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, 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 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 regulator, 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 closely 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 switching 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 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 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 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 ℃, 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 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-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 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 off 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 points: