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Development of Capacitive Energy-storage High-speed Solenoid Driver (2)
Circuit work is as follows. When the ECU output injection pulse width INJ1, Q4 selected cylinder conduction, capacitor C1 IN1 at the start of the discharge solenoid valve L1. At this moment, there is no signal of cylinder selection in Q5, the solenoid valve L3 is off, Q1 is off, 100V is prohibited to charge the capacitor C1, and 12V self-reverse stop. Until C1 discharges below 12V, 12V energizes solenoid valve L1 through Q2 in PWM mode. PWM duty cycle through the current sense amplifier feedback control. After INJ1 is completed, Q4 is off, L1 is off, Q1 is on, and 100V starts to charge C1. When the engine after a working cycle, ECU output fuel injection pulse width INJ3 after the cylinder, the capacitor C1 has been fully charged, then high-end part of the above process is repeated, Q5 election cylinder conduction solenoid valve L3 work, solenoid valve L4 deadline . Figure 2 for the solenoid valve current waveform, which can be seen from the solenoid valve throughout the work process. At point A, C1 starts to discharge and the current of the solenoid valve rises rapidly; at the time point B, the solenoid current reaches a peak current of about 30A; at C1, the voltage of C1 drops from 100V to 12V, and the 12V power supply starts to supply current. 10A, D point when the fuel injection pulse ends, the solenoid valve is turned off, the capacitor C1 starts charging; E point capacitor C1 is full, the voltage rose to 100V. Similar to the above, the main injection pulse width signal INJ2 of the front cylinder of the rotor and the main injection pulse width signal INJ4 of the rear cylinder work in the same manner by the other discharge capacity C2. By setting C1 and C2 two discharge capacitors, INJ1 and INJ2, INJ3 and INJ4 time coincidence of the working state to ensure that the opening voltage of each stable at 100V, thus ensuring a reliable solenoid valve open. Figure 2 is easy to see the point A to point C capacitor discharge voltage at the same time in the process of decline. This is fully in line with the aforementioned solenoid valve operating characteristics. Compared with the dual-voltage pulse-width modulation drive circuit, the capacitive storage drive circuit consumes less power. And due to the capacitor is limited each time the energy storage, it can prevent the solenoid valve in some accidental overload overload burned. In the meantime, unlike the other several driving circuits, the capacitor-driven driving circuit does not need to generate an on-pulse width as a control signal of high voltage through pulse width synchronization of injection, thereby simplifying the circuit logic. PWM and high-end driver circuit In this design, PWM generation chip selects TL494 PWM chip, two error amplifiers are used for the front and rear two cylinder ignition and the main spray current detection negative feedback interface, without additional op amp. High-end drive selected IR's dedicated floating-drive chip IR2103. It should be noted that the IR2103 peripheral bootstrap capacitor and the choice of reverse diodes. In the IR2103 high-end part of the work, both the need to ensure that the boot switch off during bootstrap capacitor charging time is short enough, but also to ensure that the switch in the process of capacitor voltage drop is not large, which requires the bootstrap capacitor has a suitable Capacitance and leakage current should be small. The choice of the reverse diode requires that the reverse leakage current must be small enough to maintain the voltage differential across the bootstrap capacitor when turned on on high side. Capacitor Selection To ensure that the high-voltage switch-on provides sufficient energy, the capacity of the discharge capacitor needs to be calculated. From Figure 3, the solenoid valve current waveform, the approximate curve of the curve to estimate the solenoid valve to open the required power C is about 24mF, consider a certain margin, select the capacity of 33mF capacitor. It should be noted that the discharge capacitor should meet the high voltage, high frequency, high current conditions of repeated charge and discharge. After comparison, this design uses a metalized polypropylene film capacitors. High-Side Current-Sense Circuit Another feature of this drive circuit is the use of high-side current-sense feedback control PWM outputs. Compared with the constant PWM duty cycle control mode, the current closed-loop feedback PWM control can ensure the solenoid valve to maintain a constant current when the battery voltage changes. This is necessary to ensure the accuracy of fuel injection. The current general current feedback control is often used at the low end of the grounding resistor for current sampling. The benefits of this approach is simple structure, low cost. However, there are some problems, such as current detection solenoid valve freewheel is difficult to include, low accuracy and so on. The driver circuit uses a high-side current detection method. The advantage of high-side current detection is that it not only solves the problem that the free-wheeling loop can not be included in the current detection, but also provides short-circuit protection in the high-end part. In addition, the measurement accuracy is also high. However, the high-speed solenoid valve opening voltage up to 100V, far more than the normal IC operating voltage. In general, high-end current detection chip is often difficult to apply in the field of high voltage due to the limitation of its own working voltage. Therefore, in the application of the need to design and build a peripheral circuit to achieve the floating current detection chip work, the circuit diagram shown in Figure 3. The current sense chip uses Maxim's MAX4172. The device is a differential input, current output high-side current sense amplifier, the output current value is proportional to the input differential mode, easily converted to the value of the ground voltage. The periphery circuit function in Fig. 3 is as follows. Z9, R38 and Q14 form a shunt regulator. Zener diode Z9 clamps the voltage between IN +, IN-, VCC and GND to 10V, and resistor R38 and transistor Q14 ensure that the Zener diode Z9's reverse bias current is maintained at a suitable value. As long as the zener diode Z9 within the operating current range, by adjusting the size of R38 can make the high-side current detection circuit at any high voltage operation. The clamp voltage is set to 10V, and the purpose of setting the diode D13 and the capacitor C35 is to ensure the stability of the supply voltage of the current detection circuit during the low-voltage hold PWM phase. The transistor Q13 and the resistor R39 convert the output current value into the voltage value of the ground. The voltage value is fed back to the error comparison port of the PWM generator TL494, and compared with the set feedback comparison voltage V1, so as to realize the feedback control of the PWM . Which R39 resistance and feedback compare the size of the voltage Vl is based on the solenoid valve operating current back-push calculated. Known MAX4172 output and input scaling factor Gm = 10mA / V, set the detection resistance Rs = 10mW, the solenoid valve to maintain the current value of 10A. The calculated V1 is 1.5V. From the 2 solenoid valve current waveform can be seen in the set feedback comparison voltage V1 = 1.5V parameters, the current sense feedback control solenoid valve to maintain the current stability of about 10A. Conclusion Capacitor energy storage solenoid valve drive circuit has the following characteristics. 1. Especially suitable for such as the rotor in the ignition and the main two fuel injection pulse width timing may overlap. To ensure that the solenoid valve to open the high-voltage stability; 2. Capacitor discharge mode more in line with the current response characteristics of the solenoid valve. Help protect the solenoid valve and reduce power consumption; 3. No need to generate turn on pulse width. As long as the single-chip fuel injection pulse width can be given to work to simplify the drive circuit; 4. Circuit using high-end current sense feedback control PWM output. Compared with the current detection method of setting the sampling resistance at the low end, the invention not only can accurately control the holding current of the electromagnetic valve but also solves the problem that the freewheeling ring of the solenoid valve is difficult to include during the current detection and also provides the short circuit protection of the high-end part. Through the application of this new type of drive circuit in the electronic control system of the engine, the stable operation of the rotor machine has been initially achieved.