1 small weight and high efficiency, and the existing integrated switching power supply control module on the market, which makes the power supply design debugging much easier. Therefore, it has been widely used in most electronic equipment computer TVs and various control systems. . However, the switching power supply itself generates a significant increase in the output power with the increase of the switching frequency, which poses a potential threat to the normal operation of the electronic device. Therefore, only by improving the electromagnetic compatibility of the switching power supply, the switching power supply can be adopted in those places where the power supply noise index is strictly required.
1 Switching power supply causes noise There are many types of switching power supply. According to the circuit structure of the converter, it can be divided into two types: series-parallel type and DC-transform type. According to the excitation mode, it can be divided into self-excitation and its excitation. The combination can be divided into a bridge type half bridge type push-pull type and the like. However, regardless of the type of switching power supply, the semiconductor device is turned on and off, and the output voltage is controlled by the ratio of the on and off times. Since it usually operates at switching frequencies above 2012, the heart of the power line is very hearty, generating large surge voltage surge currents and various other noises. They conduct outward through the power line in either common mode or differential mode, while also radiating noise to the surrounding space. 1 gives a typical switching power supply circuit 1.1 times the rectification loop noise in the secondary rectification loop rectifier tube wide-band only in the pulse of the cause and the noise generated loops and components, the corresponding dynamic voltage exceeds the heart of the charge The instantaneous current of the voltage flows in from the power input side. Therefore, the secondary rectifier circuit generates high-order distortion waves to form noise.
1.2 The noise of the switching circuit is electromagnetic radiation. When the power supply is in operation, the switch tube is in a high-frequency on-off state, and in the high-frequency current loop formed by the pulse transformer primary coil 1 switch tube 71 and the filter, large spatial radiation noise may be generated. If the filtering is insufficient, the high-frequency current is also conducted to the AC power source in a differential mode. It is a surge voltage caused by an inductive load. In the switching circuit, the load of the switching tube 7 is the primary coil of the pulse transformer, which is an inductive load. Therefore, when the switching tube is turned on and off, a high surge voltage appears at both ends of the primary coil of the pulse transformer, which is likely to cause This same circuit electronic device is preferably damaged by the switch tube 7.
The noise of the 1.3 rectification loop is electromagnetic radiation. When the power supply is working, the rectifier tube is also in the high-frequency on-off state. The secondary pole of the pulse transformer secondary coil 12 rectifies the pole tube, and the filter capacitor core constitutes a high-frequency switching current loop, which may radiate noise to the space. If the capacitor is insufficiently filtered, the high-frequency current will be mixed in the differential mode to the output DC voltage, which will affect the normal operation of the load circuit. It is a surge current. When the silicon transistor is forward-conducting, the charge in the junction is accumulated, and the pole tube accumulates when the reverse voltage is applied. When the switching is switched, the frequency is very high, that is, the time from the transition to the cut-off is very short, and in a short time, let When the stored charge disappears, a surge of counter current is generated. Due to the presence of the distributed capacitance distribution inductance in the DC output line, the disturbance caused by the surge becomes a high frequency attenuation oscillation.
1.4 The pulse control signal in the noise control loop of the control loop is the main source of noise.
1.5 The noise caused by distributed capacitance is the role. Although there is an insulating spacer between the fin ruler and the collector of the switch tube 71, since the contact surface is large and the insulating pad is thin, the distributed capacitance between the two cannot be ignored at a high frequency.
Therefore, the high-frequency current will flow through 0 to the heat sink, then to the chassis ground, and finally to the protective ground of the AC power source connected to the chassis ground to generate common mode. Yes, the role. The pulse transformer main frequency voltage is directly coupled to the secondary side, and the common phase noise of the same phase is generated on the two power lines used as the DC output on the secondary side.
The electromagnetic compatibility design of the switching power supply is designed to suppress the noise of the switching power supply.
It is to reduce the interference energy of the interference source; it is to destroy the interference path; it is shielded.
2.1 Reducing the energy of the interference source Since the interference source of the switching power supply is impossible to eliminate, it is necessary to reduce the energy of the interference source. The measures taken in general are 0 and connected; circuit. At the two ends of the switch tube 71, the ruler 0 4 wiring and the coupling capacitance reduction principle physical absorption circuit are used, 2. The rectifier tube in the secondary rectification circuit is added with only the absorption circuit at both ends, and 2 is known to suppress the surge voltage. 2 series of saturable core coils. In the secondary rectification loop, the coil with the saturable core is connected in series with the rectifier tube 06, such as the core is saturated, the inductance is small, and the normal operation of the circuit is not affected; when the current flows in the opposite direction, the core coil will be generated. A large back EMF prevents the reverse current from rising, so connecting it in series with the pole tube 06 effectively suppresses the reverse surge current of the pole tube 05. At present, there is an ultra-small amorphous magnetic ring finished product, which can be directly placed on the positive lead of the pole tube, and is convenient to use.
The absorbing circuit L1 is connected in parallel, and the absorbing circuit is connected to only the 0 absorbing circuit and the saturable core 2.2. The interference path is taken for the electric field noise caused by the distributed capacitance in the switching power supply. The main anti-interference measures are 4 to reduce the coupling capacitance between the collector of the switch tube and the heat sink. The material with low dielectric constant is used as the insulating pad, the thickness of the thickened pad is used, and the method of electrostatic shielding is adopted. The outer casing is a collector, and a layer of sandwich insulation is interposed between the collector and the heat sink, that is, an interlayer interlayer copper foil is used as an electrostatic shielding layer, which is connected to the input DC and the ground, and the heat sink is still connected to the casing floor, so that The coupling capacitance between the collector and the heat sink is greatly reduced, and the electric field coupling between them is reduced. 3 is the principle of reduction, the shielding layer will be 0, divided into a series of 1 and 2, and 3 is a real object. 0 reduces the distributed capacitance of the pulse transformer. An electrostatic shielding layer is applied between the secondary side and the secondary side. The shielding layer should be as close as possible to the emitter and grounded. Thus, the coupling capacitor core is also divided into a series of 1 and 2, 4, which reduces the coupling interference of the electric field on the secondary side. It is a measure for the characteristic that the switching power supply transmits noise through the power line, that is, the filtering technology is used to destroy the interference. The filtering technique used has 1 AC side filtering. The input terminal of the AC power line of the switching power supply is inserted into the common mode and differential mode filter to prevent the common mode and differential mode noise of the switching power supply from being transmitted to the power line, affecting other power devices in the power grid, and also suppressing noise from the power grid. The AC side filter 54, wherein 1 is used to suppress differential mode noise, generally takes 70, 4, 61 to suppress common mode noise, and generally takes 131, and takes 20006800 pF, which is effective for suppressing common touch noise of 150 kHz or more. For the specific switching circuit, the parameters of the above components should be debugged and determined.
2 DC side filtering. In the DC output side of the switching power supply, a 5 6 power supply filter is inserted, which consists of a common mode choke 12, a choke 13 and a capacitor, a core. In order to prevent the magnetic core from being saturated under a large magnetic field strength and causing the choke to lose its function, the core of the choke must use a constant magnetic core with high frequency characteristics and high saturation magnetic field strength.
Switching power supply output, DC load DC side filter circuit 5 filter circuit scare the 32nd page according to the magic and illusion value directly check the fuzzy control in the program memory or perform the integral operation to obtain the fuzzy control increment. Finally, the fuzzy control of the added or not added fuzzy control is based on the principle of maximum membership degree, and the appropriate scale factor is selected to obtain the control increment 4, and the calculation is +1! The value of the time, the amount of control at the moment. This value can be transmitted to other intelligent units through the 0-person bus. After the 0-in conversion, the field device or the host computer can be controlled to make progress to coordinate the normal and effective operation of each control unit of the entire system. The intelligent control unit also completes the data communication with the 0-person bus and the status display and alarm to the field device while processing the above tasks. The fuzzy control calculated by the offline method can always be directly written into the chip internal program memory in the form of a matrix, and its software design flow is 4.
The combination of the pure fuzzy control algorithm and the integration of the integral link, when the system response is far from the equilibrium point, only the effect of the fuzzy control, the response speed is fast, the slope of the curve is large; and when the response approaches the equilibrium point and there is a deviation trend Due to the integration of the integral link, the rate of change of the curve becomes slower. After several actions, the system response is finally stabilized near the equilibrium point or 4 simulation experiments are directed to the fuzzy control algorithm and control system design idea described above. We choose a controlled system. Simulation. The transfer function of the controlled system is 6, and the combination of intelligent control and field bus is the main application direction in engineering control. From the design process and simulation results of the whole control system, the hardware structure of the system is relatively simple, the software is convenient to implement, the system control effect is ideal, and the real-time performance is good.
The divergence function can be seen that the nonlinearity of the system is relatively large and purely lagging 13; 1 He Ping, Wang Hongxu. Design and application of fuzzy controllers. Beijing Science on Pure, 10 Control Algorithms and the Fuzzy Control Algorithms discussed in this paper, 1997 Step Response Curve 5.
And, =7, the system response curve using the fuzzy control algorithm.
From the system control response curve 2, because the fuzzy controller uses 2 Wang Yifeng, Li Lingqi. Based on the distributed data acquisition and control system of the human bus. Industrial Control Computer, 200053 Wang Junpu. intelligent control. Hefei University of Science and Technology of China Press, 1996 4 Lu Qiheng. Fuzzy self-correcting flow control system. Electronic Technology Application, 1999; 25 Responsibility Date 20001018 Let's go to page 29. 2.3 Effective method of shielding against radiation noise is shielding. The electric field is shielded by a conductive material, and the magnetic field is shielded by a material having a high magnetic permeability. In order to prevent the magnetic field leakage of the pulse transformer, a closed magnetic ring can be used to form a magnetic shield to shield the entire switching power supply. When shielding, heat dissipation and ventilation should be considered. The ventilation holes on the shielding box are preferably round, and the joints are preferably welded to ensure electromagnetic continuity.
There are still many factors to consider in the electromagnetic compatibility design of switching power supplies, such as the layout of printed circuit board components and the bundling configuration of various power line signal lines. There is much work to be done. The comprehensive suppression of various noises of the switching power supply will greatly improve the electromagnetic compatibility of the switching power supply, and the switching power supply will be more widely used.
1 Switching power supply causes noise There are many types of switching power supply. According to the circuit structure of the converter, it can be divided into two types: series-parallel type and DC-transform type. According to the excitation mode, it can be divided into self-excitation and its excitation. The combination can be divided into a bridge type half bridge type push-pull type and the like. However, regardless of the type of switching power supply, the semiconductor device is turned on and off, and the output voltage is controlled by the ratio of the on and off times. Since it usually operates at switching frequencies above 2012, the heart of the power line is very hearty, generating large surge voltage surge currents and various other noises. They conduct outward through the power line in either common mode or differential mode, while also radiating noise to the surrounding space. 1 gives a typical switching power supply circuit 1.1 times the rectification loop noise in the secondary rectification loop rectifier tube wide-band only in the pulse of the cause and the noise generated loops and components, the corresponding dynamic voltage exceeds the heart of the charge The instantaneous current of the voltage flows in from the power input side. Therefore, the secondary rectifier circuit generates high-order distortion waves to form noise.
1.2 The noise of the switching circuit is electromagnetic radiation. When the power supply is in operation, the switch tube is in a high-frequency on-off state, and in the high-frequency current loop formed by the pulse transformer primary coil 1 switch tube 71 and the filter, large spatial radiation noise may be generated. If the filtering is insufficient, the high-frequency current is also conducted to the AC power source in a differential mode. It is a surge voltage caused by an inductive load. In the switching circuit, the load of the switching tube 7 is the primary coil of the pulse transformer, which is an inductive load. Therefore, when the switching tube is turned on and off, a high surge voltage appears at both ends of the primary coil of the pulse transformer, which is likely to cause This same circuit electronic device is preferably damaged by the switch tube 7.
The noise of the 1.3 rectification loop is electromagnetic radiation. When the power supply is working, the rectifier tube is also in the high-frequency on-off state. The secondary pole of the pulse transformer secondary coil 12 rectifies the pole tube, and the filter capacitor core constitutes a high-frequency switching current loop, which may radiate noise to the space. If the capacitor is insufficiently filtered, the high-frequency current will be mixed in the differential mode to the output DC voltage, which will affect the normal operation of the load circuit. It is a surge current. When the silicon transistor is forward-conducting, the charge in the junction is accumulated, and the pole tube accumulates when the reverse voltage is applied. When the switching is switched, the frequency is very high, that is, the time from the transition to the cut-off is very short, and in a short time, let When the stored charge disappears, a surge of counter current is generated. Due to the presence of the distributed capacitance distribution inductance in the DC output line, the disturbance caused by the surge becomes a high frequency attenuation oscillation.
1.4 The pulse control signal in the noise control loop of the control loop is the main source of noise.
1.5 The noise caused by distributed capacitance is the role. Although there is an insulating spacer between the fin ruler and the collector of the switch tube 71, since the contact surface is large and the insulating pad is thin, the distributed capacitance between the two cannot be ignored at a high frequency.
Therefore, the high-frequency current will flow through 0 to the heat sink, then to the chassis ground, and finally to the protective ground of the AC power source connected to the chassis ground to generate common mode. Yes, the role. The pulse transformer main frequency voltage is directly coupled to the secondary side, and the common phase noise of the same phase is generated on the two power lines used as the DC output on the secondary side.
The electromagnetic compatibility design of the switching power supply is designed to suppress the noise of the switching power supply.
It is to reduce the interference energy of the interference source; it is to destroy the interference path; it is shielded.
2.1 Reducing the energy of the interference source Since the interference source of the switching power supply is impossible to eliminate, it is necessary to reduce the energy of the interference source. The measures taken in general are 0 and connected; circuit. At the two ends of the switch tube 71, the ruler 0 4 wiring and the coupling capacitance reduction principle physical absorption circuit are used, 2. The rectifier tube in the secondary rectification circuit is added with only the absorption circuit at both ends, and 2 is known to suppress the surge voltage. 2 series of saturable core coils. In the secondary rectification loop, the coil with the saturable core is connected in series with the rectifier tube 06, such as the core is saturated, the inductance is small, and the normal operation of the circuit is not affected; when the current flows in the opposite direction, the core coil will be generated. A large back EMF prevents the reverse current from rising, so connecting it in series with the pole tube 06 effectively suppresses the reverse surge current of the pole tube 05. At present, there is an ultra-small amorphous magnetic ring finished product, which can be directly placed on the positive lead of the pole tube, and is convenient to use.
The absorbing circuit L1 is connected in parallel, and the absorbing circuit is connected to only the 0 absorbing circuit and the saturable core 2.2. The interference path is taken for the electric field noise caused by the distributed capacitance in the switching power supply. The main anti-interference measures are 4 to reduce the coupling capacitance between the collector of the switch tube and the heat sink. The material with low dielectric constant is used as the insulating pad, the thickness of the thickened pad is used, and the method of electrostatic shielding is adopted. The outer casing is a collector, and a layer of sandwich insulation is interposed between the collector and the heat sink, that is, an interlayer interlayer copper foil is used as an electrostatic shielding layer, which is connected to the input DC and the ground, and the heat sink is still connected to the casing floor, so that The coupling capacitance between the collector and the heat sink is greatly reduced, and the electric field coupling between them is reduced. 3 is the principle of reduction, the shielding layer will be 0, divided into a series of 1 and 2, and 3 is a real object. 0 reduces the distributed capacitance of the pulse transformer. An electrostatic shielding layer is applied between the secondary side and the secondary side. The shielding layer should be as close as possible to the emitter and grounded. Thus, the coupling capacitor core is also divided into a series of 1 and 2, 4, which reduces the coupling interference of the electric field on the secondary side. It is a measure for the characteristic that the switching power supply transmits noise through the power line, that is, the filtering technology is used to destroy the interference. The filtering technique used has 1 AC side filtering. The input terminal of the AC power line of the switching power supply is inserted into the common mode and differential mode filter to prevent the common mode and differential mode noise of the switching power supply from being transmitted to the power line, affecting other power devices in the power grid, and also suppressing noise from the power grid. The AC side filter 54, wherein 1 is used to suppress differential mode noise, generally takes 70, 4, 61 to suppress common mode noise, and generally takes 131, and takes 20006800 pF, which is effective for suppressing common touch noise of 150 kHz or more. For the specific switching circuit, the parameters of the above components should be debugged and determined.
2 DC side filtering. In the DC output side of the switching power supply, a 5 6 power supply filter is inserted, which consists of a common mode choke 12, a choke 13 and a capacitor, a core. In order to prevent the magnetic core from being saturated under a large magnetic field strength and causing the choke to lose its function, the core of the choke must use a constant magnetic core with high frequency characteristics and high saturation magnetic field strength.
Switching power supply output, DC load DC side filter circuit 5 filter circuit scare the 32nd page according to the magic and illusion value directly check the fuzzy control in the program memory or perform the integral operation to obtain the fuzzy control increment. Finally, the fuzzy control of the added or not added fuzzy control is based on the principle of maximum membership degree, and the appropriate scale factor is selected to obtain the control increment 4, and the calculation is +1! The value of the time, the amount of control at the moment. This value can be transmitted to other intelligent units through the 0-person bus. After the 0-in conversion, the field device or the host computer can be controlled to make progress to coordinate the normal and effective operation of each control unit of the entire system. The intelligent control unit also completes the data communication with the 0-person bus and the status display and alarm to the field device while processing the above tasks. The fuzzy control calculated by the offline method can always be directly written into the chip internal program memory in the form of a matrix, and its software design flow is 4.
The combination of the pure fuzzy control algorithm and the integration of the integral link, when the system response is far from the equilibrium point, only the effect of the fuzzy control, the response speed is fast, the slope of the curve is large; and when the response approaches the equilibrium point and there is a deviation trend Due to the integration of the integral link, the rate of change of the curve becomes slower. After several actions, the system response is finally stabilized near the equilibrium point or 4 simulation experiments are directed to the fuzzy control algorithm and control system design idea described above. We choose a controlled system. Simulation. The transfer function of the controlled system is 6, and the combination of intelligent control and field bus is the main application direction in engineering control. From the design process and simulation results of the whole control system, the hardware structure of the system is relatively simple, the software is convenient to implement, the system control effect is ideal, and the real-time performance is good.
The divergence function can be seen that the nonlinearity of the system is relatively large and purely lagging 13; 1 He Ping, Wang Hongxu. Design and application of fuzzy controllers. Beijing Science on Pure, 10 Control Algorithms and the Fuzzy Control Algorithms discussed in this paper, 1997 Step Response Curve 5.
And, =7, the system response curve using the fuzzy control algorithm.
From the system control response curve 2, because the fuzzy controller uses 2 Wang Yifeng, Li Lingqi. Based on the distributed data acquisition and control system of the human bus. Industrial Control Computer, 200053 Wang Junpu. intelligent control. Hefei University of Science and Technology of China Press, 1996 4 Lu Qiheng. Fuzzy self-correcting flow control system. Electronic Technology Application, 1999; 25 Responsibility Date 20001018 Let's go to page 29. 2.3 Effective method of shielding against radiation noise is shielding. The electric field is shielded by a conductive material, and the magnetic field is shielded by a material having a high magnetic permeability. In order to prevent the magnetic field leakage of the pulse transformer, a closed magnetic ring can be used to form a magnetic shield to shield the entire switching power supply. When shielding, heat dissipation and ventilation should be considered. The ventilation holes on the shielding box are preferably round, and the joints are preferably welded to ensure electromagnetic continuity.
There are still many factors to consider in the electromagnetic compatibility design of switching power supplies, such as the layout of printed circuit board components and the bundling configuration of various power line signal lines. There is much work to be done. The comprehensive suppression of various noises of the switching power supply will greatly improve the electromagnetic compatibility of the switching power supply, and the switching power supply will be more widely used.
Suizhou simi intelligent technology development co., LTD , https://www.msmsmart.com