JP4154977B2 - Multi-output power supply circuit with overcurrent protection circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multi-output power supply circuit that generates a power supply voltage from a single main power supply to a plurality of devices, and more particularly to a multi-output power supply circuit including an overcurrent protection circuit that protects against an overcurrent.
[0002]
[Prior art]
2. Description of the Related Art In recent years, a technique has been developed in which an image around a vehicle is read by a camera and driving assistance or driving substitution is performed. For example, a technique for recognizing a lane by analyzing front and rear images of a vehicle (see Patent Document 1), and images of the rear, left and right, side front, and front of the vehicle are read by a plurality of cameras, respectively. There is a technique (see Patent Document 2) that assists parking by appropriately capturing the image.
[0003]
Thus, in order to operate a plurality of cameras, it is necessary to prepare a power source for each camera. In addition to the camera, when a sensor or actuator is provided, it is necessary to prepare a power source suitable for these devices. Usually, a vehicle is equipped with a battery, and a power supply circuit that supplies voltages (5V, 6V, 3.3V, etc.) suitable for computers, cameras, sensors, and actuators from the battery voltage (usually 12V). Is required. Also, since devices such as cameras are placed away from the battery and control circuit on the vehicle, it is necessary to take into account that the wiring between the control circuit and the device is short-circuited. Therefore, an overcurrent protection circuit is usually placed in a power supply circuit that outputs a necessary voltage from the battery voltage. For example, to protect an output-side transistor that switches the solenoid on / off (hereinafter referred to as an output boost transistor), a current detection resistor is provided to detect the current flowing through the output boost transistor, and this current is specified. There is a technique for turning off the output boost transistor when the value is exceeded (see Patent Document 3), and a technique for a regulator IC incorporating an overcurrent protection circuit as shown in FIG. 6 (see Non-Patent Document 1).
[0004]
[Patent Document 1]
JP 2002-92796 A (FIGS. 1 and 2)
[0005]
[Patent Document 2]
Japanese Patent No. 3298851 (FIG. 1)
[0006]
[Patent Document 3]
Japanese Patent Laid-Open No. 5-146058 (FIGS. 1 and 2)
[0007]
[Non-Patent Document 1]
BIPOLAR AND MOS ANALOG INTEGRATED CIRCUIT DESIGN (page 506 FIGURE 10.17), author: ALAN B. CREBENE, 1984, published by John Wiley & Sons, Inc., USA [0008]
[Problems to be solved by the present invention]
The power supply circuit can be miniaturized by integrating the small power parts excluding the output boost transistor into an IC, and the productivity is improved. However, when it is necessary to place different power supply circuits in a plurality of devices, it is necessary to provide an overcurrent protection circuit for each electron microscope circuit. For this reason, the number of parts, the circuit scale, and the number of circuit input terminals increase in proportion to the number of devices, and thus must be a large IC.
[0009]
Therefore, an object of the present invention is to enable a small IC in a multi-output power supply circuit that supplies a power supply voltage to a plurality of devices, except for an output boost transistor.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention controls a plurality of output boost transistors according to input signals from a plurality of input terminals, respectively, and adjusts voltages to be applied to a plurality of devices. In a multi-output power supply circuit, a plurality of error amplifiers that start operation according to an input signal of an input terminal and adjust a collector voltage to be constant by adjusting a base voltage of a plurality of output boost transistors, and a voltage between a base and an emitter An overcurrent channel detection circuit that determines an output boost transistor with a large current as an output boost transistor in which overcurrent flows, and a current detection resistor provided between the multiple output boost transistors and the main power supply are used as the current flowing through the current detection resistor. Threshold values are compared, and when a current larger than the threshold flows through the current detection resistor, it is detected that an abnormality has occurred, and an overcurrent is detected. It comprises overcurrent detection and current limiting amplifier for limiting stop or current control of boost transistor being a threshold setting circuit for switching threshold according to the input signal of the plurality of input terminals, a.
[0011]
According to this, it becomes possible to supply power according to each device. The threshold value setting circuit switches the threshold value according to an operating device to which a power supply voltage is applied. Here, when one device or a power supply line connected to this device is short-circuited, an overcurrent flows through the current detection resistor. The current limiting amplifier detects this overcurrent and generates an abnormal signal. The voltage between the base and the emitter of the output boost transistor in which the overcurrent flows is larger than the voltage between the base and the emitter of other normal output boost transistors. The overcurrent channel detection circuit determines that an output boost transistor having a large base-emitter voltage is a transistor in which an overcurrent flows, and in response, the current limit amplifier stops controlling only the output boost transistor. Limit current. Therefore, only the output of the channel through which the overcurrent flows is limited, and the circuit is protected. Power is supplied normally to other devices where no overcurrent flows.
[0012]
In order to solve the above problems, the present invention provides an error amplifier, an overcurrent detection / current limit amplifier, a threshold setting circuit, and an overcurrent channel detection circuit according to claim 1. Is composed of one IC.
[0013]
According to this, the part excluding the switching element and the current detection resistor can be constituted by one integrated circuit, and the assembly is simplified.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
FIG. 1 shows an in-vehicle control device that drives two cameras. The power supply circuit receives the 12V system voltage from the in-vehicle 12V battery and outputs the controller voltage Vc. The controller receives input signals from two camera switches provided on the vehicle and outputs two camera power control signals S1 and S2. The power supply circuit receives the camera power control signals S1 and S2 and outputs regulator voltages Vout1 and Vout2 to one or both of the two cameras. When the voltage rises, the camera starts operating.
[0016]
As shown in FIG. 2, the power supply circuit includes an integrated circuit IC1, one current detection resistor R, and output boost transistors Q1 and Q2 for outputting regulator voltages Vout1 and Vout2 of two cameras. In addition to these, although not shown, a circuit for generating a regulator voltage for the controller is also incorporated.
[0017]
The integrated circuit IC1 includes a number of error amplifiers AMP1 and AMP2 corresponding to the respective output boost transistors Q1 and Q2. When the camera power supply control signals S1 and S2 indicate that the camera power supply should be turned on, the error amplifiers AMP1 and AMP2 operate and the output boost transistors Q1 and Q2 are set so that the collector voltages of the output boost transistors Q1 and Q2 are constant. Control. Therefore, constant regulator voltages Vout1 and Vout2 are output. By adjusting the specified voltage VREF applied to the two error amplifiers AMP1 and AMP2 or the value of the internal resistance, the output voltage value can be set to a value corresponding to each camera. Of course, the same voltage value may be used.
[0018]
The switch SW, the comparator CP2, and the NOT circuits NOT1 to NOT3 constitute an overcurrent channel detection circuit. The switch SW is a double switch and connects the operational amplifier AMP3 and the bases of the transistors Q3 and Q4. When this switch SW is turned on, the transistors Q3 and Q4 are turned on / off according to the output of the operational amplifier AMP3. The base voltage of the output boost transistors Q1 and Q2 is applied to the input of the comparator CP2. The comparator CP2 compares the magnitudes of the emitter-base voltages of the output boost transistors Q1 and Q2. The NOT circuits NOT1 to NOT3 operate the switch SW according to the output of the comparator CP2. When the emitter-base voltage of the output boost transistor Q1 is lower than the emitter-base voltage of the transistor Q2, the base of the transistor Q3 and the operational amplifier AMP3 are connected, and the base of the transistor Q4 and the operational amplifier AMP3 are disconnected. When the emitter-base voltage of the output boost transistor Q2 is lower than the emitter-base voltage of the transistor Q1, the base of the transistor Q4 and the operational amplifier AMP3 are connected, and the base of the transistor Q3 and the operational amplifier AMP3 are disconnected.
[0019]
The transistors Q3 and Q4 and the operational amplifier AMP3 constitute an overcurrent detection / current limiting amplifier. When the transistors Q3 and Q4 are on, the base voltages of the output boost transistors Q1 and Q2 are raised, so that the output boost transistors Q1 and Q2 are off or the output current is limited. Therefore, when the output of the operational amplifier AMP3 becomes a low level with the switch SW closed, the output of the voltage to the camera can be stopped regardless of the operation of the error amplifiers AMP1 and AMP2.
[0020]
A reference threshold voltage Vocr and emitter voltages of the output boost transistors Q1 and Q2 are applied to the input of the operational amplifier AMP3. When the output boost transistors Q1 and Q2 are operating, a current flows through the current detection resistor R, and a voltage drop corresponding to this current occurs. When the emitter voltage of the output boost transistors Q1 and Q2 falls below the threshold value, the output of the operational amplifier AMP3 decreases, and the output boost transistors Q1 and Q2 are turned off. At this time, the current flowing through the current detection resistor also decreases. Therefore, the emitter voltage of the output boost transistors Q1 and Q2 exceeds the threshold value, and the output of the operational amplifier AMP3 increases. As a result, the current flowing through the current detection resistor R is limited to a current value that is uniquely determined by the threshold voltage Vocr. However, when the switch SW is turned off, the current limiting function is not effective. The output boost transistor in which an overcurrent flows is determined by an overcurrent channel detection circuit to be described later, and only the output boost transistor in which an overcurrent flows is turned on by turning on the switch SW only in the channel in which the overcurrent flows. The power supply from the other output boost transistors can be normally performed by limiting.
[0021]
Here, if the threshold value is made constant, there is a problem. If the current during camera operation is 200 mA, the current limit should be about 400 mA. However, when two cameras are operating simultaneously, the current flowing through the current detection resistor R is 400 mA, and the current is limited even in a normal case. Therefore, a threshold setting circuit for changing the threshold according to the number of cameras is provided. In FIG. 2, camera power control signals S1 and S2 are input to a NAND circuit. The output of the NAND circuit is applied to the base of transistor Q5. The collector of the transistor Q5 is connected to the gate of the FET transistor Q6. The source of the FET transistor Q6 is connected to the 12V system voltage via the resistor Ra, and the drain is connected to the 12V system voltage via the resistor Rb. The drain is connected to a constant current circuit including an operational amplifier AMP4, a transistor Q7, and a resistor Rc. Here, when both of the camera power supply control signals S1 and S2 are off or one of them is off, the output of the NAND circuit is at a high level, the transistor Q5 is turned on, and the FET transistor Q6 is turned on. A constant current flows through the parallel circuit. On the other hand, when both the camera power control signals S1 and S2 are on, the output of the NAND circuit is at a low level, the transistor Q5 is turned off, and the FET transistor Q6 is turned off, so that a constant current flows through the resistor Rb. Therefore, the threshold voltage Vocr is lowered when both of the camera power control signals S1 and S2 are turned on, so that the current limit value is increased and a larger current can be passed through the current detection resistor R1. . The current limit value is about double (400 mA) of the rated current (for example, 200 mA) of each camera when operating one camera, and is further doubled (800 mA) when simultaneously operating two cameras. The threshold voltage Vocr is determined in advance.
[0022]
In the above configuration, if only the output boost transistor Q1 is operating (S1 is on) and the output Vout1 of the output boost transistor Q1 is short-circuited, an overcurrent flows through the output boost transistor Q1. This overcurrent raises the base-emitter voltage (VBE) of the output boost transistor Q1. The base-emitter voltage (VBE) of the transistor rises according to the collector current as shown in FIG. Since the output boost transistors Q1 and Q2 are arranged in the same power supply circuit, the ambient temperature is substantially the same. Therefore, the output boost transistor Q1 with a large collector current has a larger base-emitter voltage (VBE) than the output boost transistor Q2. The overcurrent channel detection circuit compares the base potentials of the output boost transistors Q1 and Q2, connects the base of the transistor Q3 and the operational amplifier AMP3, and disconnects the base of the transistor Q4 and the operational amplifier AMP3. On the other hand, the voltage drop of the current detection resistor R1 increases due to the overcurrent, and the overcurrent detection / current limiting amplifier starts current limiting. At this time, since only the transistor Q3 operates, the output boost transistor Q1 is current-limited, and the transistor Q2 is not current-limited. Therefore, a normal channel can output a voltage normally.
[0023]
If the threshold voltage Vocr is determined so that the rated current of the camera is 200 mA, when operating one camera, 400 mA, and when operating two cameras simultaneously, the threshold voltage Vocr is determined. The current limit value is 400 mA, and 400 mA flows in the output boost transistor Q1 of the shorted channel. When the output boost transistor Q2 is on, the current limit value is 800 mA, and 200 mA flows through the normal output boost transistor Q2 and 600 mA flows through the shorted channel output boost transistor Q1. The operation of the normal channel output boost transistor Q2 is not hindered.
[0024]
The integrated circuit IC1 is connected to the 12V system voltage from the battery and the ground, the camera power supply control signals S1 and S2, lines connected to the current detection resistors, and the bases and collectors of the output boost transistors Q1 and Q2, except for the controller power supply. It can be composed of 9 terminals. When the power supply for the controller is built-in, two additional parts, the base and collector of the output boost transistor for the controller, are added. The number of terminals is 11.
[0025]
In the above embodiment, in addition to the camera, the present invention can be applied to other devices such as an actuator and a sensor. Further, it may be used for purposes other than in-vehicle use.
[0026]
FIG. 4 shows a power supply circuit (within dotted lines) of n devices 1 to n and one controller. Output boost transistors Q1 to n and Qc for each device 1 to n and controller IC2 are provided. There is one current detection resistor R, and the other part is integrated into the integrated circuit IC1. The number of terminals of this IC is 3 + 3 · n. FIG. 5 shows a configuration having a conventional type current limiting circuit. In this case, the number of terminals is 2 + 4 · n. If the number of channels is large, an enormous number of terminals is required. When the controller is built in the integrated circuit IC1, the terminals for the control signals S1 to Sn from the controller become unnecessary. In the configuration of FIG. 4, the number of terminals is 3 + 2 · n, and in the conventional configuration of FIG. n, and this embodiment requires a much smaller number of terminals.
[0027]
【The invention's effect】
As described above, according to the present invention, it is possible to supply power according to each device, and it is possible to limit the current only to the channel in which the power line is short-circuited, and supply a normal voltage to a normal channel. it can.
[0028]
Further, when the portion excluding the current detection resistor and the output boost transistor is integrated, it can be integrated with a small number of terminals.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of a multi-output power supply circuit of a vehicle-mounted camera according to an embodiment of the present invention.
FIG. 2 is a circuit diagram of the power supply circuit in FIG.
FIG. 3 is a characteristic diagram showing collector current versus base voltage of a transistor.
FIG. 4 is a circuit diagram of a multi-output power supply circuit according to an embodiment of the present invention.
FIG. 5 is a circuit diagram of a multi-output power supply circuit in the prior art.
FIG. 6 is a circuit diagram of a regulator IC having a built-in overcurrent protection circuit in the prior art.
[Explanation of symbols]
AMP1, AMP2 error amplifier
AMP3, AMP4 operational amplifier
VREF Specified voltage
Vocr threshold voltage CP2 comparator IC1 integrated circuit IC2 controller NOT1 to NOT circuit Q1 to n, Qc output boost transistor Q3, Q4, Q5, Q7 transistor Q6 FET transistor R, R1 current detection resistor Ra, Rb, Rc resistor S1, S2 Camera power control signal S1 to n Control signal SW Switch Vout1, Vout2 Regulator voltage Vc Voltage

Claims (2)

In a multi-output power supply circuit that controls a plurality of output boost transistors according to input signals of a plurality of input terminals and adjusts a voltage applied to a plurality of devices, starts operation according to the input signals of the input terminals, and Multiple error amplifiers that adjust the collector voltage to be constant by adjusting the base voltage of the output boost transistor, and the overcurrent that determines the output boost transistor with a large base-emitter voltage as the output boost transistor in which overcurrent flows A current detection resistor is provided between the channel detection circuit, the plurality of output boost transistors, and the main power supply, and a current flowing through the current detection resistor is compared with a threshold value. When it flows, it is detected as abnormal, and control of the boost transistor in which overcurrent is flowing is stopped or An overcurrent detection and current limiting amplifier for limiting a threshold setting circuit for switching said threshold in response to an input signal of said plurality of input terminals,
A multi-output power supply circuit comprising: 2. The multi-output power supply circuit according to claim 1, wherein the error amplifier, the overcurrent detection / current limit amplifier, the threshold setting circuit, and the overcurrent channel detection circuit are configured by a single IC.

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