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1、DC Switching Power Supply Protection Technology Abstract: The DC switching power supply protection system, protection system design principles and machine protection measures, an analysis of switching power supply in the range of protected characteristics and its design methodology,introduced a numb
2、er of practical protection circuit. Keywords: switching power supply protection circuit system design1、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 genera
3、lly used a large number of highly integrated electronic systems installed devices. Transistors and integrated device tolerance electricity, less heat shocks. Switching Regulators therefore should take into account the protection of voltage regulators and load their own safety. Many different types o
4、f circuit protection, polarity protection, introduced here, the program protection, over-current protection, over-voltage protection, under-voltage protection and over-temperature protection circuit. Usually chosen to be some combination of protection, constitutes a complete protection system.2、pola
5、rity 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 polarity, switching power supply will be damaged. Polarity protection purposes, is to make the switching regulator only when the co
6、rrect polarity is not connected to DC power supply regulator to work at. Since the diode D to flow through switching 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 procedur
7、e to protect a link, save the power required for polarity protection diodes, power consumption will be reduced. 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, ba
8、sically can be divided into low-power and high-power part of the control part of the switch. Switch is a high-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
9、 to ensure the correct procedures. Switching Regulators generally take the input of a small inductor, the input 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 curre
10、nt may contact the general power switch or relay contact melting, and the input fuse fuse. In addition, the capacitor 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 t
11、o capacitor charging. In order not to make the current limiting resistor excessive power consumption, thus affecting 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 su
12、pply. This circuit switching regulator called a soft start circuit.Switching regulator control circuit of the 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
13、 boot process is: to identify the polarity of input power, voltage protection procedures boot auxiliary power 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 sta
14、bility switching regulator.In the switching regulator, the machines just because the output capacitance, and charge 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 char
15、acteristics of the system will force the switching of the transistor conduction time lengthened, so that switching 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 m
16、odulation circuit transistor base drive signal of the pulse width modulation, can guarantee the switching transistor 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
17、load short-circuit, overload control circuit failure or unforeseen circumstances, such as would cause the flow 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 d
18、amaged. Therefore, the switching regulator in the over-current protection is commonly used. The most economical 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
19、advantage of the protection of vulnerable, but it needs to switch transistor in accordance with specific security 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
20、.Linear voltage regulator commonly used in the protection and current limiting to protect the cut-off in the switching regulator can be applied. However, according to the characteristics of switching regulators, the protection circuit can not directly control the output transistor switches, and over
21、current protection must be converted to pulse output commands to control the modulator to protect the transistor 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-pow
22、er switching regulator of occasions. In the high-power switching power supply, by taking into account the power 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、ove
23、r-voltage protection Switching regulators input over-voltage protection, including over-voltage protection and 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 worki
24、ng properly, or even damage to internal devices, therefore, it is necessary to use the input over-voltage 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 flowin
25、g through resistor R, so that V turn-on transistor, relay, normally 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,
26、 polarity protection constitute a differential circuit and overvoltage 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, swit
27、ching regulator sudden damage to the switch transistor, the output 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 protect
28、ion circuit. When the output voltage is too high, the regulator 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 t
29、he opening time of thyristor is about 5 10s. The disadvantage 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, d
30、ifficult to debug. 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 value would result in switching regulator output voltage drops, t
31、he 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. When no voltage regulator input normal, ZD breakdown voltage regulator tube, transistors V conduction, the relay action, contact pull-in
32、, 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 regulator, as the control switch transistor circuit disorders or failure will decrease the output vol
33、tage; 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 closely related and therefore more important. Implementation of Switching Regulators in the termination
34、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 switching regulator control circuit, so that switching transistor cut-off or cut off the input power. 7
35、、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 work within the requirements of the ambient temperature is also a corresponding increase. Otherwis
36、e, 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 temperature inside the power supply temperature, when the internally generated power supply overheating, the
37、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 the switching transistor, the general high-power tube shell to allow the maximum temperature is 75
38、 , 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 hot thyristor, in the over-temperature protection, played an important role. It can be used as direc
39、ted 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-on. When placed near the power switching transistor or power device, it will be able to play the r
40、ole 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 light. If the optocoupler with, would enable the whole circuit alarm action to protect the switchin
41、g 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 off the collector current to prevent overheating.8、Conclusion Discussed above in the switching regul
42、ator 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 points: 1) the switching regulator used in the switching transistor in the DC security restrictions on
43、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-current protection. However, the instantaneous maximum value should be converted to the average cu
44、rrent. 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 voltage value. 2) the switching regulator output limit given by the technical indicators within. Work w
45、ithin 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 on the maximum output current to determine. False alarm in order not to protect the value of a cer
46、tain 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 general alarm sound and light alarm two police. Voice of the police applied to more complex machine
47、s, 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 location and type. Protection measures should be protected as to determine the location. In the hig
48、h-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 se
49、nsitive it is convenient and economic. This eliminated large, long response time, the price of your high-power relay or circuit breaker. 4) the power of putting in the protection circuit will be affected after the reliability of the system, for which want to protect the reliability of the circuit itself is higher in order to improve the reliability of the entire power system, thereby increasing its own power supply MTBF. This requires the protection of strict logic, the circuit is simple, at least component