The present invention relates to a soft-switching circuit for a power supply that connects an auxiliary circuit to a bridgeless rectifier circuit to accomplish the soft switching with zero voltage transition for reducing switching loss and simultaneously providing low conducting loss and low switching loss which suitable for use in a power supply or the like.
Due to the development of technology, the power has wider applications. The power supplies are indispensable to more and more products. For example, personal computers, industrial computers, switches, printers and so forth require respective AC/DC converters to turn on the power source.
Most existing power supplies employ boost-type power converter that employ power factor correction. The boost-type power converter transforms AC current into DC current by a bridge rectifier, and it is operated in a boost-type converter mode. It has two operation states. In first state, when the switch is turned on, the inductor can store the energy. In the second state, when the switch is turned off, the inductor can release the energy to a load via a diode and change the continuous input current into a sine wave by using power factor regulation technology so as to achieve the purpose of regulating output voltage and input current.
In addition, the
However, the power converters shown in both
In view of the above-mentioned drawbacks, the present inventor makes diligent studies in providing general public with a soft-switching circuit for a power supply that connects an auxiliary circuit to a bridgeless rectifier circuit to provide low conducting loss and low switching loss.
It is a primary object of the present invention to provide a soft-switching circuit for a power supply that connects an auxiliary circuit to a bridgeless rectifier circuit to allow the main switches and the auxiliary switch to accomplish zero voltage switching and zero current switching respectively for providing low conducting loss and low switching loss.
It is a secondary object of the present invention to provide a soft-switching circuit for a power supply that removes a bridge rectifier from an input terminal by providing a bridgeless rectifier circuit to reduce conducting loss and to provide the circuit with low conducting loss.
In order to achieve the foregoing objects, a soft-switching circuit for a power supply of the present invention is comprised of a bridgeless rectifier circuit and an auxiliary circuit. The auxiliary circuit is connected to the bridgeless rectifier circuit, which comprises at least one filtering inductor, two main switches, two diodes and a capacitor. The filtering inductor is connected to the first diode. The first diode is connected to the second diode. The second diode is connected to the first main switch. The first main switch is connected to the second main switch. The two diodes and the two main switches are connected in parallel with the capacitor to reduce conducting loss. The auxiliary circuit comprises at least one resonant inductor, an auxiliary switch, at least two diodes and a voltage source circuit. The diodes are connected to the resonant inductor and further connected to the voltage source circuit. The voltage source circuit is connected to the auxiliary switch, whereby the soft-switching circuit can accomplish zero voltage switching and zero current switching to provide low conducting loss and low switching loss.
The aforementioned and other objects and advantages of the present invention will be readily clarified in the description of the preferred embodiments and the enclosed drawings of the present invention.
Referring to
Referring to
Mode 0 (t9˜t0): During the period of t9≦t≦t0, the main switches S and the auxiliary switch Sr are turned off, the input current Ii flows to a load via the diode Da, and then flows back to the input via the body diode of Sb. In the diode Da, when current iDa=Ii, the voltage across the main switches is (i.e. resonant capacitor voltage) vs=Vo. Mode 1 (t0˜t1): When t=t0, the main switches S are delayed and the auxiliary switch Sr is turned on to enter the mode 1, Dra conduced. At this moment, the current iLr flows through the winding Np of Dra, Lr and Tr to create an induced current is in the winding Ns, wherein the induced current is flows to Vo via D1 and returns via D4. At this moment, the Tr crosses the constant voltage source Vo at a secondary side and the magnetizing current im ascends linearly so it can induce the constant voltage source at a primary side. Besides, since Da is still in the on state, the current iLr starts to ascend linearly and the auxiliary switch Sr is soft turn-on. When the current iLr ascends to Ii, this mode is terminated, i.e. t=t1. Mode 2 (t1˜t2): When the current iLr ascends to Ii, the diode Da is cut off to enter the mode 2. At this mode, the auxiliary switch is maintained in the on state, and the resonant inductor and the resonant capacitor form a tank circuit jointly. The inductance and the current keep ascending, and the resonant capacitor voltage namely the main switch voltage (vs) descends. When vs descends from Vo to zero, this mode is terminated, i.e. t=t2. Mode 3 ( t2˜t3): When t=t2, the resonant capacitor voltage (vs) descends to zero to enter the mode 3 and the resonant capacitor voltage keeps descending, causing the body diode Dsa of the main switch to be conduced so that the current i Lr starts to descend linearly and the current isa starts to ascend linearly. At this moment, the main switch voltage is zero. When t≧t2, the main switch Sa can be triggered and turned on under the zero voltage switching (ZVS) condition. When the current isa ascends from a negative value to zero, this mode is terminated, i.e. t=t3. Mode 4 (t3˜t4): When t=t3, the current isa ascends from a negative value to zero, the body diode Dsa of the main switch is turned off to enter the mode 4. At this moment, isa keeps ascending linearly from zero and the current iLr keeps descending linearly so that the energy stored in the resonant inductor Lr can be released to the load by means of Tr. When iLr descends to the magnetizing current im, this mode is terminated, i.e. t=t4. Mode 5 (t4˜t5): When t=t4, iLr descends to the magnetizing current im. At this moment, the span voltage Tr is equal to zero, the diodes D1 and D4 are cut off, and the diode D2 is conduced. The im flows circularly from the primary side and the secondary side via Sr. However, the magnetizing current is generally designed to be considerably smaller than the load current so the current that flows through the auxiliary switch Sr can be regarded as a zero current. When t≧t4 the auxiliary switch Sr can be turned off under the zero current switching (ZCS) condition so as to terminate this mode, i.e. t=t5. Mode 6 (t5˜t6): When t=t5, the auxiliary switch is turned off to enter the mode 6. At this moment, the magnetizing current im can charge the parasitic capacitor Csr of the auxiliary switch Sr to ascend the voltage vsr. When the voltage vsr ascends to V0, D3 and D2 are conduced and this mode is terminated, i.e. t=t6. Mode 7 (t6˜t7): When t=t6, the voltage vsr ascends to V0 to enter the mode 7. At this moment, D3 and D2 are conduced, the magnetizing inductance Lm has a span voltage V0 to allow the magnetizing current im to be descended linearly. When the magnetizing current im descends linearly to zero, Tr accomplishes reset and this mode terminates, i.e. t=t7. Mode 8 (t7˜t8): When t=t7, the magnetizing current im descends linearly to zero to enter the mode 8, and the diodes D3 and D2 are both cut off. At this moment, the main switch is still in the on state, and the inductor L can store the energy to enter an operation condition that the main switch of the general boost converter is full turned on. When the main switch is turned off, this mode is terminated, i.e. t=t8. Mode 9 (t8˜t9): When t=˜t8, the main switch is turned off to enter the mode 9. At this moment, the constant current Ii can charge the resonant capacitor Csa to ascend the switching voltage linearly. When the capacitor voltage reaches the output voltage V0, this mode is terminated, and the diode Da is conduced. At this moment, vsa=V0 and the mode 0 is returned to start another switching period.
According to the foregoing analysis, the additional auxiliary circuit mentioned above allows the main switch to accomplish the zero voltage switching (ZVS) when it is in the on state. In addition, the auxiliary switch is soft turn-on when it is in the on state and it can accomplish the zero voltage switching (ZVS) when it is in the off state. For the same reason, when the input current is in the negative half cycle, the input current flows through another route so the identical auxiliary circuit can be employed to accomplish zero voltage switching and zero current switching. As a result, the above-mentioned bridgeless soft-switching circuit can improve the switching loss of the circuit switch effectively, thereby promoting the efficiency of the converter.
In accordance with the foregoing description, the present invention has the following practical advantages:
1. The auxiliary circuit gives the delay time to the conducting timing of the control signal of the main switch of the bridgeless rectifier circuit during every switching period, and the present invention inserts the conducting time of the auxiliary switch in the delay time to allow the resonant inductor to accomplish the resonance within the delay time so as to accomplish the soft-switching operation with zero voltage transition for reducing switching loss.
2. The present invention connects the auxiliary circuit to the bridgeless rectifier circuit so as to allow the main switch and the auxiliary switch to accomplish the zero voltage switching and the zero current switching respectively for providing low conducting loss and low switching loss.
To sum up, the present invention is capable of achieving the anticipated objects described above. Therefore, this application is filed according to the patent law.
While the preferred embodiment of the invention has been set forth for the purpose of disclosure, modifications of the disclosed embodiment of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments, which do not depart from the spirit and scope of the invention.