Summary of the invention
Key the present invention is in order to address the above problem herein; a kind of storage capacitor protective circuit is provided; it has very little leakage current when operate as normal; substantially do not consume capacitive energy; and when electric voltage exception raises; can realize overvoltage protection, bleed off, the explosion hazard of avoiding the electric capacity overvoltage to cause to storage capacitor.
For addressing the above problem, the technical solution used in the present invention is as follows:
A kind of storage capacitor protective circuit; comprise rectification circuit that is connected ac input end and the storage capacitor that is connected dc output end; a storage capacitor overvoltage crowbar in parallel between rectification circuit and storage capacitor; described storage capacitor overvoltage crowbar is by the relay with normal opened contact and normally closed contact; first voltage stabilizing didoe; second voltage stabilizing didoe and current-limiting resistance are formed; the normally closed contact of described relay is connected between the positive pole of the output of rectification circuit and storage capacitor; the normal opened contact of described relay is connected on the circuit of being made up of the current-limiting resistance and second voltage stabilizing didoe; first voltage stabilizing didoe is connected in parallel on the circuit of being made up of the normal opened contact of current-limiting resistance and relay; the positive pole of second voltage stabilizing didoe is connected the negative contacts of the current-limiting resistance and first voltage stabilizing didoe; negative pole is connected the positive pole of storage capacitor; it is in parallel with relay coil to be used for the diode that the relay reverse voltage releases; its negative pole is connected with the relay coil negative pole, and positive pole is connected with the positive pole of relay coil.
Be serially connected with semistor and negative tempperature coefficient thermistor between described ac input end and the rectification circuit.
The present invention compares with traditional implementation, can realize the overvoltage protection to storage capacitor, has the surge of powering on restriction, short circuit overcurrent defencive function again by positive and negative temperature coefficient thermistor simultaneously.
Embodiment
Circuit diagram of the present invention as shown in Figure 1, wherein L, N are ac input end, DC+, DC-are dc power output end, semistor PTC, negative tempperature coefficient thermistor NTC, rectifier circuit D1, relay J D, the diode D2 that is used for relay reverse voltage bleed off, the first voltage stabilizing didoe D3, the second voltage stabilizing didoe D4, current-limiting resistance R1, storage capacitor C1.
Its course of work is as follows:
When power supply electrifying, because the characteristic of negative tempperature coefficient thermistor NTC, it has certain resistance value when low temperature, thereby limited the surge current that powers on, and when operate as normal, because self-heating, resistance value reduces, can not exert an influence, select the negative tempperature coefficient thermistor NTC of suitable resistance as required, can will power on inrush current limitation within the acceptable range system.
When short circuit of direct current output loop or long-term overcurrent, because the characteristic of semistor PTC, when its rated current certain time-delay of current practice, its resistance will increase rapidly, thereby loop current is inhibited, thereby protect the safety of back end loop.
When loop voltage just often, relay is failure to actuate, voltage after the rectification charges to electric capacity through the normally closed contact of relay J D, when electric voltage exception raises, if the voltage after the rectification is through first voltage stabilizing, two collector D3, still surpass the action of relay after the second voltage stabilizing didoe D4 step-down, relay will move, this moment, normally closed contact was opened, thereby charge circuit is cut off, while normal opened contact closure, voltage on the electric capacity will be by second voltage stabilizing, two collector D4, the shunt circuit of current-limiting resistance R1 and first voltage stabilizing, two collector D3, relay coil constitutes the loop, and capacitance voltage will descend gradually, behind the return voltage that arrives relay, relay discharges, and gets back to normal operating state.By selecting suitable first, second voltage stabilizing two collector D3, D4 can adjust the overvoltage operating value; can adjust the relay return value by selecting suitable current-limiting resistance R1 value; owing to exist certain pressure reduction between operating value and return value; even if also can frequent movement under the situation of often overvoltage, thereby protection relay.
Because the leakage current of first, second voltage stabilizing two collector D3, D4 is the microampere rank during operate as normal, therefore be that the electric weight on the electric capacity also can keep a few hours to go into after convenient charge power supply disappeared.