1. Field of the Invention
The invention relates to an isolated power converter; in particular, to an isolated power converter with an inverting type shunt regulator and its operating method thereof
2. Description of the Prior Art
Please refer to
When the flyback converter 1 is operated at a stable state, if the output load of the flyback converter 1 becomes larger, the feedback voltage VFB will have a higher level. The switch-driving signal VG can have a longer duty cycle through a pulse-width modulator PWM shown in
When the feedback voltage VFB is smaller than the threshold voltage VL, the pulse-width modulator PWM will stop outputting the driving signal, and it will output the driving signal again until the feedback voltage VFB comes back to the threshold voltage VH. Please refer to
However, because the current ILED flowing through the light-emitting diode OC1 of the optocoupler and the current IFB flowing through the phototransistor OC2 of the optocoupler are increased when the conventional flyback converter 1 is operated at a light-load state, the energy consumption will be increased. As a result, the standby power consumption of the isolated power converter will be large and the light-load efficiency of the isolated power converter will be poor, making the feedback circuit shown in
Therefore, the invention provides an isolated power converter with an inverting type shunt regulator and its operating method thereof to solve the above-mentioned problems occurred in the prior arts.
A scope of the invention is to provide an isolated power converter. In a preferred embodiment, the isolated power converter includes a transformer, an inverting type shunt regulator, a controller, and an optocoupler. The inverting type shunt regulator is located on the secondary side of the transformer. The inverting type shunt regulator includes an error amplifier and a MOSFET. The controller is located on the primary side of the transformer. The controller includes an inverting unit cooperated with the MOSFET. The controller receives a feedback voltage. The optocoupler is coupled to the inverting type shunt regulator and the controller to provide an opto-coupling current to the controller.
In an embodiment, the MOSFET is a p-type MOSFET or an n-type MOSFET.
In an embodiment, the controller further includes a pulse-width modulator. If the feedback voltage received by the controller is a positive-phase feedback voltage, the inverting unit will convert the positive-phase feedback voltage into an inverting feedback voltage and the pulse-width modulator will generate a switch-driving signal according to the inverting feedback voltage.
In an embodiment, the controller further includes an inverting-type pulse-width modulator. If the feedback voltage received by the controller is a positive-phase feedback voltage, the inverting-type pulse-width modulator will convert the positive-phase feedback voltage into an inverting feedback voltage and generate a switch-driving signal according to the inverting feedback voltage.
In an embodiment, the controller further includes a pulse-width modulator. If the feedback voltage received by the controller is an inverting feedback voltage, the pulse-width modulator will generate a switch-driving signal according to the inverting feedback voltage.
In an embodiment, the inverting type shunt regulator further includes a first terminal, a second terminal, a third terminal, and a fourth terminal. The first terminal is coupled to an external reference voltage. The third terminal is coupled to the optocoupler. The fourth terminal is coupled to a ground terminal. A compensating circuit is coupled between the first terminal and the third terminal The MOSFET is coupled between the second terminal and the third terminal.
In an embodiment, the inverting type shunt regulator further includes a first terminal, a second terminal, a third terminal, and a fourth terminal. The first terminal is coupled to an external reference voltage. The third terminal is coupled to the optocoupler. The third terminal is coupled to a ground terminal The fourth terminal is coupled between the error amplifier and the MOSFET. One terminal of a compensating circuit is coupled to the first terminal, and the other terminal of the compensating circuit is coupled to the fourth terminal The MOSFET is coupled between the second terminal and the third terminal.
In an embodiment, the controller is a pulse-width modulation controller. The optocoupler is coupled to the pulse-width modulation controller and a ground terminal The optocoupler provides a positive-phase feedback voltage to the pulse-width modulation controller.
In an embodiment, the controller is a pulse-width modulation controller. The pulse-width modulation controller is coupled to a supply voltage. The optocoupler is coupled to the supply voltage and the pulse-width modulation controller. The optocoupler provides an inverting feedback voltage to the pulse-width modulation controller.
Another scope of the invention is to provide an inverting type shunt regulator. In a preferred embodiment, the inverting type shunt regulator is applied in an isolated power converter including a transformer and a controller. The controller is located on the primary side of the transformer and includes an inverting unit. The inverting type shunt regulator is located on the secondary side of the transformer and cooperates with the inverting unit. The inverting type shunt regulator includes a first terminal, a second terminal, a third terminal, an error amplifier, and a MOSFET. The first terminal is coupled to an external reference voltage. The error amplifier has a first input terminal, a second input terminal, and an output terminal. The first input terminal is coupled to the first terminal and the second input terminal is coupled to an internal reference voltage. The MOSFET is coupled between the second terminal and the third terminal The gate electrode of the MOSFET is coupled to the output terminal of the error amplifier.
Another scope of the invention is to provide an operating method of an isolated power converter. In a preferred embodiment, the isolated power converter includes a transformer, an inverting type shunt regulator, a controller, and an optocoupler. The controller is located on the primary side of the transformer and includes an inverting unit. The inverting type shunt regulator is located on the secondary side of the transformer and includes an error amplifier and a MOSFET. The inverting unit cooperates with the MOSFET.
The operating method includes following steps of: using the inverting type shunt regulator to control an opto-coupling current provided for the controller by the optocoupler; using the controller to receive a feedback voltage which is determined according to the opto-coupling current and generate a switch-driving signal according to the feedback voltage; decreasing the opto-coupling currents and increasing the feedback voltage when the output power of the isolated power converter becomes smaller; and using the controller to reduce the duty cycle of the switch-driving signal according to the feedback voltage having a higher level.
Compared with the prior arts, when the output power of the isolated power converter becomes smaller, the invention can lower down the currents flowing through the optocoupler to reduce its energy consumption. In addition, because the energy consumption is reduced, the total energy that the isolated power converter should provide is also reduced. And in the meantime, the operating consumption of the isolated power converter, such as switching loss, conduction loss, and transformer loss, can all be reduced as well. Therefore, the invention can enhance the light-load efficiency of the isolated power converter and reduce the standby power consumption of the isolated power converter.
The advantage and spirit of the invention may be understood by the following detailed descriptions together with the appended drawings.
A preferred embodiment of the invention is an isolated power converter. In fact, the isolated power converter in this embodiment can be, but not limited to, a flyback converter having an isolated transformer. Please refer to
In the embodiment shown in
It should be mentioned that the inverting type shunt regulator is formed by an error amplifier, a reference voltage generator, and a MOSFET. The output terminal of the error amplifier is coupled to the gate electrode of the MOSFET. If the MOSFET used in the inverting type shunt regulator is a p-type MOSFET, the internal reference voltage is connected to the inverting input terminal of the error amplifier; if the MOSFET used in the inverting type shunt regulator is a n-type MOSFET, the internal reference voltage is connected to the non-inverting input terminal of the error amplifier.
As shown in
The first input terminal+is coupled to the first terminal T1, and the second input terminal−is coupled to the internal reference voltage (2.5 V in this embodiment). The p-type MOSFET Mp is coupled between the second terminal T2 and the third terminal T3, and the gate electrode of the p-type MOSFET Mp is coupled to the output terminal J of the error amplifier AMP. In this embodiment, the first terminal T1 of the inverting type shunt regulator SR is coupled to an external reference voltage VOF. The second terminal T2 is coupled to an output voltage VOUT of the isolated power converter 5, the third terminal T3 is coupled to a light-emitting diode LED and a compensating resistor RC. The compensating circuit 54 includes the compensating resistor RC and a compensating capacitor CC which are coupled in series, and the compensating circuit 54 is coupled between the first terminal T1 and the third terminal T3 of the inverting type shunt regulator SR.
When the output voltage VOUT of the isolated power converter 5 is increased, the inverting type shunt regulator SR will lower down the conduction current of the p-type MOSFET MP to make ILED flowing through the light-emitting diode LED become smaller. On the contrary, when the output voltage VOUT of the isolated power converter 5 is decreased, the inverting type shunt regulator SR will increase the conduction current of the p-type MOSFET MP to make ILED flowing through the light-emitting diode LED become larger.
Because the inverting type shunt regulator SR and the light-emitting diode LED are located on the secondary side of the isolated transformer TR, the LED current ILED is a secondary-side current. A primary-side opto-coupling current induced by the optocoupler OC on the primary side of the isolated transformer TR is a feedback current IFB, and a feedback voltage VFB will be determined by the feedback current IFB. After the feedback voltage VFB is processed by an inverting amplifier INV of the controller 50, it will be sent to the pulse-width modulator PWM to determine the duty cycle of a switch-driving signal VG which is output to a switch SW.
Therefore, when the isolated power converter 5 is operated at a stable state, the feedback voltage VFB will have a lower level if the isolated power converter 5 has a heavier load. Then, after the feedback voltage VFB is processed by the inverting amplifier INV, the switch-driving signal VG determined by the pulse-width modulator PWM will have a longer duty cycle. On the contrary, if the isolated power converter 5 has a lighter load or even no load, the feedback voltage VFB will have a higher level. Then, after the feedback voltage VFB is processed by the inverting amplifier INV, the switch-driving signal VG determined by the pulse-width modulator PWM will have a shorter duty cycle. This will make the LED current ILED and the feedback current IFB have less energy consumption under a lighter-load or the no-load condition.
In addition, when the load of the isolated power converter 5 is smaller than a threshold power PTH, the feedback voltage VFB will swing between two threshold voltages VH′ and VL′. However, the two threshold voltages VH′ and VL′ in
Please refer to
Different from that shown in
Please refer to
Please refer to
Another preferred embodiment according to the present invention is an operating method for an isolated power converter. In this preferred embodiment, the isolated power converter includes a transformer, an inverting type shunt regulator, a controller, and an optocoupler. The controller is located on the primary side of the transformer and includes an inverting unit. The inverting type shunt regulator is located on the secondary side of the transformer and includes an error amplifier and a MOSFET. The inverting unit is cooperated with the MOSFET. The light-emitting diode (LED) of the optocoupler is coupled between the inverting type shunt regulator and a resistor, and the resistor is coupled to the ground terminal The LED can also be coupled between the output voltage of the isolated power converter and the inverting type shunt regulator. Please refer to
As shown in
The step S14 is to decrease the opto-coupling currents and increase the feedback voltage when the output power of the isolated power converter becomes smaller. The step S16 is to use the controller to reduce the duty cycle of the switch-driving signal according to the feedback voltage having a higher level.
Compared with the prior arts, when the output power of the isolated power converter becomes smaller, the invention can lower down the currents flowing through the optocoupler to reduce its energy consumption. In addition, because the energy consumption is reduced, the total energy that the isolated power converter should provide is also reduced. And in the meantime, the operating consumption of the isolated power converter, such as switching loss, conduction loss, and transformer loss, can all be reduced as well. Therefore, the invention can enhance the light-load efficiency of the isolated power converter and reduce the standby power consumption of the isolated power converter.
With the example and explanations above, the features and spirits of the invention will be hopefully well described. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Number | Date | Country | Kind |
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101142907 | Nov 2012 | TW | national |