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1、Translated from: XiongFusheng, DC Switching Power Supply Protection Technology, Guangzhou:The World of Power Supply P,2002.2.DC Switching Power Supply Protection TechnologyAbstract: The DC switching power supply protection system, protection system design principles and machine protection measures,
2、an analysis of switching power supply in the range of protected characteristics and its design methodology,introduced a number of practical protection circuit. Keywords: switching power supply protection circuit system design1、Introduction DC switching regulator used in the price of more expensive h
3、igh-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 electronic systems installed devices. Transistors and integrated device tolerance electricity, less heat shocks. Switching Regulato
4、rs therefore should take into account the protection of voltage regulators and load their own safety. Many different types of circuit protection, polarity protection, introduced here, the program protection, over-current protection, over-voltage protection, under-voltage protection and over-temperat
5、ure protection circuit. Usually chosen to be some combination of protection, constitutes a complete protection system.2、polarity protection DC switching regulator input are generally not regulated DC power supply. Operating errors or accidents as a result of the situation will take its wrong polarit
6、y, switching power supply will be damaged. Polarity protection purposes, is to make the switching regulator only when the correct polarity is not connected to DC power supply regulator to work at. Connecting a single device can achieve power polarity protection. Since the diode D to flow through swi
7、tching regulator input total current, this circuit applied in a low-power switching regulator more suitable. Power in the larger occasion, while the polarity protection circuit as a procedure to protect a link, save the power required for polarity protection diodes, power consumption will be reduced
8、. In order to easy to operate, make it easier to identify the correct polarity or not, collect the next light.3、procedures to protect Switching power supply circuit is rather complicated, basically can be divided into low-power and high-power part of the control part of the switch. Switch is a high-
9、power transistors, for the protection of the transistor switch is turned on or off power safety, we must first modulator, amplifier and other low-power control circuit. To this end, the boot to ensure the correct procedures. Switching Regulators generally take the input of a small inductor, the inpu
10、t filter capacitor. Moment in the boot, filter capacitor will flow a lot of surge current, the surge current can be several times more than the normal input current. Such a large surge current may contact the general power switch or relay contact melting, and the input fuse fuse. In addition, the ca
11、pacitor surge current will damage to shorten the life span of premature damage. To this end, the boot should be access to a current limiting resistor, through the current limiting resistor to capacitor charging. In order not to make the current limiting resistor excessive power consumption, thus aff
12、ecting the normal switching regulator, and the transient process in the boot after a short period then automatically relays it to DC power supply directly to the switching regulator power supply. This circuit switching regulator called a soft start circuit.Switching regulator control circuit of the
13、logic components required or op-amp auxiliary power supply. To this end, the auxiliary power supply must be in the switch circuit. This control circuit can be used to ensure the boot. Normal boot process is: to identify the polarity of input power, voltage protection procedures boot auxiliary power
14、supply circuit and through current limiting resistor R of the switching regulator input capacitor C charge modulation switching regulator circuit, short-circuit current limiting resistor stability switching regulator.In the switching regulator, the machines just because the output capacitance, and c
15、harge to the rated output voltage value of the need for a certain period of time. During this time, sampling the output amplifier with low input voltage sampling, closed-loop regulation characteristics of the system will force the switching of the transistor conduction time lengthened, so that switc
16、hing transistor during this period will tend to continuous conduction, and easily damaged. To this end, the requirements of this paragraph in the boot time, the switch to switch the output modulation circuit transistor base drive signal of the pulse width modulation, can guarantee the switching tran
17、sistor by the cut-off switches are becoming more and more normal state, therefore the protection of the setting up of a boot to tie in with the soft start.4、over-current protection When the load short-circuit, overload control circuit failure or unforeseen circumstances, such as would cause the flow
18、 of switching voltage regulator transistor current is too large, so that increased power tubes, fever, if there is no over-current protection device, high power switching transistor may be damaged. Therefore, the switching regulator in the over-current protection is commonly used. The most economica
19、l way is to use simple fuse. As a result of the heat capacity of small transistors, general fuse protection in general can not play a role in the rapid fuse common fuse. This method has the advantage of the protection of vulnerable, but it needs to switch transistor in accordance with specific secur
20、ity requirements of the work area to select the fuse specifications. This disadvantage is over-current protection measures brought about by the inconvenience of frequent replacement of fuses.Linear voltage regulator commonly used in the protection and current limiting to protect the cut-off in the s
21、witching regulator can be applied. However, according to the characteristics of switching regulators, the protection circuit can not directly control the output transistor switches, and overcurrent protection must be converted to pulse output commands to control the modulator to protect the transist
22、or switch. In order to achieve over-current protection are generally required sampling resistor in series in the circuit, this will affect the efficiency of power supply, so more for low-power switching regulator of occasions. In the high-power switching power supply, by taking into account the powe
23、r consumption should be avoided as far as possible access to the sampling resistor. Therefore, there will usually be converted to over-current protection, and under-voltage protection. 5、over-voltage protection Switching regulators input over-voltage protection, including over-voltage protection and
24、 output over-voltage protection. Switching regulator is not used in DC power supply voltage regulator and rectifier, such as battery voltage, if too high, so switching regulator is not working properly, or even damage to internal devices, therefore, it is necessary to use the input over-voltage prot
25、ection circuit. Using transistors and relays protection circuit.In the circuit, when the input DC power supply voltage higher than the voltage regulator diode breakdown voltage value, the breakdown voltage regulator tube, a current flowing through resistor R, so that V turn-on transistor, relay, nor
26、mally closed contact off open, cut off the input. Voltage regulator voltage regulator which controls the value of Vz = ESrmax-UBE. The polarity of input power with the input protection circuit can be combined with over-voltage protection, polarity protection constitute a differential circuit and ove
27、rvoltage protection. Output over-voltage protection switching power supply is essential. In particular, for the 5V output of the switching regulator, it is a lot of load on a high level of integration of the logic device. If at work, switching regulator sudden damage to the switch transistor, the ou
28、tput potential may be increased immediately to the importation of non-regulated DC power supply voltage value, causing great loss instantaneous. Commonly used method is short-circuit protection thyristor. The simplest over-voltage protection circuit. When the output voltage is too high, the regulato
29、r tube breakdown triggered thyristor turn-on, the output short-circuit, resulting in over-current through the fuse or circuit protective device to cut off the input to protect the load. This circuit is equivalent to the response time of the opening time of thyristor is about 5 10s. The disadvantage
30、is that its action is fixed voltage, temperature coefficient, and action points of instability. In addition, there is a voltage regulator control parameters of the discrete, model over-voltage start-up the same but has different values, difficult to debug. Esc a sudden increase in output voltage, tr
31、ansistors V1, V2 conduction, the thyristor conduction. Reference voltage Vz by type.6、under-voltage protection Output voltage below the value to reflect the input DC power supply, switching regulator output load internal or unusual occurrence. Input DC power supply voltage drops below the specified
32、value would result in switching regulator output voltage drops, the input current increases, not only endanger the switching transistor, but also endanger the input power. Therefore, in order to set up due to voltage protection. Due to simple voltage protection. When no voltage regulator input norma
33、l, ZD breakdown voltage regulator tube, transistors V conduction, the relay action, contact pull-in, power-switching regulator. When the input below the minimum allowable voltage value, the regulator tube ZD barrier, V cut-off, contact Kai-hop, switching regulator can not work. Internal switching re
34、gulator, as the control switch transistor circuit disorders or failure will decrease the output voltage; load short-circuit output voltage will also decline. Especially in the reversed-phase step-up or step-up switching regulator DC voltage of the protection due to over-current protection with close
35、ly related and therefore more important. Implementation of Switching Regulators in the termination of the output voltage comparators.Normally, there is no comparator output, once the voltage drops below the allowable value in the comparator on the flip, drive alarm circuit; also fed back to the swit
36、ching regulator control circuit, so that switching transistor cut-off or cut off the input power. 7、over-temperature protection Switching regulator and the high level of integration of light-weight small volume, with its unit volume greatly increased the power density, power supply components to its
37、 work within the requirements of the ambient temperature is also a corresponding increase. Otherwise, the circuit performance will deteriorate, premature component failure. Therefore, in high-power switching regulator should be set up over-temperature protection. Relays used to detect the temperatur
38、e inside the power supply temperature, when the internally generated power supply overheating, the temperature of the relay on the action, so that whole circuit in a warning alarm, and the realization of the power supply over-temperature protection. Temperature relay can be placed in the vicinity of
39、 the switching transistor, the general high-power tube shell to allow the maximum temperature is 75 , adjust the temperature setting to 60 . When the shell after the temperature exceeds the allowable value to cut off electrical relay on the switch protection. Semiconductor switching device thermal h
40、ot thyristor, in the over-temperature protection, played an important role. It can be used as directed circuit temperature. Under the control of p-hot-gate thyristor (TT102) characteristics, by RT value to determine the temperature of the device turn-on, RT greater the temperature the lower the turn
41、-on. When placed near the power switching transistor or power device, it will be able to play the role of temperature instructions. When the power control the temperature of the shell or the internal device temperature exceeds the allowed value, the heat conduction thyristor on, so that LED warning
42、light. If the optocoupler with, would enable the whole circuit alarm action to protect the switching regulator. It can also be used as a power transistor as the over-temperature protection, crystal switch the base current by n-type gate control thyristor TT201 thermal bypass, cut-off switch to cut o
43、ff the collector current to prevent overheating.8、Conclusion Discussed above in the switching regulator of a variety of conservation, and introduces a number of specific ways to achieve. Of a given switching power supply is concerned, but also protection from the whole to consider the following poin
44、ts: 1) the switching regulator used in the switching transistor in the DC security restrictions on the work of regional work. The transistor switches selected by the manual available transistors get DC safe working area. According to the maximum collector current to determine the input value of over
45、-current protection. However, the instantaneous maximum value should be converted to the average current. At rated output current and output voltage conditions, the switch of the dynamic load line does not exceed a safe working area DC maximum input voltage, input over-voltage protection is the volt
46、age value. 2) the switching regulator output limit given by the technical indicators within. Work within the required temperature range, the switching regulators output voltage, the lower limit of the output is off, due to the voltage value of voltage protection. Over-current protection can be based
47、 on the maximum output current to determine. False alarm in order not to protect the value of a certain margin to remain appropriate. 3) from the above two methods to determine the protection after the power supply device in accordance with the needs of measures to determine the alarm. Measures the
48、general alarm sound and light alarm two police. Voice of the police applied to more complex machines, power supply parts and do not stand out in a place, it can give staff an effective warning of failure; optical Police instructions can be eye-catching and fault alarm and pointed out that the fault
49、location and type. Protection measures should be protected as to determine the location. In the high-power, multi-channel power supply, always paying, DC circuit breakers, relays, etc. high-sensitivity auto-protection measures, to cut off the input power supply to stop working the system from damage. Through the logic control circuit to make the appropriate program cut-off switch transistor is sensitive it is convenient and economic. This eliminated large, long response time, the price of your high-po
