Power supply circuit

Abstract

To reduce the safety risks associated with lithium-ion batteries. [Solution] The memory function unit comprises a plurality of MOS semiconductors, each connected in parallel with a fuse resistor to the load side from a lithium-ion battery, with drain-source connections; a photorelay, interposed between the battery and the gate terminals of the plurality of MOS semiconductors via a first resistor that applies a gate voltage to the plurality of MOS semiconductors on its output side, and connected to the battery via a second resistor for turning on the photorelay on its input side; a set switch interposed in a first line consisting of the battery, the input side of the photorelay, and the second resistor; a second line connecting one of the drains or sources of one of the plurality of MOS semiconductors to the output terminal of the input side of the photorelay; and a third line connecting the other of the drains or sources to the gate terminal of the MOS semiconductor via a third resistor for removing the gate charge of the MOS semiconductor.

Description

Technical Field

[0001] The present invention relates to a power supply circuit that supplies power from a lithium-ion battery to a load and has a fail-safe characteristic.

Background Art

[0002] Although lithium-ion batteries have various advantages such as high energy density, long life, and low self-discharge rate, it has been pointed out that there is a risk of fire accidents when a short circuit of the load or the like occurs because the internal resistance value of the battery is as low as several milliohms (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Due to the low internal resistance of the lithium-ion battery, it is considered that a large current flows through the load, causing a firing phenomenon.

[0005] Focusing on this point, the present invention aims to provide a power supply circuit that can reduce the safety risk caused by the lithium-ion battery by melting the fuse provided in the fuse resistor when an abnormal large current occurs due to a short circuit of the load or the like.

Means for Solving the Problems

[0006] The power supply circuit according to the present invention comprises a plurality of MOS semiconductors, each with drain-source connections in parallel to the load side via fuse resistors from a lithium-ion battery; a photorelay, interposed between the lithium-ion battery and the gate terminals of the plurality of MOS semiconductors via a first resistor on its output side that applies a gate voltage to the plurality of MOS semiconductors, and connected between the + and - terminals of the lithium-ion battery via a second resistor for turning on the photorelay; a set switch interposed in a first line consisting of the lithium-ion battery, the input side of the photorelay and the second resistor; a second line connecting one of the drains or sources of one of the plurality of parallel-connected MOS semiconductors to the output terminal of the input side of the photorelay; and a third line connecting the other of the drains or sources to the gate terminal of the one MOS semiconductor via a third resistor for removing the charge from the gates of the plurality of parallel-connected MOS semiconductors.

[0007] The power supply circuit according to the present invention is inserted into a fourth line consisting of the lithium-ion battery and the second resistor, and includes a reset switch.

[0008] The power supply circuit according to the present invention is configured such that the resistance value of the first resistor is greater than that of the third resistor, and when a voltage is applied to the gate of the one MOS semiconductor, the drain-source of the one MOS semiconductor is made conductive based on the ratio of the resistance value of the first resistor to the resistance value of the third resistor.

[0009] Conventional power controllers pose risks such as fires caused by lithium-ion batteries due to electrical short circuits resulting from mechanical switch failures caused by component malfunctions, and they cannot detect risks such as overcurrents because the contacts of the electromagnetic relay may fuse together, preventing the electrical circuit from being shut off. In contrast, the power supply circuit according to the present invention uses a MOS semiconductor device, a photorelay, and a fuse resistor to shut off the power supply state by melting the fuse resistor when an overcurrent occurs in the DC current of a lithium-ion battery. If the overcurrent state continues due to a component failure, the power circuit is shut off by melting the fuse resistor, thus providing fail-safe functionality. This reduces the safety risks associated with lithium-ion batteries.

[0010] A power supply circuit according to another aspect of the present invention includes a photorelay, a set switch for supplying power from the power source via a resistor on the input side of the photorelay's light-emitting section, and a voltage applied to the output terminal on the output side of the photorelay and the gate of a MOS semiconductor, thereby causing the MOS semiconductor to conduct and maintaining the same potential as the ground voltage, thus creating a memory function. The voltage applied to the gate is distributed to other gates connected in parallel, causing all parallel-connected MOS semiconductors to conduct, and the drain voltage becomes the ground voltage. This ground voltage is connected to the load terminal via a parallel-connected fuse resistor, and the negative terminal on the power supply side of the lithium-ion battery is connected. The device is connected to the terminals on the side, and a load is connected between it and the positive terminal on the power supply side of the lithium-ion battery. If a current exceeding the current limit of the lithium-ion battery flows due to a short circuit in the load or a short circuit in the MOS semiconductor, the fuse in the fuse resistor melts and the power supply is stopped, thereby ensuring fail-safety and preventing risks such as fires caused by the lithium-ion battery. The reset switch is located at ground potential at the negative terminal of the photorelay, so when necessary for inspection purposes, turning on this reset switch brings it to ground voltage, turning off the output side of the photorelay, eliminating the applied voltage to all gate voltages connected in parallel, and turning off all MOS semiconductors. [Effects of the Invention]

[0011] According to the present invention, safety risks associated with lithium-ion batteries can be reduced under fail-safe conditions, and chattering can be suppressed. [Brief explanation of the drawing]

[0012] [Figure 1] This is a circuit diagram showing the configuration of a power supply circuit according to an embodiment of the present invention. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below with reference to the drawings.

[0014] Figure 1 is a circuit diagram showing the configuration of a power supply circuit according to one embodiment of the present invention, in which the input gate of a commercially available IGBT-type N-type semiconductor MOS transistor is connected by a group of resistors that function as a memory.

[0015] In Figure 1, reference numeral 1 denotes a lithium-ion battery, reference numeral 2 denotes a photorelay that is normally off (no voltage is applied for driving), reference numeral 3 denotes a resistor that supplies the gate voltage, reference numeral 4 denotes a resistor that turns on the photorelay, reference numeral 5 denotes a resistor that removes the charge from the gate, reference numeral 6 denotes an on switch for resetting the memory (normally off), reference numeral 7 denotes an on switch for setting the memory (normally off), reference numeral 8 denotes an N-type MOS semiconductor, reference numeral 9 denotes a fuse resistor, reference numeral 10 denotes the load supply terminal on the + side, reference numeral 11 denotes the terminal that becomes the ground voltage on one side, and reference numeral 12 denotes the direction of the current. Also, reference numeral 13 denotes a light-emitting diode that indicates a blown fuse or an open fault in the N-type MOS semiconductor, and reference numeral 14 denotes a current protection resistor for the light-emitting diode.

[0016] Here, the N-type MOS semiconductor 8 is designed for high currents, and four of them are connected in parallel with the fuse resistors 9. Of course, the present invention is not limited to the number of parallel connections. Here, if the maximum current per semiconductor is X amperes, then since the four semiconductors are connected in parallel, up to four times that amount, or 4X amperes, can flow. Each fuse resistor 9 is designed to blow at X amperes.

[0017] Photorelay 2 is normally off, and the combination of this photorelay 2 and the N-type MOS semiconductor 8 at the bottom of the diagram provides the memory function.

[0018] When the onset switch 7 is turned on, a voltage is applied from the lithium-ion battery 1 to the light-emitting input side of the photorelay 2 via the resistor 4. This causes the output side of the photorelay 2 to conduct, and a voltage is applied from the output terminal on the output side of the photorelay 2 to the gate of each N-type MOS semiconductor 8, causing the drain-source of each N-type MOS semiconductor 8 to conduct.

[0019] Here, the resistance value of resistor 3 is set to be larger than the resistance value of resistor 5, and the ratio of the resistance values ​​of resistor 3 and resistor 5 determines the voltage applied to the gate of the lowest N-type MOS semiconductor 8 in the diagram (referred to as the on-voltage), which causes conduction between the drain-source of the lowest N-type MOS semiconductor 8 and the remaining N-type MOS semiconductors 8. By making conduction between the drain-source of the lowest N-type MOS semiconductor 8 in the diagram with this configuration, the output terminal on the input side, which is the light-emitting part of photorelay 2, becomes at the same potential as the ground voltage (the negative side of the lithium-ion battery) via the drain-source of the lowest N-type MOS semiconductor 8 (when conduction occurs), and an on-voltage is applied to the gate of the lowest N-type MOS semiconductor 8. Even when the set switch 7 is opened and turned off, the photorelay 2 continues to emit light and the on-voltage is applied to the gate of the lowest N-type MOS semiconductor 8, thereby exhibiting a memory function.

[0020] Note that the set switch 7 should normally be kept in the OFF position. This is because resistor 5 is intended to remove any remaining charge from the gate capacitors of each N-type MOS semiconductor 8. The values ​​of resistors 3 and 5 are determined by the characteristics of the N-type MOS semiconductor 8 under the above conditions.

[0021] When the drain-source voltage (during conduction) of the N-type MOS semiconductor 8 at the lowermost part in the figure is in the ground voltage state, if the reset switch 6 is turned on, the secondary side (output side) of the photo relay 2 will turn off. Therefore, no voltage is applied to the gates of the four N-type MOS semiconductors 8 connected in parallel, and all four N-type MOS semiconductors 8 connected in parallel will turn off. As a result, the power supply from the power supply circuit is stopped. However, the present invention is not limited to this as a method for turning off (resetting) the memory function. For example, when turning off (resetting) the memory function, there is a method according to Patent Document 2. When using this method, it is necessary to connect a fuse resistor corresponding to the bias that blows at a maximum of 4×X amperes.

[0022] The power supply circuit configured as described above supplies a load between the + side load supply terminal 10 and the terminal 11 with a ground voltage on the - side by controlling the current while keeping the voltage constant from the lithium ion battery 1.

[0023] For a large current load, due to the current limit of the MOS transistor, the N-type MOS semiconductor 8 is made redundant with respect to the load current and is connected in parallel. On the other hand, since the lithium ion battery 1 has a low internal resistance value and can handle a large current, a current exceeding the current supply capacity of the lithium ion battery 1 may cause a fire. Therefore, in the power supply circuit according to the present embodiment, based on the gate voltage of the circuit by the memory function of the N-type MOS semiconductor 8 and the photo relay 2, a gate voltage is simultaneously applied to the N-type MOS semiconductors 8 connected in parallel, and they are connected through the N-type MOS semiconductors 8 and the fuse resistor 9 connected in parallel, and a large current is applied to the load.

[0024] Although the internal resistance of the lithium-ion battery 1 is said to be low, at a few milliohms, if it becomes even lower for some reason, or if a load or N-type MOS semiconductor 8 short-circuits and a large current flows, there is a risk that the lithium-ion battery 1 may catch fire. To prevent this risk, the lithium-ion battery 1 is connected via a fuse resistor 9. This prevents the fuse in the fuse resistor 9 from blowing and the large current that would cause a risk from flowing, thus ensuring safety against risks to the lithium-ion battery 1 under fail-safe conditions. Furthermore, the blowing of the fuse resistor 9, which is multiplexed in parallel by the light-emitting diode 13 and the current protection resistor 14 for the light-emitting diode, and an open fault in the N-type MOS semiconductor are indicated by the light-emitting diode turning off.

[0025] Furthermore, in the power supply circuit according to this embodiment, the gate control of the N-type MOS semiconductor 8 is performed using the memory function of the photorelay 2. Therefore, even though the switch is mechanically structured, chattering does not occur in the normal set and reset states.

[0026] The present invention is not limited to the embodiments described above, and can be implemented in various modified forms, with the scope of such implementation also falling within the technical scope of the present invention.

[0027] For example, in the above embodiment, an N-type MOS semiconductor 8 was used as the MOS semiconductor, but the same can be done with a P-type MOS semiconductor. In that case, the source of the N-type MOS semiconductor 8 was connected to the negative side of the power supply, but with a P-type MOS semiconductor configured similarly, the source should be connected to the positive side of the power supply.

[0028] Furthermore, the power supply circuit according to the present invention may have a lithium-ion battery 1, or it may be interposed between the lithium-ion battery 1 and the load. [Explanation of Symbols]

[0029] 1. Power supply such as lithium-ion batteries 2. Photorelay is normally off (no voltage is applied for operation). 3. Resistors that supply gate voltage 4. Resistor to turn on the photorelay 5. Resistors for removing charge from gates 6. On switch to reset memory; normally off. 7. On switch for setting memory; normally off. 8 N-type MOS semiconductor 9. Fuse resistor 10+ Load supply terminal 11 - Terminal that becomes the ground voltage on the negative side 12 Current direction 13. Light-emitting diodes that indicate fuse blowouts or open circuit faults in N-type MOS semiconductors. 14. Current protection resistor for light-emitting diodes

Claims

1. Multiple MOS semiconductors are connected in parallel to the load side from a lithium-ion battery, with drain-source connections via fuse resistors, The output side of the photorelay is interposed between the lithium-ion battery and the gate terminals of the multiple MOS semiconductors via a first resistor that applies a gate voltage to multiple MOS semiconductors, and the input side of the photorelay is connected between the positive and negative terminals of the lithium-ion battery via a second resistor for turning on the photorelay. A set switch is inserted into the first line, which is composed of the lithium-ion battery, the input side of the photorelay, and the second resistor. A memory function unit having a second line connecting one of the parallel-connected MOS semiconductors, either the drain or the source, to the input-side output terminal of the photorelay, and a third line connecting the other of the drain or source to the gate terminal of the parallel-connected MOS semiconductor via a third resistor for removing the charge from the gates of the parallel-connected MOS semiconductors. A power supply circuit equipped with the following.

2. A power supply circuit according to claim 1, A reset switch is inserted into the fourth line, which consists of the lithium-ion battery and the second resistor. A power supply circuit equipped with the following.

3. A power supply circuit according to claim 1 or 2, The resistance value of the first resistor is set to be larger than that of the third resistor, and the ratio of the resistance values ​​of the first resistor and the third resistor is configured such that when a voltage is applied to the gate of the first MOS semiconductor, the drain-source junction of the first MOS semiconductor becomes conductive. Power supply circuit.

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