Active current surge limiters with voltage detector and relay
Active current surge limiters and methods of use are disclosed. One exemplary system, among others, comprises a current limiter, including an interface configured to be connected between a power supply and a load; a disturbance sensor, configured to monitor the power supply for a disturbance during operation of the load; and an activator, configured to receive a control signal from the disturbance sensor and to activate the current limiter based on the control signal.
1. An active current surge limiting apparatus for reduction of inrush current to an electrical load in response to detection of a disturbance in an input AC power supply coupled to the electrical load, comprising:
a current-limiting circuit coupled between the input power supply and the electrical load, the current-limiting circuit comprising a parallel arrangement of (a) a negative temperature coefficient (NTC) component and (b) a relay having contacts that are in a normally-open position at start-up and close in response to a control signal to couple the input power supply to the electrical load and bypass the NTC component;
a relay activator circuit responsive to the control signal for activating the relay to place the relay into a closed position;
a voltage detector circuit coupled to the input power supply for detecting a disturbance occurring on the AC power supply; and
a control circuit responsive to detection of disturbance by the voltage detector circuit for (a) providing the control signal to maintain the relay in the closed position during normal operation of the power supply and (b) open the relay in response to detection of the disturbance in the input power supply to couple the input power supply to the electrical load through the NTC component, said control circuit further operative to detect resumption of normal conditions on the input power supply close the relay between the input power supply and the electrical load,
whereby inrush current that would result from removal of the disturbance is resisted by the NTC component when the relay is the open position.
2. The apparatus of claim 1 , wherein the relay activator circuit comprises a retriggerable monostable multi-vibrator (MMV) circuit that controls activation of the coil of the relay by maintaining the contacts in the closed position during provision of the control signal, and
wherein the control signal comprises signal pulses from the control circuit that correspond to the cycles of AC power from the input power supply, the signal pulses operative to retrigger the MMV circuit during normal conditions on the input power supply and maintain the relay contacts closed,
whereby the relay contacts open if the signal pulses from the control circuit are not provided to retrigger the MMV.
3. The apparatus of claim 1 , wherein the relay contacts are in the open position during start-up of power provided to the electrical load.
4. The apparatus of claim 1 , wherein the voltage detector is operative to detect start-up of the power supply, and wherein the control circuit provides the control signal to close the relay after a preset time delay after detection of start-up of the power supply and bypass the NTC component.
5. The apparatus of claim 1 , wherein the apparatus is coupled to a reactive load, and wherein the relay activator circuit maintains the relay in an open position during an initial startup condition of power being provided from the input power supply, and further comprising a timer circuit operative to place the relay in the closed position after expiration of a predetermined time period after the startup condition.
6. The apparatus of claim 1 , wherein the voltage detector circuit and the control circuit comprise a programmed microprocessor connected to receive signals representing the voltage of the input power supply provided from an analog-to-digital (A/D) converter, the microprocessor programmed to identify when the voltage falls outside a nominally acceptable boundary defined by a preset limit, and to provide the control signal.
7. The apparatus of claim 1 , wherein the control circuit comprises a programmed microprocessor connected to receive signals representing the voltage of the input power supply provided from an analog-to-digital (A/D) converter, the microprocessor providing the control signal to cause the switch to open and then close after a predetermined time after the voltage returns to a normal level.
8. The apparatus of claim 1 , further comprising a voltage clamping component coupled to the apparatus at the point of connection of the input power supply for providing additional voltage surge protection for the electrical load and the current surge limiting apparatus.
9. The apparatus of claim 1 , wherein the disturbance in the input power supply is a voltage disturbance, a current disturbance, or a combination thereof.