【正文】 re is a voltage regulator control parameters of the discrete, model overvoltage startup the same but has different values, difficult to debug. Esc a sudden increase in output voltage, transistors V1, V2 conduction, the thyristor conduction. Reference voltage Vz by type. undervoltage 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, 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 normal, ZD breakdown voltage regulator tube, transistors V conduction, the relay action, contact pullin, powerswitching regulator. When the input below the minimum allowable voltage value, the regulator tube ZD barrier, V cutoff, contact Kaihop, switching regulator can not work. Internal switching regulator, as the control switch transistor circuit disorders or failure will decrease the output voltage。 also fed back to the switching regulator control circuit, so that switching transistor cutoff or cut off the input power. overtemperature protection Switching regulator and the high level of integration of lightweight small volume, with its unit volume greatly increased the power density, power supply ponents to its work within the requirements of the ambient temperature is also a corresponding increase. Otherwise, the circuit performance will deteriorate, premature ponent failure. Therefore, in highpower switching regulator should be set up overtemperature protection. Relays used to detect the temperature 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 overtemperature protection. Temperature relay can be placed in the vicinity of the switching transistor, the general highpower 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 hot thyristor, in the overtemperature protection, played an important role. It can be used as directed circuit temperature. Under the control of photgate thyristor (TT102) characteristics, by RT value to determine the temperature of the device turnon, RT greater the temperature the lower the turnon. 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 light. If the optocoupler with, would enable the whole circuit alarm action to protec t the switching regulator. It can also be used as a power transistor as the overtemperature protection, crystal switch the base current by ntype gate control thyristor TT201 thermal bypass, cutoff switch to cut off the collector current to prevent overheating. Conclusion 6 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 points: 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 overcurrent protection. However, the instantaneous maximum value should be converted to the average current. At rated