JPH07123706A - Dc-dc converter - Google Patents

Abstract

PURPOSE:To prevent the breakdown or deterioration of the switching means of a DC-DC converter while the output voltage and output current of the converter are maintained at prescribed levels. CONSTITUTION:A DC-DC converter is provided with a power supply voltage detecting means 10 which detects the power supply voltage of the converter, frequency switching means 14 which changes the turning-on/off frequencies of switching means 5 and 16 in accordance with the power supply voltage detected by means of the detecting means 10 and the turning-on/off frequencies of the switching means 5 and 16, namely, the turning-on/off frequencies of the DC-DC converter are switched based on the power supply voltage when the converter starts operations.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a DC / DC converter which boosts / decreases the voltage of a DC power source such as a battery to a predetermined voltage and outputs the boosted / downconverted voltage.

[0002]

2. Description of the Related Art Conventionally, DC / DC converters have been widely used in systems in which batteries or DC power supplies are mounted. FIG. 19 shows an example of this type of DC / DC converter.

In FIG. 19, 1 is a battery serving as a power source, 2 is a coil connected to the battery 1 and having a predetermined inductance, 3 is a backflow prevention diode connected to one end of the coil 2, and 4 is a diode 3. An output capacitor of a DC / DC converter connected to the anode side, 5 is a switching transistor for turning on / off the coil 2, 6 is a current detection resistor for detecting a current flowing through the switching transistor 5, and 7 is an anode of the diode 3. And a capacitor circuit connected to the capacitor 4 to smooth the output voltage.

Reference numeral 8 is an output voltage V _{OUT of the} filter circuit 7.
Is an output voltage detection circuit for detecting the output voltage. The voltage output from the output voltage detection circuit is high when the output voltage V _OUT is low, and is low when the output voltage V _OUT is high.
Reference numeral 9 denotes a voltage and current detection resistor 6 from the output voltage detection circuit 8.
Of the operation switch 12 which will be described later, by comparing with the voltage of (1) and inverting them (the former voltage becomes lower than the latter voltage) to output a high level signal (comparison signal). Oscillation circuit 1 by detecting ON / OFF
Control circuit for driving and stopping 3; 12 is DC /
An operation switch for starting the DC converter, 20 is a frequency dividing circuit for frequency-dividing the signal from the oscillation circuit 13, 15 is a maximum duty setting circuit for setting the maximum duty for turning on the switching transistor 15, and 16 is the maximum duty setting. This is a drive circuit that turns on the switching transistor 15 by inputting a signal from the circuit 15, and then turns off the switching transistor 15 when the maximum duty time elapses or when a signal is input from the comparison circuit 9.

In the above structure, the output voltage V of the DC / DC converter when the switching transistor 15 is on.
_OUT is detected by the output voltage detection circuit 8. Comparison circuit 9
Is the output voltage V detected by the output voltage detection circuit 8.
_The voltage correlated to _OUT is compared with the voltage converted by the current detection resistor 6 for the current value corresponding to the coil current, and both are inverted to send a signal to the drive circuit 16. The drive circuit 16 turns off the switching transistor 5 by receiving this signal.

When the above operation is repeated several times, the output voltage V _OUT gradually rises and reaches a predetermined voltage value.

In the DC / DC converter having such a structure, since the switching current is directly detected and controlled, the maximum inrush current can be easily regulated and the switching transistor 5 can be turned on and off. Since the duty resolution is virtually infinite (noise level), it excels in ripples and the like and is very convenient.

In such a DC / DC converter,
In many cases, the power source is a battery that is convenient for portability, and as a recent tendency, it is necessary to be able to obtain a predetermined output voltage and output current at a low voltage because of its small size and light weight.

[0009]

However, in the above-mentioned conventional example, since the predetermined output voltage and output current can be obtained at a low voltage, the battery 1 is replaced or the output voltage V _{OUT is changed.} When the DC / DC converter is started from 0 V, a rush current much larger than the rush current flowing to supply the output current in the steady state is generated until the output voltage V _OUT stabilizes at a predetermined voltage. 1, coil 2,
In many cases, the electrical components were destroyed by continuing to flow in the switching transistor 5 and the current detection resistor 6. In particular, the coil 2 causes magnetic saturation when a current of a predetermined value or more flows, and the inductance component becomes close to "0", so that the phenomenon is virtually equivalent to a power supply short circuit, and the switching transistor 5 is destroyed or deteriorates. It was exhausted.

In order to avoid this, if the output voltage detection circuit 8 is set so as to suppress the inrush current at 0V, the predetermined output current cannot be obtained at the predetermined output voltage at the low voltage, or the steady state is established. However, if there is a load change on the output side after that, the output voltage will change significantly.

(Object of the Invention) An object of the present invention is to provide a DC / DC converter capable of preventing the destruction and deterioration of the switching means while securing a predetermined output voltage and output current.

[0012]

According to the present invention, there is provided a power supply voltage detecting means for detecting a power supply voltage in a control means for driving a switching means so that the voltage detected by the output voltage detecting means becomes a predetermined voltage. ON of the switching means based on the power supply voltage detected by the power supply voltage detection means,
Frequency switching means for changing the off frequency is provided, and
A power supply voltage detecting means for detecting a power supply voltage, and a maximum duty setting means for changing the maximum duty of ON / OFF of the switching means based on the power supply voltage detected by the power supply voltage detecting means are provided. And a voltage correlating to the output voltage detected by the output voltage detection means based on the output of the power supply voltage detection means, and the corrected voltage and the coil current are corrected. DC / DC is provided with switching control means for controlling the switching means according to a corresponding voltage.
Based on the power supply voltage during the operation of the converter, the switching means is turned on and off, that is, the frequency at which the DC / DC converter is turned on or off, or the maximum duty to be turned on is switched, and the voltage is correlated to the output voltage. I try to put it on.

Further, according to the present invention, in the control means for driving the switching means so that the voltage detected by the output voltage detecting means becomes a predetermined voltage, the time counting operation is interlocked with the operation start of the DC / DC converter. And a frequency switching means for changing the on / off frequency of the switching means in accordance with the output of the counting means, and the clocking operation is linked with the operation start of the DC / DC converter. A counting means for starting and a maximum duty setting means for changing the on / off maximum duty of the switching means according to the output of the counting means are provided, and the clocking operation is linked with the operation start of the DC / DC converter. And the output voltage detected by the output voltage detection means according to the output of the counting means A switching control unit that corrects the pressure and controls the switching unit according to the corrected voltage and the voltage corresponding to the coil current is provided, and the output voltage is stable after the operation of the DC / DC converter is started, for example. Until (when it reaches the specified voltage)
On / off of the switching means, that is, the on / off frequency of the DC / DC converter, or the maximum duty to be turned on is switched based on the output of the counting means for counting I try to put it on.

Further, according to the present invention, a current detecting means for detecting a current correlated with a current flowing through the coil, a detecting means for detecting that the output from the current detecting means is larger than a predetermined current value, and the detecting means. A switching control means for forcibly turning off the switching means is provided by the detection by, and the switching means is forcibly turned off when the current correlated with the current flowing to the coil exceeds a predetermined current value. There is.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the illustrated embodiments.

FIG. 1 shows a DC according to the first embodiment of the present invention.
3 is a block diagram showing a schematic configuration of a / DC converter, FIG.
The parts having the same functions as those in FIG.
Most of the description is omitted.

In FIG. 1, 10 is a power supply voltage detection circuit connected to the positive side of the battery 1 for detecting the power supply voltage V _BAT , and 14 is for dividing the clock signal (b) from the oscillation circuit 13 and for supplying the power supply. A frequency switching circuit for switching the divided output according to the output from the voltage detection circuit 10, 15
Is a maximum duty setting circuit that receives the output (c) from the frequency switching circuit 14 and sets the maximum duty of the switching transistor 5 in the ON period and the OFF period, and 16 is an output from the maximum duty setting circuit 15 and the comparison circuit 9. Direct switching transistor 5 by (d, f)
Is a drive circuit for driving the.

The operation of the DC / DC converter configured as described above will be described with reference to the timing charts of FIGS. 2 and 3.

First, the operation when the voltage V _BAT of the battery 1 is relatively high will be described with reference to the timing chart of FIG.

First, when the operation switch 12 for activating the DC / DC converter is turned on, the signal a changes from high level to low level. As a result, the oscillation start signal is sent from the control circuit 11 to the oscillation circuit 13, and the oscillation circuit 13
Starts oscillating (signal b). At the same time, the power supply voltage detection circuit 10 detects the voltage V _{BAT of the} battery 1 and sends the result to the frequency switching circuit 14. Frequency switching circuit 14
Divides the frequency of the clock signal b from the oscillating circuit 13, switches the frequency at which the switching transistor 5 is turned on and off by the output from the power supply voltage detecting circuit 10, and sends this to the maximum duty setting circuit 15. This time, a relatively high frequency is selected because the power supply voltage V _BAT is high (see signal c in FIG. 2). The maximum duty setting circuit 15 sets the maximum duty for the ON period and the OFF period of the switching transistor 5, and sends this to the drive circuit 16 as a signal d.

On the other hand, before the DC / DC converter is started, the switching transistor 5 is turned off, and a certain voltage is output as the output voltage V _OUT through the battery 1, the coil 2, the diode 3 and the filter circuit 7. The output voltage V _OUT is detected by the output voltage detection circuit 8 becomes higher enough low correlated voltage (V _OUT to the output voltage V _OUT,
The higher the voltage, the lower the voltage) is output. The comparator circuit 9 compares this value and the current value corresponding to the coil current with the current detection resistor 6
Compare with the value converted into voltage value.

Here, when the DC / DC converter is started, the switching transistor 5 is turned on, and the inrush current is roughly according to the equation shown by I = V _BAT / L × t _ON (1) Flows. Note that I
Is a rush current flowing through the coil 2, that is, the switching transistor 5 and the current detection resistor 6, L is an inductance of the coil 2, and t _ON is a time during which the switching transistor 5 is on.

In FIG. 2, the power supply voltage V _BAT is relatively high,
That is, although the slope of the voltage e is steep, t _ON is set short by the power supply voltage detection circuit 10 and the frequency switching circuit 14 so that the inrush current exceeds the magnetic saturation current of the coil 2 and the maximum rating of the switching transistor 5. It is set not to. Further, the output voltage from the output voltage detection circuit 8 has a high value because the output voltage V _{OUT is} almost 0 V, and the coil current must also increase accordingly, but it depends on the maximum duty t _ON time. The electricity was cut off before.

The signal d from the maximum duty setting circuit 15
As a result, when the switching transistor 5 is turned off after the time t _ON , the coil 2 works to flow a current, and the current flows through the diode 3 to the capacitor 4 side. Then, the output voltage V _OUT rises slightly.

Then, in the next cycle, the switching transistor 5 is turned on again, and the same operation is repeated thereafter.

When the above operation is repeated several times, the output voltage V _OUT gradually rises (see FIG. 2). The output voltage detection circuit 8 detects this voltage as described above and outputs a voltage correlated therewith, and the comparison circuit 9 outputs this value and the voltage e corresponding to the current obtained by the above equation (1). Compare. Here, the output voltage detection circuit 8 outputs the output voltage V _OUT
Is higher than the previous time, a lower voltage is output than the previous time, and therefore the comparison circuit 9 has a lower voltage value,
That is, the comparison signal is output at a lower current value. Then, it becomes smaller than the coil current of the above formula (1). Then, the output signal f of the comparison circuit 9 causes the drive circuit 9 to turn off the switching transistor 5 even within the maximum duty period.

The DC / DC converter in this embodiment operates as described above, and when the power supply voltage V _BAT is high, a sufficient output voltage and output current can be obtained, inrush current is suppressed, and element deterioration and There is no destruction.

Next, the operation when the voltage V _{BAT of the} battery 1 is low will be described with reference to the timing chart of FIG.

First, when the operation switch 12 for activating the DC / DC converter is turned on, the signal a changes from high level to low level. As a result, the oscillation start signal is sent from the control circuit 11 to the oscillation circuit 13, and the oscillation circuit 13
Starts oscillating (signal b). At the same time, the power supply voltage detection circuit 10 detects the voltage V _{BAT of the} battery 1 and sends the result to the frequency switching circuit 14. Frequency switching circuit 14
Divides the frequency of the clock signal b from the oscillating circuit 13, switches the frequency at which the switching transistor 5 is turned on and off by the output from the power supply voltage detecting circuit 10, and sends this to the maximum duty setting circuit 15. This time, a relatively low frequency is selected because the power supply voltage V _BAT is low (see signal c in FIG. 3). The maximum duty setting circuit 15 sets the maximum duty for the ON period and the OFF period of the switching transistor 5, and sends this to the drive circuit 16 as a signal d.

On the other hand, before the DC / DC converter is activated, the switching transistor 5 is off, and a certain voltage is output as the output voltage V _OUT through the battery 1, the coil 2, the diode 3 and the filter circuit 7. The output voltage V _OUT is detected by the output voltage detection circuit 8 and output as a voltage correlated with the output voltage V _OUT . Comparison circuit 9
Compares this value with the current value corresponding to the coil current converted into a voltage value by the current detecting resistor 6.

Here, when the DC / DC converter is activated, the switching transistor 5 is turned on, and an inrush current flows in accordance with the equation (1).

In FIG. 3, since the power supply voltage V _BAT is low, that is, the slope of the voltage is gentle, even if t _ON is set to be long by the power supply voltage detection circuit 10 and the frequency conversion circuit 14, a predetermined inrush current is obtained. It is set so that it can be limited to a value. Since the inrush current at this time can flow almost the same as when the power supply voltage V _BAT is high, it is possible to take a predetermined output voltage and output current.

When the maximum duty setting circuit 15 turns off the switching transistor 5 after the time t _ON , the coil 2 works to pass a current, and a current flows through the diode 3 to the capacitor 4 side. Then, the output voltage V _OUT rises slightly.

Then, in the next cycle, the switching transistor 5 is turned on again, and the same operation is repeated thereafter.

When the above operation is repeated several times, the output voltage V _OUT gradually rises (see FIG. 3). The output voltage detection circuit 8 detects this voltage as described above and outputs a voltage corresponding to this, and the comparison circuit 9 outputs this value and the voltage e corresponding to the current obtained by the above equation (1). Compare. Here, the output voltage detection circuit 8 outputs the output voltage V _OUT
Is higher than the previous time, a lower voltage is output than the previous time, and therefore the comparison circuit 9 has a lower voltage value,
That is, the comparison signal is output at a lower current value. Then, it becomes smaller than the coil current of the above formula (1). Then, by the output signal f of the comparison circuit 9, the drive circuit 9 turns off the switching transistor 5 even within the maximum duty period. This operation continues until the output voltage reaches the target predetermined voltage, and also works to supply a current corresponding to the output current every time after stabilization.

As described above, when the power supply voltage is low, the frequency at which the switching transistor 5 is turned on and off becomes low. Therefore, it is necessary to keep the inrush current within a predetermined value while maintaining a stable output voltage. Output current can be supplied.

In this embodiment, DC using a coil is used.
Although the / DC converter has been described, the same effect can be obtained by using this as a transformer type DC / DC converter.

Further, an example in which the frequency is divided once by the frequency switching circuit and an example in which the frequency is divided twice are shown, but the invention is not limited to this.

Further, only two cases, that is, the case where the power supply voltage is high and the case where the power supply voltage is low, are shown, but the same effect can be obtained even if this distinction is plural or stepless.

(Second Embodiment) FIG. 4 is a block diagram showing a schematic structure of a DC / DC converter according to a second embodiment of the present invention. The parts having the same functions as those in FIG. There is.

The difference from the configuration of FIG. 1 is that the output from the power supply voltage detection circuit 10 is not the frequency switching circuit 14,
This is a point input to the maximum duty setting circuit 15, and the maximum duty is changed by this signal.

The operation of the DC / DC converter configured as described above will be described with reference to the timing charts of FIGS.

First, the operation when the voltage V _BAT of the battery 1 is relatively high will be described with reference to the timing chart of FIG.

First, when the operation switch 12 for activating the DC / DC converter is turned on, the signal a changes from high level to low level. As a result, the oscillation start signal is sent from the control circuit 11 to the oscillation circuit 13, and the oscillation circuit 13
Starts oscillating (signal b). The frequency switching circuit 14 to which the signal b is input divides the frequency into a predetermined frequency and sends it as a signal c to the maximum duty setting circuit 15. At the same time, the power supply voltage detection circuit 10 _causes the voltage V _{BAT of the} battery 1 to _rise.
Is detected, and the result is detected by the maximum duty setting circuit 1
Send to 5. The maximum duty setting circuit 15 sets the maximum duty in the ON period and the OFF period of the switching transistor 5 based on the output from the power supply voltage detection circuit 10,
This is sent to the drive circuit 16 as a signal d. This time, a relatively low duty ratio is selected because the power supply voltage V _BAT is high.

On the other hand, before the DC / DC converter is activated, the switching transistor 5 is off, and a certain voltage is output as the output voltage V _OUT through the battery 1, the coil 2, the diode 3 and the filter circuit 7. The output voltage V _OUT is detected by the output voltage detection circuit 8 becomes higher enough low correlated voltage (V _OUT to the output voltage V _OUT,
The higher the voltage, the lower the voltage). Comparison circuit 9
Compares this value with the current value corresponding to the coil current converted into a voltage value by the current detecting resistor 6.

Here, when the DC / DC converter is activated, the switching transistor 5 is turned on, and an inrush current flows in accordance with the equation (1).

In FIG. 5, the power supply voltage V _BAT is high, that is, the slope of the voltage e is steep, and the current flowing through the coil 2 also increases in normal control, but the power supply voltage detection circuit 10,
Since the maximum duty is set to a low value by the maximum duty setting circuit 15, t _ON is shortened, and the predetermined inrush current is suppressed.

With this maximum duty setting circuit 15, t
_{When the} switching transistor 5 is turned off after being turned on, the coil 2 works to pass a current, and the current flows to the capacitor 4 side via the diode 3. Then, the output voltage V _OUT rises slightly.

Then, in the next cycle, the switching transistor 5 is turned on again, and the same operation is repeated thereafter.

When the above operation is repeated several times, the output voltage V _OUT gradually rises (see FIG. 5). The output voltage detection circuit 8 detects this voltage as described above and outputs a voltage corresponding to this, and the comparison circuit 9 outputs this value and the voltage e corresponding to the current obtained by the above equation (1). Compare. Here, the output voltage detection circuit 8 outputs the output voltage V _OUT
Is higher than the previous time, a lower voltage is output than the previous time, and therefore the comparison circuit 9 has a lower voltage value,
That is, the comparison signal is output at a lower current value. Then, it becomes smaller than the coil current of the above formula (1). Then, the output signal f of the comparison circuit 9 causes the drive circuit 9 to turn off the switching transistor 5 even within the maximum duty period.

The DC / DC converter in the second embodiment operates as described above, and because the power supply voltage is high, a sufficient output voltage and output current can be obtained even when the maximum duty is relatively low, and the rush current is high. The current is suppressed, and the deterioration or destruction of the element is eliminated.

Next, the operation when the voltage V _{BAT of the} battery 1 is low will be described with reference to the timing chart of FIG.

First, when the operation switch 12 for activating the DC / DC converter is turned on, the signal a changes from high level to low level. As a result, the oscillation start signal is sent from the control circuit 11 to the oscillation circuit 13, and the oscillation circuit 13
Starts oscillating (signal b). The frequency switching circuit 14 to which the signal b is input divides the frequency into a predetermined frequency and sends it as a signal c to the maximum duty setting circuit 15. At the same time, the power supply voltage detection circuit 10 _causes the voltage V _{BAT of the} battery 1 to _rise.
Is detected, and the result is detected by the maximum duty setting circuit 1
Send to 5. The maximum duty setting circuit 15 sets the maximum duty in the ON period and the OFF period of the switching transistor 5 based on the output from the power supply voltage detection circuit 10,
This is sent to the drive circuit 16 as a signal d. This time, a relatively high duty ratio is selected because the power supply voltage V _BAT is low.

On the other hand, before the DC / DC converter is activated, the switching transistor 5 is turned off, and a certain voltage is output as the output voltage V _OUT through the battery 1, the coil 2, the diode 3 and the filter circuit 7. The output voltage V _OUT is detected by the output voltage detection circuit 8 and output as a voltage correlated with the output voltage V _OUT . Comparison circuit 9
Compares this value with the current value corresponding to the coil current converted into a voltage value by the current detecting resistor 6.

Here, when the DC / DC converter is activated, the switching transistor 5 is turned on, and an inrush current flows in accordance with the equation (1).

In FIG. 6, since the power supply voltage V _BAT is low, that is, the slope of the voltage e is gentle, the current flowing through the coil cannot be taken in the normal control, but the power supply voltage detecting circuit 1
0, the maximum duty is set to a high value by the maximum duty setting circuit 15, so that t _ON becomes long and is suppressed to a predetermined inrush current.

With this maximum duty setting circuit 15, t
_{When the} switching transistor 5 is turned off after being turned on, the coil 2 works to pass a current, and the current flows to the capacitor 4 side via the diode 3. Then, the output voltage V _OUT rises slightly.

Then, in the next cycle, the switching transistor 5 is turned on again, and the same operation is repeated thereafter.

When the above operation is repeated several times, the output voltage V _OUT gradually rises (see FIG. 6). The output voltage detection circuit 8 detects this voltage as described above and outputs a voltage corresponding to this, and the comparison circuit 9 outputs this value and the voltage e corresponding to the current obtained by the above equation (1). Compare. Here, the output voltage detection circuit 8 outputs the output voltage V _OUT
Is higher than the previous time, a lower voltage is output than the previous time, and therefore the comparison circuit 9 has a lower voltage value,
That is, the comparison signal is output at a lower current value. Then, it becomes smaller than the coil current of the above formula (1). Then, the output signal f of the comparison circuit 9 causes the drive circuit 9 to turn off the switching transistor 5 even within the maximum duty period.

As described above, when the power supply voltage V _BAT is low, the time during which the switching transistor 5 is turned off becomes long, that is, the maximum duty becomes long.
It is possible to supply a necessary current with a stable output voltage while suppressing the inrush current within a predetermined value.

Although the DC / DC converter using the coil has been described in this embodiment as well, the same effect can be obtained by using it as a transformer type DC / DC converter.

Also, an example has been shown in which the maximum duty is set to 50% and 75% in the maximum duty setting circuit, but the present invention is not limited to this.

Further, only two cases, that is, the case where the power supply voltage is high and the case where the power supply voltage is low, are shown, but the same effect can be obtained even if this distinction is plural or stepless.

(Third Embodiment) FIG. 7 is a block diagram showing the schematic arrangement of a DC / DC converter according to the third embodiment of the present invention. The parts having the same functions as those in FIG. There is.

The difference from the configurations of FIGS. 1 and 4 is that the output from the power supply voltage detection circuit 10 is input to the comparison circuit 9, and the level from the output voltage detection circuit 8 is changed by this signal. I am trying.

[0066] That is, in equation (1), since the rush current is proportional to the supply voltage V _BAT, when the power supply voltage V _BAT is high, the output voltage detecting circuit 8 for comparing the voltage value corresponding to the coil current By lowering the output value of (the output voltage after being varied according to the power supply voltage is referred to as a comparison level), the switching transistor 5 is turned off before the maximum duty is _reached , and the power supply voltage V _BAT
If is low, by increasing the comparison level,
The switching transistor 5 is turned off up to the maximum duty.

The operation of the DC / DC converter configured as above will be described with reference to the timing charts of FIGS. 8 and 9.

First, the operation when the voltage V _BAT of the battery 1 is relatively high will be described with reference to the timing chart of FIG.

First, when the operation switch 12 for activating the DC / DC converter is turned on, the signal a changes from the high level to the low level. As a result, the oscillation start signal is sent from the control circuit 11 to the oscillation circuit 13, and the oscillation circuit 13
Starts oscillating (signal b). The frequency switching circuit 14 to which the signal b is input divides the frequency into a predetermined frequency and sends it as a signal c to the maximum duty setting circuit 15. The maximum duty setting circuit 15 sets the maximum duty of the ON period and the OFF period of the switching transistor 5 based on the output from the power supply voltage detection circuit 10, and sends this to the drive circuit 16 as a signal d.

On the other hand, before the DC / DC converter is activated, the switching transistor 5 is off, and a certain voltage is output as the output voltage V _OUT through the battery 1, the coil 2, the diode 3 and the filter circuit 7. The output voltage V _OUT is detected by the output voltage detection circuit 8 becomes higher enough low correlated voltage (V _OUT to the output voltage V _OUT,
The higher the voltage, the lower the voltage). Comparison circuit 9
Compares this value with the current value corresponding to the coil current converted into a voltage value by the current detecting resistor 6. At that time, the comparison level of the comparison circuit 9 is changed according to the value of the battery voltage V _BAT detected by the current voltage detection circuit 10.

In FIG. 8, the comparison level is low because the power supply voltage V _BAT is relatively high. Then, since the output voltage V _OUT is originally low, the output of the output voltage detection circuit 8 becomes high, and the comparison circuit 9 generates the output signal f when the coil current becomes large, but the output of the power supply voltage detection circuit 8 is generated. Is lower than the original voltage, the output signal f is small when the coil current is small.
To occur. Therefore, deterioration of the element due to inrush current,
Does not cause destruction. In terms of electric power, as indicated by "P = IV", although the rush current is low, the voltage is originally high, so that it is possible to obtain a sufficient output voltage and output current.

When the DC / DC converter is activated, the switching transistor 5 is turned on, and a rush current flows in accordance with the equation (1). Then, the comparison circuit 9 compares the voltage from the output voltage detection circuit 8 with the voltage e corresponding to the coil current, but the power supply voltage detection circuit 10
Due to this, the comparison level is lowered, and the signal f is generated when it becomes equal to that value. When the signal f is generated, the drive circuit 16 forcibly turns off the switching transistor 5 even though the off period of the maximum duty is not yet reached.

When the switching transistor 5 is turned off, the coil 2 works to flow a current, and the current flows through the diode 3 to the capacitor 4 side. Then the output voltage V
_OUT rises slightly.

Then, in the next cycle, the switching transistor 5 is turned on again, and the same operation is repeated thereafter. Then, the output voltage gradually approaches the target predetermined voltage, and the maximum inrush current also gradually decreases with it.

When the power supply voltage is high as described above, the maximum inrush current is suppressed to a low level, so that deterioration or destruction of the element does not occur, and sufficient output voltage and output current can be obtained in terms of power. it can.

Next, the operation when the voltage V _{BAT of the} battery 1 is low will be described with reference to the timing chart of FIG.

First, when the operation switch 12 for activating the DC / DC converter is turned on, the signal a changes from the high level to the low level. As a result, the oscillation start signal is sent from the control circuit 11 to the oscillation circuit 13, and the oscillation circuit 13
Starts oscillating (signal b). The frequency switching circuit 14 to which the signal b is input divides the frequency into a predetermined frequency and sends it as a signal c to the maximum duty setting circuit 15. The maximum duty setting circuit 15 sets the maximum duty of the ON period and the OFF period of the switching transistor 5 based on the output from the power supply voltage detection circuit 10, and sends this to the drive circuit 16 as a signal d.

On the other hand, before the DC / DC converter is activated, the switching transistor 5 is turned off, and a certain voltage is output as the output voltage V _OUT through the battery 1, the coil 2, the diode 3 and the filter circuit 7. The output voltage V _OUT is detected by the output voltage detection circuit 8 and output as a voltage correlated with the output voltage V _OUT . Comparison circuit 9
Compares this value with the current value corresponding to the coil current converted into a voltage value by the current detecting resistor 6. At that time, the comparison level of the comparison circuit 9 is changed according to the value of the battery voltage V _BAT detected by the current voltage detection circuit 10.

In FIG. 9, the comparison level is high because the power supply voltage V _BAT is relatively low. Then, since the output voltage V _OUT is originally low and the output of the output voltage detection circuit 8 becomes high, the comparison circuit 9 generates the output signal f when the coil current becomes large. Therefore, even if the power supply voltage is low,
Since the coil current I is large due to “P = I · V”, in terms of electric power, a sufficient output voltage, similar to when the power supply voltage is high,
Output current can be obtained. In addition, when the power supply voltage V _BAT becomes extremely small, the maximum duty setting circuit 15 defines the ON period, so that a rush current of a predetermined amount or more does not flow and deterioration or destruction of the element is not caused. .

When the DC / DC converter is activated, the switching transistor 5 is turned on, and the coil current flows according to the equation (1). Then, the comparison circuit 9 outputs the voltage e corresponding to the coil current and the output voltage V.
_The voltage value correlated with _OUT is compared. In FIG. 9, since the power supply voltage is low, the coil current is large as described above, and the maximum duty is longer than the output signal f from the comparison circuit 9 during the ON period. Since it is shorter, the switching transistor 5 is turned off after the lapse of a predetermined on period.

When the switching transistor 5 is turned off, the coil 2 works to flow a current, and the current flows through the diode 3 to the capacitor 4 side. Then the output voltage V
_OUT rises slightly.

Then, in the next cycle, the switching transistor 5 is turned on again, and the same operation is repeated thereafter.

When the above operation is repeated several times, the output voltage V _OUT gradually rises (see FIG. 9). The output voltage detection circuit 8 detects this voltage as described above and outputs a voltage corresponding to this, and the comparison circuit 9 outputs this value and the voltage e corresponding to the current obtained by the above equation (1). Compare. Here, the output voltage detection circuit 8 outputs the output voltage V _OUT
Is higher than the previous time, a lower voltage is output than the previous time, and therefore the comparison circuit 9 has a lower voltage value,
That is, the comparison signal is output at a lower current value. Then, it becomes smaller than the coil current of the above formula (1). Then, the output signal f of the comparison circuit 9 causes the drive circuit 9 to turn off the switching transistor 5 even within the maximum duty period.

As described above, when the power supply voltage V _BAT is low, it works to increase the value of the maximum inrush current, so that the predetermined output voltage and output current can be secured even if the power supply voltage is low. Further, even when the power supply voltage V _BAT is extremely low, the ON period is regulated by the maximum duty, so that the element is not deteriorated or destroyed.

Although the DC / DC converter using the coil has been described in this embodiment, the same effect can be obtained by using the DC / DC converter as a transformer.

Further, only two cases, that is, the case where the power supply voltage is high and the case where the power supply voltage is low, are shown, but the same effect can be obtained even if this distinction is plural or stepless.

According to the above-described first to third embodiments, the power supply voltage is detected at the time of power supply replacement and the DC / DC converter start-up, and the on / off frequency of the DC / DC converter is changed according to this value, or , The maximum duty to be turned on, or the comparison level for comparing the voltage correlated with the output voltage with the voltage corresponding to the coil current is switched, so that the inrush current can be limited, and the device may be destroyed or destroyed. It is possible to prevent deterioration and obtain a predetermined output voltage and output current even at a low voltage.

Even if the output load current fluctuates greatly,
It is possible to provide a DC / DC converter in which the output voltage does not change much, that is, the regulation characteristic is good.

(Fourth Embodiment) FIG. 10 is a block diagram showing a schematic structure of a DC / DC converter according to a fourth embodiment of the present invention. Parts having the same functions as those in FIG. , Most of the details are omitted.

In FIG. 10, reference numeral 14 is a frequency switching circuit which divides the clock signal from the oscillation circuit 13 into several frequencies and outputs the divided output selected by the control circuit 11 to the maximum duty switching circuit 15. 19 is a drive circuit 1
6 is a counter circuit that counts the number of times the switching transistor 5 is turned on and off from 6 onward.

The operation of the DC / DC converter configured as above will be described with reference to the timing chart of FIG.

First, when the operation switch 12 for activating the DC / DC converter is turned on, the signal a changes from high level to low level. As a result, the oscillation start signal is sent from the control circuit 11 to the oscillation circuit 13, and the oscillation circuit 13
Starts oscillating (signal b). The frequency switching circuit 14 for inputting this clock signal b divides this into a predetermined frequency. At this time, as shown by the signal c in FIG. 11, until the counter circuit 19 counts a predetermined count value. Switches to make the frequency faster (higher) and slower (lower) the frequency after counting up. The maximum duty setting circuit 15 to which the basic frequency c is input sets the maximum duty in the ON period and the OFF period of the switching transistor 5 based on this, and outputs the signal d as the drive circuit 1
Send to 6. Then, the drive circuit 16 outputs the signal g to drive the switching transistor 5.

On the other hand, before the DC / DC converter is started, the switching transistor 5 is turned off, and a certain voltage is output as the output voltage V _OUT through the battery 1, the coil 2, the diode 3 and the filter circuit 7. The output voltage V _OUT is detected by the output voltage detection circuit 8 becomes higher enough low correlated voltage (V _OUT to the output voltage V _OUT,
The higher the voltage, the lower the voltage). Comparison circuit 9
Compares this value with the current value corresponding to the coil current converted into a voltage value by the current detecting resistor 6.

When the DC / DC converter is activated, the switching transistor 5 is turned on, and an inrush current flows according to the equation (1).

In FIG. 11, the power supply voltage V _BAT is in a relatively high state. Therefore, the rising slope of the current I, that is, the voltage e
The rising slope of is relatively large. Here, the counter circuit 19
Since the basic frequency is set high by the frequency switching circuit 14 until reaches a predetermined count value, t _ON becomes short and the inrush current I is suppressed within a predetermined value.

When the switching transistor 5 is turned off after a predetermined time by the maximum duty setting circuit 15, the coil 2 works to pass the current, and the current flows through the diode 3 to the capacitor 4 side. Then, the output voltage V _OUT rises slightly.

Then, in the next cycle, the switching transistor 5 is turned on again, and the same operation is repeated thereafter.

When the above operation is repeated several times, the output voltage V _OUT gradually rises (see FIG. 11). The output voltage detection circuit 8 detects this voltage as described above and outputs a voltage corresponding to this, and the comparison circuit 9 outputs this value and the voltage e corresponding to the current obtained by the above equation (1). Compare. Here, the output voltage detection circuit 8 outputs the output voltage V _OUT
Is higher than the previous time, a lower voltage is output than the previous time, and therefore the comparison circuit 9 has a lower voltage value,
That is, the comparison signal is output at a lower current value. Then, it becomes smaller than the coil current of the above formula (1). Then, the output signal f of the comparison circuit 9 causes the drive circuit 9 to turn off the switching transistor 5 even within the maximum duty period. Then, by the output signal f of the comparison circuit 9, the drive circuit 9 starts to turn off the switching transistor 5 even within the maximum duty period.

After such a state, that is, when the output voltage V _OUT approaches the target predetermined voltage,
The counter circuit 9 generates the signal h. Then, the frequency switching circuit 14 lowers the fundamental frequency. Therefore, the maximum time that the maximum duty setting circuit 15 can turn on the switching transistor 5 also becomes long.

However, since the switching transistor 5 is turned off by the signal f as described above, the inrush current can be suppressed. Also, since the maximum on time will be longer,
When the power supply voltage V _OUT is low, the rising slope of the inrush current is low, but after the output is stabilized, a sufficient inrush current can be secured, and thus a sufficient output current and output voltage can be obtained.

Although the DC / DC converter using the coil has been described in this embodiment as well, the same effect can be obtained by using it as a transformer type DC / DC converter.

Further, although the output from the counter circuit 19 after the DC / DC converter is activated is one type and the frequency is switched in two ways, of course, the present invention is not limited to this, and the frequency can be changed by a plurality of counter outputs. The same effect can be obtained by switching to a plurality of frequencies or continuously changing the frequency. Furthermore, this counter circuit 19
May be a microcomputer or the like, and the same effect can be obtained by outputting counter signals in the microcomputer or by outputting a switching signal after completion of a series of sequences.

(Fifth Embodiment) FIG. 12 is a block diagram showing the schematic arrangement of a DC / DC converter according to the fifth embodiment of the present invention. The parts having the same functions as those in FIG. There is.

The difference from FIG. 1 is that the output from the counter circuit 19 is input to the maximum duty setting circuit 15, and the maximum duty is switched by this signal.

The operation of the DC / DC converter thus configured will be described with reference to the timing chart of FIG.

First, when the operation switch 12 for activating the DC / DC converter is turned on, the signal a changes from high level to low level. As a result, the oscillation start signal is sent from the control circuit 11 to the oscillation circuit 13, and the oscillation circuit 13
Starts oscillating (signal b). The frequency switching circuit 14 which inputs the clock signal b divides this into a predetermined frequency and sends the signal c to the maximum duty setting circuit 15.
The maximum duty setting circuit 15 sets the maximum duty for turning on and off the switching transistor by the output of the counter circuit 19 and sends it to the drive circuit 16 as a signal d. In this case, the duty “50%” is output before the output of the output signal h of the counter circuit 19, and the duty “75” is output after the output.
% ”. The drive circuit 16 receiving this signal outputs the signal g to drive the switching transistor 5.

On the other hand, before the DC / DC converter is activated, the switching transistor 5 is off, and a certain voltage is output as the output voltage V _OUT through the battery 1, the coil 2, the diode 3 and the filter circuit 7. The output voltage V _OUT is detected by the output voltage detection circuit 8 becomes higher enough low correlated voltage (V _OUT to the output voltage V _OUT,
The higher the voltage, the lower the voltage). Comparison circuit 9
Compares this value with the current value corresponding to the coil current converted into a voltage value by the current detecting resistor 6.

Here, when the DC / DC converter is activated, the switching transistor 5 is turned on, and the above (1)
An inrush current roughly indicated by the formula flows. Immediately after DC / DC activation, the signal h from the counter circuit 19 is at a low level at the start of activation, so the maximum duty is “50%” and the t _ON time is relatively short. Therefore, even when the power supply voltage V _BAT is relatively high, that is, even when the slope of the voltage e is steep, the t _ON time is short, so that the inrush current is suppressed within a predetermined value and there is no fear of deterioration or destruction of the element. .

When the switching transistor 5 is turned off after a predetermined time by the maximum duty setting circuit 15, the coil 2 tries to pass a current, and the current flows through the diode 3 to the capacitor 4 side. Then, the output voltage V _OUT rises slightly.

Then, in the next cycle, the switching transistor 5 is turned on again, and the same operation is repeated thereafter.

When the above operation is repeated several times, the output voltage V _OUT gradually rises (see FIG. 13). The output voltage detection circuit 8 detects this voltage as described above and outputs a voltage corresponding to this, and the comparison circuit 9 outputs this value and the voltage e corresponding to the current obtained by the above equation (1). Compare. Here, the output voltage detection circuit 8 outputs the output voltage V _OUT
Is higher than the previous time, a lower voltage is output than the previous time, and therefore the comparison circuit 9 has a lower voltage value,
That is, the comparison signal is output at a lower current value. Then, it becomes smaller than the coil current of the above formula (1). Then, the output signal f of the comparison circuit 9 causes the drive circuit 9 to turn off the switching transistor 5 even within the maximum duty period.

When the output voltage V _OUT approaches the target predetermined voltage in this way, the counter circuit 9 generates the signal h. Then, the maximum duty setting circuit 15 switches the maximum duty from “50%” to “75%” (FIG. 13).
Signal d). Therefore, the maximum duty setting circuit 15
Therefore, the maximum time for turning on the switching transistor 5 via the drive circuit 16 also becomes long.

However, since the switching transistor 5 is turned off by the signal f as described above, the inrush current can be suppressed. Further, since the maximum on-time becomes long, the slope of the rise of the inrush current becomes low when the power supply voltage V _{BAT (} not shown) is low, but since the time becomes long, the inrush current does not exceed the maximum value after the output is stabilized. Sufficient inrush current can be secured, and thus sufficient output voltage and output current can be obtained.

Although the DC / DC converter using the coil has been described in this embodiment as well, the same effect can be obtained by using it as a transformer type DC / DC converter.

Further, although the output from the counter circuit 19 after the DC / DC converter is activated is one type and the maximum duty is switched in two ways, the present invention is not limited to this, and the maximum duty can be changed by a plurality of counter outputs. The same effect can be obtained by switching a plurality of switches or continuously switching. Further, the counter circuit 19 may be a microcomputer or the like, and the same effect can be obtained by outputting the switching signal after the counter means in the microcomputer or after the completion of a series of sequences.

(Sixth Embodiment) FIG. 14 is a block diagram showing the schematic arrangement of a DC / DC converter according to the sixth embodiment of the present invention. The parts having the same functions as those in FIG. There is.

The difference from FIGS. 10 and 12 is that the output from the counter circuit 19 is input to the comparison circuit 9 (the comparison circuit 9 here has the same function as in FIG. 7). , The comparison level is changed by this signal.

That is, in the above (1), since the inrush current is proportional to the power supply voltage V _BAT , the output value from the output voltage detecting means 8 and the voltage value corresponding to the coil current are kept until the predetermined count value is reached. By lowering the comparison level, the switching transistor 5 is turned off before reaching the maximum duty, and after the predetermined count, the comparison level is increased to obtain a sufficient output current at a predetermined output voltage. It is something to try.

The operation of the DC / DC converter configured as above will be described with reference to the timing chart of FIG.

First, when the operation switch 12 for activating the DC / DC converter is turned on, the signal a changes from high level to low level. As a result, the oscillation start signal is sent from the control circuit 11 to the oscillation circuit 13, and the oscillation circuit 13
Starts oscillating (signal b). The frequency switching circuit 14 which inputs the clock signal b divides this into a predetermined frequency and sends the signal c to the maximum duty setting circuit 15.
The maximum duty setting circuit 15 sets the maximum duty in the ON period and the OFF period of the switching transistor 5,
This is sent to the drive circuit 16. Then, the drive circuit 16 outputs the signal g to drive the switching transistor 5.

On the other hand, before the DC / DC converter is started, the switching transistor 5 is turned off, and a certain voltage is output as the output voltage V _OUT through the battery 1, the coil 2, the diode 3 and the filter circuit 7. The output voltage V _OUT is detected by the output voltage detection circuit 8 and output as a voltage correlated with the output voltage V _OUT . Comparison circuit 9
Compares this value with the current value corresponding to the coil current converted into a voltage value by the current detecting resistor 6. At that time, the output of the counter circuit 19 acts to lower the output voltage from the output voltage detection circuit 8.

When the DC / DC converter is activated, the switching transistor 5 is turned on, and the inrush current roughly shown by the above equation (1) starts to flow. Then, since the output voltage V _OUT is originally low, the output of the output voltage detection circuit 8 becomes high, and the comparison circuit 9 generates the signal f when the coil current becomes large, but it is output by the signal from the counter circuit 19. The output of the voltage detection circuit 8 becomes lower than the original voltage, and the comparison circuit 9 generates the signal f when the coil current is small.

The signal f causes the drive circuit 16 to forcibly turn off the switching transistor 5 even though the off period of the maximum duty is not yet reached.

When the power supply voltage is low, the inrush current does not exceed the maximum inrush current within a predetermined time according to the equation (1), and the switching transistor 5 is turned off after the predetermined maximum duty-on period ends. To do.

When the switching transistor 5 is turned off, the coil 2 works to flow a current, and the current flows through the diode 3 to the capacitor 4 side. Then, the output voltage V
_OUT rises slightly.

Then, in the next ON period, the switching transistor 5 is turned ON again, and the same operation is repeated thereafter. Then, the output voltage V _OUT gradually approaches the target predetermined voltage, and the maximum value of the inrush current gradually decreases accordingly.

When the counter circuit 19 counts up to a predetermined count value, the signal h becomes high level, and the comparison circuit 9 outputs the value of the output of the output voltage detection circuit 8 as it is and the output of the current detection resistor 6 (voltage e). ) Will be compared with. Then, a sufficient output current can be obtained at a predetermined output voltage as originally set, and the regulation characteristic is improved.

As described above, according to this embodiment, the maximum value of the inrush current at the time of starting the DC / DC converter can be suppressed to a low level, the deterioration and destruction of the element can be prevented, and the predetermined output can be obtained after the output voltage is stabilized. It becomes a DC / DC converter that can obtain a sufficient output current with a voltage and has a good regulation characteristic.

Although the DC / DC converter using the coil has been described in this embodiment, the same effect can be obtained by using the DC / DC converter as the transformer.

Further, although the output from the counter circuit 19 after the DC / DC converter is started is one type and the comparison level of the comparison circuit 9 is switched in two ways, the present invention is not limited to this, and a plurality of counters can be used. Even if a plurality of comparison levels are switched by the output, the same effect can be obtained. Further, the counter circuit 19 may be a microcomputer or the like, and the same effect can be obtained by outputting the switching signal after the counter means in the microcomputer or after the completion of a series of sequences.

According to the above fourth to sixth embodiments, the switching transistor 5 of the DC / DC converter is turned on during the power supply replacement and after the DC / DC converter is started until the output voltage V _OUT becomes stable. , The frequency to turn off, the maximum duty to turn on, or the comparison level of the voltage corresponding to the coil current and the voltage correlated with the output voltage V _OUT is switched, so that the inrush current can be limited. Therefore, the device can be prevented from being destroyed or deteriorated, a sufficient output current can be obtained at a predetermined output voltage V _OUT even at a low voltage, and the output voltage V _OUT does not change much even if the output load current changes greatly, that is, The DC / DC converter can have good regulation characteristics.

(Seventh Embodiment) FIG. 16 is a block diagram showing the schematic arrangement of a DC / DC converter according to the seventh embodiment of the present invention. Parts having the same functions as those in FIG. , Its details are omitted.

In FIG. 16, reference numeral 17 is a maximum current detection circuit for determining the current flowing through the switching transistor 5 based on the output from the current detection resistor 6 and detecting whether or not it exceeds a predetermined maximum current, and 18 is the maximum current detection circuit. When the current detection circuit 17 detects that the current flowing through the switching transistor 5 exceeds the maximum current, even if the output from the drive circuit 16 turns on the switching transistor 5, it is forcibly turned off. A for
It is an ND gate.

The operation of the DC / DC converter thus configured will be described with reference to the timing charts of FIGS. 17 and 18.

First, the case where the power supply voltage V _BAT is relatively high will be described with reference to the timing chart of FIG.

First, when the operation switch 12 for activating the DC / DC converter is turned on, the signal a changes from the high level to the low level. As a result, the oscillation start signal is sent from the control circuit 11 to the oscillation circuit 13, and the oscillation circuit 13
Starts oscillating (signal b). The frequency switching circuit 14 which inputs the clock signal b divides this into a predetermined frequency and sends it to the maximum duty setting circuit 15. Based on this, the maximum duty setting circuit 15 sets the maximum duty in the ON period and the OFF period of the switching transistor 5, and sends it to the drive circuit 16 as a signal d. Then, the drive circuit 16 outputs the signal g to output the switching transistor 5
To drive.

On the other hand, before the DC / DC converter is activated, the switching transistor 5 is turned off, and a certain voltage is output as the output voltage V _OUT through the battery 1, the coil 2, the diode 3 and the filter circuit 7. The output voltage V _OUT is detected by the output voltage detection circuit 8 becomes higher enough low correlated voltage (V _OUT to the output voltage V _OUT,
The higher the voltage, the lower the voltage). Comparison circuit 9
Compares this value with the current value corresponding to the coil current converted into a voltage value by the current detecting resistor 6.

Here, when the DC / DC converter is activated, the switching transistor 5 is turned on, and the above (1)
The rush current flows along the formula shown by the formula.

In FIG. 17, the power supply voltage V _BAT is relatively high and the current, that is, the slope of the voltage e is steep, and the inrush current I becomes too large during a predetermined maximum ON period (see FIG. 17). (See signal e), the coil 2 causes magnetic saturation, and the power supply is short-circuited, and the maximum rating of the switching transistor 5 is exceeded, possibly causing deterioration or destruction of the element.

Therefore, this current is supplied to the maximum current detection circuit 17
Is detected and the coil 2 does not cause magnetic saturation, that is, compared with the maximum current within the maximum rating of the switching transistor 5. If this maximum current is exceeded, the maximum current detection circuit 17 outputs the low level output signal h to the AND gate 18
Output to. Therefore, even if the switching transistor 5 is on, it is forcibly turned off, and the inrush current does not exceed the maximum current.

When the switching transistor 5 is turned off by the off signal d'from the maximum current detection circuit 17 or the drive circuit 16, the coil 2 works to pass the current, and the current flows to the capacitor 4 side via the diode 3. Flows. Then, the output voltage V _OUT rises slightly.

Then, in the next ON period, the switching transistor 5 is turned ON again, and the same operation is repeated thereafter.

When the above operation is repeated several times, the output voltage V _OUT gradually rises (see FIG. 17). The output voltage detection circuit 8 detects this voltage as described above and outputs a voltage corresponding to this, and the comparison circuit 9 outputs this value and the voltage e corresponding to the current obtained by the above equation (1). Compare. Here, the output voltage detection circuit 8 outputs the output voltage V _OUT
Is higher than the previous time, a lower voltage is output than the previous time, and therefore the comparison circuit 9 has a lower voltage value,
That is, the comparison signal is output at a lower current value. Then, it becomes smaller than the coil current of the above formula (1). Then, since the output of the maximum current detection circuit 17 does not change until now, the output signal f of the comparison circuit 9 causes the drive circuit 9 to operate even within the maximum duty period.
Turns off the switching transistor 5.

This operation continues until the output voltage V _OUT reaches the target predetermined voltage, and after stabilization, the current corresponding to the output current is supplied each time.

The DC / DC converter in this embodiment operates as described above, and even if the power supply voltage V _BAT is high _,
Inrush current can be suppressed and deterioration or destruction of the element can be prevented. Further, since the power supply voltage V _BAT is high, sufficient output voltage and output current can be obtained even if the inrush current is suppressed.

Next, the case where the power supply voltage V _BAT is low will be described with reference to the timing chart of FIG.

First, when the operation switch 12 for activating the DC / DC converter is turned on, the signal a changes from the high level to the low level. As a result, the oscillation start signal is sent from the control circuit 11 to the oscillation circuit 13, and the oscillation circuit 13
Starts oscillating (signal b). The frequency switching circuit 14 which inputs the clock signal b divides this into a predetermined frequency and sends it to the maximum duty setting circuit 15. Based on this, the maximum duty setting circuit 15 sets the maximum duty in the ON period and the OFF period of the switching transistor 5, and sends it to the drive circuit 16 as a signal d. Then, the drive circuit 16 outputs the signal g to output the switching transistor 5
To drive.

On the other hand, before the DC / DC converter is activated, the switching transistor 5 is turned off, and a certain voltage is output as the output voltage V _OUT through the battery 1, the coil 2, the diode 3 and the filter circuit 7. The output voltage V _OUT is detected by the output voltage detection circuit 8 and output as a voltage correlated with the output voltage V _OUT . Comparison circuit 9
Compares this value with the current value corresponding to the coil current converted into a voltage value by the current detecting resistor 6.

When the DC / DC converter is activated, the switching transistor 5 is turned on, and an inrush current flows according to the equation (1).

Since the power supply voltage V _BAT is relatively low in FIG. 18, the slope of the inrush current I is gentler than in the case of FIG. That is, the slope of the voltage e is also gentle. In this example, the current is smaller than the maximum current set by the maximum current detection circuit 17 during the predetermined maximum ON period, and the signal h remains at the high level. Therefore, the inrush current does not cause deterioration or destruction of the element. Further, as the output, since the power supply voltage V _BAT is lower, t _ON becomes longer and the inrush current is increased, so that it is possible to obtain a sufficient output current with a sufficient output voltage.

When the switching transistor 5 is turned off by the off signal d'from the drive circuit 16, the coil 2 tries to flow a current, and the current flows through the diode 3 to the capacitor 4 side. Then, the output voltage V _OUT rises slightly.

Then, in the next ON period, the switching transistor 5 is turned ON again, and the same operation is repeated thereafter.

When the above operation is repeated several times, output voltage V _OUT gradually rises (see FIG. 18). The output voltage detection circuit 8 detects this voltage as described above and outputs a voltage corresponding to this, and the comparison circuit 9 outputs this value and the voltage e corresponding to the current obtained by the above equation (1). Compare. Here, the output voltage detection circuit 8 outputs the output voltage V _OUT
Is higher than the previous time, a lower voltage is output than the previous time, and therefore the comparison circuit 9 has a lower voltage value,
That is, the comparison signal is output at a lower current value. Then, it becomes smaller than the maximum current of the maximum current detection circuit 17. Then, similarly, the drive circuit 9 turns off the switching transistor 5 by the output signal f of the comparison circuit 9. This operation continues until the output voltage reaches a target predetermined voltage, and after stabilization, operates so as to supply a current corresponding to the output current every time.

As described above, when the power supply voltage is high or low, the current is prevented from flowing for the maximum inrush current or more, so that there is no fear of destruction or deterioration of the element. Further, when the power supply voltage V _BAT becomes low, t _ON becomes long until the maximum on-time, so that sufficient output voltage and output current can be obtained.

Although the DC / DC converter using the coil has been described in this embodiment as well, the same effect can be obtained by using it as a transformer type DC / DC converter.

Further, it can be applied to both step-up and step-down converters.

Further, the current detection method determined by the maximum current detection circuit 17 is not limited to the above embodiment. For example, in a transformer type DC / DC converter, the same effect can be obtained even if the current flowing in the coil is detected by using the current detection winding or the element that can directly detect the non-contact type coil current is used. be able to.

According to the seventh embodiment described above, the rush current is detected when the power source is replaced or when the DC / DC converter is started, and when it exceeds the predetermined current, the DC / DC is detected.
Since the switching transistor of the converter is forcibly turned off, it is possible to prevent the deterioration or destruction of the element due to the inrush current, and it is possible to obtain the predetermined output voltage and output current even at a low voltage.

[0159]

As described above, according to the present invention,
A power supply voltage detection means for detecting a power supply voltage, and a power supply voltage detected by the power supply voltage detection means in a control means for driving the switching means so that the voltage detected by the output voltage detection means becomes a predetermined voltage. Frequency switching means for changing the on / off frequency of the switching means based on the power supply voltage detecting means, and a power supply voltage detecting means for detecting the power supply voltage, and a switching means based on the power supply voltage detected by the power supply voltage detecting means. A maximum duty setting means for changing the maximum duty of turning on and off, and a power supply voltage detecting means for detecting a power supply voltage; and the output voltage detecting means based on the output of the power supply voltage detecting means. A voltage that is correlated with the output voltage is corrected, and the switching means is controlled according to the corrected voltage and the voltage corresponding to the coil current. Provided and etching control means, DC
Based on the power supply voltage at the start of the operation of the / DC converter, the switching means is turned on / off, that is, DC / DC
The on / off frequency of the converter or the maximum duty to keep it on is switched, and the voltage correlated with the output voltage is corrected.

Further, according to the present invention, the control means for driving the switching means so that the voltage detected by the output voltage detecting means becomes a predetermined voltage is linked to the operation start of this DC / DC converter. A counting means for starting the time counting operation and a frequency switching means for changing the on / off frequency of the switching means according to the output of the counting means are provided, and the time counting is performed in conjunction with the operation start of the DC / DC converter. A counting means for starting the operation and a maximum duty setting means for changing the maximum duty for turning on and off the switching means in accordance with the output of the counting means are provided, and in association with the operation start of the DC / DC converter. Counting means for starting the time counting operation, and a phase for the output voltage detected by the output voltage detecting means according to the output of the counting means. The output voltage is corrected after the operation of the DC / DC converter is started, for example, by providing a correction control to the corrected voltage and controlling the switching means according to the corrected voltage and the voltage corresponding to the coil current. On / off of the switching means, that is, the frequency of on / off of the DC / DC converter, or switching of the maximum duty to be turned on, based on the output of the counting means for counting the time until it stabilizes,
The voltage correlated with the output voltage is corrected.

According to the present invention, the current detecting means for detecting the current correlated with the coil current, the detecting means for detecting that the output from the current detecting means is larger than the predetermined current value, and the detecting means. A switching control means for forcibly turning off the switching means is provided by the detection by, and the switching means is forcibly turned off when the current correlated with the current flowing to the coil exceeds a predetermined current value. There is.

Therefore, it is possible to prevent the switching means from being destroyed or deteriorated while securing a predetermined output voltage and output current.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a DC / DC converter according to a first embodiment of the present invention.

FIG. 2 is a timing chart of each part when the power supply voltage is high in the DC / DC converter of FIG.

FIG. 3 is a timing chart of each part when the power supply voltage is low in the DC / DC converter of FIG.

FIG. 4 is a block diagram showing a schematic configuration of a DC / DC converter according to a second embodiment of the present invention.

5 is a timing chart of each part in the DC / DC converter of FIG. 4 when the power supply voltage is high.

6 is a timing chart of each part when the power supply voltage is low in the DC / DC converter of FIG.

FIG. 7 is a block diagram showing a schematic configuration of a DC / DC converter according to a third embodiment of the present invention.

8 is a timing chart of each part in the DC / DC converter of FIG. 7 when the power supply voltage is high.

9 is a timing chart of each part when the power supply voltage is low in the DC / DC converter of FIG.

FIG. 10 is a block diagram showing a schematic configuration of a DC / DC converter according to a fourth embodiment of the present invention.

11 is a timing chart of each part in the DC / DC converter of FIG.

FIG. 12 is a block diagram showing a schematic configuration of a DC / DC converter according to a fifth embodiment of the present invention.

13 is a timing chart of each part in the DC / DC converter of FIG.

FIG. 14 is a block diagram showing a schematic configuration of a DC / DC converter according to a sixth embodiment of the present invention.

15 is a timing chart of each part in the DC / DC converter of FIG.

FIG. 16 is a block diagram showing a schematic configuration of a DC / DC converter in a seventh embodiment of the present invention.

17 is a timing chart of each part in the DC / DC converter of FIG. 16 when the power supply voltage is high.

18 is a timing chart of each part in the DC / DC converter of FIG. 16 when the power supply voltage is low.

FIG. 19 is a block diagram showing a schematic configuration of a conventional DC / DC converter.

[Explanation of symbols]

1 Battery 2 Coil 4 Capacitor (Accumulating Means) 5 Switching Transistor (Switching Means) 8 Output Voltage Detection Circuit 9 Comparison Circuit 10 Power Supply Voltage Detection Circuit 11 Control Circuit 14 Frequency Switching Circuit 15 Maximum Duty Setting Circuit 16 Driving Circuit 17 Maximum Current Detection Circuit 18 AND gate 19 counter circuit

Claims (7)

[Claims] 1. A coil having a predetermined inductance, and switching means connected in series to the coil,
A storage means for supplying energy to store energy generated in the coil, an output voltage detection means for detecting the energy stored in the storage means as an output voltage, and a voltage detected by the output voltage detection means In a DC / DC converter comprising a control means for driving the switching means to a predetermined voltage, a power supply voltage detection means for detecting a power supply voltage in the control means and a power supply voltage detection means for detecting the power supply voltage. And a frequency switching means for changing the on / off frequency of the switching means based on the power supply voltage. 2. A coil having a predetermined inductance, and switching means connected in series to the coil,
A storage means for supplying energy to store energy generated in the coil, an output voltage detection means for detecting the energy stored in the storage means as an output voltage, and a voltage detected by the output voltage detection means In a DC / DC converter comprising a control means for driving the switching means to a predetermined voltage, a power supply voltage detection means for detecting a power supply voltage in the control means and a power supply voltage detection means for detecting the power supply voltage. DC / DC, wherein maximum duty setting means for changing the maximum duty of ON / OFF of the switching means based on the power supply voltage is provided.
converter. 3. A coil having a predetermined inductance, and switching means connected in series to the coil,
Current detecting means for detecting a current flowing to the coil, accumulating means for accumulating energy generated in the coil by being supplied with power, and output voltage detecting means for detecting the energy accumulated in the accumulating means as an output voltage. A DC / DC converter comprising: a control unit that drives the switching unit so that a current corresponding to the difference between the voltage detected by the output voltage detection unit and a predetermined voltage is passed through the coil. In the control means, a power supply voltage detecting means for detecting the power supply voltage, and a voltage correlated with the output voltage detected by the output voltage detecting means based on the output of the power supply voltage detecting means is corrected, and this correction is performed. DC / DC converter provided with switching control means for controlling the switching means according to the voltage corresponding to the coil current and the voltage corresponding to the coil current. Over data. 4. A coil having a predetermined inductance, and switching means connected in series with the coil,
A storage means for supplying energy to store energy generated in the coil, an output voltage detection means for detecting the energy stored in the storage means as an output voltage, and a voltage detected by the output voltage detection means In a DC / DC converter provided with a control means for driving the switching means so as to have a predetermined voltage, in the control means, a counting means for starting a time counting operation in synchronization with the start of operation of the DC / DC converter. And a frequency switching means for changing the on / off frequency of the switching means according to the output of the counting means.
C converter. 5. A coil having a predetermined inductance, and switching means connected in series to the coil,
A storage means for supplying energy to store energy generated in the coil, an output voltage detection means for detecting the energy stored in the storage means as an output voltage, and a voltage detected by the output voltage detection means In a DC / DC converter provided with a control means for driving the switching means so as to have a predetermined voltage, in the control means, a counting means for starting a time counting operation in synchronization with the start of operation of the DC / DC converter. And a maximum duty setting means for changing the maximum duty of ON / OFF of the switching means according to the output of the counting means. 6. A coil having a predetermined inductance, and switching means connected in series to the coil,
Current detecting means for detecting a current flowing to the coil, accumulating means for accumulating energy generated in the coil by being supplied with power, and output voltage detecting means for detecting the energy accumulated in the accumulating means as an output voltage. A control means for driving the switching means so that the voltage detected by the output voltage detecting means becomes a predetermined voltage.
A C / DC converter, in the control means, a counting means for starting a time counting operation in synchronization with the operation start of the DC / DC converter, and the output voltage detecting means according to the output of the counting means. DC / characterized by providing a voltage correlating with the detected output voltage, and providing switching control means for controlling the switching means according to the corrected voltage and the voltage corresponding to the coil current. DC converter. 7. A coil having a predetermined inductance, and switching means connected in series to the coil,
In a DC / DC converter including a storage unit that is supplied with power and stores energy generated in the coil, a current detection unit that detects a current correlated with a current flowing in the coil, and an output from the current detection unit. Is provided with a detection means for detecting that the current is larger than a predetermined current value, and a switching control means for forcibly turning off the switching means by the detection by the detection means.