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Under the premise that the degree of automotive electronics has become an important standard for measuring the advanced level of automobiles in the world, all countries have developed this industry, constantly applying high technology and improving the electrification performance of automobiles in order to obtain a larger market. It is in this environment that stimulates and promotes the continuous development of the automotive electronics industry.
As is known to all, poor stability and short life is a common problem of current automotive voltage regulators. The instability of the regulator will lead to instability of the generator output voltage, which will cause large fluctuations in the power supply voltage of the vehicle's electrical equipment. The normal operation of the vehicle circuit is unfavorable, and it also reduces the life of the power supply. The short life of the regulator not only brings an economic burden, but also is detrimental to the stability of the generator output voltage.
The voltage regulator is designed as a monolithic CMOS integrated circuit, which reduces the size of the regulator so that it can be fabricated with an alternator. This not only improves the stability of the regulator, improves the power quality of the whole vehicle, effectively prolongs the service life of the automotive electronic equipment, but also adapts to the current development trend of small size and high output power of the automobile alternator. At the same time, the design also adapts to the pursuit of the current regulator "high performance, multi-function, high power, long life".
1 circuit principle and structure The schematic diagram of the car electronic regulator is shown in Figure 1.
When the car starts to add the input voltage, the reference voltage source generates a reference voltage for use in the internal circuit; the error amplifier receives the output voltage signal; the overcurrent protection circuit samples the output current of the power tube; the thermal protection circuit checks the temperature of the circuit; the error is amplified, The flow safety zone protection and the overheat protection circuit are fed into the power tube. When only one abnormal phenomenon occurs, the adjustment tube will be turned off to adjust the voltage and protect the function.
2 circuit design
2.1 Front-end reference source The front-end reference voltage in the designed chip circuit is to provide a reference voltage that is stable to the power supply voltage and temperature to the subsequent differential comparison circuit, which is then sampled by the differential comparison circuit. The voltage output from the generator is compared to control the output of the generator. The circuit is shown in Figure 2. In Figure 2, M1, M2, and M5 form a mirror current source, so that the current flowing through the three tubes is equal, and both are I; M3 and M4 form a voltage clamping circuit, so that the voltages at points A and B are consistent. The mirror current source and the voltage clamping circuit together form a PTAT source, and its positive temperature coefficient is used to compensate the negative temperature coefficient of the PN junction, thereby obtaining a reference voltage that does not substantially change with temperature.
2.2 Differential Comparison Circuit The function of the differential comparison stage circuit is to compare the reference voltage from the front-end reference and the sampled voltage of the generator. When the generator output voltage is lower than 14 V, the excitation current adjustment tube works normally, the excitation current flowing through the generator rotor winding rises rapidly, and the generator output voltage also rises rapidly. When the output voltage of the generator reaches 14 V, the differential output voltage is sufficient to drive the subsequent control circuit to control the grounding of the excitation current regulating tube, and the gate current is divided, which reduces the excitation current of the generator rotor winding, thereby reducing power generation. The machine output voltage reaches the voltage regulation function. Its circuit is shown in Figure 3.
2.3 Generator output voltage sampling circuit The function of the vehicle regulator is to adjust the output voltage of the generator to control it near a certain value. Since the output voltage of the generator is to be controlled, the output of the generator needs to be sampled. There are two ways to sample the voltage of the electronic regulator, namely the output voltage of the sampling generator and the voltage of the sampling battery. In the separate device regulator, the double sampling method is mostly used. In this design, the front reference voltage source has provided an accurate comparison voltage, so the output voltage of the alternator can be sampled. The sampling circuit is shown in Figure 4. In Figure 4, resistors R5, R6 and M13 form an energy-saving circuit. When the car stops working, this part of the circuit cuts off the connection between the regulator circuit and the battery, thereby avoiding the loss of battery power.
2.4 Temperature Protection Circuit The power device handles high voltage and high current. High voltage and high current will cause the device temperature to rise. When the temperature is high to some extent, the device will be damaged due to overheating. Therefore, the integrated circuit with power device The thermal protection circuit is designed to protect it from temperature. The temperature protection circuit of the power tube is shown in Figure 5. Since the temperature characteristics of the MOS device are good, the parameters (mainly the threshold voltage) vary little with temperature, so this part of the circuit is implemented by a PNP tube. In the circuit, the B and C poles of the Q5 tube are connected to form a PN junction, and the temperature of the power tube is detected. When the temperature of the power tube reaches the limit temperature (here, 150 Â° C), the NMOS tube M15 is controlled by the PN junction voltage ( The tube is also used as a switch tube to conduct, and the input current of the power tube gate is separated, so that the current flowing through the power tube is reduced, thereby reducing the temperature of the power tube and achieving the overheat protection of the power tube.
2.5 The overcurrent and overvoltage protection circuit of the power tube in the overcurrent and overvoltage protection regulator is shown in Figure 6. In Figure 6, the M17 tube is the excitation current adjustment tube (ie, the high power tube), the resistors R9 and M16 form the overcurrent protection circuit, and the resistor R14 regulator tube DZ2 and M16 tubes form the overvoltage protection circuit for the power tube, of which M16 and M14 The tube is also used as a switch tube.
3 overall circuit and simulation
3.1 Circuit Integration According to the above design of the various parts of the regulator chip, combining them together is the overall circuit of the regulator to be designed, as shown in Figure 7.
3.2 Functional Verification The analog verification waveform is shown in Figure 8, where the abscissa is the generator output voltage and the ordinate is the change in the base voltage of the excitation regulator. Figure 8(a) shows the verification waveform at a fixed temperature, and Figure 8(b) shows the verification waveform at full temperature.
It can be seen from Fig. 8 that when the voltage at the output of the generator does not reach the regulation voltage, the base potential of the regulator approaches zero potential, and the adjustment tube is turned off. It can be seen from Fig. 8(b) that the regulator can still obtain good regulation performance at different operating temperatures.
4 Conclusion A monolithic CMOS automotive electronic regulator is proposed. The chip mainly adjusts the current in the excitation coil of the generator by controlling the conduction and cut-off of the adjustment tube, thereby stabilizing the output voltage. The automobile power generation system composed of the chip has the characteristics of high reliability, small number of peripheral components, low cost and convenient use, and is of great significance for breaking the monopoly of foreign automobile core technology.
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