first and a second FET (field effect transistor) each FET defining a gate, a drain and a source, wherein the control node controls the conduction between the drain and source of each transistor, and wherein the gates of each transistor are functionally connected to and controlled by the controller, and wherein the full bridge rectifier further comprises;

a third and fourth FET each defining a gate, a drain and a source, wherein the control node controls the conduction between the drain and source of each transistor, and wherein the gates of each FET are functionally connected to and controlled by the controller, and wherein each of the first, second, third and fourth switching devices has a diode with its anode functionally connected to the source and its cathode to the drain.

3. The circuit of claim 1 wherein the means for sensing current comprises toroid current transformers constructed to sense currents at a frequency higher than 50/60 Hz.

4. The circuit of claim 1 further comprising a circuit disposed functionally connecting the AC signal to the controller, the circuit comprising:

a differential amplifier that receives the AC signal; and

a rectifier, arranged to receive the output of the differential amplifier and rectify that signal and present that signal to the controller, and wherein the cross over points and peaks of the rectified AC signal are determined and used by the controller together with the sensed current to control the timing of the turning on and off of the four controllable switching devices so that the PF of the synchronous full bridge rectifier circuit approaches unity.

5. The circuit of claim 4 wherein the controller comprises:

a fast PWM function to control the drive of the switches as a function the AC half cycles to emulate the rectified and multiplied AC input;

a slow DC output regulator loop that controls the DC output; and

means for controlling the switching times of the rectifiers to prevent shoot through and provide ZVS operation.

6. The circuit of claim 1 wherein the AC input has two current carrying leads, and wherein the boost inductor comprises two mutually coupled inductors, one in each leg of the AC input.

7. A method for synchronously full wave rectifying an AC input to provide a DC output, the method comprising:

inductively reacting to current traveling from the AC input to a full bridge rectifier circuit, the full bridge having at least two controllable switches;

coupling the output from the full wave rectifier circuit to the DC output;

sensing current in the DC output;

sensing the charging currents to the inductive reactance;

sensing the AC signal and sending the sensed AC and the sensed currents to a controller; and

wherein in response to the received signals, the controller turns on and off the at least two controllable switching devices in a manner where the PF of the synchronous full bridge rectifier approaches unity with respect to the AC source.

8. The method of claim 7 wherein the step of sensing the AC signal comprises the steps of:

differential amplifying the AC input;

rectifying the differentially amplified AC signal; and

presenting rectified differentially amplified signal to the controller, wherein the controller performs the method comprising the steps of;

determing the zero crossing over points and peaks of the rectified AC signal;

comparing the zero crossing points and peaks to the sensed current, and in response therefrom; and

timing the turning on and off of the four controllable switching devices so that the PF of the synchronous full bridge rectifier circuit approaches unity.