Voltage regulating circuit for uninterruptible power supply

A voltage regulating circuit has a first switch, a transformer and a second switch. The first switch has an input node, a first node and a second node. The transformer is connected to the switches has a first coil and a second coil. The first coil and the second coil respectively have an end, and the second coil is connected to the first coil in series at a node. The node between the first and second coils is connected to the second node of the first switch. The second switch is connected to the transformer and has a first node, a second node and an output node. The first node is connected to the end of the first coil. The second node is connected to the first node of the first switch. The transformer will not heat up when the transformer needs not to be used.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a voltage regulating circuit, and more particularly to a voltage regulating circuit for an uninterruptible power supply (UPS).

2. Description of Related Art

With reference toFIG. 2, a conventional voltage regulating circuit for an uninterruptible power supply (UPS) comprises a transformer (10) and a switch (23). The transformer (10) is connected to AC power inputs L and N and comprises a first coil (11) and a second coil (12) connected in series. The first coil (11) is formed with multiple turns and has an end. The second coil (12) is formed with multiple turns with two ends respectively connected to the AC power inputs L and N. The switch (23) is connected to the transformer (10) and has a normal close node (232), a normal open node (233) and a common node (231). The normal close node (232) is connected to the end of the first coil (11). The normal opened node (233) is connected to the AC power input L through the transformer (10). When the input voltage is at a normal level, the common node (231) of the switch (23) is switched to connect to the normal close node (232). The input voltage passes through the first and second coil (11,12) of the transformer (10) and the switch (23) as an output voltage. When input voltage is at a low level, the common node (231) of the switch (23) is switched to connect to the normal open node (233). The input voltage passes through the second coil (12) of the transformer (10) and the switch (23) to be transformed into an output voltage. The coupling ratio of the output voltage to the input voltage is the ratio of the sum of turns of the two coils (11)(12) to the number of turns of the second coil (12). Therefore the output voltage is higher than the input voltage in voltage level.

However, the input voltage still passes through the transformer (10) even when the input voltage is at a normal level. When the input voltage passes through the transformer (10), the transformer (10) heats up and may be damaged by constantly heating up.

To overcome the shortcomings, the present invention provides a voltage regulating circuit for an UPS to mitigate or obviate the aforementioned problems.

SUMMARY OF THE INVENTION

The main objective of the invention is to provide a voltage regulating circuit for an uninterruptible power supply (UPS).

A voltage regulating circuit in accordance with the present invention comprises a first switch, a transformer and a second switch. The first switch has an input node, a first node and a second node. The transformer is connected to the first switch and comprises a first coil and a second coil. The first coil and the second coil respectively have an end, and the second coil is connected to the first coil in series at a node. The node between the first and second coils is connected to the second node of the first switch. The second switch is connected to the transformer and has a first node, a second node and an output node. The first node is connected to the end of the first coil. The second node is connected to the first node of the first switch. The first nodes of the first and second switches are normal close. The second nodes of the first and second switches are normal open.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

With reference toFIG. 1, a voltage regulating circuit for an uninterruptible power supply (UPS) in accordance with the present invention is connected to AC power inputs L and N and comprises a first switch (21), a transformer (10) and a second switch (22).

The first switch (21) is connected to the AC power input L and has an input node (211), a first node (212) and a second node (213).

The input node (211) is connected to the AC power input L and can be a common node. The first node (212) can be a normal close node. The second node (213) can be a normal open node.

The transformer (10) is connected to the AC power input N and the first switch (21) and comprises a first coil (11) and a second coil (12).

The first coil (11) and the second coil (12) are respectively formed with multiple turns and respectively have an end, and the second coil (12) is connected to the first coil (11) in series at a node. The end of the second coil (12) is connected to the AC power input N. The node between the first and second coils (11,12) is connected to the second node (213) of the first switch (21).

The second switch (22) is connected to the first switch (21) and the transformer (10) and has a first node (222), a second node (223) and an output node (221). The first node (222) is connected to the end of the first coil (11) and can be a normal close node. The second node (223) is connected to the first node (212) of the first switch (21) and can be a normal open node.

When input voltage is at a normal level, the input node (211) and the output node (221) are switched to respectively connect to the first node (212) of the first switch (21) and the second node (223) of the second switch (22). The input voltage is directly transmitted through the two switches (21,22) as the output voltage.

When input voltage is at a low level, the input node (211) and the output node (221) are switched to respectively connect to the second node (213) of the first switch (21) and the first node (222) of the second switch (22). The ratio of the output voltage to the input voltage is the ratio of the sum of turns of the first and the second coils (11,12) to turns of the second coil (12) and thereby the output voltage is at a higher level than the input voltage.

With such a voltage regulating circuit, the input voltage does not need to pass through the transformer (10) when input voltage is at a normal level and the transformer (10) will not heat up when the transformer (10) needs not to be used. Therefore, the present invention decreases the chance to damage the transformer (10) and can lengthen the span life of the transformer (10).