Low cost redundant AC to DC power supply

[0002] The present invention relates to power supplies, and more particularly to redundancy in power supplies.

[0003] Redundant AC to DC power supplies are well known in the art. FIG. 1 illustrates a first conventional circuit for providing redundant AC to DC power. The circuit 100 comprises a first AC voltage source 102 coupled to a first power supply 106 in a first power train. The circuit 100 also comprises a second AC voltage source 104 coupled to a second power supply 108 in a second power train. The DC voltages from the first 106 and second 108 power supplies are combined and provided as DC outputs. However, this conventional circuit requires two independent power supplies 106 and 108 connected to two separate AC sources. This adds to the cost of the power system.

[0004] FIG. 2 illustrates a second conventional redundant AC power system. The system 200 comprises a first AC voltage source 202 and a second AC voltage source 204. Both sources provide AC voltages to an AC transfer switch 206. The transfer switch 206 supplies either the voltage from the first AC voltage source 202 or the voltage from the second AC voltage source 204 to a power supply 208, which provides DC outputs. However, the transfer switch 206 is very expensive, adding significant cost to the circuit 200.

[0005] Accordingly, there exists a need for a low cost redundant AC to DC power supply. This power supply should provide AC power redundancy in a cost effective manner. The present invention addresses such a need.

[0006] The power supply in accordance with the present invention provides AC redundancy while also preventing voltages from multiple AC voltage sources from adding at a common node. The adding of voltages is avoided by ensuring that only one AC voltage source at a time is providing the voltage at the output. Even if the other AC voltage sources are connected afterwards, these later AC voltage source are prevented from providing power at the output. In addition, diodes prevent current from back flowing to the AC voltage sources which are not supplying power to the output. Because the power supply in accordance with the present invention neither uses redundant AC to DC power supplies from independent AC voltage sources, nor does it use a costly transfer switch, the power supply in accordance with the present invention is more cost effective than conventional redundant power supplies.

[0007] FIG. 1 illustrates a first conventional circuit for providing redundant AC to DC power.

[0008] FIG. 2 illustrates a second conventional redundant AC power system.

[0009] FIG. 3 illustrates a preferred embodiment of a redundant AC to DC power supply in accordance with the present invention.

[0010] The present invention provides a low cost redundant AC to DC power supply. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.

[0011] The power supply in accordance with the present invention provides redundancy while also preventing voltages from multiple AC voltage sources from adding. The adding of voltages is avoided by ensuring that only one AC voltage source at a time is providing a voltage at the output. Even if the other AC voltage sources are connected afterwards, these later AC voltage sources are prevented from providing power at the output. In addition, currents are prevented from back flowing to the AC voltage sources which are not supplying power to the output.

[0012] To more particularly describe the features of the present invention, please refer to FIG. 3 in conjunction with the discussion below.

[0013] FIG. 3 illustrates a preferred embodiment of a redundant AC to DC power supply in accordance with the present invention. The power supply 300 comprises leads for voltages from a first AC voltage source 302 and a second AC voltage source 304. The power supply 300 comprises a first bridge rectifier 306 (D1). The first and third nodes of D1 306 are coupled to the first AC voltage source 302. Coupled to a second node of D1 306 is a resistor 326 (R1) and an anode of diode 314 (D4). The cathode of D4 314 is coupled to an output 338. In the preferred embodiment, a DC—DC switcher 340 is coupled to the output 338.

[0014] Coupled to R1 326 is a first opto-coupler 310. The first opto-coupler 310 comprises a diode 342 and a transistor 344. The diode 342 of the first opto-coupler 310 is coupled to a resistor 328 (R2). R2 328 is coupled to a fourth node of the first bridge rectifier 306. Coupled to the common node of diode 342 and R2 328 is a first set-reset latch 318. Coupled to the first latch 318 is a gate of a first silicon controller rectifier (SCR) 322 (Q1). The anode of Q1 322 is coupled to the DC—DC switcher 340. The cathode of Q1 322 is coupled to R2 328 and the fourth node of the first bridge rectifier 306. Coupled to the gate and cathode of Q1 322 is a capacitor 330 (C1).

[0015] The power supply 300 further comprises a second bridge rectifier 308 (D2). The first and third nodes of D2 308 are coupled to the second AC voltage source 304. Coupled to a second node of D2 308 is a resistor 332 (R3) and an anode of diode 316 (D5). The cathode of D5 316 is coupled to the output 338. Coupled to R3 332 is a second opto-coupler 312. The second opto-coupler 312 comprises a diode 346 and a transistor 348. The transistor 348 is coupled across R2 328. The diode 346 of the second opto-coupler 312 is coupled to a resistor 334 (R4). The transistor 344 of the first opto-coupler 310 is coupled across R4 334. R4 334 is also coupled to a fourth node of D2 308. Coupled to the common node of diode 346 and R4 334 is a second set-reset latch 320. Coupled to the second latch 320 is a gate of a second SCR 324 (Q2). The anode of Q2 324 is coupled to the DC—DC switcher 340. The cathode of Q2 324 is coupled to R4 334 and the fourth node of the second bridge rectifier 308. Coupled to the gate and cathode of Q2 324 is a capacitor 336 (C2).

[0016] Assume that the first AC voltage source 302 is connected to the power supply 300 before the second AC voltage source 304. The voltage, V1, from the first AC voltage source 302 is rectified by D1 306. The rectified voltage turns “on” the first opto-coupler 310. Current flows through R1 326, the diode 342, and R2 328. This causes the S pin of the first latch 318 to go high, setting the first latch 318. The setting of the first latch 318 turns Q1 322 “on”. A current path is thus created from D1 306 to D4 314, to the DC—DC switcher 340, Q1 322, and back to D1 306. The first AC voltage source 302 thus is providing power at the output 338.

[0017] With the transistor 344 “on” and connected across R4 334, the voltage across R4 334 is approximately zero volts. The S pin of the second latch 320 remains low, so the second latch 320 is not set, and Q2 324 is not turned “on”. Thus, only the first AC voltage source 302 is providing power to the output 338.

[0018] Assume that after the first AC voltage source 302 is connected to the power supply 300, the second AC voltage source 304 is connected to the power supply 300 at any phase angle. The voltage, V2, from the second AC voltage source 304 is rectified by D2 308. The rectified voltage turns “on” the second opto-coupler 312. Current will flow through R3 332, diode 346, and R4 334. However, since transistor 344 of the first opto-coupler 310 is “on”, the voltage across R4 334 remains approximately zero volts. The second latch 320 remains unset, and Q2 324 remains “off”. Since the transistor 348 of the second opto-coupler 312 is now “on”, the voltage across R2 328 becomes approximately zero volts. However, since the first latch 318 has not been reset, it remains in the set state, and Q1 322 remains “on”. Thus, the first AC voltage source 302 remains the only one providing power to the output 338.

[0019] The second AC voltage source 304 becomes the source providing power to the output 338 when the first AC voltage source 302 is disconnected. Disconnecting the first AC voltage source 302 resets the first latch 318. It allows the S pin of the first latch 318 to go low, turning “off” Q1 322. The voltage provided to the output 338 by the first AC voltage source 302 is removed. The first opto-coupler 310 is also turned “off”. This removes the short across R4 334, allowing the S pin of the second latch 320 to go high, setting the second latch 320. Setting the second latch 320 turns Q2 324 “on”. A current path is thus created from D2 308 to D5 316, to the DC—DC switcher 340, Q2 324, and back to D2 308. Thus, the second AC voltage source 304 is the only one providing power to the output 338.

[0020] The power supply 300 functions in the same manner when the second AC voltage source 304 is connected to the power supply 300 before the first voltage source 302. The voltage, V2, from the second AC voltage source 304 is rectified by D2 308. The rectified voltage turns “on” the second opto-coupler 312. Current flows through R3 332, the diode 346, and R4 334. This causes the S pin of the second latch 320 to go high, setting the second latch 320. The setting of the second latch 320 turns Q2 324 “on”. A path is thus created from D2 308 to D5 316, to the DC—DC switcher 340, Q2 324, and back to D2 308. The second AC voltage source 304 thus is providing power at the output 338.

[0021] With the transistor 348 “on” and connected across R2 328, the voltage across R2 328 is approximately zero volts. The S pin of the first latch 318 remains low, and the first latch 318 is not set. Q1 322 is not turned “on”. Thus, only the second AC voltage source 304 is providing power to the output 338.

[0022] Assume that after the second AC voltage source 304 is connected to the power supply 300, the first AC voltage source 302 is connected to the power supply 300 at any phase angle. The voltage, V1, from the first AC voltage source 302 is rectified by D1 306. The rectified voltage turns “on” the first opto-coupler 310. Current will flow through R1 326, diode 342, and R2 328. However, since transistor 348 of the second opto-coupler 312 is “on”, the voltage across R2 328 remains approximately zero volts. The first latch 318 remains unset, and Q1 322 remains “off”. Since the transistor 344 of the first opto-coupler 310 is now “on”, the voltage across R4 334 becomes approximately zero volts. However, since the second latch 320 has not been reset, it remains in the set state, and Q2 324 remains “on”. Thus, the second AC voltage source 302 remains the only one providing power to the output 338.

[0023] The first AC voltage source 302 becomes the source providing power to the output 338 when the second AC voltage source 304 is disconnected. Disconnecting the second AC voltage source 304 resets the second latch 320. This allows the S pin of the second latch 320 to go low, turning “off” Q2 324. The voltage provided to the output 338 by the second AC voltage source 304 is removed. The second opto-coupler 312 is also turned “off”. This removes the short across R2 328, allowing the S pin of the first latch 318 to go high, setting the first latch 318. Setting the first latch 318 turns Q1 322 “on”. A current path is thus created from D1 306 to D4 314, to the DC—DC switcher 340, Q1 322, and back to D1 306. Thus, the first AC voltage source 302 becomes the only one providing power to the output 338.

[0024] The power supply 300 in accordance with the present invention provides AC redundancy while also preventing voltages from the first 302 and second 304 AC voltage sources from adding. This adding of voltages may occur if the AC voltage sources 302 and 304 are out of phase and of different amplitudes. The adding of voltages is avoided by ensuring that only one AC voltage source at a time is providing the voltage at the output. Even if the other AC voltage source is connected afterwards, this later AC voltage source is prevented from providing power at the output. In addition, diodes prevent current from back flowing to the AC voltage source which is not supplying power to the output. Because the power supply in accordance with the present invention does not use multiple power supplies in independent power trains, nor does it use a costly transfer switch, the power supply in accordance with the present invention is more cost effective.

[0025] Although the preferred embodiment is described above with two AC voltage sources, one of ordinary skill in the art will understand that the power supply may be modified for three or more AC voltage sources without departing from the spirit and scope of the present invention.

[0026] A low cost redundant AC to power supply using two independent AC voltage sources has been disclosed. The power supply in accordance with the present invention provides redundancy while also preventing voltages from multiple AC voltage sources from adding at a common node. In addition, current is prevented from back flowing to the AC voltage sources which are not supplying power to the output. Because the power supply in accordance with the present invention neither uses redundant AC to DC power supplies from independent AC voltage sources, nor does it use a costly transfer switch, the power supply in accordance with the present invention is more cost effective.

[0027] Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.