直流开关电源保护技术.doc

本科毕业设计
外文文献及译文

文献、资料题目：DC switching power supply
protection technology
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外文文献 1
DC switching power supply protection technology
Abstract: This paper discusses the DC switching power supply system of protection, put forward the principle of the protection system design and complete machine protective measures, the switching power supply analysis of the various protection features and design methodology, introduced several practical protection circuit .
Keyword: Switching Power Supply System Protection Circuit Design
1 Introduction
DC switching regulator used in high-power switching devices more expensive prices, the control circuit is more complicated, and, switching regulators are generally supported by the large number of highly integrated devices installed electronic systems. Transistors and integrated device, tolerance, the ability of poor thermal shock. Thus switching regulators should take into account the protection of their own regulator and load security. Many of the types of protection circuit here on polarity protection, procedural protection, over-current protection, over-voltage protection, under-voltage protection and thermal protection circuits. Usually use several ways to protect the combination of a complete system of protection.
2 polarity protection
DC switching regulator input are generally not regulated DC power supply. The operation will be mistakes or accidents to its polarity wrong, will be damaged switching power supply. Polarity protection purpose, which is to enable switching regulator only when connected with the correct polarity of the DC power supply regulator, to work. Wizard of single-use devices can achieve power supply polarity protection. The diode D to flow switching regulator of the input current, this circuit applications in low-power switching regulators to be more suitable. In the larger power of the occasion, put procedures polarity protection circuit as a link in the protection, eliminating the polarity protection for high-power diodes, power will be reduced.

3 procedural protection
Switching power supply circuit complexity, basically can be divided into low-power and high-power control part of the switch. Is a high-power switching transistors, for the protection of switching transistors in the open or shutdown the safety of power, we must let modulator, such as a low-power amplifier control circuit. Accordingly, we must ensure that the correct procedures boot. Switching Regulators general of the inputs to a small inductance, capacitance of the input filter. Boot in an instant, filter capacitor will flow through large inrush current, inrush current can be several times more than the normal input current. This large inrush current general will contact the power switch or relay contacts melting, and the input fuse links. In addition, the inrush current will damage capacitors to shorten the life of premature damage. To this end, a boot should access the current limiting resistor, through the current limiting resistor capacitor to the charge. In order not to limit the flow resistance of the excessive consumption of power, which affects the normal switching regulator, in the boot after the end of the transient process, with a short then automatically relays it to DC power directly to the switching regulator electricity. This circuit switching regulator known that the "soft-start" circuit.Switching Regulators in the control circuit logic components or operational amplifiers required auxiliary power supply. To this end, auxiliary power switch must be in the circuit. This circuit can be controlled to ensure the boot. The procedure is generally boot: Identification of the polarity of the input power supply voltage protection circuit → work boot → auxiliary power supply and work through the current limiting resistor R of the switching regulator's input capacitor C → Switching Regulators charge modulation circuit, Short-circuit current limiting resistor → Switching Regulators stability.
In the switching regulator, to start the machine, because of its large output capacitor capacity, filling the needs of the rated output voltage of a certain period of time. During this time, the importation of low sampling amplifier output voltage sampling, in accordance with the closed-loop system of regulation will be forced to switch transistor on-time lengthened this way, the switching transistor during this
period will become discontinuous conduction , and easy to damage. To this end, the boot this request within a certain period of time, switch output modulation circuit switching transistor base to the drive pulse width modulation signal can be guaranteed by the deadline for switching transistor switching gradually become normal state, and therefore should be set up to cope with boot protection Soft Start.
4 overcurrent protection
When a load short-circuit, overload control circuit malfunction or accident situation, it will cause a flow regulator in the current triode switch off, causing increased power tubes, fever, if not overcurrent protection devices, high power switching transistors may be damaged. Therefore, the switching regulator in the over-current protection is used. The most economical way is to use simple fuse. Because of the heat capacity of small transistors, can not play an ordinary fuse general protective effect of commonly used is quick fuse fuse. This method has the advantage of easier to protect, but, according to the specific needs of the switching transistor safety zone requirements to select fuse specifications. This overcurrent protection measures brought about the shortcomings of the regular replacement of the fuse inconvenience.
Linear voltage regulators used in the current limit protection and the protection of the current deadline for the switching regulator can be applied. However, according to the characteristics of switching regulators, the protection circuit can not directly control the output triode switch, and the need to over-current protection for the output pulse conversion instructions, to control the modulator to protect switch transistor. In order to achieve overcurrent protection generally require sampling resistor in series circuit, which would affect the efficiency of power supply, and more for small power switching regulator occasions. In the high-power switching power supply, taking into account power, should be avoided as far as possible sampling resistor access. Therefore, the usually over-current protection for the conversion, less voltage protection.
5 Overvoltage Protection
Switching Regulators Overvoltage protection including input and output
overvoltage protection over-voltage protection. Switching Regulators used by the regulator did not, such as batteries and DC power supply voltage of the rectifier If too high, so that switching regulator not work, and even damaged internal device, and it is therefore necessary to use the importation of over-voltage protection circuit，By transistor and relay protection circuit composed.
In this circuit, when the input DC power supply voltage is higher than the breakdown voltage regulator diode value, the regulator of the breakdown, there is current flowing through resistor R, V conduction transistor, relay, normally closed contact off open, and to cut off the importation. Regulators one of the regulators of Vz = ESrmax-UBE. Power input polarity protection circuit can be imported with the combination of over-voltage protection, the identification and protection of a polar overvoltage protection circuit.
Output over-voltage protection in the switching power supply is essential. Especially for a 5 V output switching regulator, it is a lot of the load highly integrated logic devices. If at work, Switching Regulators switching transistor suddenly damage, potential output may not immediately rise to the input DC power supply voltage regulator value of the instantaneous cause great losses. Commonly used method is short-circuit protection thyristor. When the output voltage too high, the regulator of the breakdown was triggered thyristor conduction, the output short-circuit, resulting in a current through the fuse or circuit protection for the importation cut, the protection of the load. This circuit equivalent to the response time of the opening of thyristor time, which is about 5 to 10 μ s. It is the shortcomings of action voltage is fixed, and the temperature coefficient, action point of instability. In addition, there is a regulator of the discrete parameters, but the same type of over-voltage start-up is different, and difficult to debug brought.
Output voltage Esc suddenly escalate, transistors V1, V2 conduction, the thyristor conduction. When the 7 V regulator, and its temperature coefficient and the launch of transistors V1 guitar (BE) voltage temperature coefficient can be offset by the temperature coefficient can drop very low. However, the output of 5 to 5.5 V DC switching regulators, its common action voltage is 5.5 V-6. Regulators will then tube
voltage below 3.5 V, the voltage regulator near the temperature variation of the coefficient is -20 to -30 mV / ℃. Therefore, the temperature change will be occasions protection circuit false moves. Use integrated circuit voltage comparator to detect switching regulator output voltage is more commonly used method, using the comparison of the output state change with the corresponding logic circuit with a overvoltage protection circuit, this circuit is sensitive and stability.
6 owed voltage protection
Output voltage is lower than the specified value to reflect the input DC power supplies, switching regulators internal or output load anomalies occurred. DC power input voltage drops below the specified value, would result in switching regulator output voltage drops, increased input current not only endanger the switching transistor, but have also endangered the input power supply. Therefore, in order to set up less voltage protection.
When the input voltage regulator of normal value, the ZD breakdown voltage regulator, on-V transistor, relay, contact suction line switching regulator power. When the input below the minimum allowed by the voltage value, the regulator of ZD unreasonable, V deadline, a jump contacts, switching regulator can not work. Switching Regulators internal, control circuit disorders or failure will switch transistor output voltage drop in load output voltage short circuit will also decline. Particularly in the RP-step-up or step-up DC switching regulator in less voltage protection is with the over-current protection is closely related and, therefore, become even more important. Implementation of the switching regulator's output termination voltage comparator.
Normal, compared with no output, once the voltage drop in the value allowed under the overturned comparator, driven alarm circuit at the same time switching regulator feedback to the control circuit, closing or switching transistor input supply cut off.
7) overheating protection
Switching Regulators highly integrated and size of a small amount of light to the unit volume greatly improved power density, power supply components to its internal
temperature of the work environment demands increased accordingly. Otherwise, the circuit performance will deteriorate, parts premature failure. Therefore, in high-power switching regulator should be established overheating protection.
Using temperature relay power devices to detect internal temperature, the internal generated when the power supply overheating, the temperature relay on the action to complete machine warning alarm circuit in the state to achieve the protection of the power supply overheating. Relay can also be placed switching transistor temperature in the vicinity of, the general power of the shell allows the maximum temperature is 75 ℃, and regulating the temperature setting of 60 ℃. When the shell temperature exceeds the allowable cut off after electrical relays on the switch protection. Thermal semiconductor switching device "hot thyristor" overtemperature protection plays an important role. It can be used for temperature instructions circuit. According gate p-type thermal control thyristor (TT102) the characteristics of the RTdetermines that the value of the on-device temperature, the greater the RT, and on-the lower the temperature. When placing it near the power switch transistor, or power devices, it will be able to play a direct role in temperature. When the power of the shell and tube temperature devices or internal temperature exceeds the allowable values, thermal conduction on the thyristor, light-emitting diodes illuminated warning. If with Optocoupler, would enable the complete machine alarm circuit moves, the protection switching regulator. It can Crystal switch to the base current is n-type gate thermal control thyristor TT201 bypass switch deadline, and to cut off the collector current to prevent overheating.
8) Conclusion
These were discussed in the switching regulator in the way of protection, and introduced a number of specific ways to achieve. For a given switching power supply, should be protected from the complete machine consider the following points:
1) Switching Regulators in the application of restrictions in DC switching transistor regional security within the work. For the selected switch transistor, the transistor manual can be found by the DC appropriately safe work areas. According to the collector current to determine the maximum input overcurrent protection value.
However, this should be converted to maximum instantaneous current average. At the rated output current and output voltage conditions, the dynamic switching of the load DC line does not exceed the maximum safe working input voltage, input over-voltage protection is the voltage value.
2) the switching regulator's output to be limited by the technical indicators within. In the work required temperature range, switching regulator output voltage, the output is lower, less voltage protection voltage value. Overcurrent protection can be based on the maximum output current to determine. In order not to misuse warning, the protection of certain values should be appropriate to stay the cushion.
3) identify protection from the above two methods, according to the needs of power supply devices to determine warning measures. General alarm sound measures by the police and two light. Police applied to complete machine sound more complicated, power and installed in some inconspicuous place, it could effectively to the staff to the fault alarm;-Police instructions can be prominently fault alarm and pointed out that the fault location and type. Depending on protective measures to protect the site to determine. In the high power