JPH08205531A - Dc power supply device - Google Patents

Abstract

PURPOSE: To prevent abnormal low voltage of an output voltage generated at the time of rising by providing a soft start control circuit for changing the rise time of a soft start circuit at the same time when a current starts flowing to operate so that the output voltage rises at a uniform rate. CONSTITUTION: When a voltage value detected by a current detecting resistor 24 exceeds the output voltage value of a current detecting reference power supply 26, an error amplifier 27 amplifies the potential difference to bring a transistor 28 into the conduction state. The transistor 28 increases a current which flows into a capacitor 14 through a current limiting resistor 29 in accordance with the output voltage value of the error amplifier 27 to accelerate the drop of a signal voltage sent to a comparator 17. Therefore, at the same time when a load current starts flowing, a pulse width is expanded to be wider than the ON width of a switching transistor by an ordinary soft start circuit and more energy than an ordinary one is supplied to a load device 22. Therefore, the output voltage can rise at a constant rate and a low voltage abnormality is prevented from being generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load device such as a load device including many digital integrated circuits, in which a load current starts flowing at the same time when a voltage supplied from a DC power supply exceeds a certain value. , A low-voltage protection circuit that supplies stable power and sends a voltage drop warning signal for the purpose of protecting the load side when the power supply voltage to be supplied drops, or that stops or forcibly reduces the output of the power supply. Prepare,
Further, the present invention relates to a highly reliable DC power supply device having a soft start function when the power supply is turned on.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional DC power supply device. In FIG. 7, 1 is a DC power supply, 2 is an input capacitor, 3 is a transformer for power conversion, 4 is a switching transistor, 5 is a transistor 4. Drive circuit to drive, 6
Is a rectifying diode, 7 is a smoothing choke coil, 8 is a smoothing capacitor, 9 is a voltage control circuit for controlling the output voltage, and 10 is an input inrush current generated when the DC power supply device is started up or a transient output voltage. A soft start circuit that slowly raises the output voltage so that an overvoltage phenomenon (hereinafter referred to as overshoot) does not occur, 11 is a reference power supply used in the DC power supply device, and 12, 13 and 14 are resistors that configure the soft start circuit. And a capacitor, 15 is an error amplifier in the voltage control circuit, 16 is an oscillator generating a sawtooth wave in the voltage control circuit, 17 and 18 are comparators in the voltage control circuit, 19 is a comparator in the voltage control circuit. A logical circuit (hereinafter referred to as an AND circuit) that obtains the logical product of the outputs of 17 and 18 and outputs it, 20 is an output transistor in the voltage control circuit, 2
Reference numeral 1 is a reference power source for voltage control, 22 is a load device that starts to flow current when the input voltage exceeds a certain value, and 23 is a low voltage protection circuit.

FIG. 8 shows an outline of the operation of the conventional device shown in FIG. 7, where a is a diagram showing the output voltage waveform of the oscillator 16 and the voltage signal waveform sent from the soft start circuit 10, Is the output voltage waveform of the oscillator 16 and the error amplifier 1
5 shows the output voltage waveform of No. 5, C shows the output voltage waveform of the comparator 17, D shows the output voltage waveform of the comparator 18, and E shows the output voltage waveform of the AND circuit 19. In the figure, F is a diagram showing the load current, and K is a diagram showing the output voltage of the DC power supply device.

Next, the operation of the conventional apparatus shown in FIG. 7 will be described. The DC power supply device shown in FIG. 7 is a switching power supply which is most frequently used at present. The operation is such that the transistor 4 is turned on / off and a pulse current is passed through the primary side of the transformer 3, thereby transmitting power to the secondary side of the transformer 3 and rectifying the power generated on the secondary side of the transformer 3. After being rectified by the diode 6, it is stored in the smoothing capacitor 8 via the smoothing choke coil 7 and supplied to the load device 22 as a predetermined DC voltage (V _out ).
The voltage control circuit 9 detects the voltage across the capacitor 8,
A signal is sent to the transistor drive circuit 5 so as to widen the ON width of the transistor 4 when the voltage drops and narrow the ON width when the voltage rises. Therefore, by controlling the on / off ratio of switching of the transistor 4, the voltage across the capacitor 8 is always kept constant. Also,
Since the output voltage (V _out ) of the soft start circuit 10 is 0 V when the DC power supply device is started, the ON width of the transistor 4 suddenly becomes the maximum and an excessive rush current flows toward the capacitor 8. The ON width of the transistor 4 is controlled so as to gradually increase so that the output voltage does not overshoot due to the delay of the control system when V _out rises to a predetermined voltage value. Further, after the low voltage protection circuit 23 that exceeds the voltage value V _out is the load device 22 are operable to (V _{mi n),} a DC power supply or the load device 22 is abnormally, V _out is below V _min In the event of a failure, the load device 22 outputs a warning signal of a voltage drop so that the load device 22 can retain the data and protect the load device 22 itself, and a DC power supply is assumed assuming a short circuit failure in the power supply output line and the load device 22. Stop the device,
It works to forcibly reduce either or both of voltage and current.

Further, the operation of the soft start circuit is shown in FIG.
This will be described in detail with reference to FIG. The error amplifier 15 includes an output voltage (V _out ) of the DC power supply device and a reference power supply 21 for voltage control.
A signal obtained by amplifying the potential difference from the output voltage (V _ref1 ) of the above is sent to the comparator 18. As shown in FIG. 8A, the signal is transmitted at the maximum voltage when the DC power supply device is activated, and the transmission voltage gradually decreases as V _out increases.
The comparator 18 compares the output voltage of the oscillator 16 with the output voltage of the amplifier 15 as shown in FIG.
If the output voltage of 6 is higher, the higher voltage signal (High
h) and a low voltage signal (Low) when the output voltage of the amplifier 15 is higher, the signal is Hi.
The period (pulse width) of gh becomes narrower as V _out increases. On the other hand, the signal sent from the soft start circuit 25 to the comparator 17 is, as shown in FIG.
The output voltage (V _ref2 ) of the reference power source 11 is output as it is via the, and gradually decreases to the potential divided by the resistors 12 and 13 as time passes. Therefore, the comparator 17
The pulse width of the output voltage gradually increases as shown in FIG. At the output of the AND circuit 19,
The logical product of the comparators 17 and 18 and the output of the low voltage protection circuit 23 is taken, and the output of the low voltage protection circuit 23 indicates normal.
If it is high, as shown in FIG.
_The pulse width gradually expands until _out rises to a certain value. Therefore, when the load current is pulled as it is, the rising waveform of V _out is as shown by the dotted line in FIG.

However, if the current consumed by the load device 22 begins to flow while V _out is rising, as shown in FIG. 8C, the waveform of V _out is shown by the solid line in FIG. It will draw a trace like this. In particular, in the case of a load device equipped with many digital integrated circuits, the operation is unstable near the operable voltage of the integrated circuits, and a current value above the rated value may be drawn. In such a case, V _out waveform will be decreased temporarily below V _min values immediately beyond the V _min value, so that the low voltage protection circuit in the low-voltage abnormality will operate.

[0007]

Since the conventional DC power supply device is configured as described above, if a load current is suddenly drawn while the output voltage is slowly increasing by the soft start circuit, a low voltage abnormality will occur. Then, the low voltage protection circuit stops the DC power supply device or the output voltage is forcibly reduced. Therefore, there are problems that it is impossible to rise to a predetermined voltage, and even when the power is turned on, a low voltage abnormality signal or the like is transmitted during the rise, and the load device cannot operate normally.

The present invention has been made in order to solve the above problems, and a soft start is performed at the same time when the load device starts to draw a load current or when the load device starts to draw a current. An object of the present invention is to prevent a low voltage abnormality of the output voltage generated at the time of rising by controlling the rising speed of the circuit and controlling the output voltage of the DC power supply device to rise at a constant speed.

[0009]

The DC power supply device according to the first embodiment of the present invention detects the time when the load device starts to draw current by directly monitoring the load current and the switching current, and is limited by the soft start circuit. Equipped with a soft start control circuit that controls the switching operation so that the ON width of the switching of the DC power supply unit is changed according to the magnitude of the load current and the output voltage of the DC power supply unit can rise at a constant speed. Is.

Further, the DC power supply device according to the second embodiment of the present invention predicts the time when the load device starts to draw a current from the operation signal on the load device side, and the switching of the DC power supply device is restricted by the soft start circuit. The on-width is varied when the operation signal of the load device changes from High to Low, and the soft start control circuit is provided to control the switching operation so that the output voltage of the DC power supply device can rise at a constant speed. .

The DC power supply device according to the third embodiment of the present invention compares the output voltage of the DC power supply device with an arbitrary reference voltage waveform simulating the rising waveform of the output voltage, and compares It is provided with a soft start control circuit capable of controlling the ON width of switching of the DC power supply device only at the time of rising so as to rise.

[0012]

According to the DC power supply device of the first embodiment of the present invention, even if the load current suddenly starts flowing while the output voltage is slowly rising by the soft start circuit, the load current is controlled by the soft start control circuit. At the same time that the current starts flowing, the ON width of switching can be widened according to the load current, and the output voltage rises at a substantially constant speed. Therefore, even if the load current suddenly starts to flow when the DC power supply device is started up, it is possible to prevent the DC power supply device from suddenly stopping due to an abnormal low voltage and the load device from malfunctioning.

According to the DC power supply device of the second embodiment of the present invention, the load device suddenly starts operating while the output voltage is slowly rising by the soft start circuit,
Even when the load current starts to flow, the soft start control circuit can widen the ON width of the switching by a predetermined value immediately before the load current starts to flow, and the output voltage increases without decreasing. Therefore, the same operation as that of the invention shown in the first embodiment can be obtained, and additional circuits such as a current detection circuit can be omitted, and a DC power supply device which is simple and similar to that of the invention shown in the first embodiment can be obtained.

According to the DC power supply device of the third embodiment of the present invention, the output voltage is slowly raised by the soft start control circuit so as to have a waveform similar to the arbitrarily given reference voltage waveform. Therefore, even if the load current suddenly starts to flow while the output voltage is increasing, the switching operation of the DC power supply device is controlled so as to be similar to the reference voltage waveform. Therefore, the same operation as that of the invention shown in the first embodiment can be obtained, and the peripheral circuits such as the current detection circuit and the soft start circuit can be omitted, and the same DC power supply device as that of the invention shown in the first embodiment can be obtained.

[0015]

【Example】

Embodiment 1 FIG. 1 is a circuit configuration diagram showing Embodiment 1 of the present invention, in which 1 to 23 are the same as the above-mentioned conventional device and circuit, and 24 is the simplest current detecting element as a current detecting element. Resistor, 25 is a soft start control circuit, 26 is a current detection reference power source, 27 is an error amplifier, 28 is a transistor, and 29 is a current limiting resistor.

FIG. 2 is a signal waveform diagram for explaining the operation of the present invention. The symbols used in the figure are the same as the symbols shown in FIG. 8 for explaining the operation of the conventional device. The newly added symbol K is a diagram showing the output voltage waveform of the oscillator 16 and the voltage signal waveform sent from the soft start control circuit 25.

The operation will be described in detail below with reference to the drawings. In the configuration as shown in FIG. 1, the error amplifier 27 is
When the voltage value detected from the current detection resistor 24 exceeds the output voltage value (V _ref3 ) of the current detection reference power supply 26, the potential difference is amplified and the transistor 28 is turned on. The transistor 28 increases the current flowing through the capacitor 14 via the current limiting resistor 29 according to the output voltage value of the error amplifier 27, and accelerates the drop of the signal voltage sent to the comparator 17. Therefore, the two voltage signals input to the comparator 17 are as shown by the solid line in FIG. 2 and the signal for driving the switching transistor 4 is as shown by the solid line in FIG. As can be seen from the waveform of the solid line in FIG. 2A, at the same time when the load current begins to flow, the pulse width is widened than the ON width of the switching transistor by the normal soft start circuit, and more energy than usual is applied to the load device. 22 is supplied. As a result, it can be seen that the rising waveform of V _out can also rise at a substantially constant speed as indicated by the solid line in FIG. 2 and no low voltage abnormality occurs.

In the above embodiment, the current is detected by using the resistor, but it can be easily imagined that the same effect can be obtained even if the current is detected by using the transformer or another element.

Second Embodiment FIG. 3 is a circuit configuration diagram showing a second embodiment of the present invention, wherein 1 to 29 in the figure are the same as or equivalent to the above-mentioned conventional circuit and the circuit described in the first embodiment. Reference numeral 30 is a driver circuit which is an output of one integrated circuit, 31 is a receiver circuit in the soft start control circuit, 32 is an inverter circuit for signal inversion, and 33 is a bias resistor.

FIG. 4 is a signal waveform diagram for explaining the operation of the embodiment in FIG. 3, and the symbols used in FIG. 4 indicate the operation in FIG. 8 for explaining the operation of the conventional apparatus and the operation in the first embodiment. It is the same as the symbol shown in FIG. 2 described above, and the symbol newly added is a diagram showing the output voltage signal of the driver circuit 30.

The operation will be described in detail below with reference to the drawings. In the configuration of FIG. 3, the input of the driver circuit 30 is directly connected to the output voltage from the DC power supply device. FIG.
The output signal of the driver circuit 30 as shown in Ke, the DC power supply immediately after the activation of the device increases with increasing V _{ou t,} but the output at the same time exceeds the voltage V _min value integrated circuit is operable in Low become. Speaking of the output impedance of the driver circuit 30, the impedance is high until the driver circuit 30 starts to operate, and becomes low at the same time when it becomes operable. Therefore, the receiver circuit 31 transmits a high signal to the inverter circuit 31 at the same time that the output impedance of the driver circuit 30 becomes low, the output of the inverter circuit 31 becomes Low, and the transistor 28 becomes conductive. When the transistor 28 becomes conductive, the capacitor 1 is connected via the resistor 29.
4 increases, the voltage signal sent to the comparator 17 drops faster than the signal of the normal soft start circuit as shown by the solid line in FIG. Therefore, as shown by the solid line in FIG. 4A, the pulse width is wider than the ON width of the switching transistor by the normal soft start circuit, and a large amount of energy is supplied to the load device 22. As a result, the rising waveform of V _out also rises at a substantially constant speed as shown by the solid line in FIG. 4, and it can be seen that the low voltage abnormality does not occur.

For the sake of convenience of explanation, a signal indicating when the load device starts operating is taken from the integrated circuit in the load device. The same effect can be obtained by placing one integrated circuit of the same series and operating the soft start control circuit with a signal from the integrated circuit.

Third Embodiment FIG. 5 is a circuit configuration diagram showing a third embodiment of the present invention, in which 1 to 25 are the same as or equivalent to the above-mentioned conventional circuit and the circuits described in the first and second embodiments. Reference numeral 27 is an amplifier for amplifying the output voltage of the DC power supply device and the potential difference from the signal generator for producing a pseudo waveform, and 34 is a signal generator for producing a pseudo waveform.

FIG. 6 is a signal waveform diagram for explaining the operation of the embodiment in FIG. 5, and the symbols used in FIG. 6 indicate the operation in FIG. 8 for explaining the operation of the conventional apparatus and the operation in the first embodiment. 4 is the same as the symbol shown in FIG. 2 described in FIG. 2 and the operation described in the second embodiment, and the newly added symbol C is a diagram showing an output waveform from the signal generator 34 that creates a pseudo waveform. .

The operation will be described in detail below with reference to the drawings. In the configuration of FIG. 5, the signal generator 34 sets what waveform the output voltage of the DC power supply device should rise, and as the simplest, the waveform of charging the capacitor can be raised. FIG. 5 shows an embodiment using a charging waveform for a capacitor. The voltage of the reference power supply 11 output at the same time when the DC power supply is started is charged to the capacitor 14 via the resistor 11 and the DC power supply is used. It activates the output of the device. The charging voltage is resistance 1
1 rises at a time constant determined by each constant of the capacitor 14, and its waveform becomes as shown in FIG.
As shown in FIG. 6C, the error amplifier 27 has a signal generator 34.
And the output voltage of the DC power supply device are compared, and the output voltage proportional to the potential difference is transmitted to the comparator 17. The output voltage of the signal generator 34 finally rises until the maximum pulse width required by the voltage control circuit 9 can be output, and when the output voltage of the DC power supply device approaches a predetermined value, the pulse width control is performed. It is controlled by the error amplifier 15 which controls the voltage. That is, the voltage control circuit 9 controls the switching operation so as to follow the output voltage waveform of the signal generator 34 until the output voltage reaches a predetermined voltage as shown in FIG. As a result, the switching operation becomes as shown by the solid line in FIG. 6 and the output voltage of the DC power supply becomes as shown by the solid line in FIG. 6 as well. It can be seen that it is possible to realize a DC power supply device that does not cause an abnormal low voltage without affecting the startup waveform even if a load current is drawn.

In the present embodiment, for convenience of explanation,
Although the signal generator was composed of a capacitor charging circuit,
It is also possible to form a signal generator capable of simulating a complicated rising waveform in consideration of how to draw the load current and the characteristics of the DC power supply device. Further, it can be easily imagined that the same effect can be obtained by using the error amplifier in the voltage control circuit as the error amplifier or using the signal generator as the reference power source for voltage control.

Furthermore, in the first to third embodiments, the power supply system is the forward type among the pulse width control systems, but any other power supply of the pulse width control system is used, and the frequency control is performed. It can be easily imagined that the same effect can be obtained by varying the pulse width and the frequency with the same configuration even if the DC power supply device of the system is used.

[0028]

As described above, according to the first embodiment of the present invention, the rush current and the output generated at the start-up of the DC power supply device can be obtained by slightly changing the circuit used in the conventional circuit configuration. While realizing the soft start function that suppresses voltage overshoot, even if a load current suddenly starts to flow during startup, the output voltage does not drop and abnormal low voltage does not occur, and a stable DC power supply device can be realized. it can.

In addition, according to the second embodiment of the present invention, the circuit used in the conventional circuit configuration can be realized as it is, and it can be realized more easily and cheaply than that shown in the first embodiment.
You can get exactly the same effect as.

Further, according to the third embodiment of the present invention, since the startup speed can be controlled arbitrarily, the soft start circuit of the conventional soft start circuit and the soft start time constants shown in the first and second embodiments can be changed. The circuit for changing is unnecessary,
In addition to being able to realize a DC power supply device that can obtain the same effect as that of the first embodiment more simply and cheaply, it is possible to arbitrarily control the rising waveform of the output voltage of the DC power supply device.
It is possible to realize a startup that better suits the load characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a DC power supply device according to the present invention.

FIG. 2 is a diagram showing an operation of the first embodiment of the DC power supply device according to the present invention.

FIG. 3 is a diagram showing a second embodiment of a DC power supply device according to the present invention.

FIG. 4 is a diagram showing an operation of the second embodiment of the DC power supply device according to the present invention.

FIG. 5 is a diagram showing Embodiment 3 of the DC power supply device according to the present invention.

FIG. 6 is a diagram showing an operation of the third embodiment of the DC power supply device according to the present invention.

FIG. 7 is a diagram showing a conventional DC power supply device.

FIG. 8 is a diagram showing an operation of a conventional DC power supply device.

[Explanation of symbols]

 1 DC power supply 2 Input capacitor 3 Transformer 4 Switching transistor 5 Driving circuit 6 Rectifying diode 7 Smoothing choke coil 8 Smoothing capacitor 9 Voltage control circuit 10 Soft start circuit 11 Reference power supply 12 Resistor 13 Resistor 14 Capacitor 15 Error amplifier 16 Oscillator 17 Comparison Device 18 Comparator 19 AND circuit 20 Transistor 21 Voltage control reference power supply 22 Load device 23 Low voltage protection circuit 24 Current detection element 25 Soft start control circuit 26 Current detection reference power supply 27 Error amplifier 28 Transistor 29 Resistor 30 Driver circuit 31 Receiver Circuit 32 Inverter circuit 33 Bias resistance 34 Signal generator

Claims (3)

[Claims] 1. A transistor for switching a current from a DC power supply through a transformer, a transistor drive circuit for driving the transistor, and a rectifier diode connected to the secondary side of the transformer for rectifying the current.
A choke coil and a capacitor for smoothing the current from the rectifier diode, a voltage control circuit that controls the switching-on width of the transistor so that the voltage between the terminals of the capacitor becomes a predetermined voltage, and the voltage control circuit is connected to the voltage control circuit. However, a soft start circuit that controls the voltage control circuit so as to slowly raise the output voltage at a predetermined time at the initial stage of operation, and a load device that is connected in parallel with the capacitor and starts to flow when the load current exceeds a specific voltage. In a DC power supply device comprising a low voltage protection circuit connected to the voltage control circuit and protecting the DC power supply device and the load device when the output voltage drops, a time point when the load device starts to draw a current is the load device and the capacitor. Detected by the current detection circuit connected between the and DC power supply rise time by road varied, the output voltage is characterized by comprising a soft start control circuit operative to increase constant. 2. The output signal of the integrated circuit used in the load device is H when the load device starts to draw current.
2. The DC power supply according to claim 1, further comprising a soft start control circuit which is predicted from a time point when it changes from high to low and operates so as to widen a switching ON width of the DC power supply device limited by the soft start circuit. apparatus. 3. A soft start circuit, a voltage waveform shaping circuit for outputting a reference voltage waveform simulating a rising waveform of the output voltage of the DC power supply device, an output voltage of the DC power supply device, and an output voltage of the voltage waveform shaping circuit. The output voltage of the DC power supply device rises according to the voltage waveform arbitrarily set by the voltage waveform shaping circuit, so that the output voltage of the DC power supply device is switched instead of the voltage control circuit only when the DC power supply rises. 2. The DC power supply device according to claim 1, further comprising a variable soft start control circuit for controlling the DC power supply.