Wireless power transmitter
A transmission antenna includes a resonant capacitor and a transmitter coil coupled in series. The driver includes a bridge circuit structured to apply a driving voltage to the transmission antenna. A current sensor detects current I S flowing through the bridge circuit. A foreign object detector detects the current I S flowing through the bridge circuit while changing switching frequency of the bridge circuit and determines whether a foreign matter is present or absent based on a difference between two frequencies f H and f L giving current lower than a peak by a predetermined ratio.
1. A wireless power transmitter structured to transmit a power signal to a wireless power receiver, comprising:
a transmission antenna including a resonant capacitor and a transmitter coil coupled in series;
a diver including a bridge circuit structured to apply a driving voltage to the transmission antenna;
a current sensor structured to detect a current flowing through the bridge circuit; and
a foreign object detector structured to detect the current flowing through the bridge circuit while changing switching frequency of the bridge circuit and determine whether a foreign object is present or absent based on a difference between two frequencies f H and f L giving current lower than a peak by a predetermined ratio, wherein
the foreign object detector is structured to
(i) acquire frequency f 0 at which the current peaks and a current value I MAX at that time while sweeping up the switching frequency of the bridge circuit from a frequency lower than a resonance frequency of the transmission antenna as a starting point,
(ii) calculate current I LOW by multiplying the current value I MAX by a predetermined ratio,
(iii) acquire frequency f H when the detected current reaches the current I LOW while further sweeping up the switching frequency, and
(iv) acquire the frequency f L at which the detected current reaches the current I LOW while sweeping down the switching frequency.
2. The wireless power transmitter according to claim 1 , wherein the predetermined ratio is 1/√2.
3. The wireless power transmitter according to claim 1 , wherein the foreign object detector calculates a Q value according to Q=f 0 /(f H −f L ), and determines whether a foreign object is present or absent based on the calculated Q value.
4. The wireless power transmitter according to claim 3 , wherein the foreign object detector determines whether a foreign object is present or absent based on a comparison result between the calculated Q value and a predetermined threshold value.
5. The wireless power transmitter according to claim 4 , wherein the foreign object detector receives the threshold value from the wireless power receiver.
6. The wireless power transmitter according to claim 1 , wherein the current sensor is structured to detect the current flowing into an upper power supply terminal of the bridge circuit from a DC power supply.
7. The wireless power transmitter according to claim 6 , further comprising a smoothing capacitor coupled to the upper power supply terminal of the bridge circuit.
8. The wireless power transmitter according to claim 1 , wherein the current sensor includes:
a detection resistor provided on a path of current to be detected;
a sense amplifier structured to amplify voltage drop across the detection resistor;
a low-pass filter structured to receive an output of the sense amplifier, and
an A/D converter structured to convert an output of the low-pass filter to a digital value.
9. The wireless power transmitter according to claim 1 , wherein a current detection circuit structured to detect current required to calculate transmission power is also used as the current sensor.
10. The wireless power transmitter according to claim 1 , wherein the wireless power transmitter conforms to a Qi standard.
11. A wireless power transmitter structured to transmit a power signal to a wireless power receiver, comprising:
a transmission antenna including a resonant capacitor and a transmitter coil coupled in series;
a diver including a bridge circuit structured to apply a driving voltage to the transmission antenna;
a current sensor structured to detect a current flowing through the bridge circuit; and
a foreign object detector structured to detect the current flowing through the bridge circuit while changing switching frequency of the bridge circuit and determine whether a foreign object is present or absent based on a difference between two frequencies f H and f L giving current lower than a peak by a predetermined ratio, wherein
the foreign object detector is structured to
(i) acquire frequency f 0 at which the current peaks and a current value I MAX at that time while sweeping down the switching frequency of the bridge circuit from a frequency higher than a resonance frequency of the transmission antenna as a starting point,
(ii) calculate current I LOW by multiplying the current value I MAX by a predetermined ratio,
(iii) acquire frequency f L when the detected current reaches the current I LOW while further sweeping down the switching frequency, and
(iv) acquire the frequency f H at which the detected current reaches the current I LOW while sweeping up the switching frequency.
12. The wireless power transmitter according to claim 11 , wherein the predetermined ratio is 1/√2.
13. The wireless power transmitter according to claim 3 , wherein the foreign object detector calculates a Q value according to Q=f 0 /(f H −f L ), and determines whether a foreign object is present or absent based on the calculated Q value.
14. The wireless power transmitter according to claim 13 , wherein the foreign object detector determines whether a foreign object is present or absent based on a comparison result between the calculated Q value and a predetermined threshold value.
15. The wireless power transmitter according to claim 3 , wherein the current sensor is structured to detect the current flowing into an upper power supply terminal of the bridge circuit from a DC power supply.
16. The wireless power transmitter according to claim 15 , further comprising a smoothing capacitor coupled to the upper power supply terminal of the bridge circuit.
17. The wireless power transmitter according to claim 3 , wherein the current sensor includes:
a detection resistor provided on a path of current to be detected;
a sense amplifier structured to amplify voltage drop across the detection resistor;
a low-pass filter structured to receive an output of the sense amplifier, and
an A/D converter structured to convert an output of the low-pass filter to a digital value.
18. The wireless power transmitter according to claim 11 , wherein a current detection circuit structured to detect current required to calculate transmission power is also used as the current sensor.
19. A foreign object detection method in a wireless power receiver including
a transmission antenna including a resonant capacitor and a transmitter coil coupled in series, and
a bridge circuit structured to apply a driving voltage to the transmission antenna, the foreign object detection method comprising:
detecting a current flowing through the bridge circuit while changing switching frequency of the bridge circuit; and
determining whether a foreign object is present or absent based on a difference between two frequencies f H and f L giving current lower than a peak by a predetermined ratio, wherein the determining includes
(i) acquire frequency f 0 at which the current peaks and a current value I MAX at that time while sweeping down the switching frequency of the bridge circuit from a frequency lower than a resonance frequency of the transmission antenna as a starting point,
(ii) calculate current I LOW by multiplying the current value I MAX by a predetermined ratio,
(iii) acquire frequency f H when the detected current reaches the current I LOW while further sweeping down the switching frequency, and
(iv) acquire the frequency f L at which the detected current reaches the current I LOW while sweeping up the switching frequency.
20. A foreign object detection method in a wireless power receiver including
a transmission antenna including a resonant capacitor and a transmitter coil coupled in series, and
a bridge circuit structured to apply a driving voltage to the transmission antenna, the foreign object detection method comprising:
detecting a current flowing through the bridge circuit while changing switching frequency of the bridge circuit; and
determining whether a foreign object is present or absent based on a difference between two frequencies f H and f L giving current lower than a peak by a predetermined ratio, wherein the determining includes
(i) acquiring frequency f 0 at which the current peaks and a current value I MAX at that time while sweeping down the switching frequency of the bridge circuit from a frequency higher than a resonance frequency of the transmission antenna as a starting point,
(ii) calculating current I LOW by multiplying the current value I MAX by a predetermined ratio,
(iii) acquiring frequency f L when the detected current reaches the current I LOW while further sweeping down the switching frequency, and
(iv) acquiring the frequency f H at which the detected current reaches the current I LOW while sweeping up the switching frequency.