Nowadays, magnetic induction wireless charging can only provide low-power charging mode, and in order to shorten the charging time, the technology is gradually developing to medium power; through the new demodulation and modulation technology of the power supply end and the power receiving end, the coil transmission control data is improved. The way to effectively improve the medium power magnetic induction wireless charging speed.
In wireless charging, it is simply divided into a power supply end and a power receiving end. The power supply end converts power into electromagnetic wave energy, and the power receiving end receives the electromagnetic wave energy, performs electrical conversion, and outputs the power to the back end to provide charging to the power receiving device. Or run to use.
Control signal is the basis of wireless charging systemIn an electromagnetic induction type wireless power system, the amount of energy required at the power receiving end or the charging function to be turned on or off may vary depending on the state of use of the power receiving device. Corresponding to the power supply end coil can transmit energy through the design of different adjustment energy sizes to match. Since the power receiving end and the power supply end are not physically connected, but the functional power supply end needs to know the state of the power receiving end to perform power adjustment, so as to complete the transmission of the control signal to the power receiving end and then analyze and then control to form a Control loop, wireless communication becomes a must-have function of wireless charging system.
The electromagnetic induction wireless charging architecture transmits electromagnetic energy, that is, a carrier signal, to the power supply end, and the receiving end modulates the carrier signal while receiving the electromagnetic energy, and reflects the encoded communication data into the carrier signal, and the power supply end The communication data is parsed from the carrier signal on the power supply coil for control. This technology is a common product operation principle in the industry. This method is used by many Qi series products on the market.
The power receiving end modulates the communication data into the carrier signal on the power supply coil. The biggest advantage lies in the cost. In this way, no additional communication module is needed, and the actual communication only needs to be transmitted from the power receiving end to the power supply end, which is a one-way transmission. Most of the functional requirements can be fulfilled, and the biggest disadvantage is that it affects the state of the carrier signal on the power supply coil, mainly the load and induced resonance factors on the power receiving end.
This article specifically discusses the technology of communication modulation and demodulation between wireless charging power supply and power receiving coil. Due to limited space, other principles of wireless charging will not be described in detail.
Carrier characteristics of the power supply coil limit low frequency / signal high voltage unfavorable communicationUnlike the antennas that are specifically designed for communication, wireless charging is designed with coils that are primarily targeted for power delivery, and communication functions are developed on top of functional requirements.
In electromagnetic induction wireless charging, the characteristics of the signal on the power supply coil are: low frequency and not fixed, high signal voltage and current driving force, and these two characteristics are not conducive to communication purposes.
The frequency used by the electromagnetic induction type is about 100 ∼ 300 kHz. Compared with other communication technologies, the frequency is very low, and the modulation data rate is reliable, usually much lower than the main carrier frequency, plus the communication technology. The carrier only provides the frequency for the power supply terminal, and the power receiving terminal can only modulate through the amplitude modulation (AM). In addition, the power transmission power itself is changed by the frequency mode, thereby adjusting the amplitude of the resonance on the coil to improve or decrease. The power output function, so the main carrier frequency is not fixed and the amplitude variation is large, the design of the filter required for the signal analysis of the power supply terminal becomes difficult.
In addition, to increase the power on the power supply coil, the coil voltage must be pushed above 100V, and the current on the coil has a considerable current thrust to push the energy to the power receiving coil, because the power is increased after the power is increased. Under the condition of large current, the difficulty of re-modulating the signal on the receiving end is also improved. In the modulation principle, the receiving end must change the impedance on the receiving coil to reflect on the power supply coil to affect its signal amplitude and impedance. The larger the change, the larger the amplitude change after reflection, and the easier the signal is recognized.
However, the implementation is not so ideal. In order to improve the power transmission efficiency, the power supply coil uses a low-impedance wire and a low-inductance configuration. The current driving force on the coil is quite strong, and even if the load on the power receiving end changes, it can still provide considerable. The amplitude of the signal is used to maintain the thrust. This setting makes it more difficult for the power receiving end to perform signal modulation on the carrier. That is, the carrier that changes the impedance of the coil cannot be effectively reflected on the power supply coil, and the carrier amplitude is significantly changed. The modulation depth is insufficient and the signal analysis becomes difficult.
Moreover, the signal on the power supply coil itself has a large amount of noise, and the source of the noise is quite complicated. It is mainly caused by the signal jitter of the resonance of the power supply end itself, and the load reaction of the power receiving end, so the reflection is modulated into the power supply coil. The signal must be much larger than its noise, so it can be decoded and decoded. Here, it is explained that both the power receiving end modulation signal and the power supply end demodulation signal have technical challenges to be overcome, and the power receiving end must generate a clear modulation signal; the power supply end must also have the ability to take out the demodulation method in the coil high voltage resonance signal. .
Medium Power Receiver Improvement Method: New Displacement Modulation TechnologyIn the past common sense, in order to achieve the use of switching elements, it is necessary to achieve the reflection of the communication data from the power receiving end coil to the power supply coil through the modulation technique to change the impedance on the power receiving coil. The load increases the load effect on its coil for reflection during modulation.
In this way, the bottleneck will be encountered after the power is increased. When the load on the back end of the power receiving end is large, the equivalent load resistance of the power receiving coil is already low. If the modulation signal is increased, the load is close to the coil. Short circuit, this operation will increase the power loss and the problem of easily burning components. In this way, the modulation signal is applied to both ends of the coil at the same time, and the load is equal to the hard end of the power supply. The signal reflected strongly to the power supply ring is also modulated at a high power. Not easy to improve.
An improved modulation method is proposed here, which has two main points. The first one is that the modulation signal does not emphasize the load on the coil alone. The target of the modulation is the change of the impedance of the coil, so the reverse reduction of the impedance of the coil can also achieve the purpose of modulation. The second is that the modulation signal does not have to be modulated at both ends of the coil at the same time. It can be alternately modulated at both ends of the coil to alternately interact with the resonance of the power receiving end reflection signal to the coil of the power supply end, avoiding high power. Hard touch modulation technology can effectively increase the modulation depth.
Referring to FIG. 1 , a practical circuit diagram is shown. The receiving coil (Coil) senses that the electromagnetic energy is connected in series with the C1 resonant capacitor connected to the back end rectifying circuit, and the end points S1 and S2 thereof are inverted signals, and the S1 and S2 are actually viewed from the rectifier. The voltage signal is alternately pulled, and the S1 and S2 waveforms are close to the inverted square wave under load. The rectifier is designed to have a slightly different structure than the traditional four-pole rectifier. The upper end maintains two diodes D1 and D2. When S1 and S2 are at a high potential, the current is brought to the high end, and the lower end is different from the lower end. Generally, the rectifier is changed into two switching elements, and the action is that when S1 or S2 is low, the connected switching element Q13 or Q23 is in an on state, so that the ground current of the back load can lead to the coil.
Figure 1 Power receiving terminal module
The following rectifier operation principle is illustrated by one end, and the two ends are symmetric structures, so they operate in reverse phase. When S1 is cut from high potential to low potential, S2 will cut from low potential to high potential. At this time, Q13 should enter conduction, and Q23 should be open. In the past, this circuit is called half-bridge synchronous rectification, Q13. Interact with the Q23 through the phase signal.
In Figure 1, the improved circuit can improve its switching performance, and the Q12 and Q22 can be easily combined with the acceleration circuit. According to Q12, when S1 is high, Q12 will be turned on and the upper end S12 will be pulled down to low potential, while R121 will consume some current, but because of the large resistance, the loss is not much.
When S1 is ready to cut to a low potential, Q12 will cut into. At this point, a concept is described. The gate terminal of the switching circuit can be regarded as a capacitor. At the moment of switching, there will be charging and discharging time, and MOSFET as the switching element will be used. One characteristic is that it can withstand large currents and voltages. The capacitance of the gate terminal will be large, which means that the switching speed is slow. On the contrary, the fast component cannot withstand large current and voltage. In this case, the parts with the general price are close to this. characteristic.
In Figure 1, Q13 and Q23 are slow for high-current components, and Q12 and Q22 are low-current high-speed components. The action is that S1 cuts to a low potential, and the Q12 gate extreme voltage will quickly release Q12 through D122. After that, S2 will also cut to a high potential, and its S12 voltage is charged through R121, and after S12 is charged, Q13 is turned on, and this action is a continuous action.
In addition, when S2 cuts into a low potential, the voltage of the terminal capacitance of Q13 will be quickly released through D121 to accelerate the state of Q13 into an open circuit. Therefore, the principle of this region is that R121 and R122 charge the gate as a high potential. When D121 and D122 are cut into low potential, the voltage used to quickly release the gate capacitance is accelerated, and the action of Q12 is similar to that used by the seesaw to switch directions.
In addition, Q131 is used to suspend Q13 conduction, and Q131 is connected to RX-U1 for control. When the input is high from U1, the effect of Q131 is turned on, so that S12 is kept at a low potential.
Referring to FIG. 2, W6_3 is a coil signal, W6_2 is S12, that is, Q13 gate extreme signal, and W6_1 is a Q131 gate extreme signal. When RX-U1 outputs a high potential to Q131, the section S12 signal is maintained at a low potential, resulting in a rectifier. The conduction state does not occur in this section, and the intention is to suspend the rectification action.
Figure 2 Receiver coil signal, rectifier switch signal and modulation signal
In response to the previous paragraph, the coil impedance is changed in the modulation technique, and the impedance on the power receiving coil can be reduced by suspending rectification under the condition that the back end output is loaded, but this mode must be under the condition of the back end load. It works, and the rectification is suspended when the back end is unloaded, and the impedance on the coil is not changed.
Therefore, it is necessary to design a method of modulating the signal under no-load, and add R5 and R6 as the signal modulation under no-load, which respectively perform load modulation from both ends of the coil. Since they are alternately operated, the two resistors adopt different resistance values. To correspond to the modulation intensity that produces a difference under different load conditions. Therefore, the entire modulation technique is simply described as when the back end is unloaded or lightly loaded, and R5 and R6 serve to increase the impedance of the receiving coil during modulation. When the back end output load is increased, the impedance is less than R5 and R6. The modulation effect will be lost, so the modulation effect is produced by temporarily reducing the impedance on the power receiving coil by suspending the operation of the rectifier.
Referring to FIG. 3, the dislocation signal diagram, W7_3 is the power receiving coil signal, W7_1 and W7_2 are P04 and P11 signals, and W7_4 is S1 signal, which is different from W7_3 in that a strong current thrust is obtained after a resonance effect of a C1 capacitor. The waveform will also be close to the square wave signal; W7_5 and W7_6 are the S12 and S22 signals respectively. From Fig. 3, it can be seen that the modulation signal in the design is separately modulated from both ends of the coil, and is divided into modulation single-end, demodulation, modulation and other The modulation is completed after a single-ended operation. The purpose of this design is to generate the maximum modulation signal when the power received by the power receiving coil has the least impact.
Figure 3: Displaced modulation signal diagram
The preceding paragraph proposes a modulation method adopted at the power receiving end, which is intended to reflect the transmission of the maximum modulation signal and the least interference power after the power receiving end and the power supply end coil are induced, and the signal is reflected on the power supply coil to generate an amplitude thereon. fluctuation. What is described in this paragraph is how to convert this fluctuation into a signal that allows the power supply host to decode the IC.
Referring to the power supply terminal block diagram of FIG. 4, this example is a power supply terminal structure driven by a DC 24 volt (V) power supply. The switch drive components U4 and U5 are full bridge drive coils and resonant capacitor C1. Ideally, the coil and C1 are used. The middle should be a sinusoidal signal, but because of the efficiency, the coil and capacitor are configured with low-impedance components, so the switching signal is switched to a straight-pull type voltage switching signal, and the signal is a non-resonant component, so the first channel The process removes the pure resonant signal for removing the driving voltage component.
Figure 4 power supply module
In FIG. 4, two operational amplifiers OPA1 and OPA2 form two differential amplifying circuits, and the OPA1 acts as a differential reference point by dividing the driving power supply by R608 and R609; in addition, the coil resonant signals are performed by R610 and R605. The partial voltage is used as the amplification signal input. Here, there is a configuration in which the voltage division ratios of R608, R609, R610, and R605 are both 50 to 1. The intention is to take out the difference between the power supply driving voltage and the switching signal distortion in the resonant signal. The amplified signal is amplified above the component of the power drive.
After amplification, the output is divided into two paths. One is the effective DC voltage of the simple detection circuit to form the signal after the D701 and R703, R704 and C704. The voltage is V_dc signal with reference to FIG.
Figure 5 Power supply coil signal peak sampling amplification
The other route D603 is input to the OPA2 as the differential amplifier input terminal through the voltage dividing resistors R603 and R604, and the signal is the V_hw signal in FIG. 5 and then amplified by the OPA2 to output the V_hwa signal. The D603 and D701 are used to control the V_dc and V_hw. There is the same voltage drop, and R603, R604, R703, and R704 are used to set the voltage division ratio so that V_dc can be kept slightly below the V_hw signal, ensuring that OPA2 can only amplify the high and low variations in the peak.
The OPA2 output signal is transmitted to D601, R612, and C612 as a detection circuit. Referring to Figure 6, the D601 signal is V_env. The signal is the detection result of the peak signal, but the DC steady state of the signal is not fixed, so it is transmitted through C613. The waveform obtained by the R614 and R615 decoupling coupling circuit is V_trig, and the waveform is finally transmitted to the TX-U1 for decoding processing. In Fig. 6, the difference between the signal V_coil and the V_trig on the original power supply coil can be seen. .
Figure 6 Power supply coil signal detection and cross-coupling coupling
In addition, referring to FIG. 7, the V_coil has a trigger signal with unequal spacing, and the clear trigger signal is parsed through the design demodulation circuit V_trig, and the TX_U1 receives the continuous trigger signal combination for decoding.
Figure 7 Power supply coil signal and take-out trigger signal waveform
In Figure 8, corresponding to the corresponding signal from the power receiving end modulation signal to the power supply end demodulation signal, which can be seen that the modulation signal time is very short, but can demodulate a considerable and clear trigger signal on the power supply end, this is the article Introduce the purpose of the new signal modulation and demodulation method, and complete the maximum signal demodulation under the minimum modulation. This design can effectively complete the transmission of control data through the coil in the medium power electromagnetic induction wireless charging.
Figure 8 The power-modulated signal corresponds to the power-side demodulation signal
to sum up:In general, the wireless charger for mobile phones is still very safe in daily use, so you can buy it with confidence. Of course, if you want to charge very fast, or even reach the speed of the second charge, a large wireless charger like a car to charge the phone, close-range use will still bring magnetic field radiation damage, it is not recommended to play like this.
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