JP3428536B2 - DC / DC converter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC converter, and more particularly to a DC / DC converter suitable for supplying a DC voltage to a plurality of loads .

[0002]

2. Description of the Related Art A DC / DC converter stably supplies a DC voltage of a predetermined value to a load. However, when supplying a DC voltage to a plurality of loads dispersed from an output section of the DC converter, a DC voltage near each load is provided. The voltage value may vary. For example, when the DC voltage is supplied from the DC converter to the load by the printed wiring, the impedance between the DC / DC converter and the load is limited to the impedance between the DC / DC converter and the load due to various restrictions on the printed wiring board. And the length and thickness of the printed wiring pattern. As a result, in the vicinity of each load, voltage variation occurs due to the voltage drop from the DC converter output section. Further, when the impedance due to the print pattern is large, it may be considered that the voltage regulation value is below the standard, as shown on the left side of FIG.

Therefore, in the conventional DC / DC converter of this type, the output voltage (set voltage) of the DC / DC converter is set to be higher than the target output voltage in consideration of the influence of the voltage drop due to the printed wiring pattern as described above. The method of setting it high beforehand is adopted. That is, the input voltage to the DC / DC converter is switching-controlled so that an output voltage higher than the target output voltage is output. Specifically, the output voltage of the DC / DC converter is set to a higher value of the reference voltage in the error amplifier. For this purpose, the divided voltage value of the DC / DC converter output voltage is normally input to the error amplifier. Error amplifier is DC / DC
The output voltage of the converter is compared with a constant voltage reference voltage, and a signal for switching control is output to the switching control circuit according to the comparison result.
As a result of such setting, DC /
Since the output voltage of the DC converter does not reach the reference voltage for a longer time, the input voltage of the DC / DC converter is switched on for a longer time, and thus the output voltage of the DC / DC converter can be set higher. is there.

[0004]

However, in the above-mentioned conventional DC / DC converter, in order to control the output voltage of the DC / DC converter, only the output voltage of the DC / DC converter is compared with the reference voltage. Therefore, when there are a plurality of loads, there is a first problem that it is difficult to perform an appropriate correction because the voltage drop of each load is different.

Further, since the output voltage (set voltage) of the DC / DC converter is set higher than the target voltage in advance, the DC voltage is output high when the load current is light.
Second, the power consumption of the C / DC converter increases
There is also a problem.

The present invention has been made to solve the above problems. A first object of the present invention is to reduce the output voltage value even when a plurality of loads are located discretely from each other. It is to provide a DC / DC converter that is automatically set to an optimum value in consideration of voltage drop and variation in the vicinity of each load.

A second object is to provide a DC / DC converter capable of suppressing power consumption under light load.

[0008]

[0009]

[0010]

DC / DC converter of the present invention
The barter is a DC / DC that supplies DC voltage to multiple loads.
ON in the converter in response to the switching signal
/ OFF, and a switching circuit for converting the input pulse into ripple DC and smoothing the ripple DC
A smoothing circuit that uses the output voltage of the DC converter, an average voltage generation circuit that obtains an average voltage of the output voltage and a DC voltage near the load with the largest voltage drop from the output voltage, and the average voltage and a predetermined voltage. Compare with reference voltage,
An error amplifier that outputs the difference voltage and a switching control circuit that generates the switching signal by the output of the error amplifier are provided.

More specifically, the average voltage generation circuit compares the output voltage with a DC voltage near the load and outputs a voltage drop from the output voltage to the load in a one-to-one correspondence.
An error amplifier group composed of corresponding error amplifiers, a maximum value detection circuit that outputs the maximum voltage drop value among the outputs of the error amplifier group, and an amount that outputs a value of 1/2 of the maximum voltage drop value. A voltage circuit, and a subtraction circuit that outputs an average voltage of the output voltage and the minimum DC voltage near the load by subtracting 1/2 of the maximum voltage drop value from the output voltage. You may comprise.

Further, an error amplifier is provided which compares the maximum voltage drop value from the maximum value detection circuit with a predetermined reference voltage and, when the maximum voltage drop value is exceeded, triggers the operation of the overcurrent protection circuit incorporated in the switching control circuit. Good.

In the DC / DC converter according to the present invention, when a plurality of loads are located discretely, the output voltage near each load is detected to set the set voltage value of the DC / DC converter to the pattern voltage. This is to automatically correct to an optimum voltage value in consideration of the influence of the drop.

Specifically, in FIG. 1, the voltages in the vicinity of the load 8, the load 9, and the load 10 are detected, and among them, the lowest voltage having the largest voltage drop and the DC / DC converter output section voltage 7 are detected. The switching FET 2 is controlled by comparing the average voltage with the reference voltage 5. As a result, the DC voltage in each load is always within 1/2 of the maximum voltage drop value centering on the target output voltage value, and it is possible to minimize the deviation from the target output voltage value. .

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1 showing an embodiment of the present invention, the present DC / DC converter 1 stably supplies a DC voltage to three loads 8, 9 and 10 which are discretely arranged, Switching FET2, switching FE
It comprises a T control circuit 3, an error amplifier 4 and an average voltage generation circuit 6.

The switching FET 2 controls the width of the pulse input from the left side in accordance with the switching signal from the switching FET control circuit 3 and produces a DC with ripples.
Converted to and output. The smoothing circuit composed of the inductance and the capacitance on the right side of the switching FET 2 smoothes the rippled DC from the switching FET 2 to obtain the DC / DC converter output voltage 7. This D
The C / DC converter output voltage 7 is supplied to the loads 8, 9 and 10 by the printed wiring pattern.

The average voltage generating circuit 6 has the lowest voltage among the DC voltage values in the vicinity of the load 8, the load 9, and the load 10 from the DC / DC converter output section voltage 7, and the DC / DC converter. An average voltage with the output voltage 7 is generated. The error amplifier 4 uses the average voltage generation circuit 6
And the reference voltage 5 are compared, and the difference voltage is output. The switching FET control circuit 3 turns ON / OFF the switching FET 2 according to the output of the error amplifier 4.
A switching signal for performing F control is generated.

FIG. 2 shows the average voltage generating circuit 6 shown in FIG.
3 is a detailed block diagram showing a configuration example of FIG. Referring to FIG. 2, the average voltage generation circuit 6 includes an error amplifier group 1, a maximum value detection circuit 12, a voltage dividing circuit 13, and a subtraction circuit 14. The error amplifier group 11 includes three loads 8,
9 and 10 and three error amplifiers in a one-to-one correspondence, the DC / DC converter output voltage 7 is compared with the DC voltage value near each load, and the DC / DC converter output voltage 7 from each load is compared. Output voltage drop. The maximum value detection circuit 12 outputs the maximum voltage drop value among the outputs of the error amplifier group 11. The voltage dividing circuit 13 outputs a value that is ½ of the maximum voltage drop value. The subtraction circuit 13
A value obtained by subtracting 1/2 of the maximum voltage drop value from the DC / DC converter output section voltage 7, that is, DC / DC
The average voltage of the converter output voltage 7 and the lowest voltage near the load is output.

Next, the operation of this embodiment will be described.

In FIG. 1, the switching FET 2 is
The width of the pulse input from the left side is changed according to the switching signal from the switching FET control circuit 3.
The output of the switching FET2 is converted to DC by the smoothing circuit,
The loads 8, 9 and 10 are supplied. Since the loads 8, 9 and 10 are located separately from the DC / DC converter output voltage 7, they are connected to the DC / DC converter 1 by printed wiring patterns having different lengths and thicknesses. Therefore, the DC / DC converter
The DC voltage actually supplied to the load from 1 has different voltage values in the vicinity of each load due to the voltage drop of the pattern wired on the printed board.

The DC voltage near the load 8, the load 9, and the load 10 and the DC / DC converter output section voltage 7 are introduced to the average voltage generation circuit 6. In the average voltage generation circuit 6, the DC voltage near the load and the DC / DC converter output section voltage 7
Are compared with each other, each voltage drop is detected, and a value obtained by subtracting 1/2 of the maximum value in the voltage drop from the DC / DC converter output section voltage 7 is output. This is D
It is the average voltage of the C / DC converter output voltage 7 and the lowest voltage in the vicinity of the load.

Then, the average voltage and the reference voltage 5 are compared by the error amplifier 4, and the error signal F
The ET control circuit 3 turns ON / OFF the switching FET 2.
To control. That is, the error amplifier 4 changes its output depending on the relative magnitude relationship between the average voltage and the reference voltage. Thereby, if the average voltage is less than the reference voltage, the switching FET control circuit 3
Outputs a switching signal that widens the width of the pulse output by the switching FET2. When the average voltage exceeds the reference voltage, the switching FET control circuit 3 outputs a switching signal that narrows the width of the pulse output by the switching FET 2.

In this way, by controlling the average voltage of the DC / DC converter output section voltage 7 and the minimum voltage near the load to be the target DC voltage value, the DC voltage value near each load is It is possible to minimize the deviation from the target output voltage value by keeping the voltage value within a half of the maximum voltage drop value centering on the target output voltage value. Referring to the right side of FIG. 3, since the DC / DC converter output section voltage 7 is controlled so that the DC voltage value near each load fluctuates around the target output voltage value, a deviation from the target output voltage occurs. It is shown to be minimal.

In the above embodiment, the case where there are three loads has been described, but it is clear that the present invention does not limit the number of loads.

Next, another embodiment of the present invention will be described.

Referring to FIG. 4, in this embodiment,
An error amplifier 16 is added to compare the maximum voltage drop value and the variable reference voltage 15. When the maximum value of the voltage drop near the load exceeds a certain DC voltage value, this additional unit determines that an overcurrent is flowing, and the short protection circuit (included in the switching FET control circuit 30). ) Is operated.

In this embodiment, when the load is far away from the DC / DC converter, that is, the load and the DC / DC converter are
This is effective for short-circuit protection when the impedance between DC converters is large. If the load is located near the DC / DC converter, and if the load is short-circuited due to an interlayer short circuit of the printed wiring board or the like, it is easy to detect the short-circuit due to a large drop in the load voltage.
However, it becomes difficult when the load is far away from the DC / DC converter, that is, when the impedance between the load and the DC / DC converter is large. In the method of operating the short-circuit protection circuit by decreasing the DC / DC converter output section voltage 7, when the load is short-circuited, the DC / DC converter output section voltage 7 does not decrease much due to the impedance of the pattern and the short-circuit protection does not function. Is possible.

In the present embodiment, the reference voltage 15
Is set so that a voltage drop due to an overcurrent when the load is short-circuited can be detected. When the voltage drop maximum value signal input from the average voltage generation circuit 60 exceeds the reference voltage 15, the error amplifier 16 detects a short circuit of the load and operates the short circuit protection circuit.

FIG. 5 is a detailed block diagram of the average voltage generation circuit 60 in this embodiment. It can be seen from comparison with FIG. 2 that the maximum value detection circuit 12 outputs the maximum voltage drop value signal to the error amplifier 16.

[0031]

The first effect of the present invention is that the set voltage value of the DC / DC converter is automatically set to an optimum value in consideration of the voltage drop and variations in the vicinity of each load. . As a result, the output voltage of the DC / DC converter can solve the problem of the related art in which the voltage regulation standard cannot be satisfied near the load.

The reason is that the output voltage of the DC / DC converter is controlled so that the voltage value near each load fluctuates around the target output voltage value as shown on the right side of FIG. This is because the deviation from the output voltage of 1 is minimized.

The second effect is that the power consumption at a light load can be suppressed.

The reason is that the voltage near the load is detected and the output voltage of the DC / DC converter is automatically controlled according to the weight of the load.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a detailed block diagram of an average voltage generation circuit in FIG.

FIG. 3 is a diagram comparing the relationship between the DC / DC output voltage and the target output voltage for the related art and the present invention.

FIG. 4 is a block diagram of a second embodiment of the present invention.

5 is a detailed block diagram of the average voltage generation circuit in FIG.

[Explanation of symbols]

1 DC / DC converter 2 switching FET 3 Switching FET control circuit 4 Error amplifier 5 Reference voltage 6 Average voltage generation circuit 7 DC / DC converter output voltage 8 load 9 load 10 load 11 Error amplifier group 12 Maximum value detection circuit 13 voltage divider 14 Subtraction circuit 15 Reference voltage 16 Error amplifier 30 switching FET control circuit 60 Average voltage generation circuit

Claims (4)

(57) [Claims] 1. A DC / DC device for supplying a DC voltage to a plurality of loads.
In the DC converter, a switching circuit that turns ON / OFF in response to a switching signal and converts an input pulse into a ripple DC; a smoothing circuit that smoothes the ripple DC to obtain an output voltage of the DC / DC converter; An average voltage generation circuit for obtaining an average voltage of the output voltage and the DC voltage in the vicinity of the load having the largest voltage drop, and the average voltage is compared with a predetermined reference voltage, and the difference voltage is output. A DC / DC converter comprising an error amplifier and a switching control circuit that generates the switching signal according to the output of the error amplifier. 2. The average voltage generating circuit compares the output section voltage with a DC voltage near the load,
A load that outputs a voltage drop from the output voltage;
An error amplifier group composed of error amplifiers corresponding to one to one, a maximum value detection circuit that outputs the maximum voltage drop value among the outputs of the error amplifier group, and a value that is 1/2 of the maximum voltage drop value. And a D divider near the load by subtracting ½ of the maximum voltage drop value from the output voltage.
The DC / D according to claim 1, wherein the DC / D is composed of a subtraction circuit that outputs an average voltage of the lowest voltage of the C voltage.
C converter. 3. The overcurrent protection circuit operation is triggered when the voltage drop of the DC voltage near the load from the output voltage exceeds a predetermined value.
The DC / DC converter described in 1. 4. An error amplifier is provided which compares the maximum voltage drop value from the maximum value detection circuit with a predetermined reference voltage and, when the maximum voltage drop value is exceeded, triggers the operation of the overcurrent protection circuit incorporated in the switching control circuit. The DC / DC converter according to claim 3, wherein