System and method for improving efficiency of a power factor correction boost pre-regulator

A power supply device comprises a driver circuit, a transistor switch, and a first transistor. The driver circuit is configured to provide a stable driving signal and a floating driving signal. The transistor switch has a first terminal, a second terminal connected to a first terminal of the driver circuit, and a third terminal connected to a second terminal of the driver circuit, and is configured to prevent a reverse current based on the floating driving signal. The first transistor has a first current electrode connected to the first terminal of the transistor switch, a second current electrode connected to the first voltage reference, and a control electrode connected to the third terminal of the driver circuit, and is configured to activate and deactivate based on the stable driving signal, and further configured to regulate an input voltage to a substantially constant direct current output voltage.

FIELD OF THE DISCLOSURE

This disclosure generally relates to power supplies, and more particularly relates to a system and method for improving the efficiency of a boost pre-regulator.

BACKGROUND

Computer systems typically rely on switch mode power supplies to assure the hardware interface between the available power source, such as an alternating current (AC), and the information handling system components. During start-up (first turned ‘ON’) or after brown-out events (temporary loss of an input voltage), a switch mode power supply may draw an inrush input current. The inrush current can lead to major problems in the switch mode power supplies. The inrush current can over-stress the internal input components and can lead to a safety circuit breaker disconnecting an external electrical power circuit. The inrush current can also momentarily distort the available AC input voltage, generating power grid perturbations that can affect other electronic devices connected to the same AC power source. Additionally, a boost switch can have large switching losses based on a reverse recovery phenomenon of a boost silicon diode in the boost switch.

DETAILED DESCRIPTION OF DRAWINGS

The power supply device100includes a diode bridge102, a metal-oxide-semiconductor field-effect transistor (MOSFET) switch104, a feedback circuit106, a power factor correction (PFC) module108, and a driver circuit110. The power supply device100can also include an inductor112, a capacitor114, a transistor116, and a current sensor118. The inductor112can be a boost inductor, and the transistor116can be a MOSFET, or a similar type of transistor.

The diode bridge102includes first and second terminals connected to a first voltage reference, VIN, a third terminal, and a fourth terminal connected to a second voltage reference, GND. The MOSFET switch104includes first and second terminals, a third terminal coupled to the third terminal of the diode bridge102, and a fourth terminal connected to an output voltage, VOUT. The feedback circuit106includes a first terminal connected to the third terminal of the diode bridge102, a second terminal, and a third terminal connected to the first terminal of the MOSFET switch104. The feedback circuit106also includes a fourth terminal connected to the fourth terminal of the MOSFET switch104, a fifth terminal, and a sixth terminal connected to the second voltage reference, GND.

The PFC module108has a first terminal connected to the second terminal of the feedback circuit106, and second and third terminals. The driver circuit110has a first terminal connected to the third terminal of the PFC module108, and a second terminal connected to the second terminal of the PFC module. The driver circuit110also has a third terminal connected to the second terminal of the MOSFET switch104, a fourth terminal connected to the first terminal of the MOSFET switch, a fifth terminal, and a sixth terminal connected to the second voltage reference, GND.

The inductor112has a first terminal connected to the third terminal of diode bridge102, and a second terminal connected to the third terminal of the MOSFET switch104. The capacitor114has a first terminal connected to the fourth terminal of the MOSFET switch104, and a second terminal connected to the fourth terminal of the diode bridge102. The transistor116has a first current electrode connected to the third terminal of the MOSFET switch104, a second current electrode connected to the second voltage reference, and a control electrode connected to the fifth terminal of the driver circuit110. The current sensor118has a first terminal connected to the fifth terminal of the feedback circuit106.

The diode bridge102rectifies an alternating current (AC) input voltage, VIN, received across the first and second terminals. The MOSFET switch104receives a floating driving signal. Based on the floating driving signal, the MOSFET switch can either activate to allowing a current to pass through the MOSFET switch, or can deactivate to prevent the current from passing through the MOSFET switch. The feedback circuit106provides a control signal based on a rectified input voltage, an input current level, a drain voltage, Vd, and a DC output voltage, VOUT.

The PFC module108provides a high-side pulse width modulated (PWM) signal and a low-side PWM signal based on the rectified input voltage, the input current level, the drain voltage, Vd, and the output voltage, VOUT. Based on variations in the rectified input voltage, the input current level, the drain voltage, and the output voltage, the PFC module108varies a duty cycle of the PWM signals so that the output voltage is regulated to a substantially constant DC voltage.

The driver circuit110provides a stable driving signal based on a low-side PWM signal, and provides a floating driving signal based on a high-side PWM signal. The driver circuit110can preferably include a high-side input/output, along with a low-side input/output. The high-side and low-side input/outputs can be used to provide different driving signal to different devices within the power supply device100. The stable driving signal can have a zero to ten volts range in relation to the second voltage reference, GND. The floating driving signal can also have a zero to ten volts range, however the stable driving signal is in relation to a floating source point. The floating source point can be the voltage provided to the fourth terminal of the driver circuit110.

Based on the input current associated with the rectified input voltage, the inductor112stores energy for discharge. The capacitor114stores the bulk voltage based on the rectified input voltage. The transistor116activates and deactivates based on the stable driving signal, and regulates the rectified input voltage based on the frequency and duty-cycle at which the transistor activates and deactivates. The current sensor118measures an input current level to determine whether the power supply device is under a high current load or a light current load.

During operation, the rectified input voltage is applied to the MOSFET switch104and to the transistor116. At start-up, the feedback circuit106monitors the rectified input voltage, and transmits a start-up control signal to the PFC module108upon detecting a zero crossing of the rectified input voltage. Upon receiving the start-up control signal, the PFC module108sends a high-side PWM signal202, as shown inFIG. 2, to the driver circuit110. The floating driving signal is then transmitted to the MOSFET switch104as a voltage difference between the voltages on the third and fourth terminals of the driver circuit110. Upon receiving the floating driving signal, the MOSFET switch104is activated.

The floating driving signal is preferably a floating source signal, such that the MOSFET switch104can be gradually brought to saturation over a few cycles of the rectified input voltage to limit an inrush current present in the power supply device100at start-up. While the MOSFET switch104is gradually brought to saturation, the capacitor114is charged and the input current is preferably kept at low levels. When the capacitor114is completely charged, the voltage across the capacitor, VOUT, is substantially equal to the drain voltage, Vd. When the feedback circuit106detects Vd, the feedback circuit sends a steady-state control signal to the PFC module108. At this point, the voltage at node Vdcan also be substantially equal to VOUT, because there is a relative short circuit created by the MOSFET switch104when it is saturated.

Upon receiving the steady-state control signal, the PFC module108outputs the high-side PWM signal202and a low-side PWM signal204to the driver circuit110, as shown inFIG. 2. At t1, the high-side PWM signal202deactivates the MOSFET switch104, and the low-side PWM signal204activates the transistor116. Upon receiving the low-side PWM signal204, the impedance of the transistor116continually decreases until the transistor reaches saturation. Thus, the impedance of the transistor116is substantially equal to zero creating a short circuit between the node Vdand the second voltage reference, GND, and dropping a voltage level206, at node Vd, to zero as shown inFIG. 2. Additionally, when the transistor116is activated, the current from the inductor112, merely constant during the switching process, starts flowing through the transistor116as shown as a current208inFIG. 2. The activation and saturation of the transistor116produces a power loss210, as shown inFIG. 2, in the power supply device100. The smaller the spike in the power loss210, the greater the efficiency of the power supply device100. Also at this time, the current through the MOSFET switch104gradually drops to zero. Prior to the voltage level206, at the node Vd, dropping to zero, the MOSFET switch104is off. Thus, there is no reverse current through the MOSFET switch104, and as a result the amount of switching losses is significantly reduced.

At t2the low-side PWM signal204deactivates the transistor116, and the current from the inductor112stops flowing through the transistor as shown by the current208inFIG. 2. The MOSFET switch104and transistor116are both off, and thus the current from the inductor112discharges the parasitic output capacitors (not shown) of the MOSFET switch and charges the parasitic output capacitors of the transistor. The charging/discharging of the parasitic capacitors allows the voltage level206, at node Vd, to ramp-up until it reaches VOUT. At t3the feedback circuit106determines that the voltage level206, at node Vd, is substantially equal to VOUTand sends a control signal to the PFC module108to activate the MOSFET switch104in a lossless zero switching voltage transition (ZVT). The MOSFET switch104is activated in a lossless ZVT because at activation Vdis substantially equal to VOUT, such that there is not a voltage drop across the MOSFET switch. Thus, there are not any energy losses resulting from the activation of the MOSFET switch104. The power supply device100operates in substantially the manner at t4, t5, t6, and t7as t1, t2, t3, and t4as shown inFIG. 2.

Additionally, if a brown-out event is detected by the feedback circuit106, a brown-out control signal is sent to the PFC module108. A brown-out event occurs when the input voltage level is zero for an extended amount of time. Upon receiving the brown-out control signal, the PFC module108sends PWM signals to the driver circuit110which results in the MOSFET switch104and the transistor116being deactivated. After the brown-out event, the feedback circuit106prevents the inductor112from being saturated from an inrush current because the MOSFET switch104and the transistor116are deactivated. Upon detection of a zero crossing of the rectified input voltage, the feedback circuit106sends the start-up signal to the PFC module and to the power supply device100operates as stated above.

FIG. 3shows the power supply device100including the MOSFET switch104having transistors320and322, and the driver circuit110having a high-side driver324and a low-side driver326. The transistor320has a first current electrode connected to the second terminal of the inductor112, a second current electrode, and a control electrode. The transistor322has a first current electrode connected to the second current electrode of the transistor320, a second current electrode connected to the first terminal of the capacitor114, and a control electrode connected to the control electrode of the transistor320. The high-side driver324has an input terminal connected to the second terminal of the PFC module108, an output terminal connected to the control electrode of the transistor320, and a floating source point terminal connected to the second current electrode of the transistor320. The low-side driver326has an input terminal connected to the third terminal of the PFC module108, an output terminal connected to the control electrode of the transistor116, and a stable source point terminal connected to the second voltage reference, GND.

Upon start-up of the power supply device100, the high-side driver324receives the high-side PWM signal202from the PFC module and sends the floating source point driving signal to the transistors320and322. The floating source point driving signal activates the transistors320and322, and allows the current from the inductor112to flow through the transistors. As the transistors320and322saturate and the feedback circuit106detects that the output voltage, VOUT, is substantially equal to Vd, the high-side PWM signal202drops to zero along with the floating driving signal, so that the transistors are deactivated. At substantially the same time the low-side PWM signal204goes high, and the low-side driver326provides the stable driving signal to the transistor116thus activating the transistor.

At this point, the power supply device100is preferably operating in a steady-state mode, such that the transistor116and the transistors320and322have alternating activation periods as shown by the high-side PWM signal202and the low-side PWM signal204ofFIG. 2. The alternating activation periods of the transistor116and the transistors320and322regulate the rectified input voltage from the diode bridge102to the substantially constant DC output voltage, VOUT, across the capacitor114. Additionally, a brown-out event can be detected when the input voltage is zero for a specific amount of time. The feedback circuit106then sends the brown-out control signal to the PFC module108, which ends both the high-side PWM signal202and the low-side PWM signal204. Thus, the high-side driver324and the low-side driver324end the driving signals, and the transistors116,320, and322are deactivated. Upon the next zero crossing after the input current resumes, the power supply device100begins in start-up mode. Based on the start-up beginning at a zero crossing, the inrush current of the power supply device100is reduced. It should be understood that the feedback circuit106and the PFC module108could be implemented with a dedicated Application Specific Integrated Circuit (ASIC) and the like.

The transistor116and MOSFET switch104are configured to increase the efficiency of the power supply device100.FIG. 4shows a flow diagram of a method400for using synchronous switches to improve the efficiency of a power supply device. At block402, a zero crossing of an input voltage is detected. A transistor switch is activated at block404. The transistor switch can include two MOSFET transistors. At block406, a capacitor and the transistor switch are saturated. The transistor switch is deactivated at block408. At block410, a first current through the transistor switch is reduced based on the transistor switch being deactivated.

At block412, a first transistor is activated. The first transistor can be a MOSFET transistor. At block414, a reverse current through the transistor switch is prevented based on the transistor switch being deactivated. The first transistor is saturated at block416. At block418, the first transistor is deactivated. A plurality of parasitic capacitors charge at block420. Each of the parasitic capacitors is associated with either the first transistor or the transistor switch. At block422, the transistor switch is activated in a zero voltage switching transition based on the charge of the parasitic capacitors being substantially equal to VOUT. The input voltage is regulated to a direct current output voltage at block424. At block426, a brown-out event is detected. At block428, it is ensured that the first transistor and the transistor switch are deactivated, and the flow diagram continues as stated above at block402.