Power circuit

Abstract

To provide a power-supply circuit.SOLUTION: A power-supply circuit according to the present invention that suppresses the back electromotive force generated by a drive unit inside an electronic device includes an ON / OFF switching circuit that turns ON / OFF the power supply to the drive unit inside the electronic device, a time constant circuit that controls a time according to a desired time after the ON / OFF switching circuit, and a voltage control circuit that is connected to the ON / OFF switching circuit and the drive unit so as to delay the fall of the voltage to the drive unit as controlled by the time constant circuit when the ON / OFF switching circuit is turned OFF.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a power supply circuit.

Background Art

[0002] Some surveillance cameras have a zoom - focus function. These zoom - focus functions are usually realized by controlling a stepping motor. In some cases, a switch for turning on / off the motor power is provided in the circuit so that current does not always flow through the motor drive unit.

[0003] This on / off switch may use a transistor, which is a semiconductor. In order to suppress inrush current and the like using this transistor, it may be made to rise gently. In this case, as an example, a load switch may be used (Non - Patent Document).

Prior Art Documents

Non - Patent Documents

[0004] Texas Instruments, "TPS22918 5.5 - V, 2 - A, 52 - mΩ On - Resistance Load Switch Data Sheet (Rev. C)", P11 "7 Parameter Measurement Information" - P15, [online], June 14, 2017, [January 28, 2022], Internet, (https: / / www.ti.com / jp / lit / ds / symlink / tps22918.pdf?ts=1643324135341&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252Fja - jp%252FTPS22918)

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when switching the ON / OFF switch, the current between the power supply and the motor fluctuates rapidly, causing the charge accumulated in the motor's coil to generate a back electromotive force through self-induction. This force can then be transmitted through the power supply within the camera, potentially affecting the video signal.

[0006] For example, there is a wiring method called "one-cable" in which power and video signals are superimposed and transmitted between a surveillance camera and a power supply unit on a single coaxial cable. In cameras that use this one-cable method, the noise caused by the back electromotive force mentioned above can be transmitted to the wiring between the camera and the power supply unit, resulting in video noise.

[0007] To solve the above problem, the present invention turns the motor power ON / OFF The purpose is to control the back electromotive force that occurs when the current between the power supply and the motor fluctuates rapidly after the switch is turned OFF. [Means for solving the problem]

[0008] The present invention relates to a power supply circuit for suppressing back electromotive force generated by a drive unit inside an electronic device, comprising: an ON / OFF switching circuit for switching the power supply to the drive unit inside the electronic device ON / OFF; a time constant circuit downstream of the ON / OFF switching circuit for controlling the time to a desired duration; and a voltage control circuit connected to the ON / OFF switching circuit and the drive unit to delay the rate at which the voltage to the drive unit falls when the ON / OFF switching circuit is turned OFF, according to the control of the time constant circuit. [Effects of the Invention]

[0009] This invention makes it possible to suppress the back electromotive force that occurs when a drive unit or the like is installed in an electronic device and its power is turned off. [Brief explanation of the drawing]

[0010] [Figure 1]Figure 1 shows a camera system 1 including the circuit configuration of the present invention. [Figure 2] Figure 2 shows the circuit configuration of the present invention. [Figure 3] Figure 3 shows the startup circuit. [Figure 4] Figure 4 is a simplified diagram showing the voltage changes at the gate 222 and source 223 of MOSFET 311 when using the circuit configuration of the present invention. [Figure 5] Figure 5 shows the change in voltage at the gate 222 of the motor 32 over time when using the circuit configuration of the present invention. [Figure 6] Figure 6 is a diagram of Embodiment 2 of the present invention. [Modes for carrying out the invention] [Examples]

[0011] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is an example diagram showing a camera system including the circuit configuration of the present invention (hereinafter referred to as camera system 1). Camera system 1 is a camera system comprising a camera 2, a one-cable 4 which is a transmission path connecting camera 2 and power supply unit 5, a power supply unit 5 which supplies power to camera 2 using the one-cable 4 and outputs video signals from camera 2 to recorder 6, and a recorder 6 which receives video from power supply unit 5 and performs recording. Camera system 1 is used, for example, when simultaneously outputting video and supplying power to a surveillance camera using a one-cable, and then extracting and checking only the video afterwards.

[0012] Camera 2 is a permanently installed analog surveillance camera that includes a video / power superimposed circuit 23, a DC / DC converter 24, a power start / power stop circuit and drive unit 3, and a video signal processing unit 25 (not shown) which includes an image sensor that converts captured video into an electrical signal.

[0013] The video / power superimposition circuit 23 is supplied with power from the power supply unit 5 using the single cable 4, superimposes the power supply to the DC / DC converter 24 via the power line 22 and the video signal received from the video signal processing 25 via the video line 21 for the video shot, and transmits it to the power supply unit 5 using the single cable 4.

[0014] The DC / DC converter 24 changes the voltage of the power supply from the video / power superimposition circuit 23 to the voltage required for the drive unit 32 etc. Also, it supplies power via the power line 2 2 to the start-up / shut-down circuit and the drive unit 3.

[0015] The start-up / shut-down circuit and the drive unit 3 consists of the start-up / shut-down circuit 31 and the drive unit 32. The start-up / shut-down circuit 31 performs the start-up and shut-down of the drive of the drive unit 32. Details will be described in FIG. 2.

[0016] The single cable 4 transmits the video signal superimposed by the video / power superimposition circuit 23 to the power supply unit 5 and supplies power to the drive unit etc.

[0017] The power supply unit 5 transmits the power from the commercial power supply via the single cable 4 and supplies power to the entire camera 2 including the drive unit 32. Also, it receives the video signal from the video / power superimposition circuit 23 via the single cable 4 and outputs it to the recorder 6.

[0018] The recorder 6 records and plays back the video output from the power supply unit 5 via the video line 51.

[0019] FIG. 2 describes the details of the start-up / shut-down circuit and the drive unit 3 described in the camera system 1. The start-up / shut-down circuit and the drive unit 3 are configured such that power is input from Vin26 via the DC / DC converter 24 and the drive unit 32 is driven via the start-up / shut-down circuit 31.

[0020] The startup / shutdown circuit 31 consists of a drive unit ON / OFF signal switch 224 that transmits a signal to control the ON / OFF status of the drive unit 32, a capacitor 315 and startup circuit 314 for controlling the startup of the drive unit 32 to be gradual, and a MOSFET 311, capacitor 312, and resistor 313 for controlling the shutdown of the power supply to be gradual and prevent the drive unit 32 from generating back electromotive force.

[0021] First, let's explain how to control the rise time smoothly. When an ON signal is input from the drive unit ON / OFF signal switch 224, charge accumulates in capacitor 315, and the rise time circuit 314 controls the power supply input Vin26 by a voltage control circuit (not shown). Furthermore, as the voltage across capacitor 315 rises, the voltage control circuit is gradually driven in accordance with that voltage. This applies voltage to the gate 222 of MOSFET 311. The voltage at the source 223 of MOSFET 311 also gradually rises in accordance with the voltage at the gate 222, thus controlling the rise time of the voltage in the drive unit 32 to be smooth. Note that when the rise time circuit 314 is driven and MOSFET 311 is driven, capacitor 312 also accumulates charge. Details of the rise time circuit 314 will be explained in Figure 3.

[0022] Next, we will explain how to control the falling edge smoothly. To control the falling edge smoothly, a MOSFET 311, a capacitor 312, and a resistor 313 are used. For this example, an N-type MOSFET is used for MOSFET 311. Therefore, the Vin 26 side becomes the drain 221, the voltage to drive MOSFET 311 is applied to the gate 222, and the source 223 is connected to the drive unit 32. Capacitor 312 and resistor 313 are connected in parallel between gate 222 and the rise circuit 314, and are connected to ground 317 and 318, respectively. By connecting in this manner, when an OFF signal is input from the drive unit ON / OFF signal switch 224, the charge accumulated in capacitor 312 does not flow to MOSFET 311, but instead passes through resistor 313 and startup circuit 314 to ground 318. Therefore, the charge can be controlled to drain slowly over a desired time by adjusting the capacitance of capacitor 312 and the value of resistor 313, and accordingly, the voltage applied to gate 222 also falls slowly over a desired time in accordance with capacitor 312.

[0023] Next, we will explain the drive unit 32. For this explanation, we will describe the drive unit 32 as a motor (hereinafter referred to as motor 32). A source 223 is connected to one end of the motor 32, and ground 322 is connected to the other end. With this connection, a voltage is applied to the source 223 in order to drive the motor 32. Generally, when a load is connected to the source side of a MOSFET, a voltage is also applied to the source side. When connected in this way, the voltage on the source side of the MOSFET follows the voltage on the gate side. This function is called a source follower. By utilizing this property of the MOSFET, the source 223 is connected in such a way that it exhibits a source follower function where the voltage on the source 223 follows the voltage on the gate 222, and by making the falling edge of the voltage on the gate 222 gradual, the voltage on the source 223 also falls gradually. As a result, no sudden voltage difference occurs, and the back electromotive force caused by the charge accumulated in the motor 32 is not generated and is released to ground 322.

[0024] Figure 3 illustrates the details of the startup circuit. Note that the startup circuit 314 in Figure 3 uses a load switch as an example, so this explanation will use the TEXAS INSTRUMENTS TPS22918 as a specific example. The startup circuit 314 consists of a charge pump 340, control logic 342, and N-type MOSFETs 341 and 343. The control logic 342 controls the MOSFET 341 to drive when an ON signal is input from the drive unit ON / OFF signal switch 224. At this time, the capacitor 315 begins to accumulate charge, and the voltage at the gate 352 of MOSFET 341 rises gradually in accordance with the speed at which the charge accumulates, so the voltage at source 353 also rises gradually. As a result, the voltage rise of MOSFET 311 connected to source 353 is also gradual.

[0025] Furthermore, when an OFF signal is input from the drive unit ON / OFF signal switch 224, the control logic 342 stops driving MOSFET 341 and controls it to drive MOSFET 343. As a result of stopping the driving of MOSFET 341, the charge accumulated in capacitor 315 is released to ground 316.

[0026] When MOSFET343 is driven, the charge accumulated in capacitor 312 is discharged through resistor 313 to ground 318. Because the charge accumulated in capacitor 312 passes through resistor 313, unlike free discharge, it is discharged slowly to ground 318 over a time determined by the value of resistor 313 and the capacitance of capacitor 312. At this time, the voltage at gate 222 of MOSFET311 falls in line with the falling edge of the capacitor 312 voltage. Consequently, the voltage at source 223 of MOSFET311 also falls in line with the gate 222 voltage. Although MOSFET343 can also be considered a resistor, in this case its resistance is very small and therefore does not affect the falling edge time.

[0027] The charge pump 340 adjusts the voltage of the gate 352 to make the voltage of the source 353 the same as the voltage of the drain 351. Due to the characteristics of the MOSFET, it consumes voltage when driven, so the voltage of the source 353 is lower than the voltage of the drain 351 by the amount of voltage consumed by the MOSFET 341. Therefore, to prevent the voltage of the source 353 from dropping, the charge pump 340 increases the voltage of the gate 352 to adjust the voltage of the source 353 to be the same as the voltage of the drain 351.

[0028] Figure 4 shows the voltage changes at the gate 222 and source 223 of the MOSFET 311 of the present invention. More specifically, as mentioned above, due to the nature of MOSFETs, voltage is consumed during operation, so the figure shows that the source voltage becomes lower than the gate voltage. Furthermore, as mentioned above, the present invention has a circuit configuration that allows it to exhibit a source follower function, so the figure also shows that the voltage of source 223 follows the voltage of gate 222. Note that VS is the voltage of source 223 and VG is the voltage of gate 222 2 The voltage VGS refers to the power consumption voltage of the MOSFET311.

[0029] This invention achieves the desired rate of fall of the gate 222 voltage by connecting a capacitor 312 and a resistor 313 in parallel between the gate 222 and the rise-up circuit 314, and by connecting each capacitor 312 and resistor 313 to ground 317 and 318, respectively. However, it is sufficient for the capacitor 312 and resistor 313 to be connected in parallel, and they can be connected in any order. The voltage between the gate 222 and the source 223 can be calculated using the formula VS = VG - VGS.

[0030] The following provides a more detailed explanation of the diagram. When an ON signal is input from the drive unit ON / OFF signal switch 224, the rise time circuit 314 causes the VG of MOSFET 311 to rise slowly, and at the same time, VS also rises in accordance with VG. After a certain period of time has elapsed, when VG stabilizes at a constant voltage, the voltage of VS also stabilizes at the same time. However, as mentioned above, due to the characteristics of the MOSFET, VS will be the voltage obtained by subtracting VGS.

[0031] Next, when an OFF signal is input from the drive unit ON / OFF signal switch 224, VG also fluctuates in accordance with the voltage across capacitor 312. Since the charge in capacitor 312 is discharged to ground 318 through resistor 313, the time constants of capacitor 312 and resistor 313 cause VG to fall slowly over a desired period of time. Simultaneously with the fall of VG, VS also falls in accordance. By controlling the source voltage 223 in this way so that it falls over a desired period of time using the time constants of capacitor 312 and resistor 313, the charge accumulated in motor 32 is discharged slowly to ground 322, and no back electromotive force is generated.

[0032] Figure 5 is a simplified diagram showing the change in voltage at the gate 222 of the motor 32 over time when using the present invention. When an ON signal is input from the drive unit ON / OFF switch 224, the voltage rises slowly due to the rise circuit 314. After a certain period of time, the voltage stabilizes, and when an OFF signal is input from the drive unit ON / OFF switch signal 224, the voltage falls slowly due to the MOSFET 311, capacitor 312, and resistor 313. In this invention, since there is a fall-off circuit separate from the rise circuit 314, the fall-off time can be set by the capacitor 312 and resistor 313 to be different from the rise time. Therefore, this diagram shows the case where the fall-off is set to be even slower than the rise time. [Examples]

[0033] Figure 6 shows another embodiment of the present invention. More specifically, it uses a MOSFET 331, which is different from the MOSFET 311 in Example 1. Note that the same reference numerals as in Example 1 refer to the same components, so a detailed explanation is omitted. As mentioned above, the present invention uses a MOSFET 331, which is different from the MOSFET 311 in Example 1. MOSFET 311 is an N-type MOSFET, while MOSFET 331 is a P-type MOSFET. These are well-known transistors, so a detailed explanation is omitted, but the main difference is that the source and drain positions are reversed. Also, unlike Example 1, there is a motor 32 between Vin 26 and MOSFET 331, and there is no motor 32 between MOSFET 331 and ground 319.

[0034] I will explain in more detail below. In this embodiment, the MOSFET 331 has a source 226 between Vin 26 and MOSFET 331. The drain 224 is between MOSFET 331 and ground 319. The position of gate 225 remains unchanged. In other words, the source 224 is the same as in Embodiment 1. 6 Since motor 32 is connected to it, it can perform a source follower function in the same way as in Example 1. Also, capacitor 312 and resistor 313 are connected to gate 225 in the same way as in Example 1. Furthermore, since capacitor 312 and resistor 313 are connected in the same way as in Example 1, the voltage of gate 225 can be lowered in the desired time, in the same way as in Example 1.

[0035] As described above, each embodiment of the present invention has been explained as an example. However, the present invention is not limited to the forms and configurations of this application, and can be applied to embodiments that have been modified, replaced, added, or omitted as appropriate.

[0036] For example, resistor 313 is configured to allow charge to escape to ground 318 through the rise-up circuit 314 when it falls down, but it could also be connected to ground 318 without going through the rise-up circuit 314.

[0037] Furthermore, while the present invention uses MOSFETs 311 and 331 as transistors, any field-effect transistor capable of exhibiting source follower functionality will suffice.

[0038] Furthermore, although the drive unit in this invention is a motor, any motor with low impedance and that easily generates back electromotive force will suffice.

[0039] Furthermore, although this invention uses the TPS22918 from Texas Instruments as an example for the startup circuit, it is not limited to the TPS22918 transistor from Texas Instruments; any semiconductor can be used.

[0040] Furthermore, the present invention is preferably implemented in the following forms. For example, this invention is preferable when it is not possible to obtain a high power supply voltage. In this invention, noise caused by back electromotive force from the drive unit becomes a large noise in the DC / DC converter. Therefore, if the power supply voltage is low to begin with, the DC / DC converter will produce a large noise, making the system more susceptible to noise. Thus, this invention is more effective when it is not possible to obtain a high power supply voltage.

[0041] Furthermore, this invention is preferable for use in cases where parasitic diodes cannot suppress back electromotive force. When suppressing back electromotive force with parasitic diodes, a certain voltage is required to drive the parasitic diode, but if the voltage is lower than that certain voltage, the parasitic diode may not be driven. In such cases, this invention is effective because it suppresses the back electromotive force itself.

[0042] Furthermore, this invention is preferable for analog cameras using a single cable. When using a single cable, the video signal and power supply are superimposed, so noise occurring in the power line can be directly superimposed on the video signal. Therefore, this invention is effective for devices using a single cable. Also, when the video signal of an analog camera is Fourier transformed and viewed in terms of frequency bandwidth, it uses a very wide bandwidth, so even slight noise can affect the bandwidth used by the video. For this reason, this invention is effective when it is desirable to suppress noise when using a wide frequency bandwidth such as that of an analog camera.

[0043] Furthermore, even if a startup circuit is already being used to supply power to the drive unit, the present invention can be added if noise such as back electromotive force occurs during shutdown. As described above, the present invention is not limited to the embodiments and configurations exemplified, but can also be applied to embodiments that are modified, replaced, added, or omitted as appropriate. [Explanation of symbols]

[0044] 1. Overall diagram of the system including the present invention 2 cameras 3. Startup / downstart circuit and drive unit 4 One Cable 5 Power supply machine 6. Recorder 21, 51 Video Line 22 Power Lines 23. Video / Power Overlay Circuit 24 DC / DC Converters 25 Video signal processing unit 26 Vin 31. Startup / Shutdown Power Supply Circuits 32 Drive unit / motor 221, 224, 351 drains Gates 222, 225, and 352 Sources 223, 226, 353 311, 321, 323, 341, 343 MOSFET (N type) 312, 315 Capacitors 313 Resistor 314 Startup Circuit 316, 317, 318, 322 Grand 331 MOSFT (P type) 340 Charge Pump 342 Control Logic

Claims

1. A power supply circuit for suppressing back electromotive force generated by a drive unit inside an electronic device, A startup circuit that outputs a signal to control the power supply to the drive unit, and a circuit provided downstream of the startup circuit, having a capacitor and a resistor, which controls the voltage fall time by discharging the charge stored in the capacitor through the resistor, A MOSFET is connected in series between the power supply and the drive unit, and when the power supply is stopped by the startup circuit, it delays the falling edge of the output voltage to the drive unit in accordance with the voltage controlled by the circuit having the capacitor and the resistor. Equipped with, The MOSFET has the drive unit connected to its source side, and its gate connected to a circuit having the capacitor and the resistor. power circuit.

2. The power supply circuit according to claim 1, wherein the MOSFET is configured to operate as a source follower circuit that causes the output voltage to the drive unit to follow the voltage change of the gate when the power supply is stopped by the startup circuit.

3. The power supply circuit according to Claims 1 to 2, wherein one end of the capacitor is connected to the gate side of the MOSFET and the other end is connected to ground.

4. The power supply circuit according to any one of claims 1 to 3, wherein the drive unit is a motor.

5. The power supply circuit according to any one of claims 1 to 4, wherein the electronic device is an analog camera using a single cable.

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