CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of priority to Taiwan Patent Application No. 109110743, filed on Mar. 30, 2020. The entire content of the above identified application is incorporated herein by reference.

Some references, which may include patents, patent applications and various publications, may be cited and discussed in the description of this disclosure. The citation and/or discussion of such references is provided merely to clarify the description of the present disclosure and is not an admission that any such reference is “prior art” to the disclosure described herein. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to a power converter, and more particularly to a power converter that can converge a waveform of a current of an inductor without using an equivalent series resistor (ESR).

BACKGROUND OF THE DISCLOSURE

When a conventional power converter such as a DC-DC converter is connected to a light load that requires less energy, an upper bridge switch and a lower bridge switch of the conventional power converter are switched at a low frequency. An audio frequency of noise generated by an inductor and a capacitor of the conventional power converter may fall within a human hearing range of 2 KHZ to 20 KHZ.

In order to prevent the noise from being heard by a human, the upper bridge switch is turned off and the lower bridge switch is turned on in the conventional power converter to pull down an output voltage VOUT0of the conventional power converter as shown inFIG. 5. When the output voltage VOUT0of the conventional power converter is lower than a reference voltage, the upper bridge switch is turned on and the lower bridge switch is turned off to charge the output voltage VOUT0of the conventional power converter such that the output voltage VOUT0has sufficient energy. When a current of the inductor of the conventional power converter reaches zero, the upper bridge switch and the lower bridge switch are turned off. That is, a switching frequency of the upper bridge switch and the lower bridge switch increases by turning on the upper bridge switch early, such that the audio frequency of the noise does not fall within the human hearing range.

It should be understood that, if an equivalent series resistor is not disposed in the conventional power converter, the conventional power converter has a non-ideal delay characteristic that the energy of the output voltage VOUT0is dispersed and cannot be balanced in one cycle of a signal of the current of the inductor when the output voltage VOUT0is pulled down. As shown inFIG. 5, when the output voltage VOUT0of the conventional power converter is pulled down excessively within a constant time of one cycle of a signal of a current ILO of the inductor, energy of a waveform formed in a negative half cycle of the signal is higher than energy of a waveform formed in a positive half cycle of the signal. Therefore, the equivalent series resistor must be disposed in the conventional power converter. When the equivalent series resistor is disposed and the current ILO having a negative current value flows through the inductor, a ripple of the output voltage VOUT0increases and the output voltage VOUT0decreases more, such that an on-time of the lower bridge switch of the conventional power converter is shortened.

With the development of technology, in order to improve the flexibility of the circuit design, a multi-layer ceramic capacitor (MLCC) is disposed in the conventional power converter. However, a resistance of an equivalent series resistor of the multi-layer ceramic capacitor approaches zero, resulting in energy imbalance. As a result, the energy of the conventional power converter is insufficient to be exchanged between an ultrasonic working mode (USM) and a pulse frequency modulation mode (PFM). When the conventional power converter enters the ultrasonic working mode, a ripple of the output voltage VOUT0increases, and a switching frequency of the upper bridge switch and the lower bridge switch is equal to an ultrasonic frequency.

SUMMARY OF THE DISCLOSURE

In response to the above-referenced technical inadequacies, the present disclosure provides a power converter having a switch circuit, a controller circuit and a driver circuit. The driver circuit is connected between the controller circuit and the switch circuit. The controller circuit outputs a control signal for controlling the driver circuit to drive the switch circuit according to a first comparison signal. The switch circuit is connected to an input voltage source and an inductor. The inductor is connected in series with a first capacitor and grounded through the first capacitor. The power converter includes a first comparator and a reference voltage supplying circuit. The first comparator has a first comparison input terminal and a second comparison input terminal. The first comparison input terminal is connected to an output terminal between the inductor and the first capacitor. The first comparator is configured to compare a voltage of the first comparison input terminal with a target reference voltage of the second comparison input terminal to output the first comparison signal to the controller circuit. The reference voltage supplying circuit includes a second capacitor, a reference current source and a first resistor. The second capacitor has a first terminal connected to the second comparison input terminal of the first comparator, and has a second terminal grounded. The reference current source is connected to the first terminal of the second capacitor. The reference current source is configured to provide a reference current to the second capacitor to charge the second capacitor such that the second capacitor has the target reference voltage. The first resistor has a first terminal connected to the first terminal of the second capacitor, and has a second terminal coupled to a first reference level.

In certain embodiments, the power converter further includes a voltage divider circuit. The voltage divider circuit is connected between the output terminal and the first comparison input terminal. The voltage divider circuit is configured to divide an output voltage of the output terminal to output a divided voltage to the first comparison input terminal.

In certain embodiments, the reference voltage supplying circuit further includes a second resistor. A first terminal of the second resistor is connected to the second terminal of the first resistor. The first reference level is at a first reference node between the first resistor and the second resistor.

In certain embodiments, the reference voltage supplying circuit further includes a current mirror connected to a common voltage source and the first reference node.

In certain embodiments, the current mirror includes a first transistor and a second transistor. A first terminal of the first transistor and a first terminal of the second transistor are connected to the common voltage source. A second terminal of the first transistor is connected to the first reference node. A control terminal of the first transistor is connected to a control terminal and a second terminal of the second transistor. The second terminal of the second transistor is grounded.

In certain embodiments, the reference voltage supplying circuit further includes a third resistor. The second terminal of the second transistor is grounded through the third resistor.

In certain embodiments, the reference voltage supplying circuit further includes a third transistor connected between the second transistor and the third resistor. A first terminal of the third transistor is connected to the second terminal of the second transistor. A second terminal of the third transistor is grounded through the third resistor. A control terminal of the third transistor is coupled to a first control level.

In certain embodiments, the reference voltage supplying circuit further includes a third capacitor. A first terminal of the third capacitor is connected to the control terminal of the third transistor. A second terminal of the third capacitor is grounded. The third capacitor has the first control level.

In certain embodiments, the reference voltage supplying circuit further includes an operational amplifier having a first amplification input terminal and a second amplification input terminal. The first amplification input terminal of the operational amplifier is coupled to a second reference level. The second amplification input terminal of the operational amplifier is connected to a second node between the third transistor and the third resistor. An output terminal of the operational amplifier is connected to the first terminal of the third capacitor.

In certain embodiments, the reference voltage supplying circuit further includes a fourth transistor connected between the reference current source and the second capacitor. A first terminal of the fourth transistor is connected to the reference current source. A second terminal of the fourth transistor is connected to the first terminal of the second capacitor. A control terminal of the fourth transistor is coupled to a second control potential.

In certain embodiments, the power converter further includes a mode switching circuit. The mode switching circuit is connected to an output terminal of the first comparator and the control terminal of the fourth transistor. The mode switching circuit is configured to output a mode switching signal to the control terminal of the fourth transistor according to the first comparison signal.

In certain embodiments, the power converter further includes a logic circuit. An input terminal of the logic circuit is connected to the output terminal of the first comparator, an output terminal of the mode switching circuit and an input terminal of the controller circuit. The logic circuit is configured to output a logic signal to the controller circuit according to the first comparison signal and the mode switching signal.

In certain embodiments, the power converter further includes an on-time adjuster circuit. The on-time adjuster circuit is connected to the logic circuit, the switch circuit and the input voltage source. The on-time adjuster circuit is configured to receive an input voltage from the input voltage source and output an on-time signal according to an on state of the switch circuit. The logic circuit outputs the logic signal according to the first comparison signal, the mode switching signal and the on-time signal.

In certain embodiments, the power converter further includes a logic gate. Two input terminals of the logic gate are respectively connected to the output terminal of the mode switching circuit and an output terminal of the on-time adjuster circuit. An output terminal of the logic gate is connected to the input terminal of the logic circuit.

In certain embodiments, the power converter further includes a zero current detector circuit. The zero current detector circuit is connected to the switch circuit, the controller circuit, the on-time adjuster circuit and the mode switching circuit. The zero current detector circuit is configured to detect a current flowing through the switch circuit to output a current value. The on-time signal, the mode switching signal and the control signal depend on the current value.

In summary, the present disclosure provides the power converter such as a constant on-time power converter. The waveform of the current of the inductor of the power converter of the present disclosure can be converged without using the equivalent series resistor of the conventional power converter to enhance the design flexibility of the system.

These and other aspects of the present disclosure will become apparent from the following description of the embodiment taken in conjunction with the following drawings and their captions, although variations and modifications therein may be affected without departing from the spirit and scope of the novel concepts of the disclosure.

