System and method for a bridgeless power supply

A system and method for a bridgeless power supply is disclosed. The bridgeless power supply includes a digital control module that controls a first switch, a second switch, and a transistor, thereby the bridgeless power supply rectifies an alternating current (AC) variable input voltage and regulates a direct current (DC) output voltage. The digital control module applies a first and second control signal to the first and second switches thereby rectifying and regulating the AC variable input voltage. Additionally, the digital control module provides a high frequency and constant duty cycle third control signal to the transistor in series with an output transformer of the bridgeless power supply device, to assure primary-to-secondary isolation.

FIELD OF THE DISCLOSURE

This disclosure relates generally to power supplies, and relates more particularly to a bridgeless power supply.

BACKGROUND

A classic desktop computer AC-DC power supply uses three different stages to convert an AC input voltage to a regulated DC output voltage. The three power processing stages are an input diode rectification bridge, an active power factor correction (PFC) boost pre-regulator and a DC-DC buck regulator with multiple outputs. Each power processing stages has power losses, which add together to negatively impact the overall power conversion efficiency. Additionally, the complexity of the AC-DC power supply circuitry increases the cost and lowers the overall performance reliability of the AC-DC power supply.

DETAILED DESCRIPTION OF DRAWINGS

A bridgeless power supply is disclosed. The bridgeless power supply includes a digital control module that controls a first switch, a second switch, and a transistor; thereby the bridgeless power supply rectifies an alternating current (AC) input voltage and regulates a direct current (DC) output voltage. The first and second switches are in a bridge configuration with two diodes, and the digital control module applies a first and second control signal to the first and second switches thereby rectifying the AC input voltage. The digital control module provides a high frequency and constant duty cycle third control signal to the transistor in series with an output transformer of the bridgeless power supply device, to provide primary-to-secondary isolation. The output voltage of the circuit is based on the rectified input voltage and the duty cycle of the third control signal applied to the transistor.

FIG. 1shows a block diagram of a bridgeless power supply device100including a digital control module102, a switching/rectification module104, and a DC-DC converter module106. The digital control module102sends a first control signal and a second control signal to the switching/rectification module104. The switching/rectification module104uses the first and second control signals to rectify and regulate an alternating current (AC) input voltage, labeled VIN. A third control signal is applied by the digital control module102to the DC-DC converter module106, and the DC-DC converter module uses the third control signal to reduce the rectified and regulated voltage from the switching/rectification module104to a lower and constant direct current (DC) voltage. The DC-DC converter module106has a plurality of outputs that supply different DC output voltages to different components attached to the bridgeless power supply100based on the regulated DC voltage. The digital control module102receives information about the output signal, the plurality of output terminals and the input voltage from a first input terminal and a second input terminal, and uses this information to constantly adjust the duty cycle of the first and second control signals applied to the first and second switches.

FIG. 2shows a combined circuit and block diagram of a particular embodiment of a bridgeless power supply device200. The bridgeless power supply device200includes a digital control module202, a first switch204, a second switch206, a first diode208, a second diode210, a third diode212, an inductor214, a capacitor216, a transformer218, a MOSFET transistor220and an output filter module228. The digital control module202includes a first input terminal, a second input terminal, a first output terminal, a second output terminal and a third output terminal. The first switch204includes a first terminal connected to a first voltage reference of an input voltage, labeled VIN, and a second terminal. The second switch206includes a first terminal connected to a second voltage reference of the input voltage and a second terminal connected to the second terminal of the first switch204. The first diode208includes a first terminal and a second terminal connected to the first terminal of the first switch204. The second diode210includes a first terminal connected to the first terminal of the first diode208and a second terminal connected to the first terminal of the second switch206. The third diode212includes a first terminal connected to the first terminal of the first diode208and a second terminal connected to the first terminal of the first switch204.

The inductor214includes a first terminal and a second terminal connected to the first terminal of the first diode208. The capacitor216includes a first terminal connected to the first terminal of the inductor214and a second terminal connected to the second terminal of the first switch204. The transformer218includes a primary winding and a secondary winding. The primary winding of the transformer218includes a first terminal connected to the first terminal of the inductor214and a second terminal. The secondary winding of the transformer includes a first terminal connected to a third voltage. reference, labeled GND, and a plurality of terminals connected to the output filter module228. The transistor220includes a first current electrode connected to the second terminal of the primary winding of the transformer218, a second current electrode connected to the second terminal of the first switch204, and a control electrode connected to the third output terminal of the digital control module202.

The bridgeless power supply device200eliminates the need for an input rectification diode bridge to rectify an AC input voltage. Instead, the bridgeless power supply device200uses the digital control module202to drive the first switch204and the second switch206are thereby rectify and regulate the input voltage. To perform all the functions of a classic power supply without the same power losses, the first and second switches204and206and the first and second diodes208and210are placed in a bridge configuration and combined with the third diode212, a freewheeling diode. These functions of a classic power supply are input voltage rectification, power factor correction (PFC) and output voltage regulation. The bridgeless power supply device200works as a buck converter to regulate the input voltage to a constant DC output voltage. During operation of the bridgeless power supply device200, half of the bridge configuration is active at one time, alternating for each semi-period of the input voltage and only when the input voltage is higher than the regulated bulk voltage, labeled VBULK. When input voltage is lower than the regulated bulk voltage, the first switch204and the second switch206are off. The next stage in the bridgeless power supply device200uses a fixed high frequency duty cycle control signal to create a buck converter and to assure primary-to-secondary isolation. This isolated fixed duty cycle buck converter has much smaller magnetic components and the digital control module202has a much simpler control for driving the transistor220. The output filter module228includes multiple outputs of the bridgeless power supply device. The digital control module202receives information about an output voltage, VOUTand the input voltage from the first input terminal and the second input terminal, which is used to adjust the duty cycle of the first and second control signals sent to the first and second switches204and206. Additionally, the digital control module202can provide useful features such as standby low power consumption mode and protections.

FIG. 3shows the bridgeless power supply device200with a first current path222. To enable the current to flow along the first current path222, the digital control module applies a first control signal to the first switch204and a second control signal to the second switch206. The first control signal opens the first switch204and the second control signal closes the second switch206to make a first configuration of the bridgeless power supply device200. This first configuration allows current to travel along the first current path222from the first voltage reference of the input voltage, to the primary winding of the transformer218and then to the second voltage reference of the input voltage. During this first configuration the inductor214also stores part of the energy provided by the input, to be applied later to the output stage of the bridgeless power supply device200. The digital control module202applies a third control signal, having a constant duty cycle, to the transistor220. The third control signal turns the transistor220on and off with a constant high frequency duty cycle providing a load proportional with the one in the output, so that the current from the input voltage will flow along the first current path222.

FIG. 4shows the bridgeless power supply device200with a second current path224. In this configuration of the bridgeless power supply, the first control signal opens the first switch204and the second control signal opens the second switch206. When both the first switch and the second switch are open, the input voltage is not applied to the bridgeless power supply device200, allowing the energy stored in the inductor214to be transferred to the output.

The bridgeless power supply device200with the second current path224through the third diode212, the inductor214, the transformer218and the transistor220works as a buck converter with the addition of the capacitor216. The buck converter takes the input voltage and turns it on and off through an output load, such as the transformer218, at a variable duty cycle, rectifying and regulating the bulk voltage VBULKacross the capacitor216. The output voltage of the buck converter is the product of the input voltage and the duty cycle applied to the input voltage. The transformer218has a plurality of outputs based on the respective number of turns in the transformer, and the regulated DC voltage across the transformer218and the transistor220.

FIG. 5shows the bridgeless power supply device200with a third current path226. In this configuration of the bridgeless power supply device200, the first control signal closes the first switch204and the second control signal opens the second switch206. With the switches in such a configuration the current will still flow in the same direction through the transformer218and the transistor220as the first current path222, even though the polarity of the AC input voltage, VIN, has been reversed. This setup of the switches provides rectification of the input voltage so that the voltage through the transformer218and the transistor220will always be positive. The polarity of the input voltage is such that the current flows along the third current path226from the second voltage reference of the input voltage, through the inductor214, then through the primary winding of the transformer218and transistor220and then to first voltage reference of the input voltage.

FIG. 6shows the bridgeless power supply device200with the second current path224. After the first control signal closes the first switch and the second control signal opens the second switch, the first and second control signals open the first switch204and the second switch206respectively. This enables the current to flow along the second current path224again and the bridgeless power supply device200to work the same as described inFIG. 4above, after the input voltage has been rectified inFIG. 5.

FIG. 7shows a graph700of the rectification of an input voltage of 100 V AC applied to the circuit and block diagram ofFIG. 2. As shown from the graph700the output voltage, VBULK, is based on the duty cycle applied to the rectified AC input signal, labeled V D3. The current IINand the voltage VINare measured at the first voltage reference of the input voltage, whereas VBULKis measured across the capacitor216which is the same voltage as across the transformer218and transistor220.

FIG. 8shows a graph800of the rectification of an input voltage of 240V AC applied to the circuit and block diagram ofFIG. 2.FIGS. 7 and 8show that to obtain the same VBULKfor different input voltages, the duty cycle of the first control signal applied to the first switch204and second control signal applied to the second switch206have to be different.

FIG. 9shows a flow chart900of a method for supplying an output voltage in the bridgeless power supply device200. In step902the bridgeless power supply device200receives an input alternating current (AC) voltage, which will be rectified and converted to a regulated direct current (DC) output voltage. In step904a digital control module applies a first control signal to a first switch, a second control signal to a second switch and a third control signal to a transistor to control the flow of the current through the bridgeless power supply device200. The digital control module receives an input signal containing information about the input voltage, and the output voltage in step906. In step908the digital control module adjusts the first control signal applied to the first switch and the second control signal applied to the second switch based on the input signal received in the digital control module. In step910, the output voltage is regulated to a constant DC voltage that is less than the AC input voltage based on the first control signal applied to the first switch, the second control signal applied to the second switch and the control signal applied to a transistor coupled to an output load of the bridgeless power supply device200.

Each power processing stage in the bridgeless power supply device200has lower power losses than the power processing stages in classic power supplies, and as a result the overall power conversion efficiency is increased. The bridgeless power supply device200increases the performance efficiency of the different power stages, as compared to classic power supplies, so that the overall performance efficiency of the bridgeless power supply device is above 80%. The increased efficiency is accomplishes in the bridgeless power supply device200without an increase in the cost, because the circuitry for the bridgeless power supply device is less complex than other power supplies that try to increase the performance efficiency.