开关稳压电源外文文献及翻译(英文).doc

DC Switching Power Supply Protection Technology Posted:2006-2-26 10:57:00 visit:665 chinese Version Related NewsAbstract: The DC switching power supply protection system is proposed to protect the system design principles and machine protection measures, analysis of switching power supply in the range of protected characteristics and design method, introduced several practical protection of circuit. Keywords: switching power supply protection circuit system design 1 Introduction DC switching regulator used in the price of more expensive high-power switching devices, the control circuit is also more complex, In addition, the load switching regulators are generally used a large number of highly integrated devices installed electronic systems. Transistors and integrated device tolerance of electricity, less heat shocks. Thus switching regulator should take into consideration the protection of voltage regulators and load their own safety. Many different types of protection circuits introduced here polarity protection, program protection, over-current protection, over-voltage protection, under voltage protection and thermal protection circuits. Several protection methods are usually chosen to be combined to form a comprehensive protection system. 2 Polarity Protection DC switching regulators input are generally not regulated DC power supply. Due to operational errors or unforeseen circumstances will be the wrong polarity, switching power supply will be damaged. Polarity protection purposes, is to make the switching regulator only when the correct polarity is not regulated to DC power supply when connected to work. The use of a single wizard-pass device can achieve the power supply polarity protection. As the diode D to flow through the switching regulators input total current, so this circuit applied in a low-power switching regulators on the more appropriate. Power in the larger occasion, put the polarity protection circuit as a program to protect a link, eliminating the need for high power required for polarity protection diodes, power consumption will be reduced. For convenient operation, easy to identify the polarity right or wrong。3 process protections Switching power supply circuit more complicated, basically can be divided into a low-power control section and power switch part. Belong to high-power switching transistor, in order to protect the switching transistor is turned on or off the power when the security must make the modulators, amplifiers and other small power control circuit. To this end, to ensure that the correct boot process. Switching regulators input generally received a small inductance and large capacitance of the input filter. In the boot an instant, filter capacitor will flow through the large surge current, the inrush current can be several times the normal input current. Make such a large surge current ordinary power switch contact or relay contact melting, and to enter the fuse fuse. In addition, the surge current can also damage the capacitor, so that shortened life expectancy, premature damage. To this end, the boot should be access to a current-limiting resistor, through which current-limiting resistor to charge the capacitor. In order not to make the current-limiting resistors consume excessive power, thereby affecting the normal operation of switching regulators, and in the boot after the end of the transient process, with an automatic relay shorted it, so that DC power directly to the switching regulator power supply。Switching regulator control circuit of the logic components or operational amplifiers need to use auxiliary power supply. For this reason, auxiliary power must be on the switch circuit. This can be the boot process control circuitry to be guaranteed. Normal boot process are: identification of the polarity of input power, voltage protection - the boot process circuit - auxiliary power supply through current-limiting resistor R of the switching regulators input capacitor C charge - the modulation switching regulator circuit, short-circuit current-limiting resistor - switching regulator stability. In the switching regulator, by just getting on its machines, because of its large output capacitance, charge to the rated output voltage take some time. During this time, the sampling amplifier input and low output voltage sampling, according to the system characteristics of the closed-loop regulation will force the switch transistor conduction time longer, this way, the switching transistor during this period will tend to continuous conduction, and easily damaged. To this end, requests the boot this period of time, switching modulation circuit output to the switching transistor base of the pulse-width modulated drive signals, which would ensure switching transistor deadline to gradually normalize the switching state and therefore I need to create boot protection to meet the soft - Start. 4over-current protectionWhen the load short-circuit, overload control circuit failure or unexpected situations such as when, it will cause flow through the regulator in the switching transistor current is too large, so that increased power tube, fever, if there is no over-current protection devices, high power switching transistor there may be damaged. Guer in the switching regulator in the over-current protection is commonly used. The most economical way is to use simple fuse. As the transistors heat capacity is small, generally can not play a regular fuse protection, commonly used is fast fuse fuse. This approach has the advantage of the protection easy, but it needs specific switching transistor safe operating area requirements to select the fuse specifications. Such over-current protection measures, disadvantage is the inconvenience caused frequent replacement of fuse. Commonly used in linear regulator and current limiting protection cut-off protection switching regulator can apply. However, according to the characteristics of switching regulators, such protection can not directly control the output of the circuit switching transistor, while the over-current protection must convert the output of pulse commands to control the modulator to protect the switching transistor. In order to achieve over-current protection generally need to use sampling resistor in series in the circuit, this will affect the efficiency of power supply, so are used for low-power switching regulator of occasions. In the high-power switching power supply, by taking into account the power consumption, should try to avoid sampling resistor access. So it is usually over-current protection will be converted to over or under-voltage protection. Reposted elsewhere in the paper for free download 5 over-voltage protection Switching regulators input over-voltage protection, including over-voltage protection and output over-voltage protection. Switching regulator is not used by the regulated DC power supply such as batteries and rectifier voltage, if too high, so switching regulator does not work, or even damage to internal components, it is therefore necessary to use input over-voltage protection circuit.Output over-voltage protection in switching power supply is essential. In particular, output 5V switching regulator, it loads a large number of highly integrated logic devices. If you work, the switching regulator switching transistor suddenly damaged, the output potential may be an immediate increase to the input is not regulated DC power supply voltage, transient caused great losses. Commonly used method is thyristor short circuit protection. The simplest over-voltage protection circuit shown in Figure 4. When the output voltage is too high, the voltage regulator tube breakdown, triggered thyristor conduction, the output short-circuit, resulting in over-current, through the fuse or circuit protector input cut off to protect the load. A response time of this circuit is equivalent to the opening time of thyristor, about 5 10 s. Its drawback is that movements voltage is fixed, the temperature coefficient, the action point of instability. In addition, the voltage regulator control parameters of the discrete nature of existence, the models over-voltage start value is the same, but they differ, to create difficulties for debugging.6 Under Voltage ProtectionThe output voltage is below the set value, reflecting the input DC power supply, switching regulator or the output load within the exception occurred. Input DC supply voltage down to below the specified value, it will result in switching regulators output voltage drops, the input current increases, not only endanger the switching transistor, but also endanger the input power. When the input voltage is not regulated properly, the voltage regulator tube ZD breakdown, the transistor V turn, relay, contact Pick-up, switching regulator power-up. When the input voltage is below the minimum allowable value, the voltage regulator tub e ZD unreasonable, V cut-off, contact jump, switching regulator can not work. Switching regulator inside, due to disorder, or switching transistor control circuit failure will make the output voltage drops; load short-circuit also make the output voltage drops. Especially in the step-up or inverting DC step-up switching regulator in the under-voltage protection is closely related with the over-current protection, and therefore even more important. Realization method is switching regulators output termination voltage comparator, as shown in Figure 1.Normal, the comparator does not output, once the voltage falls below the value of the comparator is allowed to flip, driving alarm circuit; the same time, back to the switching regulator control circuit, so that switching transistor cut-off or cut off the input power. 7 over-temperature protection Switching regulator of high integration and small size light weight make it within the power density per unit volume greatly improved power supply components within the requirements of their work environment is also a corresponding increase in temperature. Otherwise, it will deteriorate the circuit performance, component premature failure. Therefore, in high-power switching regulator should be set up over-temperature protection. Using temperature relay to detect the temperature inside the power supply unit, when the power supply internally generated overheating, the temperature relay on the movements to machine alarms in the alarm state of the circuit to realize the power of the temperature protection. Temperature relay can also be placed near the switch transistor, the general high-power tube to allow the maximum shell temperature is 75 , adjust the temperature setting value is 60 . When the temperature exceeds the allowable value of shell and tube cut off electrical appliances after the relay, to switch protection. Semiconductor thermal switching devices hot thyristors in the ultra-temperature protection has an important role. It can be used as a temperature indicator circuit. Under the control of p-hot-gate thyristor (TT102) features, by RT Figure 2 (A) value to determine the devices turn-on temperature, RT bigger turn-on, the lower the temperature. When placed near the power switching transistor, or within the power supply unit, it will be able to play a direct role in the temperature. When the power tube shell temperature or the devices internal temperature exceeds the permitted value, the conduction heat thyristors, so that light-emitting diode warning lights. If the tie optocouplers, would enable the machine alarm circuit action, the protection switching regulators. It can also, as Figure 2 (B), as used for power transistor overheating protection, the crystal switch base current is n control gate thyristor TT201 thermal bypass switch closing, cutting off the collector current to prevent overheating. 8 Conclusion Are discussed above in the switching regulator in a variety of conservation, and introduces a number of specific implementation methods. For a given switching power supply is, but also from the machine protection consider the following: 1) the application of switching regulators in the switch transistor limits in the DC safe operating area within the work. For the selected switch transistor, the transistor manuals to be investigated by obtaining the DC safe operating area. According to the maximum collector current to determine the value of input over-current protection. However, the instantaneous maximum value should be converted to current averages. In the rated output current and output voltage conditions, the dynamic load line switch DC safe operating area does not exceed the maximum input voltage is the input voltage over-voltage protection. 2) the switching regulators output is limited by the technical specifications of a given within the. In the required operating temperature range, the switching regulators output voltage, the lower is the output over-or under-voltage protection voltage value. Over-current protection can be determined based on the maximum output current. False alarms in order not to protect the value should be appropriate to stay a certain margin. 3) The above two points are determined after the protection mode, then power supply unit according to the needs of measures to determine the alarm. General warning measures are two kinds of sound alarm and light alarm. Sound alarm for more complex machine, power supply has packed in some inconspicuous place, it can give the staff an effective fault alarms; light can be visible to the police warning that indicates a problem and pointed out that the location and type of failure occurred. Protected by conservation measures depends on the location to determine. In the high-power, multi-channel power of the occasion, always use AC and DC circui