Power management unit and wireless power system using the same

A power management unit, adapted to a wireless power system, includes: a rectifier, converts an AC power received by an input port thereof to a direct-current (DC) voltage outputted by a rectifying output terminal thereof; a first switch, wherein a first protecting capacitor is coupled between one terminal of the input port and a channel thereof; a second switch, wherein a second protecting capacitor is coupled between the other terminal of the input port and a channel thereof; a reference voltage terminal, for providing a reference voltage; and, a comparator, including two input terminals coupled to the rectifying output terminal and the reference voltage terminal respectively, and including an output terminal coupled to both the control terminals of the first switch and the second switch.

CROSS-REFERENCES TO RELATED APPLICATIONS

This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 102141886 filed in Taiwan, R.O.C. on 18 Nov. 2013, the entire contents of which are hereby incorporated herein by reference.

BACKGROUND

1. Technical Field

This present invention relates to a power management unit and a wireless power system adopting the power management unit, more specifically, to a power management unit with over-voltage protection and a wireless power system adopting the power management unit.

2. Description of Related Art

Wireless power, also known as wireless energy transmission, is a technique which takes advantage of near-field coupling, for example inductive coupling, to transmit energy from a power supplying equipment to an electric device. For example in the application of wireless charging, an electronic device receives energy via wireless power for charging a battery and providing required power for operation. Since the energy transmission between the electronic device and the power supplying equipment is realized by inductive coupling without conducting wires, no conducting point is exposed on both the electronic device and the power supplying equipment. Therefore, the danger of electric shot by contacting can be avoided, and the un-exposed metal parts can be free from oxidation by water vapor or oxygen. Besides, the mechanical degradation and the possible danger caused by spark, both of which are caused by connecting and separating the electronic device and the power supplying equipment, can also be avoided.

The technical development on wireless power brings great contribution on the medical applications and consumer electronics. The wireless power technique makes medical implant device safer. Without conducting wires penetrating skin and other body tissues, patient can charge the medical implant device without harming body tissues and free from the risk of infection. The wireless power technique also brings great convenience on consumer electronics since devices can be charged merely by being placed in the vicinity of the wireless charger, and the wires are obsoleted. Besides, technically a wireless charger can charge many electronic devices at the same time which saves wires, adaptors and power outlets.

FIG. 1is a schema of a wireless power system100of prior art. The wireless power system100includes a wireless power transmitting end and a wireless power receiving end. The wireless power transmitting end includes a power supply110, a supply coupling capacitor120and first windings130. The wireless power receiving end includes second windings150, input capacitor160. The wireless power transmitting end transmits a wireless power140of alternating current (AC), and the wireless power receiving end receives the wireless power140by near-field coupling, for example (but not limited to) inductive coupling between first windings130and second windings150, to generate an AC power into a rectifier170. The rectifier170is adopted to rectify the received AC power into a direct-current (DC) voltage. The wireless power system100can further include a regulator180which receives the DC voltage from rectifier170and generates a stable output voltage to supply a load (not shown inFIG. 1). In the application of wireless charging, the regulator180generates a regulated output voltage or output current to charge a battery.

However, on the design of the rectifier, the converting efficiency of the rectifier170should be taken into consideration. As the result, a rated maximal voltage value is usually specified to the devices of the rectifier170. If the input voltage of the rectifier170is higher than the rated maximal voltage value, the lifetime of the rectifier170will be decreased. In the worst case, the rectifier170is damaged directly. Nonetheless, with gradually prevailing of the wireless power technology, different wireless power standards of wireless power systems will be developed to apply to different application scenarios. Hence, it will possibly happen that a wireless power receiver with lower rated maximal voltage value is coupled to a wireless power transmitter with higher rated maximal voltage value, which causes a voltage higher than the rated maximal voltage value generated on the input port of the rectifier, and the lifetime of the wireless power receiver is decreased, or even the wireless power receiver is damaged. Therefore, there should be protection design on the wireless power receiver to prevent possible damage from the aforementioned cases.

SUMMARY

In view of above problems, the objective of the present invention is to provide a power management unit and a wireless power system adopting the power management unit, more specifically, to a power management unit with over-voltage protection and a wireless power system adopting the power management unit.

In one embodiment, a power management unit adapted to a wireless power system is disclosed. The wireless power system further includes second windings, an input capacitor, a first protecting capacitor and a second protecting capacitor. The second windings receive a wireless power of alternating-current (AC). The input capacitor is coupled between one terminal of the second windings and a power receiving terminal. The power management unit further includes a rectifier, a regulator, a first switch, a second switch, a reference voltage terminal, and a comparator.

The rectifier includes an input port and a rectifying output terminal. The two terminals of the input port are coupled to the power receiving terminal and the other terminal of the second windings respectively. The rectifier converts an AC power received by the input port to a direct-current (DC) voltage, and the rectifying output terminal outputs the DC voltage. The regulator is coupled to the rectifier and receives the DC voltage to either output a DC output voltage to a load or charge a battery with a CV (constant-voltage) mode or a CC (constant-current) mode.

The first protecting capacitor is coupled between the power receiving terminal and one terminal of the channel of the first switch. The other terminal of the channel of the first switch is coupled to a ground terminal. The second protecting capacitor is coupled between the other terminal of the second windings and one terminal of the channel of the second switch. The other terminal of the channel of the second switch is coupled to the ground terminal.

The reference voltage terminal provides a reference voltage. The comparator includes two comparing input terminals and a comparing output terminal. The two comparing input terminals are coupled to the rectifying output terminal and the reference voltage terminal respectively. The comparing output terminal is coupled to both the control terminal of the first switch and the control terminal of the second switch.

In another embodiment, a wireless power system, including the same circuit topology as that of the wireless power system disclosed in the embodiment of the power management unit, is disclosed.

The present invention is advantageous because the power management unit and the wireless power system adopting the power management unit can perform protection in the first place when an over-high wireless power is received. Therefore, it can prevent the power management unit from constantly receiving an over-high voltage causing the power management unit to be with a short lifetime or even being damaged directly.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the description hereinafter, the term of “coupled” or “coupling” refers to any two objects directly or indirectly electrically connected to each other. Therefore, if it is described that “a first device is coupled to a second device,” the meaning is that the first device is either directly electrically connected to the second device or indirectly electrically connected to the second device through other devices or connection means.

FIG. 2is a schema showing a wireless power system200of the first embodiment of the present invention. The wireless power system200includes second windings250, an input capacitor260, a first protecting capacitor270, a second protecting capacitor280and a power management unit290. The second windings250receive a wireless power240of alternating-current (AC). The input capacitor260is coupled between one terminal of the second windings250and a power receiving terminal265. The power management unit290further includes a rectifier291, a regulator292, a first switch293, a second switch294, a reference voltage terminal295, and a comparator296.

The rectifier291includes an input port2911and a rectifying output terminal2912. The two terminals of the input port2911are coupled to the power receiving terminal265and the other terminal of the second windings250respectively. The rectifier291converts an AC power received by the input port2911to a direct-current (DC) voltage, and the rectifying output terminal2912outputs the DC voltage. The regulator292is coupled to the rectifier291and receives the DC voltage to either output a DC output voltage to a load (not shown inFIG. 2) or charge a battery (not shown inFIG. 2) with a CV (constant-voltage) mode or a CC (constant-current) mode.

The first protecting capacitor270is coupled between said power receiving terminal265and one terminal of the channel of the first switch293. The other terminal of the channel of the first switch293is coupled to a ground terminal275. The second protecting capacitor280is coupled between the other terminal of the second windings250and one terminal of the channel of said second switch294. The other terminal of the channel of the second switch294is coupled to the ground terminal275.

The reference voltage terminal295provides a reference voltage. The comparator296includes two comparing input terminals2961,2962and a comparing output terminal2963. The two comparing input terminals2961,2962are coupled to the rectifying output terminal2912and the reference voltage terminal295respectively. The comparing output terminal2963is coupled to both the control terminal of the first switch293and the control terminal of the second switch294. The first switch293and the second switch294can be, but are not limited to, N-type field-effect transistors (FET's) or NPN-type bipolar junction transistors (BJT's). Note that a FET could be a metal-oxide-semiconductor field-effect transistor (MOSFET), a junction field-effect transistor (JFET), an insulated-gate bipolar transistor (IGBT), or any other semiconductor device with similar physical structures and functions of the above mentioned types of field-effect transistor devices. Furthermore, a control terminal of a FET means a gate terminal thereof, and a channel of a FET means a channel between a source terminal and a drain terminal thereof a control terminal of a BJT means a base terminal thereof, and a channel of a BJT means a channel between a collector terminal and an emitter terminal thereof.

Besides, the wireless power system200can further include a wireless power transmitter including a power supply210, a supply-side coupling capacitor220and first windings230. The wireless power transmitter generates the wireless power240and transmits the wireless power240through the first windings230. That is, the power supply210generates energy coupled to the first windings230through the supply-side coupling capacitor220, and the first windings230converts the energy to the wireless power240and emits the wireless power240.

Moreover, with the advance of the semiconductor process technology, the power management unit290can be an integrated circuit (IC) manufactured by the semiconductor process. That is, the devices of the power management unit290are integrated on one or more than one IC chips by the semiconductor process. The IC chips are further packaged as a package and the circuits on the chips are electrically coupled to the application circuits outside the package through the pins on the package.

Furthermore, the proper capacitance value of the first protecting capacitor270and the second protecting capacitor280are hundreds of nano-Farad (nF), such as 470 nF. Therefore, the first protecting capacitor270and the second protecting capacitor280are not suitable to be integrated into IC chips. As the results, the first protecting capacitor270and the second protecting capacitor280can be discrete electrolytic capacitors or ceramic capacitors, wherein the common electrolytic capacitors include aluminum electrolytic capacitors and tantalum electrolytic capacitors.

In more detail, when the wireless power system200is under normal operation, the voltage on the rectifying output terminal2912is lower than the reference voltage on the reference voltage terminal295, and the voltage level outputted by the comparing output terminal2963of the comparator296controlling the channels of the first switch293and the second switch294to be cut-off. Consequently the first protecting capacitor270and the second protecting capacitor280is floating, and have no substantial influence on the operation of the rectifier291. For example, when the comparing output terminal2963outputs a voltage level of 0 volts the same as the voltage level of the ground terminal275, the channels of the first switch293and the second switch294, which can be N-type FET's or NPN-type BJT's, are cut-off. Note that meanwhile, each of the floating first protecting capacitor270and the second floating protecting capacitor280is discharged through the intrinsic leakage path of a capacitor device. After a specific time, it is prone to be no electric charges existing on both electric plates of each of the first protecting capacitor270and the second protecting capacitor280.

Nonetheless, when a wireless power system200of a lower power specification receives a wireless power transmitted by a wireless power transmitter of a higher power specification, there is possible an over-high voltage on the input port2911of the rectifier291, which further causes an over-high voltage on the rectifying output terminal2912of the rectifier291. When the voltage on the rectifying output terminal2912is higher than the reference voltage on the reference voltage terminal295, the comparing output terminal2963outputs a voltage of voltage level higher than the threshold voltage value of the first switch293and the second switch294and controlling the channels of the first switch293and the second switch294conducting, which has at least the following two effects. First, the first protecting capacitor270is coupled to the ground terminal275through the first switch293, and the second protecting capacitor280is coupled to the ground terminal275through the second switch294, which effectively decreases the absolute voltages (relative to the ground terminal275) of the two terminals of the input port2911and prevents the absolute voltages of the two terminals of the input port2911from high than the rated maximal voltage thereof. Second, the input port2911is shunt to an effectively large capacitor formed by the serial connection of the first protecting capacitor270and the second protecting capacitor280, and is further serial connected to the input capacitor260and the second windings250, which forms a complete current loop. Therefore, when a somewhat larger voltage exists on the second windings250, the voltage on the input port2911, that is the voltage difference of the two terminals of the input port2911, can be prevented from higher than the rated maximal voltage by voltage dividing of the above-mentioned effectively large capacitor and relatively small input capacitor260.

According to the above descriptions, it can be understood that the protection circuit formed by the first switch293, the second switch294, the reference voltage terminal295, the comparator296, the first protecting capacitor270and the second protecting capacitor280can prevent the power management unit290from constantly receiving an over-high voltage causing the power management unit290to be with a short lifetime or even being damaged directly.

FIG. 3is a schema showing a wireless power system300of the second embodiment of the present invention. The function and the realization of each part of the wireless power system300can be referred to the description of the corresponding part of the wireless power system200disclosed inFIG. 2. The difference of the wireless power system200and300is that the power management unit390of the wireless power system300further includes a voltage limiter391. The voltage limiter391includes a voltage-limiting current path coupled between the rectifying output terminal2912and the ground terminal275. When the voltage of the rectifying output terminal2912is larger than a voltage threshold, the voltage-limiting current path is conducting, and when the voltage of the rectifying output terminal2912is smaller than the voltage threshold, the voltage-limiting current path is cut-off.

In more detail, the operation of the protection circuit of the wireless power system200disclosed inFIG. 2is activated by an over-high voltage on the rectifying output terminal2912causing the comparator296outputting a voltage controlling the first switch293and the second switch294conducting. Subsequently, the voltage on the input port2911is pulled low by the first protecting capacitor270and the second protecting capacitor280and further lowers the originally over-high voltage on the rectifying output terminal2912. However, since the response time is not short enough, the devices relating to the rectifying output terminal2912might have been damaged due to the over-high voltage before the over-high voltage is lowered. Therefore, by further including the voltage limiter391in the power management unit390of the wireless power system300, the voltage on the rectifying output terminal2912is limited in the first place when the voltage on the rectifying output terminal2912is over-high, and the devices relating to the rectifying output terminal2912are thus protected. However, the voltage-limiting current path of the voltage limiter391is effective as a finite resistor with limited current conducting ability, hence, the following protection, which is provided by the first switch293, the second switch294, the first protecting capacitor270and the second protecting capacitor280, is activated by the response of the comparator296to further protect the power management unit390.

According to the above descriptions, it can be understood that the protection circuit formed by the voltage limiter391, the first switch293, the second switch294, the reference voltage terminal295, the comparator296, the first protecting capacitor270and the second protecting capacitor280in the wireless power system300can prevent the voltage on the rectifying output terminal2912from over-high, and further prevent the power management unit390from constantly receiving an over-high voltage causing the power management unit390to be with a short lifetime or even being damaged directly.

FIG. 4is an embodiment of a voltage limiter of the present invention, which is the voltage limiter400. The voltage limiter400includes a voltage-limiting switch410, a current-limiting resistor420, a diode serial-connecting circuit430, and a control-terminal resistor440.

One terminal of the channel of the voltage-limiting switch410is coupled to the ground terminal275. The current-limiting resistor420is coupled between the rectifying output terminal2912and the other terminal of the channel of the voltage-limiting switch410. The diode serial-connecting circuit430is formed by serially connecting a plurality of diodes which is coupled between the rectifying output terminal2912and the control terminal of the voltage-limiting switch410. The control-terminal resistor440is coupled between the control terminal of the voltage-limiting switch410and the ground terminal275. The voltage-limiting switch410can be, but is not limited to, an N-type FET or an NPN-type BJT.

In more detail, assume the diode serial-connecting circuit430is formed by serially connecting N diodes in the same direction, and the forward-biasing voltage of each diode is Vf. Therefore, when the voltage on the rectifying output terminal2912is larger than N*Vf, the diode serial-connecting circuit is conducting, and the voltage on the control terminal of the voltage-limiting switch410starts to increase with the increasing of the voltage on the rectifying output terminal2912. When the voltage on the control terminal of the voltage-limiting switch410is larger than a threshold voltage value, the channel of the voltage-limiting switch410is conducting, and forms a voltage-limiting current path including the current-limiting resistor420. The voltage-limiting current path can be effective as a finite resistor and performing voltage dividing with the effective output resistor of the rectifier, which can effectively limit the increasing of the voltage on the rectifying output terminal2912.

It is worth noting that the embodiment of the voltage limiter391disclosed inFIG. 3is not limited to the embodiment disclosed inFIG. 4. The voltage limiter400disclosed inFIG. 4is only for description purpose but not to limit the scope of our invention. People skilled in the art are capable of choosing proper circuit topologies in the prior for the voltage limiter391and further realizing them according to various applications.

FIG. 5is a schema showing a wireless power system500of the third embodiment of the present invention. The function and the realization of each part of the wireless power system500can be referred to the description of the corresponding part of the wireless power system200disclosed inFIG. 2. The difference of the wireless power system200and500is that the power management unit590of the wireless power system500further includes a first voltage limiter591and a second voltage limiter592. The first voltage limiter591includes a first voltage-limiting current path coupled between the power receiving terminal265and the ground terminal275. When the voltage of the power receiving terminal265is larger than a first voltage threshold, the first voltage-limiting current path is conducting, and when the voltage of the power receiving terminal275is smaller than the first voltage threshold, the first voltage-limiting current path is cut-off. The second voltage limiter592includes a second voltage-limiting current path coupled between the other terminal of the second windings250and the ground terminal275. When the voltage of the other terminal of the second windings250is larger than a second voltage threshold, the second voltage-limiting current path is conducting, and when the voltage of the other terminal of the second windings250is smaller than the second voltage threshold, the second voltage-limiting current path is cut-off.

Furthermore, the embodiment of the first voltage limiter591and the second voltage limiter592can be referred to the voltage limiter400disclosed inFIG. 4. It is worth noting that the embodiment of the first voltage limiter591or the second voltage limiter592is not limited to the embodiment disclosed inFIG. 4. The voltage limiter400disclosed inFIG. 4is only for description purpose but not to limit the scope of our invention. People skilled in the art are capable of choosing proper circuit topologies in the prior for the first voltage limiter591or the second voltage limiter592and further realizing them according to various applications.

In more detail, by further including the first voltage limiter591or the second voltage limiter592in the power management unit590of the wireless power system500, the voltage on each of the two terminals of the input port2911of the rectifier291is limited in the first place when each of the voltage on the two terminals of the input port2911is over-high, and the devices in the rectifier291are protected. However, each of the first voltage-limiting current path and the second voltage-limiting current path is effective as a finite resistor with limited current conducting ability, hence, the following protection, which is provided by the first switch293, the second switch294, the first protecting capacitor270and the second protecting capacitor280, is activated by the response of the comparator296to further protect the power management unit590, as is described in the first embodiment and the second embodiment of the invention.

According to the above descriptions, it can be understood that the protection circuit formed by the first voltage limiter591, the second voltage limiter592, the first switch293, the second switch294, the reference voltage terminal295, the comparator296, the first protecting capacitor270and the second protecting capacitor280in the wireless power system500can prevent the voltage on the input port2911from over-high, and further prevent the power management unit590from constantly receiving an over-high voltage causing the power management unit590to be with a short lifetime or even being damaged directly.

The aforementioned description only represents the preferred embodiment of this invention, without any intention to limit the scope of this invention thereto. Various equivalent changes, alterations, or modifications based on the claims of this invention are all consequently viewed as being embraced by the scope of this invention.