JPH09215320A - Power circuit for automobile controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a switching-method constant voltage system having a little generation of heat with the minimum number of components by inserting a high-performance CPU which works as an error amplifier, a control ligic section, and a protective circuit in a circuit constituted of a switching element, an inductance, a fly wheel diode, and a reference voltage circuit. SOLUTION: A high-performance CPU 9 is inserted in a circuit constituted of a switching element 1, an inductance 2, a fly wheel diode 3, and a reference voltage circuit 7. Besides the control operation which is the primary job of the high-performance CPU 9, the CPU 9 also works as an error amplifier 4 to which A/D-converted supply voltage and reference voltage are input and a control logic section 6 which controls the switching element 1 by the amount corresponding to an error of the error amplifier 4 and conducts a feedback operation so as to maintain the supply voltage constant at all times. By this method, a switching-method constant voltage system with a little generation of heat can be manufactured with the minimum number of components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for an automobile controller.

[0002]

2. Description of the Related Art Recently, electronic control units for automobiles have been actively promoted to have 16-bit and 32-bit CPUs and high-speed clock frequency in order to achieve higher functionality and higher performance. The current consumption in the market is also increasing. On the other hand, in order to supply a constant voltage (for example, 5 V) to a logic IC such as a CPU in an electronic control unit of an automobile that uses a battery as a voltage source, what is usually called a series type constant voltage circuit is used, but it is small. On the other hand, it is a big problem because it involves heat loss proportional to the circuit current consumption. In order to solve this problem, a switching type constant voltage circuit with less loss has recently been adopted, but it is not widely used because it is more complicated and expensive than the conventional circuit.

[0003]

In the prior art, there has been a problem that an expensive structure is provided regardless of whether a heat radiating means is provided for escaping heat generation or a complicated switching type constant voltage circuit is used. .

An object of the present invention is to provide a power supply circuit having a high degree of freedom of control, with a focus on high function and high performance of a CPU, to achieve a switching constant voltage system with less heat generation with a minimum number of components. is there.

[0005]

A switching regulator generally has a switching element 1, an inductance 2, a flywheel diode 3, an error amplifier 4, an oscillator 5, a control logic section 6, a reference voltage circuit 7, and a protection circuit 8.
However, by including the functions of the error amplifier, the control logic unit, and the protection circuit in the high-performance CPU, the minimum switching element 1, the inductance 2, the flywheel diode 3, the reference voltage circuit 7, the high-performance CPU 9 and the normal CPU With half the functional configuration, the number of parts can be reduced, and an inexpensive and highly reliable switching type constant voltage circuit can be realized.

When the CPU starts to be activated by the auxiliary constant voltage source,
In addition to the original control contents, the CPU functions as an error amplifier that receives the A / D converted power supply voltage and reference voltage as input, and as a control logic that controls the switching element by an amount commensurate with the error, and always supplies a constant power supply voltage. Perform feedback action to maintain.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 2 is a block diagram of an embodiment. In FIG. 2, the voltage from the battery is supplied as Vign through an ignition switch of the vehicle, which is not shown in the figure. The diode 12 directly connected to the Vign line is provided for protection when the battery is reversely connected, the Zener diode 13 is provided for dump surge protection, and the capacitor 14 is provided for stabilizing abrupt external power fluctuation.
A three-terminal voltage regulator IC 15 connected to the cathode of the diode 12 and a capacitor 16 on the output side thereof
The first power supply circuit is composed of
Is connected to Vcc, which is a power supply terminal of the CPU 11, via a diode 17. On the other hand, from the cathode of the diode 12, a switching portion of the second power supply circuit is further constituted by the FET 18, which is a switching element, the choke coil 19, which is an inductance, the smoothing capacitor 22, and the flywheel diode 20, and similarly the output thereof is the CPU 11 Is connected to Vcc which is a power supply terminal of the. Further, the analog input terminal ADIN of the CPU 11
0 and ADIN1 have the same voltage as the voltage obtained by dividing VOUT by resistors 24 and 25 and the primary power supply circuit output VCC11.
The voltage divided by 6 and 27 is input. Also, CP
The PWM output terminal PWMOUT of U11 is connected to drive the gate of the FET 18 via the resistor 23.

Next, the operation will be described. When the ignition switch changes from the off state to the on state, the Vign voltage rises from 0V to almost the battery voltage. As a result, the output voltage of the three-terminal voltage regulator IC15 is also 0V.
To 5V. Then, although not shown in the figure, the CPU is normally operated by the power-on reset circuit arranged in the periphery.
Reference numeral 11 makes a transition from the reset state to the program execution state and starts the execution of the defined program. But the FET
In the second power supply circuit constituted by 18, the choke coil 19 which is an inductance, the smoothing capacitor 22 and the flywheel diode 20, the FET remains off until the control by the program of the CPU 11 starts. After that, when the control program of the second power supply circuit starts running, CP
PWMOUT, which is the PWM output terminal of U11, turns on and off the FET 18 so as to control Vcc constant. Next, the flow of the control program of the second power supply circuit will be described. FET now
When 18 is turned on, the input voltage VIN becomes choke coil 1
9. The smoothing capacitor 22 supplies the LC circuit, and both ends of the capacitor 22 supply the load circuit including the CPU 11. When the FET 18 is turned off, the energy stored in the choke coil 19 is supplied to the load circuit again via the flywheel diode 20. The LC circuit smooths the input and supplies the output voltage. Here, the output voltage VOUT is given by the following equation.

[0009]

[Formula 1] VOUT = TON / (TON + TOFF) * VIN = TON / T * VIN (Formula 1) From Formula 1, VOUT is proportional to the on-duty TON / T. By controlling this on-duty, VOUT is
It can be seen that can be controlled to a constant value. This movement is shown in the control flowchart of FIG. VOUT divided voltage value VOUT '
And the divided voltage value of VCC1 (for example, the same divided voltage as VOUT) VREF is always compared in the AD conversion circuit in the CPU. In step 1, VOUT 'is VC
It is determined whether it is smaller than C1 '. If true, go to step 2, else go to step 3. Conversely, in step 3, VOUT 'is (VREF + VHYS)
Determine if greater than. If true, step 4
Otherwise, exit this control flow. In step 2, the CPU 11 controls the FET 18 so as to increase the on-duty TON / T. Conversely, step 2
In order to reduce on duty TON / T, CP
U11 controls the FET 18. Here, VHYS is a hysteresis voltage for preventing hunting. Ordinary VC
C1 is set to a value slightly lower than VOUT. The reason is that when the VOUT voltage starts to be sufficiently supplied from the second power supply circuit, the current supply by the first power supply circuit is stopped to suppress the heat generation of the three-terminal voltage regulator IC15. Further, in this example, the on-duty TON / T of the FET 8 is gradually increased when the second power supply circuit is activated, and the soft start control for suppressing the inrush current is realized on the program of the CPU 11. With such a configuration, the series type constant voltage circuit is used only for a short time after the key is turned on, but after the program is executed, the switching type constant voltage circuit, which is the second power supply circuit, is switched to for efficient constant voltage operation without heat generation. realizable.

FIG. 4 shows another embodiment. In this example, the voltage Vbat from the battery is directly connected to the second power supply circuit. Although the first power supply circuit is composed of the resistor 15a and the Zener diode 15b, it may be a three-terminal voltage regulator as in the above example. Further, the reference voltage circuit is independently provided by the resistor 26a and the Zener diode 27b. Furthermore, the VC output from the first power supply circuit
C1 is connected to the input terminal D1 of the CPU 11.

Next, the operation will be described. In this example, the control after the ignition switch transitions from the OFF state to the ON state is the same as the above example, but if the ignition switch is detected from ON to OFF, Vign becomes 0V, so the first power supply circuit is stopped. To do. On the other hand, since the second power supply circuit is directly connected to the battery, the constant voltage control is continuously performed by the PWMOUT of the CPU 11. Here, the CPU 11 detects the state of the ignition switch by the DI input, so depending on the program contents, the operation of the second power supply circuit is continued for a certain time after that, and the PWMOUT output is turned off for the first time after the above-mentioned time has elapsed. It is also possible to configure the function of causing. Thus C
Since the supply voltage to the CPU 11 can be controlled by the PU itself, the self-shutoff circuit can be easily constructed.

Further, according to the program, although the CPU itself does not control ON / OFF of the large current load, the VOU
If T suddenly changes, it is judged that there is something wrong such as a short circuit, and CP
FET1 until U11 is restarted (reset start)
It is also possible to implement a protection function that keeps 8 turned off.

[0013]

According to the present invention, it is possible to provide a power supply circuit having a large degree of freedom in control such as soft start while achieving a switching type constant voltage system with less heat generation with a minimum component configuration.

[Brief description of drawings]

FIG. 1 is a system block diagram of a switching constant voltage circuit.

FIG. 2 is a circuit diagram of an embodiment according to the present invention.

FIG. 3 is a switching control flowchart of an embodiment according to the present invention.

FIG. 4 is a circuit diagram of a second embodiment according to the present invention.

[Explanation of symbols]

11 ... CPU, 12, 17 ... Diode, 13, 27a
… Zener diodes, 14, 16… Capacitors, 15
… Three-terminal voltage regulator IC, 18… FET,
19 ... Choke coil, 20 ... Flywheel diode, 22 ... Smoothing capacitor, 23 ... Injector, 2
4, 25, 26, 26a, 27 ... Resistance.

Claims (3)

[Claims] 1. An automobile control device including a CPU, a first constant voltage supply means connected to a power supply terminal of the CPU, a switching element driven by an output of the CPU, an output of the switching element and the CPU. A choke coil connected between the power supply terminals, a diode connected between the output of the switching element and the ground terminal of the CPU, and an A / D converter for taking in the voltage of the power supply terminal of the CPU. (2) A power supply circuit for a vehicle control device, comprising a constant voltage supply means. 2. The power supply circuit for an automobile controller according to claim 1, wherein the voltage by the first constant voltage supply means is smaller than the voltage by the second constant voltage supply means. 3. A power supply circuit for a vehicle control device according to claim 1, wherein the output of the first constant voltage supply means is used as a reference voltage of the second constant voltage supply means.