Switching power supply with overvoltage protection and overvoltage protection method thereof
View Patent ↗A switching power supply with overvoltage protection includes a soft start circuit, a rectifying circuit, a filter capacitor, a main supply, an auxiliary supply and a monitoring circuit. When the input voltage is higher than the predetermined protection voltage, a first electric control switch is turned off, and the main power circuit of the switching power supply is shut off. At the moment, the actuation and release of the second electric control switch is controlled so as to control the input power supply to intermittently charge the power supply module such that the output voltage downstream of the rectifying circuit inside the power supply is controlled in a safe range. For instance, the second electric control is turned on when the output voltage is lower than a certain value, and is turned off when the output voltage is higher than a certain value. Thus, it is ensured that the bus line voltage inside the power supply is controlled within a safe range, to ensure the safety of the devices inside the power supply; and at the same time to ensure the safety of the inner devices of the switching power supply, such that the auxiliary power supply and the control circuit can work normally.
1. A switching power supply:
a soft start circuit;
a rectifying circuit electrically communicating with the soft start circuit;
a filter capacitor electrically communicating with an output of the rectifying circuit;
a main power supply in parallel with the filter capacitor;
an auxiliary power supply electrically connected to the rectifying circuit and a monitoring circuit that detects voltage and is responsive to the detected voltage;
wherein the soft start circuit includes a soft start resistor and in parallel with a first switch and a second switch;
wherein after a current is applied to the rectifying circuit and to the filter capacitor via the soft start circuit, resultant rectified current is output to the main power supply and the auxiliary power supply, wherein the auxiliary power supply supplies DC voltage to the monitoring circuit;
wherein the monitoring circuit voltage associated with the main power supply and controls the first switch in accordance therewith;
wherein the second switch is connected in series with the soft start resistor wherein the monitoring circuit controls an ON or OFF state of the second switch.
2. The switching power supply of claim 1 wherein the second switch and the soft start resistor are in series, and the second switch and the soft start resistor are in parallel with the first switch.
3. The switching power supply of claim 1 further comprising a second impedance in parallel with the second switch.
4. The switching power supply of claim 1 further comprising a second impedance and a third impedance, the third impedance and the second switch being in series, the third impedance and second switch in parallel with the second impedance.
5. The switching power supply of claim 1 further comprising a second auxiliary power supply having an input connected to a battery and an output connected with the monitoring circuit ( 10 ).
6. The switching power supply of claim 1 wherein the first and second switches are relays.
7. An overvoltage protection method for a switching power supply, comprising:
a monitoring a voltage of a switching power supply;
if a monitored input is in a predetermined range, then controlling a first normally open switch and a second normally closed switch to charge a filter capacitor through a soft start resistor and the second switch, and controlling the first switch in a normal operating state following execution of a soft start;
when the monitored input indicates an overvoltage, monitoring a voltage of the filter capacitor and if the monitored voltage of the filter capacitor exceeds a first predetermined threshold, controlling the first and second switches and the energy stored in the filter capacitor maintains the second switch in a non-conducting state;
when the voltage of the filter capacitor falls below a second predetermined threshold, controlling the second switch so that the filter capacitor is charged through the soft start resistor and the second switch;
if the voltage of the filter capacitor exceeds the first predetermined threshold a second time, the second control switch will be maintained in a non-conductive state;
when the monitored voltage returns to within the predetermined range, controlling the first and second switches in normal operating state.
8. The overvoltage protection method according to claim 7 further comprising setting the second predetermined value in advance.
9. The overvoltage protection method for a switching power supply according to claim 7 further comprising controlling the first and second control switches such that a monitored voltage is less than a bus line voltage so that the current is zero when either of the first or second switches are activated.