Power feed circuit, rotation detection device, and motor and rotation actuator provided with said rotation detection device

Abstract

A power feed circuit (7c) of an encoder (5) supplies electric power from a main power supply and a battery (8) as driving electric power for a load-side memory unit (7b) via a diode OR circuit (10) provided with a first diode (D1) for reverse current protection and two second diodes (D2, D3) for reverse current protection. The diode OR circuit (10) is provided with a leakage current bypass line (16) that bypasses leakage current of the second diodes (D2, D3) to a ground potential side (GND). The leakage current bypass line (16) is formed from a third diode (D4) and a current limiting resistor (R3). This facilitates component selection and design of the diode OR circuit (10) and allows a resistive voltage divider circuit (15) to perform battery voltage detection properly.

Description

Power supply circuit, rotation detection device, and motor and rotary actuator equipped with the rotation detection device

[0001] The present invention relates to a power supply circuit equipped with a diode OR circuit for use in a battery-backed rotation detection device that stores multiple rotation information of a motor in a built-in memory device, and also to a rotation detection device equipped with the power supply circuit, and a motor and a rotary actuator equipped with the rotation detection device.

[0002] Rotation detection devices, such as rotary encoders, that detect motor rotation information are known to employ a battery backup system to store and retain the detected rotation information. A known power supply circuit that performs battery backup control automatically switches between two different power sources (main power supply and battery) via a diode OR circuit. Figure 5A shows an example of an encoder power supply circuit that supplies power from a motor servo driver power supply (+5V) and a battery (+3.6V) to a load, such as a storage device, via a diode OR circuit equipped with diodes D1 and D2 for backflow prevention. An electronic device equipped with such a power supply circuit is disclosed, for example, in Patent Document 1.

[0003] In the power supply circuit shown in Fig. 5A, if diode D2 connected to the external battery shorts out, power from the servo driver power supply (main circuit voltage +5V) will be applied directly to the external battery, and a charging current will be added to the battery, which could lead to battery destruction or an accident. To prevent such an accident, it is recommended to use two diodes D2 and D3 connected in series as diode D2 in the battery power supply line, as shown in Fig. 5B (see page 22 of Non-Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2006-211829

[0005] Toshiba Lithium Thionyl Chloride Battery Technical Catalog (May 2016), page 22

[0006] As shown in Figure 5B, when two diodes D2 and D3 are connected in series to prevent reverse current in the battery power supply line, the design must take into account the leakage current and voltage drop due to the forward voltage of these diodes. Furthermore, because there is a trade-off between leakage current and voltage drop, component selection and design require considerable effort. For example, using switching diodes or rectifier diodes with low leakage current as these diodes D2 and D3 reduces the charging current to the battery, thereby improving battery safety. However, the forward voltage drop increases, which increases design constraints such as lowering the operating voltage of the internal loads in the circuit, and in some cases may even cause the system to fail. Conversely, using Schottky barrier diodes with low forward voltage drop as these diodes D2 and D3 allows the design to be performed without lowering the operating voltage of the internal loads in the circuit. However, the diode leakage current increases (in other words, the charging current to the external battery increases), reducing battery safety. In addition, as shown in the graph in Figure 5D (excerpt from the data sheet for the ONSEMI BAT54H), the diode leakage current I Ｒ and the voltage drop V due to the forward voltage Ｆ The temperature dependency of the diode also makes the design more complex.

[0007] On the other hand, as shown in FIG. 5C, in a power supply circuit equipped with a diode OR circuit, a resistive voltage divider circuit (R1, R2) for detecting battery voltage may be attached to the battery power supply line to monitor the external battery voltage value within the encoder. In this case, if the battery is suddenly disconnected due to a disconnection or other reason in an environment with large diode leakage current, the leakage current flows through the voltage-dividing resistors R1 and R2 that make up the resistive voltage-divider circuit. As a result, a potential is generated across the voltage-dividing resistors. Ideally, the battery voltage detected by the resistive voltage-divider circuit should be 0 V. However, in such a case, the potential across the voltage-dividing resistors may rise to several volts, preventing normal battery voltage detection and making it impossible to detect a battery disconnection.

[0008] In view of the above, it is an object of the present invention to provide a power supply circuit that supplies power from a main power supply and a battery to a load via a diode-OR circuit, which eliminates the difficulty in selecting and designing components for the diode-OR circuit that is caused by diode leakage current, and which enables normal battery voltage detection using a resistive voltage divider circuit without being affected by the leakage current.It is also an object of the present invention to provide a battery-backed rotation detection device that uses the power supply circuit to supply driving power to a storage device that stores rotation information of a rotating body detected by a rotation information detection unit, and a motor and a rotary actuator that include the rotation detection device.

[0009] The present invention provides a power supply circuit that supplies power from a main power supply and a battery to a load side via a diode OR circuit including a first diode for preventing backflow arranged in a main power supply power supply line and a second diode for preventing backflow arranged in a battery power supply power supply line, the power supply circuit having a leakage current bypass line that bypasses leakage current of the second diode to the ground potential side, the leakage current bypass line including a third diode and a current limiting resistor connected in series with the third diode.

[0010] In the present invention, two diodes connected in series can be used as the second diode, in which case the leakage current bypass line can be connected to the anode of one of the two diodes in the battery power supply line.

[0011] In some cases, the power supply circuit is provided with a resistive voltage divider circuit for detecting battery voltage. The resistive voltage divider circuit can be composed of multiple voltage divider resistors connected in series between the anode of the second diode and the ground potential side of the battery power supply line. In this case, it is desirable to set the resistance value of the current limiting resistor in the leakage current bypass line to a value sufficiently larger than the combined resistance value of the voltage divider resistors in the resistive voltage divider circuit, for example, 100 times or more, to avoid false detection by the resistive voltage divider circuit due to leakage current from the second diode in the event of a battery disconnection or other problem.

[0012] In the present invention, it is preferable that the third diode in the leakage current bypass line is the same component as the second diode in the battery power supply line.

[0013] Next, the power supply circuit of the present invention can be used as a power supply circuit that supplies power from a main power supply and a battery as drive power for a battery-backed rotation detection device that stores rotation information of a rotating body detected by a rotation information detection unit in a built-in storage device. The rotation detection device is incorporated into, for example, a motor or a rotary actuator equipped with a motor and a reducer, and is used to detect motor rotation information or reducer rotation information.

[0014] In the power supply circuit of the present invention, leakage current from the second diode in the diode-OR circuit that prevents backflow flows from the battery power supply line to the leakage current bypass line, preventing it from flowing into the battery as charging current. This simplifies the selection and design of the diodes that make up the diode-OR circuit and also prevents damage to the battery caused by unnecessary charging current.

[0015] FIG. 1B is an explanatory diagram showing an example of a rotary actuator equipped with an encoder (rotation detection device) to which the present invention is applied. FIG. 1C is an explanatory diagram showing a power supply circuit incorporated in the encoder control device shown in FIG. 1A, which supplies power from a motor servo driver power supply and a battery to a load side storage device or the like via a diode OR circuit. FIG. 1B is an explanatory diagram showing the operation of the power supply circuit shown in FIG. 1B. FIG. 1C is an explanatory diagram showing the operation of the power supply circuit shown in FIG. 1B when a battery is disconnected. FIG. 1B is an explanatory diagram showing the operation of the power supply circuit shown in FIG. 1B when a third diode in a leakage current bypass line is short-circuited and destroyed. FIG. 5C is an explanatory diagram showing a power supply circuit of an encoder according to another embodiment of the present invention, in which a leakage current bypass line is connected between two series-connected diodes. FIG. 5C is a graph showing the relationship between temperature and a battery voltage detected by a resistive voltage divider circuit when the battery is connected and when the battery is disconnected (off). FIG. 5C is a graph showing the relationship between temperature and a battery voltage detected by a resistive voltage divider circuit when the battery is connected and when the battery is disconnected (off). FIG. 5C is an explanatory diagram showing a power supply circuit of an encoder that supplies power from a motor servo driver power supply and a battery to a load side via a diode OR circuit. 5B is an explanatory diagram showing an example in which two diodes connected in series to a battery power supply line are used in the power supply circuit of FIG. 5A. FIG. 5B is an explanatory diagram showing an example in which a resistive voltage divider circuit for detecting battery voltage is added to the power supply circuit of FIG. 5B. The diode leakage current I that varies with temperature is Ｒ and the voltage drop V due to the forward voltage Ｆ 1 is a graph (excerpt from the data sheet of BAT54H manufactured by ONSEMI) showing the relationship between

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings, but the present invention is not limited to the configurations of the preferred embodiments.

[0017] FIG. 1A is an explanatory diagram showing an example of a rotary actuator equipped with an encoder (rotation detection device) to which the present invention is applied. The basic configuration of the rotary actuator 1 is common, and includes a motor 2, a reducer 3, a motor controller 4, and an encoder 5. The encoder 5 includes a rotation detector 6 attached to the rear end of the motor 2 and an encoder control unit 7 attached to the motor controller 4. The rotation detector 6 detects the rotation state of the rotating shaft 2a of the motor 2 and the rotation state of the output shaft 3a of the reducer 3. The encoder control unit 7 includes a calculation unit 7a that calculates the rotational position and rotational speed of the rotating shaft 2a and the output shaft 3a based on the detection results by the rotation detector 6, a storage unit 7b that stores and holds the calculated rotation information, and a power supply circuit 7c that supplies power from an external power source to each component. The motor controller 4 includes a control unit 4a, a servo driver 4b, and the like, and controls the drive of the motor 2 based on the rotation information detected and calculated by the encoder 5. The encoder 5 is a battery backup type, and is supplied with a servo driver power supply (for example, main circuit voltage +5V) and a battery 8 (for example, +3.6V) from the motor controller 4 side as external power supplies (drive power sources).

[0018] 1B is an explanatory diagram showing a power supply circuit 7c implemented in a battery-backup type encoder control unit 7. The power supply circuit 7c supplies power from the servo driver power supply of the motor controller 4 and the battery 8 to the load-side storage unit 7b via a diode-OR circuit 10. The diode-OR circuit 10 includes a first diode D1 for preventing backflow and arranged in a main power supply line 12 extending from a main power supply terminal 11, and a second diode for preventing backflow and arranged in a battery power supply line 14 extending from a battery power supply terminal 13 (two second diodes D2 and D3 connected in series in this example). The cathode of the first diode D1 in the main power supply line 12 and the cathode of the second diode D3 in the battery power supply line 14 join together and are connected to the load-side storage unit 7b.

[0019] The power supply circuit 7c is provided with a resistive voltage divider circuit 15 for detecting the battery voltage supplied from the battery 8. The resistive voltage divider circuit 15 has two voltage dividing resistors R1 and R2 connected in series between a position on the battery power supply line 14 between the battery power supply terminal 13 and the second diode D2 and the ground potential side GND, and the battery voltage is detected by monitoring the divided voltage value.

[0020] The power supply circuit 7c is also provided with a leakage current bypass line 16 that bypasses the leakage current from the two second diodes D2 and D3, which flows backward through the battery power supply line 14, to the ground potential side GND. In this example, the leakage current bypass line 16 connects the battery power supply line 14 between the battery power supply terminal 13 and the connection point of the resistive voltage divider circuit 15 and the ground potential side GND. The leakage current bypass line 16 includes a third diode D4 and a current limiting resistor R3 connected directly to the third diode D4. The resistance of the current limiting resistor R3 is set to a value sufficiently smaller than the combined resistance of the voltage-dividing resistors R1 and R2 used to detect the battery voltage. For example, the resistance of the current-limiting resistor R3 is set to 10 kΩ, and the resistances of the voltage-dividing resistors R1 and R2 are set to 3 MΩ and 1 MΩ, respectively.

[0021] 1A and 2A, the operation of the power supply circuit 7c equipped with the leakage current bypass line 16 will be described. When the motor 2 is turned on, the power supply circuit 7c for the encoder 5 is supplied with a +5V drive current from the servo driver power supply, and a lower +3.6V drive current from the battery 8. The +5V drive current from the servo driver power supply, which has a higher voltage, is supplied to the load-side memory unit 7b via the diode OR circuit 10 of the power supply circuit 7c (arrow a1). When power is supplied, a leakage current Ir is generated in the diodes D2 and D3 (arrow a2). The leakage current Ir and the battery consumption current (arrow a3) are divided into a current passing through the voltage-dividing resistors R1 and R2 (arrow a4) and a current flowing through the leakage current bypass line 16 (arrow a5). As a result, a charging current (reverse current) to the battery 8 is prevented.

[0022] More specifically, the potential of the voltage-dividing resistors R1 and R2, i.e., the potential on the anode side of the second diode D2, is the battery voltage +3.6 V, so the current flowing through the voltage-dividing resistors R1 and R2 is limited to +3.6 V / (R1 + R2). The smaller the leakage current Ir, the more the leakage current Ir tends to flow through the voltage-dividing resistors R1 and R2. However, if the leakage current Ir is large, the leakage current tends to flow through sources other than the voltage-dividing resistors. Therefore, by implementing a leakage current bypass line 16 consisting of the third diode D4 and current-limiting resistor R3, the leakage current component that does not flow through the voltage-dividing resistors R1 and R2 but flows back through the battery power supply line 14 can be bypassed, preventing charging current to the battery 8. This is because, due to the characteristics of diodes, leakage current Ir increases in high-temperature environments (see Figure 5D), so the effect becomes greater at higher temperatures.

[0023] 2B , the function and effect of the power supply circuit 7c when the battery 8 is disconnected or suddenly disconnected for some reason will be described. In this case, if the leakage current component of the leakage current Ir that flows through the leakage current bypass line 16 is called the leakage bypass current, the following relationship holds: Leakage current Ir = [Current passing through the voltage dividing resistor] + [Leakage bypass current] The leakage bypass current becomes dominant in the leakage current Ir, and most of the leakage current Ir flows out through the leakage current bypass line 16 as the leakage bypass current.

[0024] On the other hand, if the potential of the voltage dividing resistor (the potential at the anode of the second diode D2) is VBAT_IN, the current passing through the voltage dividing resistor is Ir', and the resistance values ​​of the voltage dividing resistors R1 and R2 are respectively represented by the same notation R1 and R2, the potential of the voltage dividing resistor is expressed by the following equation: VBAT_IN = (R1 + R2) x Ir' As a specific example, when Ir' = 0.375 μA and R1 + R2 = 4 MΩ, then VBAT_IN = 4 MΩ x 0.375 μA = +1.5 V.

[0025] When the battery is disconnected, the resistive voltage divider circuit 15 detects a voltage value corresponding to this +1.5 V. By setting the battery disconnection threshold to +2.5 V (a value greater than +1.5 V), the detected voltage value of +3.6 V before the battery is disconnected becomes +1.5 V when the battery is disconnected, which is below the threshold value of +2.5 V, making it possible to detect a battery disconnection.

[0026] Since the discharge end voltage of a typical lithium-ion battery is between +2.5V and +3V, by setting the battery disconnection threshold to +2.5V and setting the combined resistance of voltage-divider resistors R1 and R2 to 4MΩ or less, the voltage-divider resistor potential VBAT_IN will not exceed +2.5V when the battery is disconnected. Therefore, by implementing the third diode D4 and current-limiting resistor R3, it becomes possible to detect a battery disconnection based on the detected voltage of the resistor voltage-divider circuit. In contrast, without the third diode D4 and current-limiting resistor R3, the voltage of the voltage-divider resistor will exceed 3V when the battery is disconnected, making it impossible to detect a battery disconnection.

[0027] 4A is a graph showing the relationship between temperature and battery voltage (voltage divider resistor potential VBAT_IN) in the power supply circuit 7c of this example when the battery is connected and when the battery is disconnected (when the battery is disconnected). FIG. 4B is a graph showing the relationship between temperature and battery voltage (voltage divider resistor potential VBAT_IN) in the conventional power supply circuit shown in FIG. 5C when the battery is connected and when the battery is disconnected (when the battery is disconnected). Comparing these graphs reveals that, in the power supply circuit of this example, the increase in battery voltage due to temperature rise is suppressed, whereas in the conventional power supply circuit, the battery voltage rises significantly with temperature, exceeding the battery disconnection threshold (+2.5V). In other words, the conventional power supply circuit cannot detect a battery disconnection based on the voltage divider resistor at high temperatures, whereas the power supply circuit of this example avoids this problem.

[0028] Next, referring to FIG. 2C , a description will be given of a case where the third diode D4 of the leakage current bypass line 16 is short-circuited for some reason. The value of the current-limiting resistor R3 of the leakage current bypass line 16 is set to a value sufficiently smaller than the combined resistance of the voltage-dividing resistors R1 and R2 used for detecting the battery voltage. For example, if the voltage-dividing resistor R1 is set to 3 MΩ, the shunt resistor R2 is set to 1 MΩ, and the current-limiting resistor R3 is set to 10 kΩ, when the third diode D4 is short-circuited, the combined resistance Z of these resistors R1, R2, and R3 can approximate the resistance of the current-limiting resistor R3. Therefore, the leakage current Ir flows almost entirely through the current-limiting resistor R3, preventing charging current to the battery. In addition, even if the battery is disconnected at this time, the voltage VBAT_IN of the voltage-dividing resistors will not exceed 2 V, making it possible to detect a battery disconnection.

[0029] If only the third diode D4 is installed in the leakage current bypass line 16 without the current limiting resistor R3, when the third diode D4 shorts out, the positive electrode of the battery will short-circuit with the ground potential GND of the encoder internal circuit, causing a large current to flow from the battery, which is dangerous. Installing the current limiting resistor R3 can avoid this danger.

[0030] (Modification of the power supply circuit) Fig. 3 is an explanatory diagram showing a modification of the power supply circuit described above. The basic configuration of the power supply circuit 7c' shown in this figure is the same as that of the power supply circuit 7c described above, so the same reference numerals are used for corresponding parts and their description will be omitted.

[0031] The difference is that in the power supply circuit 7c' of this example, a leakage current bypass line 16 including a third diode D4 and a current-limiting resistor R3 is placed between the two second diodes D2 and D3 connected in series in the battery power supply line 14. The function and effect of the power supply circuit 7c' with this configuration are the same as those of the power supply circuit 7c described above. Furthermore, this example allows the diodes D1 to D4 to be placed close to each other, improving the design flexibility of their layout. Furthermore, the ability to select a dual-element diode allows for a more compact power supply circuit 7c'. Furthermore, using the same diode as diode D2 or diode D3 as the third diode D4 makes it easier for the leakage current from the second diodes D2 and D3 to flow (bypass) through the third diode D4 as well. Note that a dual-element diode can also be used for the second diode D2 and the third diode D4, or for the second diode D3 and the third diode D4.

Claims

1. A power supply circuit that supplies power from a main power supply and a battery to a load via a diode-OR circuit having a first diode for preventing backflow arranged in the main power supply line and a second diode for preventing backflow arranged in the battery power supply line, the power supply circuit having a leakage current bypass line that bypasses the leakage current of the second diode to the ground potential side, the leakage current bypass line having a third diode and a current limiting resistor connected in series with the third diode.

2. A power supply circuit as claimed in claim 1, wherein the second diode comprises two diodes connected in series, and the leakage current bypass line connects the anode of one of the two diodes in the battery power supply line to the ground potential side.

3. A power supply circuit according to claim 1, further comprising a resistive voltage divider circuit for detecting a battery voltage, said resistive voltage divider circuit comprising a plurality of voltage divider resistors connected in series between the anode of said second diode and the ground potential side of said battery power supply line.

4. A power supply circuit according to claim 3, wherein the resistance value of the current limiting resistor in the leakage current bypass line is 1 / 100 or less of the combined resistance value of the voltage dividing resistors in the resistive voltage dividing circuit.

5. The power supply circuit according to claim 1, wherein the third diode in the leakage current bypass line is the same part as the second diode in the battery power supply line.

6. A battery-backed rotation detection device in which rotation information of a rotating body detected by a rotation information detection unit is stored in a built-in memory device, the rotation detection device comprising a power supply circuit that supplies driving power to the memory device, the power supply circuit being a power supply circuit as defined in any one of claims 1 to 5.

7. A motor equipped with a battery backed-up rotation detection device that stores motor rotation information detected by a rotation information detection unit in a built-in storage device, said rotation detection device being the rotation detection device described in claim 6.

8. A rotary actuator comprising: a motor; a reducer which reduces the output rotation of the motor; and a battery backed-up rotation detection device which stores motor rotation information or reducer rotation information detected by a rotation information detection unit in a built-in storage device, wherein the rotation detection device is the rotation detection device described in claim 6.

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