JPH0779562A - Dc/dc converter - Google Patents

Abstract

PURPOSE:To provide a DC/DC converter capable of preventing the malfunction of its circuit when using a degraded battery or immediately after connecting the battery. CONSTITUTION:A DC/DC converter is provided with a power supply voltage detecting means 7 which detects whether or not the voltage corresponding to the voltage of a battery reaches a second prescribed voltage and an operation control means 11 which inhibits the operation of a switching element driving means 8 when the means 7 detects that the power supply voltage does not reach the second prescribed voltage so that the operation of the control means 8 can be controlled in accordance with the detected results of the means 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching element for turning on and off the energization of a coil for boosting a battery voltage, and driving the switching element so that the output voltage of the DC / DC converter becomes a predetermined voltage. The present invention relates to an improvement of a DC / DC converter including a switching element driving unit that generates a signal.

[0002]

2. Description of the Related Art DC / DC converters are widely used in battery-powered systems.

[0003]

[Problems to be Solved by the Invention]
There are the following problems because the safety measures of the DC / DC converter are not taken into consideration.

In the case of using a battery as a power source, the internal resistance sometimes becomes very large depending on the characteristics and usage of the battery. That is, although the open-circuit voltage shows a sufficient value, a phenomenon occurs in which the output voltage sharply decreases when a load is applied.

When the DC / DC converter is started using such a battery, both the power supply voltage and the output voltage sharply drop at the same time as the start, and the CPU stops while the load current is still flowing, The amplifier, comparator, etc. will malfunction. If this state is left as it is, it may cause an accident such as burning of elements on the circuit.

Even when a non-defective battery is used, the amplifier, the comparator, etc., may be operated for a short period of time immediately after the battery is charged until the backup capacitor is charged to the voltage necessary for the operation of the circuit. There is a time during which it does not operate normally, and on the other hand, a power supply voltage of a predetermined value or more and a stabilization wait time are required for the clock that is the time reference to oscillate stably. Even for a short period of time, it is dangerous for a circuit to malfunction to cause a current exceeding a specified value to flow.

(Object of the Invention) A first object of the present invention is to provide a DC / DC converter which can prevent malfunction of the circuit when the capacity of the battery is lowered or immediately after the battery is turned on. .

A second object of the present invention is to provide a DC / DC converter capable of minimizing damage even if some inconvenience occurs on the circuit.

A third object of the present invention is to stop the oscillation while the switching element is on, or to extend the on-time of the switching element due to a decrease in the oscillation frequency, causing an excessive current to flow and destroying the element. DC / D that can prevent the situation that causes
It is to provide a C converter.

[0010]

According to the present invention, there is provided a power supply voltage detecting means for detecting whether or not a voltage corresponding to a battery voltage has reached a second predetermined voltage, and the power supply voltage is detected by the power supply voltage detecting means. When it is detected that the second predetermined voltage has not been reached, an operation control means for prohibiting the operation of the switching element drive means is provided, and the operation of the switching element drive means is performed according to the detection result of the power supply voltage detection means. Are trying to control.

Further, according to the present invention, the output voltage detecting means for detecting whether or not the output voltage of the DC / DC converter has reached the second predetermined voltage lower than the first predetermined voltage, and the switching element driving means. Driving signal counting means for counting the driving signals after the operation is permitted, and when the value of the driving signal counting means reaches a predetermined value, the output voltage detecting means outputs the second predetermined voltage. When it is detected that the output voltage has not been reached, an operation control means for prohibiting the operation of the switching element driving means is provided, and the output voltage after driving the switching element a predetermined number of times is detected,
When it is determined that the second predetermined voltage has not been reached, that is, the boosting operation is not normally performed, the operation of the switching element driving means is prohibited.

Further, according to the present invention, the oscillation state detecting means for detecting whether or not the oscillation frequency of the reference clock of the switching element driving means is within a predetermined range, and the oscillation frequency of the reference clock by the oscillation state detecting means. Is not within a predetermined range, an operation control means for prohibiting the operation of the switching element drive means is provided, and if the oscillation frequency is not within the predetermined range, the switching element drive means is provided. The operation of is prohibited.

[0013]

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.
It is a block diagram which shows a / DC converter.

In the figure, 1 is a battery which is a power source, 2 is a coil for storing electric energy, 3 is a switching element formed of a transistor for turning on and off the current of the coil 2, and 4 is a switching element 3 being off. When this is done, a diode for rectifying the output boosted by the coil 2, 5 a capacitor for stabilizing the output, 6 an output terminal for supplying an output voltage V _out , 7 a voltage V of the battery 1 which is a power source _BAT is detected and if it is more than a predetermined value, "H"
If it outputs a signal or detects the voltage of its own power supply and is below a second predetermined value (the level at which its own power supply voltage is inoperable), it is an "L" signal regardless of the voltage level of the battery 1. Is a power supply voltage detection circuit, 8 is a switching element drive circuit that generates a signal for appropriately turning on and off the switching element 3 according to the output voltage of the output terminal 6, 9 is a CPU, 10
Is a reference clock generation circuit for giving a reference clock to the switching element drive circuit 8, and 11 is a 2-input AND gate.

Next, the operation of the DC / DC converter having the above structure will be described.

When a start signal ("H" signal) for the DC / DC converter is generated by a command from the CPU 9, this signal is input to one of the input terminals of the 2-input AND gate 11. The output voltage of the battery 1 which is the power supply is the power supply voltage detection circuit 7
If it is higher than the judgment level of, the power supply voltage detection circuit 7 applies "H" to the other input terminal of the 2-input AND gate.
Output a signal. Therefore, in this case, the "H" signal is input from the 2-input AND gate 11 to the switching element drive circuit 8, and the switching element drive circuit 8 is permitted to start operation. That is, an appropriate pulse signal for turning on / off the switching element 3 is generated so that the output voltage V _out becomes a set value.

When the operation of the switching element drive circuit 8 is permitted and the switching operation is started, the current consumption of the power supply battery 1 increases and a voltage drop occurs due to the internal resistance of the battery 1, so that the power supply voltage decreases. Therefore, the power supply voltage detection circuit 7 is preferably a hysteresis comparator having a hysteresis in its detection level. Further, the power supply voltage detection circuit 7 is configured to output an "L" signal in order to stop the switching operation whenever the power supply voltage of the power supply voltage detection circuit 7 decreases to an inoperable level in order to prevent malfunction.

When the power supply voltage is below a predetermined value, the CPU
The operation of the switching element drive circuit 8 remains prohibited regardless of the instruction from 9, and the operation is permitted.
When the power supply voltage drops during activation of the C / DC converter and becomes lower than a predetermined value, the operation of the switching element drive circuit 8 is prohibited at that time.

The state of the above operation is shown in FIG.
2A to 2C, and FIG.
FIG. 2B shows the time when the power supply voltage drops during the activation of the DC / DC converter, and FIG. 2C shows the time when the battery 1 is turned on and the normal operation is started.

When the power supply voltage decreases, the output capability also decreases, and the fluctuation of the power supply voltage itself becomes large.
There is concern about malfunction of the circuit. In particular, a fatal accident occurs in which the operation of the circuit is stopped while the coil current is flowing, but the above-mentioned configuration has the effect of preventing such an accident. Further, it goes without saying that it is effective immediately after the battery is turned on.

According to the first embodiment, the switching element drive circuit 8 is selected according to the detection result of the power supply voltage detection circuit 7.
Since the operation of is permitted or prohibited, the output voltage does not reach the predetermined voltage immediately after the battery is charged or when a battery with low capacity is charged, and the circuit malfunctions, especially as described above. In particular, it is possible to prevent accidents such as when the coil current continues to flow.

(Second Embodiment) FIG. 3 is a block diagram showing a DC / DC converter according to a second embodiment of the present invention.

In the figure, 21 is a battery serving as a power source, 22 is a coil for accumulating electrical energy, and 23 is a coil.
Is a switching element composed of a transistor for turning on and off the current of the coil 22, 24 is a diode for rectifying the output boosted by the coil 22 when the switching element 23 is off, and 25 is a capacitor for stabilizing the output. , 26 is an output terminal for supplying an output voltage V _out , 28 is a switching element drive circuit for generating a signal for appropriately turning on and off the switching element 23 according to the output voltage of the output terminal 26, 29 is a CPU, and 30 is a switching circuit. A reference clock generation circuit for giving a reference clock to the element drive circuit 28, and 31 is a 2-input AND gate.

Reference numeral 32 is an output voltage detection circuit which detects the output voltage V _out of the output terminal 26 and outputs an "L" signal when the output voltage V _out is a predetermined value or more. A drive signal counting circuit that counts the number, and 34 is a D type flip-flop.

Next, the operation of the DC / DC converter having the above configuration will be described.

When the start signal ("H" signal) of the DC / DC converter is generated by the instruction of the CPU 29, this signal is input to one of the input terminals of the 2-input AND gate 31. At the same time, this signal releases the resets of the drive signal counting circuit 22 and the D-type flip-flop 23, which have been reset until then.

The voltage at the output terminal 26 is the output voltage detection circuit 3
When it is lower than the detection level of 2, the output voltage detection circuit 32 outputs the "H" signal. Therefore, since the battery voltage has not been boosted before the DC / DC converter is started, the output voltage detection circuit 32 should output the "H" signal. At this time, since the D-type flip-flop 34 has not received the clock signal immediately after the reset is released, the inverted output of Q outputs the “H” signal regardless of the value of the D input, and this signal is a 2-input AND gate. Three
1 is input to the other input terminal. Therefore, the operation of the switching element drive circuit 28 is permitted, the driving of the switching element 23 is started, and the boosting operation is started.

At the same time, the drive signal counting circuit 33 starts counting the number of pulses of the output signal of the switching element driving circuit 28, and outputs a "H" signal when counting a predetermined number of pulses. The D-type flip-flop 34 latches the signal of the D input because the signal of the clock input changes from “L” to “H”. That is, it is detected whether the voltage of the output terminal 26 exceeds the determination level of the output voltage detection circuit 32 at the time when the drive signal counting circuit 33 counts a predetermined number of pulses.

When the output voltage detection circuit 32 operates normally and the output voltage is boosted and exceeds the detection level of the output voltage detection circuit 32, the output voltage detection circuit 32 outputs a signal "L", but the D type flip-flop 23 outputs the signal "L". When the L ″ signal is input to the D input, the inverted output of Q does not change, and the switching element drive circuit 28 continues its operation.

On the other hand, if the output voltage is not boosted for some reason and exceeds the detection level of the output voltage detection circuit 32,
The output voltage detection circuit 32 still outputs the "H" signal. If the D input remains the "H" signal at the time when the D type flip-flop 23 latches, the inverted output of Q is "L".
Since it becomes a signal and the output of the 2-input AND gate 31 becomes an "L" signal, the operation of the switching element drive circuit 28 is prohibited.

According to the second embodiment, when the value of the drive signal counting circuit 33 for counting the number of pulses output from the switching element driving circuit 28 reaches a predetermined value, the output voltage detecting circuit 32 is If it is detected that the output voltage has not reached the predetermined value, the operation of the switching element drive circuit 28 is prohibited, so that an accident such as disconnection or short circuit occurs on the circuit. Even in the case, it has the effect of minimizing the damage.

(Third Embodiment) FIG. 4 is a block diagram showing a DC / DC converter in a third embodiment of the present invention.

In the figure, 41 is a battery serving as a power source, 42 is a coil for accumulating electrical energy, and 43 is a coil.
Is a switching element composed of a transistor for turning on / off the current of the coil 42, 44 is a diode for rectifying the output boosted by the coil 42 when the switching element 43 is off, and 45 is a capacitor for stabilizing the output. , 46 is an output terminal for supplying an output voltage V _out , 48 is a switching element drive circuit for generating a signal for appropriately turning on and off the switching element 43 according to the output voltage of the output terminal 46, 49 is a CPU, and 50 is a switching circuit. A reference clock generation circuit for giving a reference clock to the element drive circuit 48, and 51 is a 2-input AND gate.

Reference numeral 52 is an oscillation state detection circuit which detects whether or not the output signal of the reference clock generation circuit 50 is within a predetermined frequency range and outputs an "H" signal if within a predetermined range.

Next, the operation of the DC / DC converter having the above structure will be described.

When the start signal ("H" signal) of the DC / DC converter is generated by the instruction of the CPU 49, this signal is input to one of the input terminals of the 2-input AND gate 51.

The oscillation state detection circuit 52 inputs the reference clock of the switching element drive circuit 48 to determine whether or not the frequency of the reference clock is within a predetermined range. As a result, when it is within the predetermined range, the "H" signal is output, and this is applied to the other input terminal of the 2-input AND gate 51, so that the switching element drive circuit 48 operates normally.

On the other hand, if the operation of the reference clock generating circuit 50 becomes unstable for some reason and the frequency of the reference clock decreases or stops, the oscillation state detecting circuit 52 outputs the "L" signal. The operation of the switching element drive circuit 48 is prohibited, which has the effect of preventing an accident such as an overcurrent flowing through the coil 42 and the switching element 43.

Further, even when the battery is turned on, the operation of the switching element drive circuit 48 is prohibited until the reference clock oscillates stably, and the operation is permitted after the stable oscillation is obtained, so that the malfunction is prevented. effective.

Needless to say, in any of the first to third embodiments, it is necessary to turn off the switching element when the operation of the switching element drive circuit is prohibited.

In addition, the control described in the first to third embodiments is not limited to the processing by the software of the CPU 9, and is configured only by hardware, so that the CPU 9 can be reliably operated even when the CPU 9 is stopped. There is an effect that it becomes possible to perform control.

[0043]

As described above, according to the present invention,
Power supply voltage detection means for detecting whether or not the voltage corresponding to the battery voltage has reached the second predetermined voltage, and the power supply voltage detection means detects that the power supply voltage has not reached the second predetermined voltage. In this case, the operation control means for prohibiting the operation of the switching element drive means is provided, and the operation of the switching element drive means is controlled according to the detection result of the power supply voltage detection means.

Therefore, it is possible to prevent the malfunction of the circuit when the capacity of the battery is lowered or immediately after the battery is turned on.

According to the present invention, the output voltage after driving the switching element a predetermined number of times is detected, and the second
When it can be determined that the predetermined voltage has not been reached, that is, the boosting operation is not normally performed, the operation of the switching element drive means is prohibited.

Therefore, even if some inconvenience occurs on the circuit, the damage can be minimized.

According to the present invention, the oscillation state detecting means for detecting whether or not the oscillation frequency of the reference clock of the switching element driving means is within a predetermined range, and the oscillation state detecting means for detecting the reference clock When it is detected that the oscillation frequency is not within the predetermined range, an operation control means for prohibiting the operation of the switching element drive means is provided,
When the oscillation frequency is not within the predetermined range, the operation of the switching element drive means is prohibited.

Therefore, it is possible to stop the oscillation while the switching element is on, or to extend the on-time of the switching element due to the decrease of the oscillation frequency, which causes an excessive current to flow to cause the destruction of the element. It is possible to prevent it.

[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 showing how the device of FIG. 1 operates normally, when the power supply voltage drops during DC / DC converter startup, and when the power is turned on and normal operation is performed.

FIG. 3 is a block diagram showing a schematic configuration of a DC / DC converter according to a second embodiment of the present invention.

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

[Explanation of symbols]

 1, 21, 41 Battery 2, 22, 42 Coil 3, 23, 43 Switching element 7 Power supply voltage detection circuit 8, 28, 48 Switching element drive circuit 9, 29, 49 CPU 10, 30, 50 Reference clock generation circuit 11, 31, 51 2-input AND gate 32 Output voltage detection circuit 33 Drive signal counting circuit 52 Oscillation state detection circuit

Claims (5)

[Claims] 1. A switching element for turning on and off energization of a coil for boosting a battery voltage, and a drive signal for the switching element so that an output voltage of the DC / DC converter becomes a first predetermined voltage. In a DC / DC converter provided with a switching element driving means, a power supply voltage detecting means for detecting whether or not a voltage corresponding to a battery voltage has reached a second predetermined voltage, and a power supply voltage detecting means for the power supply voltage detecting means. Is detected to have not reached the second predetermined voltage, the operation control means for inhibiting the operation of the switching element drive means is provided. 2. The D according to claim 1, wherein the power supply voltage detecting means is a hysteresis comparator.
C / DC converter. 3. The power supply voltage detecting means, when the voltage applied to itself is lower than the operable voltage, outputs the same signal as when detecting that the power supply voltage has not reached the second predetermined voltage. The DC / DC converter according to claim 1, which is means for outputting to the DC / DC converter. 4. A switching element for turning on and off the energization of a coil for battery voltage boosting, and a drive signal for the switching element so that the output voltage of the DC / DC converter becomes a first predetermined voltage. In a DC / DC converter provided with a switching element driving means, an output voltage detecting means for detecting whether or not the output voltage of the DC / DC converter has reached a second predetermined voltage lower than the first predetermined voltage. A drive signal counting means for counting the drive signals after the operation of the switching element driving means is permitted, and at the time when the value of the drive signal counting means reaches a predetermined value, the output voltage detecting means When it is detected that the output voltage has not reached the second predetermined voltage, operation control means for inhibiting the operation of the switching element driving means is provided. DC / DC characterized by being
converter. 5. A switching element for turning on and off energization of a coil for boosting a battery voltage, and a switching element for generating a drive signal for the switching element so that an output voltage of the DC / DC converter becomes a predetermined voltage. In a DC / DC converter including a driving means, an oscillation state detecting means for detecting whether or not an oscillation frequency of a reference clock of the switching element driving means is within a predetermined range, and a reference by the oscillation state detecting means. A DC / DC converter comprising: an operation control means for inhibiting the operation of the switching element drive means when it is detected that the oscillation frequency of the clock is not within a predetermined range.