无线充电
A Design of Wide Input Range, High Efficiency Rectifier for Mobile Wireless Charging Receiver
Ji-Hun Kang*, Hyung-Gu Park, Jae-Hyeong Jang, Kang-Yoon Lee
College of Information and Communication Engineering, Sungkyunkwan University
2066, Seobu-ro, Jangan-gu, Suwon-si, Gyeonggi-do, Korea
*zpisup01@https://www.360docs.net/doc/b215900712.html,
Abstract—This paper presents a high-efficiency Schottky diode rectifier for the mobile wireless charging receiver. A wide input range multi-mode rectifier is proposed for a magnetic resonant wireless charging system. The configuration is automatically changed based on the input AC voltage to widen the input voltage range. It is fabricated in a 0.35 um BCD process and its area is 1mm×1.5mm. When the magnitude of the input power is 4 W at 128 kHz, the Power Conversion Efficiency of the multi-mode Schottky diode rectifier is 85%, which is improved by 10% compared with that of the full-wave MOSFET rectifier.
Keywords-Power Conversion Efficiency; Multi-Mode Rectifier; Magnetic Resonant; Wireless Charge System;
I.I NTRODUCTION
Wireless Power Transfer (WPT) is a popular research item especially at mobile phone charger. Furthermore, WPT can be applied to various applications from medical equipment to electric vehicles [1]. However, these are difficult to commercialize because of the following reasons; many portability issues, distance and efficiency. Generally, the rectifier dominates the overall power efficiency of wireless power transfer [2]. The Power efficiency of rectifier is very important, as it provides DC supply to the next stage blocks.
Forward bias voltage of Schottky diode is less than general diode with 0.7 to 0.9V, and it is useful for low voltage drop with high efficiency.
WPT is classified into inductive coupling and magnetic resonant types. In this paper, the rectifier is designed for the magnetic resonant type WPT system. We propose a wide input range multi-mode Schottky diode rectifier by implementing the voltage multiplier with additional switches, and using Schottky diode with low drop voltage of 0.2 to 0.3V at low input voltage. Additionally, bootstrap technique is adopted for low voltage drop. Three modes of multi-mode Schottky diode rectifier control input range for efficiency compensation and its configuration is automatically changed at input Power.
II.W IRELESS C HARGE S YSTEM A.Wireless Power Receiver Architecture
Fig. 1 shows the block diagram of the wireless charging receiver.
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The AC voltage at the Rx input is applied to the Rx antenna. And, it is converted into a DC Voltage by multi-mode Schottky diode rectifier. DC-DC Converter and LDO Regulator generate the DC Voltage reducing the ripple variation.
In this paper, a multi-mode Schottky diode rectifier with wide range input range and high power efficiency is proposed.
B.Active Rectifier & Voltage Multipler
Eq. (1) shows the efficiency of the rectifier.
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rectifier I
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(1)
V do is the total voltage drop along the conducting path and I loss is the total current loss that is mainly determined by the reverse leakage current I leak in the power stage.
For maximizing the power efficiency of the rectifier V do and I leak should be minimized [3].
Fig. 2 shows the schematic of the Active rectifier and voltage multiplier. Using the bootstrap technique reduces threshold voltage of PMOS, and compensates voltage drop. The gates of these PMOS transistors, M3 and M4 are driven by a larger voltage swing than diode-connected PMOS transistors and hence a higher switched current ratio can be
This research was supported by MSIP(Ministry of Science, ICT&Future Planning), Korea, under the IREC(Information Technology Research Center) support program (NIPA-2013-(H0301-13-1013) supervised by the NIPA(National IT Industry Promotion Agency).
achieved. Diode-connected NMOS transistors, M1 and M2 are used to block the reverse current [4].
When the operation of input voltage is less than operation of rectifier, voltage multiplier can be used to increase the input range. Switching active rectifier and voltage multiplier increase the efficiency at low input voltage and widens input voltage range.
Schottky diodes with a low forward drop can be used to enhance the efficiency of proposed switching system.
(a) (b)
Figure 2. Schematic of (a) Active Rectifier (b) Voltage Multiplier.
C. Multi-Mode Active Rectifier
Fig. 3 shows the block diagram of proposed multi-mode Schottky diode rectifier. When AC Voltage is too low, multi-mode rectifier should be changed to voltage multiplier mode to increase the input voltage range. Voltage multiplier mode is used to increase input range and efficiency [5].
Also efficient impedance matching improves the efficiency. Proposed impedance matching system compares load impedance to current and calibrates them to pie model
Figure 3. Proposed multi-mode rectifier with impedance matching control.
Fig. 4 shows the schematic of proposed multi-mode active rectifier. SW2 is the switch that controls the 1-stage voltage multiplier mode and 2-stage voltage multiplier mode. SW3 compares Rectifier and 1st stage voltage multiplier. When the input AC voltage is too low compared with the reference voltage, the multi-mode rectifier should be changed as the voltage multiplier mode to widen the input range. As shown in Table 1, when the SW2 and SW3 are turned on, the voltage charged at C F, is added to voltage. And it increases the voltage of 1-stage multiplier mode. If the input voltage is lower than 1-stage mode, SW2 is turned off. And system operates in 2-stage multiplier mode, when there is very small input voltage to operate. If the input voltage is higher than reference voltage, then SW1, SW2 are
turned on, and SW3 is turned off, which is called the original active rectifier mode .
Using bootstrap technique compensates for the threshold voltage of the MOSFET. When AC input voltage is applied to the path of C F , it is charged by D5 (V DC =V AC -V TH5). At the end of the charging of C F, current path of D7 charges C B (called bootstrap capacitor) (V CB =V DC -V TH7). Then threshold voltages of M1 and M2, D7 and D8 are canceled, and diode`s voltage drop is calibrated. (V DC = V AC -(V TH,M1-V TH7))
Figure 4. Schematic of the proposed multi-mode rectifier.
TABLE I.
P ROPOSED MULTI -MODE SCHOTTKY DIODE RECTIFIER `S
SWITCHING CONTROL Multi-Mode Active Rectifier Control
SW1 SW2 SW3 Mode
ON ON OFF Full-Wave Active Rectifier OFF ON ON 1-Stage Voltage Multiplier OFF
OFF
ON
2-Stage Voltage Multiplier
III. E XPERIMENTAL R ESULT
A. Chip Layout
Fig. 5 shows the chip layout pattern for wireless power system in receiver. It is fabricated in a 0.35 um CMOS process. The die area is 5mm ×2.5mm.
External filtering and bootstrapping capacitor are 10uF, respectively. Input AC power and voltage are 4 W and 10 V, respectively.
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Figure 5. Chip layout pattern
B. Simulation Result
Fig. 6 (a) shows the simulation result of the rectifier output voltage and current at the input power of 4 W. Input
voltage is 14 V and output voltage is 13.15V which means 94% voltage conversion ratio at active rectifier mode.
Fig. 6 (b) shows the output power. Power conversion
efficiency is 85% since the output power is 3.4 W.
(a) (b)
Figure 6. Simulation result of rectifier (a) output voltage and current (b)
output power at the input power of 4 W.
Figure 7.
Simulation results at three operating modes.
Figure 8.
Simulation results at rectifier mode and 2-stage voltage
multiplier mode.
Fig. 7 shows the simulation result of the multi-mode active rectifier at three operating modes. It is automatically switched by comparators depending on the input AC voltage. Output DC Voltage, VDC, is increased at the voltage multiplier modes.
Fig. 8 shows the simulation result of mode change operation at input AC voltage of 9 V . In the rectifier mode, signal of 5V VDD (VDD5) is generated and high threshold voltage of comparator is decreased. It begins to switch off and drop to the rectifier output voltage of 7.5 V. When completing the signal of 5V VDD generation, the threshold voltage is decreased and switch is on to operate as 2-stage voltage multiplier generating the output voltage of 13 V.
C. Measurement of Test Board
Fig. 9 shows the test board of wireless charging receiver.
Fig. 10 (a) shows the measurement results of the multi-mode active rectifier in the WPT Receiver board that measured output voltage at three modes.
LDO Control Bit
Active Rectifier Input
Rectifier 5V VDD Rectifier BGR
Rectifier Output Supply Voltage
Common Ground
DC-DC Converter Input
LDO INPUT DC-DC Converter
Output
LDO Output
Receiver IC
Figure 9. Test board for wlreless charging system.
(a) (b)
Figure 10. Measurement results of multi-mode rectifier (a) output voltage
on three mode (b) PCE of compared with MOSFET.
Outputs of the 1-stage voltage multiplier and active rectifier are almost same at the input voltage of 9 V. The mode is changed at the input voltage.
As shown in Table , when the input voltage is 20 V AC at rectifier mode, the voltage conversion efficiency is 94%. Fig. 10 (b) shows the measurement results of MOSFET rectifier and multi-mode Schottky rectifier`s comparison when input power is swept from 1W to 5 W. The result shows that PCE of diode is higher than MOSFET, and bootstrap technique is effective for improving the power conversion efficiency. PCE of Multi-mode Schottky diode rectifier is improved by 10% compared with that of the MOSFET rectifier.
The maximum load current of the proposed multi-mode Schottky diode rectifier is 500mA and PCE is 85% at the input power of 4 W and input voltage ranging from 2 V to 20 V.
Fig. 11 (a) shows measurement result of output voltage at each modes. When the input voltage is very small, 2-stage multiplier mode is operating until the input voltage reaches 6 V. When the input voltage is small that 1st multiplier mode is operating until the input voltage reaches 7 V. The original active rectifier mode can operate when the input voltage is over 7 V in order to increase efficency in each range.
Fig. 11(b) shows measurment result of impedance matching result and output voltage at active rectifier mode. Bootstrap and low drop voltage of schottky diode reduce V TH
to increase efficiency.
(a)
(b)
Figure 11. Measurement result of milti-mode rectifier output voltage (a) at
each modes (b) impedance matching in rectifier mode
Figure 12. Measurment result of mode change range at each mode.
Fig. 12 shows measurement result of mode change range. The rectifier operates at 2-stage voltage multiplier mode and 1-stage voltage multiplier when input AC voltage is 9 V AC and 11V AC , repectively .
TABLE II.
P ROPOSED MULTI -MODE SCHOTTKY DIODE RECTIFIER `S
SUMMARY Multi-Mode Active Rectifier Characteristic
Value
Technology 0.35um BCD Input Voltage range 2~20V Full Load Current 500mA Power Conversion
Efficiency 85% Voltage Conversion
Efficiency 94% Load Impedance
20 ~ 50
IV. C ONCLUSION
This paper proposes the wide input range, high efficiency multi-mode rectifier for a magnetic resonant wireless charging receiver. Operating modes of the rectifier is automatically changed to support with wide input range in case the distance between the transmitter and receiver is increased. When the magnitude of the input power is 4 W at 128 kHz, the Power Conversion Efficiency of the multi-mode Schottky diode rectifier is 85%,
A CKNOWLEDGMENT
This research was supported by the MSIP(Ministry of Science, ICT&Future Planning), Korea, under the ITRC(Information Technology Research Center) support program (NIPA-2013-(H0301-13-1013) supervised by the NIPA(National IT Industry Promotion Agency). This work was also supported by IC Design Education Center(IDEC)
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