JP2009011093A - PoE power supply circuit for power receiving equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To connect a power receiving device with many functions because a POE power receiving device has a limit on the maximum power consumption of the power receiving device. There was a problem of not becoming.
A polarity detection circuit 15 for detecting the polarity of an input voltage, switch circuits SW1, SW2, SW3, SW4 connected in parallel to each element of a bridge rectifier diode Di1, Di2, Di3, Di4, and the polarity detection circuit Based on the detection result, the switching circuits SW1, SW2, SW3, SW4 connected in parallel to the elements of the bridge rectifier diodes Di1, Di2, Di3, Di4 are opened and closed, so that the forward current flowing in the rectifier diodes is reduced. And means for bypassing to the switch circuit.
[Selection] Figure 3

Description

  The present invention relates to a power supply circuit of a power receiving apparatus that operates by receiving power supply from a network side.

  As a system that operates by receiving power supply from the network side, a Power over Ethernet (registered trademark) (hereinafter, referred to as a power system) that supplies power using a category 5 LAN cable standardized by IEEE 802.3af in June 2003. PoE).

  In this PoE, the input DC voltage is 48V, but its polarity is not fixed to allow the use of a crossover cable. For this reason, in PoE, a power receiving device (Powered Device) that receives power supply from a corresponding switching HUB or the like includes a bridge rectifier diode in the input stage of the POE power circuit in its power circuit (hereinafter referred to as POE power circuit). ing.

Conventionally, as a bridge rectifier diode used in a power supply circuit, there is a bridge rectifier circuit for rectifying AC power supplied from an AC power supply. In order to reduce loss in a bridge rectifier circuit connected to an AC power supply, a technology for controlling ON / OFF of a switch circuit by connecting a switch element in parallel with a diode and detecting a zero cross is known. Yes. (For example, Patent Document 1)
JP 2002-345250 A

  However, in the conventional configuration, loss caused by the diode bypassed by the switch circuit could be prevented. However, since the polarity is changed with time because it is a rectifier circuit connected to the AC power supply, Since all of the diodes cannot be bypassed, there is a problem in that losses due to the diodes occur. Especially in the power receiving equipment used in POE, there is a limit on the maximum power consumption of the power receiving equipment, so when connecting power receiving equipment with abundant functions, the margin of maximum power consumption is reduced, and the functions and power consumption to be installed are reduced. There was a problem of having to trade off.

  The present invention has been made under the circumstances described above, and an object of the present invention is to provide a power supply circuit that further reduces the loss of the power circuit of the POE power receiving device.

  In order to achieve the above object, the present invention provides a polarity detection circuit for detecting the polarity of an input voltage, a switch circuit connected in parallel to each element of a bridge rectifier diode, and a bridge rectification based on the detection result of the polarity detection circuit. And a means for bypassing forward current flowing in the rectifier diode to the switch circuit by opening and closing a switch circuit connected in parallel to each element of the diode.

  By having such a configuration, the loss in the rectifier diode can be made almost zero.

  As described above, according to the present invention, the loss in the rectifier diode can be reduced to almost zero, so that the margin is increased or the functions to be mounted are increased with respect to the maximum power consumption of the power receiving device limited to 12.95 W. Is possible.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  As an example of a system configuration to which the present invention is applied, PoE will be described with reference to FIG. PoE is a standard that supplies power using a category 5 LAN cable standardized by IEEE 802.3af in June 2003.

  FIG. 1 is a diagram showing the overall configuration of the system. In PoE, a PoE switching HUB2 corresponding to PoE having power supply capability is provided in a system to which a normal switching HUB1 is connected. Since the power supplied from the PoE switching HUB 2 has a power supply capability of 15.4 W at a DC voltage of 48 V, power receiving devices (such as IP telephones 3, LAN switch routers 4, network cameras 5, etc.) having higher functionality than conventional systems. Powered Device) can be connected.

  FIG. 2 is a diagram showing a schematic configuration diagram of the network camera 5 connected to the POE system. The network camera 5 includes a CCD unit 6 including a lens, a signal processing unit 7, and a power supply unit 8.

FIG. 3 is a diagram illustrating a configuration of a power supply unit serving as a connection unit between a network and a power receiving device.
In the POE, the polarity of the supplied DC voltage (48V) is not fixed in order to enable the use of a crossover cable. Therefore, the bridge rectifier diode 10 is provided at the input stage of the POE power circuit of the power receiving apparatus. ing.

  Each bridge rectifier diode 10 includes a diode Di1 provided in the direction from the first input end 11 to the first output end 13, and a diode Di2 provided in the direction from the second output end 14 to the second input end 12. The diode Di3 provided in the direction from the second input end 12 to the first output end 13 and the diode Di4 provided in the direction from the second output end 14 to the first output end 11 are provided. . Switch circuits SW1, SW2, SW3, and SW4 are connected in parallel to the rectifier diodes Di1, Di2, Di3, and Di4, respectively. These switch circuits SW1, SW2, SW3, and SW4 are generally composed of semiconductor elements such as FETs and transistors, but mechanical switch circuits may be used.

  Further, a polarity detection circuit 15 is provided between the first input terminal 11 and the second input terminal 13 to determine the polarity of the power supplied from the POE switching HUB2.

  FIG. 4 is a diagram illustrating an example of a configuration example of the polarity detection circuit 15. The polarity detection circuit 15 compares the voltage at point a on the first input end 11 side with the voltage at point b at the comparator 16 and outputs an output signal 17 when the voltage at point a on the input end 11 side is high. . The output signal is output to SW1 and SW2, and the logic is inverted and output to SW3 and SW4. For this reason, when the voltage at the point a on the first input end 11 side is high, SW1 and SW2 are turned ON (short-circuited), and the diode is bypassed. On the other hand, since SW3 and SW4 are inverted signals, SW3 and SW4 are controlled to be opened.

Conversely, when the voltage (point b) on the second input terminal 13 side is high, control is performed so that SW3 and SW4 are turned on (short circuit) and SW1 and SW2 are opened.
Here, the important point is that both of the two rectifier diodes serving as paths are bypassed by the switch circuit. In other words, in a rectifier circuit connected to an AC circuit as in the prior art, the polarity changes with time, so the operation at zero crossing where the polarity changes may become unstable. It was difficult to bypass the rectifier diode.

  On the other hand, the POE of the present embodiment is a DC power supply although the polarity is unknown, and therefore the polarity does not change with time. Therefore, even if all rectifier diodes on the current path are bypassed, no problem occurs.

Hereinafter, the situation of the voltage drop of the diode will be described.
In a general rectifier diode, the voltage drop is approximately 1V. For this reason, since the current flow goes back and forth through the two diodes, a voltage drop of 2 V occurs in the round trip. For this reason, the potential difference between the first output end 13 and the second output end 14 is 46V.

Here, since the maximum power consumption of the power receiving device is determined to be 12.95 W, the flowing current is
12.95W / 46V = 0.28A
Thus, the power loss in the two rectifier diodes is
2V × 0.28A = 0.56W
It becomes.
In this embodiment, the polarity determination circuit 15 bypasses the detected rectifier diode. For example, when the voltage at point a is high, both SW1 and SW2 are turned on, so the first input terminal 11 → SW1 → first output terminal → load circuit → second output terminal → SW2 → second input terminal. Since current flows through this path, no voltage drop occurs in the current circuit.

  By adopting the above configuration, the present invention can reduce the loss in the rectifier diode to almost zero, so that the margin can be increased or the function to be mounted can be provided for the maximum power consumption of the power receiving device limited to 12.95 W. It becomes possible to increase. For this reason, a surveillance camera with a PAN, TILT, and ZOOM function with abundant functions can be adapted to PoE without trade-off of power consumption.

The figure which shows the whole structure of the system in connection with embodiment of this invention. 6 is a flowchart showing the operation of the schematic configuration diagram of the network camera 5 according to the embodiment of the present invention. The figure which shows the structure of the power supply part in connection with embodiment of this invention. The figure which shows the structural example of the polarity detection circuit in connection with embodiment of this invention

Explanation of symbols

1 ... Switching HUB
2 ... PoE switching HUB
DESCRIPTION OF SYMBOLS 5 ... Network camera 6 ... CCD part 7 ... Signal processing part 8 ... Power supply part 10 ... Diode bridge circuit 15 ... Polarity determination circuit

Claims (2)

In a POE power supply circuit of a power receiving device that operates by receiving power from a network,
A polarity detection circuit that detects the polarity of the input voltage;
A switch circuit connected in parallel to each element of the bridge rectifier diode;
Means for bypassing forward current flowing in the rectifier diode to the switch circuit by opening and closing a switch circuit connected in parallel to each element of the bridge rectifier diode based on the detection result of the polarity detection circuit. A POE power supply circuit.   The POE power supply circuit for a power receiving apparatus according to claim 1, wherein the switch circuit is configured by a semiconductor element.

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