Patent Application
20200244236
The present invention relates to technology for a zero voltage switching control of an amplifier and a wireless power transmission.
Class-E amplifiers have structures capable of generating required power with high efficiency because of satisfying a zero voltage switching (ZVS) condition basically so that the Class-E amplifiers are mainly used in wireless power transmission devices in wireless charging systems.
However, a case in which a ZVS condition is not satisfied occurs according to a load condition. Particularly, in the wireless charging system, when power consumption of a load of a receiving-end increases, the ZVS condition may not be satisfied and thus a ZVS is not performed, thereby increasing the power consumption and noise.
The present invention is directed to providing a zero voltage switching control device of an amplifier and a wireless power transmission device which prevent increases in power consumption and noise and perform a stable zero voltage switching.
One aspect of the present invention provides a zero voltage switching control device including a switch voltage sensor configured to detect a drain voltage of a first switch when the first switch of an amplifier is turned on and generate a switching voltage, an error amplifier configured to receive the switching voltage, compare the switching voltage with a reference voltage, and amplify an error, a loop filter configured to receive an output voltage of the error amplifier and output a control voltage, and a duty controller configured to control a duty of a driving signal of the first switch according to the control voltage and allow the first switch to be subjected to a zero voltage switching.
The duty controller may limit a minimum duty to be 50% or more.
The switch voltage sensor may include a third switch having a source connected to a first node, a drain connected to a second node, and a gate receiving a pulse signal generated from a gate driving signal of the first switch, a first diode formed between a first ground voltage and the first node, a first resistor connected to the first node and a drain of the first switch, a capacitor (Cs) formed between a second ground voltage and the second node, and a filter formed between the second node and a third ground voltage and configured to output the switching voltage.
The switch voltage sensor may detect the drain voltage of the first switch using the first switch and the first diode when the first switch is turned on, sample a first node voltage by generating the pulse signal from the gate driving signal of the first switch and turning the third switch on using the pulse signal, hold a second node voltage on the capacitor (Cs) when the third switch is turned off, and remove noise of the second node voltage using the filter to output the switching voltage.
The error amplifier may receive the switching voltage from the switch voltage sensor to compare the switching voltage with the reference voltage, output a current proportional to a voltage difference to increase the output voltage when the switching voltage is higher than the reference voltage, and receive a current proportional to a voltage difference to decrease the output voltage when the switching voltage is lower than the reference voltage.
When the drain voltage has a positive (+) value at a time at which switching of the first switch starts, the duty controller may decrease the duty as the output voltage of the error amplifier increases and the control voltage output from the loop filter increases. When the drain voltage has a negative (−) value at a time at which switching of the first switch starts, the duty controller may increase the duty as the output voltage of the error amplifier decreases and the control voltage output from the loop filter decreases.
The duty controller may delay a clock signal on the basis of the control voltage received from the loop filter, and output a gate driving voltage of the first switch using the clock signal and the delayed clock signal. Here, a maximum duty of the gate driving voltage of the first switch may be determined on the basis of a delay time of the delayed clock signal, and a minimum duty may be 50% due to the clock signal having a duty of 50%.
The zero voltage switching control device may further include a capacitance selector configured to selectively adjust a capacitance of the first switch of the amplifier.
When a zero voltage switching operation is performed with a duty of 50% or less, the capacitance selector may decrease a capacitance of a capacitor connected to the drain of the first switch of the amplifier and allow the zero voltage switching operation to be performed with a duty of 50% or more as a capacitance selection voltage is changed into a low state and a second switch of the amplifier is turned off by a low state of a capacitance selection signal.
When the drain voltage detected by detecting the drain voltage of the first switch is equal to or higher than a preset value, the capacitance selector may increase a capacitance of a capacitor connected to the drain of the first switch of the amplifier and prevent excessive generation of the drain voltage as a capacitance selection voltage is changed into a high state and a second switch of the amplifier is turned on by a high state of a capacitance selection signal.
The capacitance selector may include a D flip-flop configured to receive an inversed clock signal and a duty generation signal, determine whether the duty generation signal has a duty of 50% or less, and output a high signal to an output (Q) when the duty is 50% or less, and a set-reset (SR) latch configured to receive a high signal at an input (R) when the D flip-flop generates the high signal and allow the capacitance selection signal output from the output (Q) to be in a low state.
The capacitance selector may further include a peak detector configured to detect a drain voltage peak of the first switch in a state in which the capacitance selection signal is in a low state, and a comparator configured to output a high signal when the drain voltage peak is equal to or higher than a preset value, apply the high signal to an input S of the SR latch, allow the SR latch to output a high signal to the output (Q), and allow the capacitance selection signal output from the output (Q) to be in a high state.
Another aspect of the present invention provides a wireless power transmission device including an amplifier including a choke coil, a first switch, a first capacitor connected to a drain of the first switch, a resonance tank, and a load, and a zero voltage switching control device configured to detect a drain voltage of the first switch when the first switch is turned on, control a duty of a driving signal of the first switch to be 50% or more on the basis of a state of the detected drain voltage, and allow the first switch to perform a zero voltage switching.
The amplifier may further include a second switch and a second capacitor connected to a drain of the second switch, and the zero voltage switching control device may selectively adjust a capacitance of the first switch to prevent a zero voltage switching with a duty of 50% or less.
According to one embodiment of the present invention, since a duty of a switch driving signal is controlled to be 50% or more and a zero voltage switching (ZVS) is performed, problems occurring in a case in which the duty is 50% or less can be solved. For example, when the duty decreases in a case in which power consumption of a receiving-end load is high, problems in which power supplied from a power source decreases so that enough power cannot be supplied to a load and a switch is not operated with a stable duty due to a switch-on time being affected by noise during a process in which a drain voltage of the switch is detected can be solved. In addition, in a case in which the switch is driven at a high speed, a problem of difficulty to synchronize a time due to operational delay of a comparator which detects the drain voltage dropping below a specific potential can be solved.
In addition, since the duty is gradually controlled such that the drain voltage becomes 0 V at a time at which a switching starts, even when an error occurs due to noise during a process in which the drain voltage is detected, a change in duty does not suddenly occur, and thus the duty can be stably controlled. In addition, since the drain voltage is not compared by the comparator, a high speed comparator is not necessary, and thus a significantly stable operation can be performed.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the present invention, when it is determined that detailed descriptions of related well-known functions or constructions may unnecessarily obscure the gist of the present invention, the detailed descriptions will be omitted. In addition, some terms described below are defined in consideration of functions in the present invention, and meanings thereof may vary depending on, for example, a user or operator's intentions or customs. Therefore, the meanings of terms should be interpreted on the basis of the scope throughout this specification.
Referring to
Referring to
When all elements including the resonance tank 14 are properly determined, the drain voltage Vd 200 decreases to 0 V before the first switch M111-1 is turned on again like a first drain voltage Vd1200-1. Here, as the first switch M111-1 is turned on (ON), a zero voltage switching (ZVS) may be performed. When the drain voltage Vd 200 is 0 V and the first switch M111-1 is turned on, since a switching loss of the first switch M111-1 is zero at the moment and a current which discharges the capacitor Cd 12 is not generated, electromagnetic interference (EMI) as noise is minimized.
The drain voltage Vd 200 may be changed to the first drain voltage Vd1200-1, a second drain voltage Vd2200-2, or a third drain voltage Vd3200-3 according to a capacitance of the capacitor Cd 12 as illustrated in
When the capacitance of the capacitor Cd 12 is lower than the ideal capacitance, since the capacitor Cd 12 is rapidly charged, a positive gradient of the drain voltage Vd 200 increases and a negative gradient thereof also increases like the second drain voltage Vd2200-2, and thus the drain voltage Vd 200 reaches 0 V earlier than in the case of the first drain voltage Vd1200-1 (ZVS but high peak). Next, as a current flows through a parasitic diode between the drain and a source of the first switch M111-1 until the first switch M111-1 is turned on (ON) again, loss is additionally generated due to forward voltage drop of the diode. In addition, since a maximum value of the voltage increases, the first switch M111-1 may be broken down in a case in which the voltage increases higher than a peak drain operating voltage of the first switch M111-1.
In a case in which the capacitance of the capacitor Cd 12 increases, although a positive gradient and a peak value of the drain voltage Vd 200 decrease like the third drain voltage Vd3200-3, since the drain voltage Vd 200 does not drop to 0 V or less before the first switch M111-1 is turned on again, the ZVS may not be performed (hard switching). In the state of hard switching, since charges charged in the capacitor Cd 12 are rapidly discharged by the first switch M111-1 when the first switch M111-1 is turned on again, a current having a high peak value flows through the first switch M111-1, and since the third drain voltage Vd3200-3 is not 0 V, a considerable amount of power is consumed and heat is generated at the first switch M111-1 at the moment of switching. In addition, since a high speed and high peak current causes emission of a considerable amount of EMI, the high speed and high peak current is not desirable from a viewpoint of noise.
The Class-E amplifier may be analyzed as below. When the Class-E amplifier is in an ideal operation state, a maximum value of the drain voltage Vd 200 will be determined by Equation 1.
Vd,max=1.134×π×VDD≈3.56×VDD Equation 1
In Equation 1, VDD is a magnitude of a supply voltage of the Class-E amplifier.
Referring to
According to Equation 2, since an equivalent resistance is inversely proportional to the load RL 320, in a case in which the load RL 320 decreases, that is, a large amount of power is required, the load Rp 350 increases.
A change in load affects operation of the Class-E amplifier. When the load RL 320 decreases, since the load Rp 350 increases and the current i 210 of a resonance tank decreases, the charging/discharging speed of a capacitor Cd 12 decreases, and finally, the Class-E amplifier may be in a hard switching state like the third drain voltage Vd3200-3 of
Referring to
Meanwhile, in a case in which the load Rp 350 is a high load, the first switch M111-1 enters a hard switching state in which a switching is performed in a state in which the drain voltage Vd is not 0 V as illustrated in
However, in a case in which the first switch M111-1 operates with a duty of 50% or less, many problems occur. For example, a status of
Referring to
The switch voltage sensor 50 detects an output voltage of a first switch M111-1 at a time at which the first switch M111-1 of a Class-E amplifier 60a is turned on and maintains the output voltage. Accordingly, whenever a switching starts, the switch voltage sensor 50 detects a drain voltage Vd 200 and generates a switching voltage VSH 500.
The error amp 52 receives the switching voltage VSH 500 from the switch voltage sensor 50, compares the switching voltage VSH 500 with a reference voltage, and amplifies an error. Here, the reference voltage may be 0 V. In a case in which the switching voltage VSH 500 is higher than 0 V, an output of the error amp 52 increases, and in the reverse case, the output of the error amp 52 decreases.
The error amp 52 according to one embodiment is a transconductance amp which converts a difference in input voltage into a current. Accordingly, when the difference in input voltage has a positive (+) value, the error amp 52 outputs a current proportional to the voltage difference, and when the difference in input voltage has a negative (−) value, the error amp 52 receives a current proportional to the voltage difference. Due to such an operation, a capacitance of a capacitor Cc of the loop filter 54 gradually decreases or increases. The loop filter 54 outputs a control voltage Vcontrol 510 and applies the control voltage Vcontrol 510 to the duty controller 56.
When the received control voltage Vcontrol 510 is high, the duty controller 56 decreases a duty of a driving signal of the first switch M111-1, and conversely, when the control voltage Vcontrol 510 is low, the duty controller 56 increases the duty. Accordingly, in a case in which the drain voltage Vd 200 has a positive (+) value at a moment of switching, the duty decreases gradually, and in a case in which the drain voltage Vd 200 has a negative (−) value, the duty increases gradually. Here, a maximum duty may be set to a value less than a predetermined value, and a minimum duty may be limited to 50%.
The error amp 52 may be the transconductance amp as illustrated in
When the circuit of
When a ZVS control device 5b of
The reason why a minimum duty is limited to 50% in the present invention is that, when the duty is 50% or less, although a ZVS condition may be satisfied, power required by a load may not be supplied. However, when the duty is not allowed to be 50% or less, since a status in which the ZVS operation may not be performed may occur, the ZVS control device 5b additionally includes the capacitance selector 58 as illustrated in
Referring to
In this state, when the load decreases, the drain voltage Vd 200 may decrease and the duty controller 56 may increase the duty as illustrated in
Since the ZVS condition is satisfied under various load conditions through a series of the above-described operations and a maximum duty does not decrease to 50% or less, there is no problem of power supply to the load. Although there is a demerit in that the second switch M211-2 is additionally necessary, since cost of a switch has been very cheap, the additional second switch M211-2 may be readily acceptable in consideration of safety of a system.
Hereinafter, a structure of the switch voltage sensor 50 will be described. Referring to
In the third switch M3720, a source is connected to the first node 731, a drain is connected to the second node 732, and a pulse signal Vs 710 generated from a gate driving signal Vgate 700 of the first switch M111-1 is applied to a gate. A first node voltage Va 730 is applied to the first node 731, and a second node voltage Vb 760 is applied to the second node 732. The first diode D1750 is formed between the first ground voltage 791 and the first node 731. The first resistor R1794 is connected to the first node 731 and the drain of the first switch M111-1. The capacitor Cs 740 is formed between the second ground voltage 792 and the second node 732. The resistor RF 770 and the capacitor CF 780 of the filter are formed between the second node 732 and the third ground voltage 793 and output a switching voltage VSH.
Hereinafter, operation of the switch voltage sensor 50 will be described. A short pulse signal Vs 710 the same as the pulse signal Vs 710 of
The drain voltage Vd 200 is detected using the first switch M111-1 and the first diode D1750. In the present invention, since a magnitude of the drain voltage Vd 200 of the first switch M111-1 is not important and only positive (+), negative (−), and zero values thereof are important, even when the voltage is clamped using the first diode D1750, there is no problem in the operation. When the first diode D1750 is used, since voltage swing of the first node voltage Va 730 is limited to a turn-on voltage of the diode, a fast operation may be performed.
A smooth signal of the switching voltage VSH 500 from which noise is removed is generated from the sampled and held second node voltage Vb 760 by the resistor RF 770 and the capacitor CF 780 of the filter. The error amp 52 compares the switching voltage VSH 500 with 0 V which is the reference voltage and uses the comparison result to control the duty.
Referring to
The duty controller 56 according to one embodiment outputs the gate driving voltage Vgate 820 using a clock signal CLK 800 with a duty of 50% and the CLK_ON_MAX signal 810 which is delayed from the clock signal CLK 800 by a delay time Toff 815. The CLK_ON_MAX signal 810 is used as a signal for determining a maximum duty.
The fourth switch M4840 of the duty controller 56 is a p-channel metal-oxide-semiconductor (PMOS) transistor and is used as a variable resistor. For example, when a gate signal of the fourth switch M4840 increases, the resistance thereof increases, and conversely, as the gate signal approaches 0 V, the resistance has a minimum value. The variable resistor and the capacitor Cdly 842 delay the CLK_ON_MAX signal 810. Since the gate signal of the fourth switch M4840 relates to the control voltage Vcontrol which is an output signal of the error amp 52, the delay is changed on the basis of the output voltage of the error amp 52. Accordingly, when the control voltage Vcontrol increases, the duty decreases. Then, the OR block 87 receives the duty generation signal DUTY_GEN 830 generated by the logic circuit 85 and the CLK signal inverted by the inverter 86 and outputs the gate driving voltage Vgate 820 though the OR operation. Accordingly, the duty is generated by the duty controller 56, wherein the duty is changed from the maximum duty which is the same as that of the CLK_ON_MAX signal 810 to the minimum duty of 50%. Since the maximum duty is determined by the delay time Toff 815, the maximum duty is calculated as T−Toff/T×100%, wherein T is one period.
Referring to
Meanwhile, when power consumption of the load decreases in the low state of the capacitance selection signal CAP_SEL, a peak value of the drain voltage of the first switch M111-1 increases as illustrated in
In Equation 4, Vd,pk is a peak voltage of the drain voltage Vd.
When the voltage Vpk 900 is higher than k×VDD, a comparator 96 outputs a high signal, the high signal is input to an input S of the SR latch 94, and a high signal is output to an output Q of the SR latch 94. The capacitance selection signal CAP_SEL becomes a high state due to the high signal of the output Q, the second switch M211-2 is turned on again, and the capacitance of the drain of the first switch M111-1 increases to the capacitance of the first capacitor Cd1 and the second capacitor Cd2. Since the capacitance has increased, the charging/discharging speed decreases, and thus the peak voltage decreases. Here, the Vd,pk voltage by which a high signal is output from the comparator 96 is expressed as the following Expression 5.
When a Class-E amplifier operates normally, since a relational expression between the Vd,pk and the VDD is as shown in Equation 1, k, RA, and RB may be set to meet the following Expression 6.
A diode D197 of the capacitance selector 58 compensates a voltage drop due to a diode D2950. In addition, a voltage of the diode D197 may be used as a voltage Va needed by the switch voltage sensor 50.
Referring to
Referring to
Referring to
While this inventive concept has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims. The exemplary embodiments should be considered in a descriptive sense only and not for purposes of limitation. Therefore, the scope of the present invention is defined not by the detailed description of embodiments but by the appended claims, and all differences within the scope will be construed as being included in the inventive concept.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2015-0135788 | Sep 2015 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2016/010473 | 9/20/2016 | WO | 00 |
