JP2003324941A - Power source apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a rush current at a voltage reset time even when a temporary voltage drop occurs at an input power source voltage. <P>SOLUTION: A capacitor 27 is gradually charged by a constant-current circuit 38 at a voltage VB applying time, and an operational amplifier 36 controls an output voltage Vo based on a detected voltage Va and the terminal voltage Vc of a capacitor 27. If the output voltage Vo (detected voltage Va) is lowered when the voltage VB is temporarily lowered so that Vd>Va is satisfied, a diode 44 is turned on to lower the terminal voltage Vc. When the voltage VB is reset to a normal voltage, the voltage Vc starts gradually increasing from the voltage which is once lowered according to the drop of the detected voltage Vs, and hence soft starting is effectively functioned. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device having a soft start function.

[0002]

FIG. 3 shows an electrical configuration of a power supply circuit with a soft start function which has been conventionally used for vehicle mounting, for example. The power supply circuit 1 shown in FIG. 3 includes a battery 2 and an ignition switch 3.
The input power supply voltage VB applied via the
Is a switching power supply circuit that supplies a constant output voltage Vo (for example, 7 V). When the MOSFET 5 is turned on, the capacitor 7 is charged via the reactor 6 and MO
When the SFET 5 turns off, the diode 8 turns on temporarily.

The MOSFET 5, the control circuit, that is, the voltage dividing circuit 9, the operational amplifier 10, the reference voltage generating circuit 11, the constant current circuit 12, the power-on reset circuit 13, the comparator 14, the triangular wave generating circuit 15, and the gate drive circuit 1.
6 is configured as an IC, and the soft-start capacitor 17 is externally attached to the IC.

FIG. 4 is an operation waveform of the power supply circuit 1, showing the input power supply voltage VB, the detection voltage Va, the terminal voltage Vc of the capacitor 17, the output voltage Vo, and the current IL flowing in the reactor 6 in order from the top. There is. The ignition switch 3 is turned on and the input power supply voltage VB is reset voltage V.
When the voltage exceeds POR, the terminal voltage Vc of the capacitor 17 starts gradually increasing due to charging. The operational amplifier 10 performs differential amplification by using the lower one of the reference voltage Vr and the terminal voltage Vc as the voltage on the inverting input side. As a result, the output voltage Vo
Gradually increases according to the terminal voltage Vc, and eventually reaches the target voltage (7V) corresponding to the reference voltage Vr. This can reduce the inrush current flowing from the MOSFET 5 to the capacitor 7 via the reactor 6 when the power is turned on.

On the other hand, after the output voltage Vo reaches the target voltage, if the input power supply voltage VB temporarily drops to the target voltage or less (time ta), the output voltage Vo cannot maintain the target voltage and drops. . The reset voltage VPOR is set to a value (for example, 2V) at which the power-on reset does not operate due to the temporary voltage drop expected in such normal operation, and the control circuit also sets the input power supply voltage VB to the reset voltage VPOR. It operates normally until the voltage drops to a near voltage (for example, 3V). Therefore, the terminal voltage Vc of the capacitor 17 is maintained at the charged value, and when the input power supply voltage VB sharply returns to the normal voltage thereafter (time tb), the soft start does not operate effectively and a large inrush current flows. There were cases.

The present invention has been made in view of the above circumstances, and its object is not only when the input power supply voltage is turned on, but also when the output voltage temporarily drops due to a decrease in the input power supply voltage or the like. Another object of the present invention is to provide a power supply device capable of reducing the inrush current when the voltage is restored.

[0007]

According to the means described in claim 1, the reference limiting voltage generating means outputs the reference limiting voltage gradually increased by charging the capacitor, and the output voltage controlling means outputs the reference limiting voltage. The output voltage is controlled based on the voltage deviation from the detected voltage while limiting the reference voltage using.
As a result, the output voltage gradually increases while being limited according to the reference limit voltage, and eventually reaches the target voltage according to the reference voltage. This soft start function can reduce the inrush current when the input power is turned on.

The inrush current is generated by the voltage difference between the reference voltage limited by the reference limit voltage and the detected voltage when the output voltage control means performs the feedback control. Therefore, in the conventional means for resetting the reference limit voltage only based on the decrease in the input power supply voltage, there is no feedback from the output voltage to the reference limit voltage, and even if the output voltage drops, it is not reflected in the reference limit voltage. There were cases.

On the other hand, in the present invention, since the reference limit voltage control means is provided and the reference limit voltage is controlled according to the detected voltage, the output power voltage drops due to the input power supply voltage drop and the load increase. When it occurs, the decrease is reflected in the reference limit voltage, and the voltage difference is controlled to be reduced. As a result, when the input power supply voltage and load status return to normal, the reference limit voltage starts to gradually increase again from the value that reflects the reduced output voltage, so soft start is effective as when input power is turned on. And can effectively reduce the inrush current.

According to the means described in claim 2, when the output voltage is lower than the target voltage, the output voltage control means controls the output voltage by using the reference limit voltage lower than the reference voltage as the command voltage. Therefore, the output voltage can be gradually increased as the reference limit voltage increases. Further, after the output voltage reaches the target voltage, the output voltage control means controls the output voltage by using the reference voltage lower than the reference limit voltage as the command voltage, so that the output voltage can be matched with the target voltage. .

According to the means described in claim 3, when the detection voltage (that is, the output voltage) decreases, the reference limiting voltage also decreases accordingly. Therefore, when the output voltage returns to the normal voltage, the reference limiting voltage decreases. The soft start function works effectively again starting from the value you set.

According to the means described in claim 4, since the reference limit voltage is controlled so as not to become higher than the detection voltage by a predetermined voltage or more, the rush current when the output voltage starts increasing increases to the predetermined voltage at most. It will be a value according to it. It should be noted that if the reference limit voltage is always controlled to be equal to the detection voltage, the increase in the output voltage stops. Therefore, the above-mentioned predetermined voltage may be appropriately determined based on the magnitude of the allowable inrush current, the stability of starting, and the like.

According to the means described in claim 5, when the reference limit voltage is higher than the detection voltage by a predetermined voltage or more, the reference limit voltage is lowered to the voltage level of (detection voltage + predetermined voltage). When the input power supply voltage returns from the temporary lowering state to the normal state, the output voltage can immediately increase to increase without dead time.

According to the means described in claim 6, when the reference limit voltage becomes higher than the detection voltage by a predetermined voltage or more, the discharging means discharges the capacitor to set the reference limit voltage to (detection voltage + predetermined voltage). Reduce to voltage level. With this means, only the discharge of the capacitor is controlled, so the structure can be simplified.

According to the means described in claim 7, the amplifying means differentially amplifies the divided reference limiting voltage and the detected voltage, and the divided reference limiting voltage outputted from the dividing means is obtained. When the voltage exceeds the detection voltage, the charge stored in the capacitor is discharged through the rectifying means and the amplifying means. Here, the predetermined voltage is determined by the voltage division ratio of the voltage dividing means.

According to the means described in claim 8, when the input power supply voltage is applied, the electric charge of the capacitor is discharged and the reference limit voltage becomes 0V. Therefore, the output voltage is limited according to the reference limit voltage. It gradually increases from 0V to reach the target voltage. By this power-on reset, it is possible to more reliably suppress the occurrence of inrush current when the input power is turned on.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a power supply device according to the present invention will be described below with reference to FIGS. FIG. 1 shows a vehicle (automobile) ECU (Electronic Cont
The electrical configuration of the switching power supply circuit installed in the rol unit) is shown. The switching power supply circuit 21 shown in FIG. 1 includes a battery 22 and an ignition switch 2.
Input power supply voltage VB applied via 3 is stepped down, and EC
A constant output voltage Vo (for example, 7V) is supplied to various loads 24 provided in U.

Among the components of the switching power supply circuit 21, the N-channel MOSFET 2 which is the main transistor
5 and its control circuit are configured as an IC 26, and the soft start capacitor 27 is externally attached to the terminal 26e of the IC 26 because of its large capacitance. IC
The terminals 26a and 26b of 26 are an input power supply terminal and a ground terminal, respectively, and the terminals 26c and 26d are an output terminal and a voltage detection terminal, respectively.

A reactor 28 functioning as a filter is connected between the terminal 26c and the output terminal 21a of the switching power supply circuit 21, and the terminals 26c and 26b are connected.
Between the output terminal 21a and the output terminal 21a, and between the output terminal 21a and the output terminal 21b are a diode 29 and a capacitor 30 having the polarities shown in the drawing.
Are connected. Further, the output terminal 21a and the terminal 26d are connected to feed back the output voltage Vo.

The IC 26 is constructed as follows.
The terminals 26a and 26b are the power supply lines 3 of the IC 26, respectively.
1. The circuits in the IC 26 are connected to the ground line 32, and operate by receiving the input power supply voltage VB from the power supply line 31 and the ground line 32. The MOSFET 2 is provided between the terminals 26a and 26c.
The drain and source of 5 are connected, and this MOS
A diode 25a having the illustrated polarity is connected in parallel to the FET 25 (or integrally formed as an element).

A voltage dividing circuit 35 (voltage detecting means) composed of resistors 33 and 34 is connected between the terminal 26d and the ground line 32, and the voltage dividing point is a non-point of the operational amplifier 36 (output voltage controlling means). It is connected to the inverting input terminal. This divided voltage is the detection voltage Va proportional to the output voltage Vo. The operational amplifier 36 has two inverting input terminals. One of the inverting input terminals is connected to the terminal 26e to input the terminal voltage Vc (reference limiting voltage) of the capacitor 27, and the other inverting input terminal has a band gap. The reference voltage Vr (1.2V) corresponding to the target voltage (7V) is connected to the output terminal of the reference voltage generation circuit 37 (reference voltage generation means).
To enter. The operational amplifier 36 amplifies a difference voltage between the detected voltage Va and the lower one of the terminal voltage Vc and the reference voltage Vr.

A constant current circuit 38 (charging means) that outputs a constant current Ic for charging the capacitor 27 is connected between the power supply line 31 and the terminal 26e. The circuit composed of the capacitor 27 and the constant current circuit 38 is
It corresponds to the reference limiting voltage generating means in the present invention.

Further, between the terminal 26e and the ground line 32, the collector-emitter of the transistor 40 which constitutes the power-on reset circuit 39 (power-on reset means) is connected. The power-on reset circuit 39 includes a comparison circuit 41 that compares the input power supply voltage VB with the threshold voltage VPOR, and when the input power supply voltage VB drops below the threshold voltage VPOR, the comparison circuit 41.
The transistor 40 is turned on in accordance with the determination signal from. By providing the power-on reset circuit 39, the output voltage Vo is turned on when the input power is turned on.
Can be increased from 0V.

Further, a capacitor 27 is connected to the terminal 26e.
The operational amplifier 43 (amplifying means), the diode 44 (rectifying means) and the voltage dividing circuit 4 are used to discharge the charged electric charge of
A discharge control circuit 42 (reference limiting voltage control means) composed of 5 (voltage dividing means) is connected. The non-inverting input terminal of the operational amplifier 43 is connected to the non-inverting input terminal of the operational amplifier 36, and the output terminal of the operational amplifier 43 is the diode 44.
It is connected to the terminal 26e via.

The direction of the diode 44 is the direction of the capacitor 27.
The terminal 26e side serves as an anode so that the charged electric charge can be discharged. In addition, the resistors 46 and 4 forming the voltage dividing circuit 45 are respectively provided between the terminal 26e and the inverting input terminal of the operational amplifier 43 and between the inverting input terminal and the ground line 32.
7 is connected. As a result, the divided voltage Vd represented by the following equation (1) is input to the inverting input terminal of the operational amplifier 43. Vd = Rb / (Ra + Rb) × Vc (1) where Ra and Rb are resistance values of the resistors 46 and 47, respectively.

The comparator 48 is the operational amplifier 36.
Of the output signal and the triangular wave signal output from the triangular wave generation circuit 49 are output, and the comparison signal is applied to the gate of the MOSFET 25 through the gate drive circuit 50. Where MOSF
The gate drive circuit 50 is provided with a booster circuit (not shown) so that the gate of the ET 25 can be sufficiently driven.

Next, the operation of this embodiment will be described with reference to FIG. FIG. 2 shows the switching power supply circuit 2.
1 is an operation waveform of the input power supply voltage VB,
The detection voltage Va, the terminal voltage Vc of the capacitor 27, the output voltage Vo, and the current IL flowing through the reactor 28 are shown. When the ignition switch 23 is turned on and the input power supply voltage VB becomes equal to or higher than the reset voltage VPOR, the transistor 40 is turned off in the power-on reset circuit 39, and the terminal voltage Vc of the capacitor 27 is charged by the constant current Ic and gradually increases from 0V. (Time t1).

Until time t2 when the terminal voltage Vc reaches the reference voltage Vr, the operational amplifier 36 amplifies the difference voltage between the detection voltage Va and the terminal voltage Vc. The comparator 48 drives the MOSFET 25 by generating a drive signal having a duty ratio proportional to the output voltage of the operational amplifier 36. MO
When the SFET 25 is turned on, the capacitor 30 is charged through the reactor 28, and when the MOSFET 25 is turned off, the diode 29 is turned on temporarily to suppress generation of surge voltage.

By this feedback control, the output voltage Vo increases in accordance with the terminal voltage Vc and reaches the target voltage (7V) corresponding to the reference voltage Vr at time t2. Further, during this period, the detected voltage Va and the terminal voltage Vc substantially match, so that the relationship of Vd <Va is established, and the diode 4
4 is in the off state.

After time t2, the terminal voltage Vc is the reference voltage V
Since r is exceeded, the operational amplifier 36 performs constant voltage control so that the output voltage Vo becomes equal to the target voltage based on the difference voltage between the detection voltage Va and the reference voltage Vr. in this case,
When Vd ≧ Va, the diode 44 is turned on and a discharge current flows, so that the terminal voltage Vc is prevented from rising, and the terminal voltage Vc does not exceed Vc shown below. Vc = (Ra + Rb) / Rb × Va (2)

When the input power supply voltage VB drops below the target voltage due to the operation of the engine starter or the like at time t3, the capacitor 30 causes the reactor 2 to pass.
8, the current flows through the diode 25a, the output voltage V
Also, o cannot be maintained at the target voltage and decreases. Due to this decrease in the output voltage Vo, Vd is generated in the discharge control circuit 42.
Since> Va, the diode 4 remains until Vd = Va.
The electric charge of the capacitor 27 is extracted through 4, and the terminal voltage Vc is lowered to the value shown by the above-mentioned equation (2).
This terminal voltage Vc is (3) below with respect to the detection voltage Va.
The value is higher by the voltage ΔV (corresponding to the predetermined voltage in the present invention) shown by the formula. ΔV = Vc−Va = Ra / Rb × Va (3)

Eventually, when the input power supply voltage VB sharply returns to the target voltage at time t4 because the operation of the engine starter is stopped, the operational amplifier 36 operates with a voltage deviation of ΔV when returning. A rush current IL having a magnitude corresponding to the voltage ΔV temporarily flows. However, since the voltage ΔV can be set to be sufficiently small, the inrush current IL can also be suppressed to be sufficiently small. As a result, the detected voltage Va follows the terminal voltage Vc, and then the terminal voltage Vc gradually increases from the voltage once lowered according to the decrease of the detected voltage Va. As a result, similarly to when the input power is turned on, the output voltage Vo increases in accordance with the terminal voltage Vc, and the inrush current is suppressed to a sufficiently small value.
It is possible to increase o to the target voltage.

As described above, the switching power supply circuit 21 of this embodiment gradually increases the terminal voltage Vc by charging the capacitor 27, and uses the terminal voltage Vc as the command voltage until the output voltage Vo reaches the target voltage. Since the output voltage Vo is controlled, the output voltage Vo is equal to its terminal voltage Vc.
Is gradually increased while being restricted according to. With this soft start function, the MOSFET 25
Also, the inrush current flowing through the reactor 28 can be reduced, and the occurrence of failures such as burnout and disconnection of these components can be prevented.

Further, the discharge control circuit 42 is provided, and when the output voltage Vo (detection voltage Va) decreases due to a temporary decrease of the input power supply voltage VB, the terminal voltage Vc of the capacitor 27 decreases according to the voltage decrease. And As a result, when the input power supply voltage VB is restored from the temporary lowering state to the normal state, the terminal voltage Vc starts to gradually increase again from the value in which the output voltage Vo at the time of the lowering is reflected. Similar to, soft start works effectively.

In this case, since the terminal voltage Vc is controlled so as not to exceed the detection voltage Va by the voltage ΔV shown in the expression (3), the inrush current flowing when the input power supply voltage VB recovers from the temporary lowered state. Can be reduced to a value corresponding to the voltage ΔV. Since the increase of the output voltage Vo is stopped when the voltage ΔV is set to 0V, the voltage ΔV may be appropriately determined based on the magnitude of the allowable inrush current and the stability of the start.

Further, the discharge control circuit 42 has a terminal voltage Vc.
Does not decrease beyond the voltage level of (detection voltage Va + voltage ΔV) when the voltage exceeds the detection voltage Va by ΔV, the input power supply voltage VB returns from a temporary decrease state to a normal state. When this happens, the output voltage Vo can immediately start increasing without wasting time.

The discharge control circuit 42 used in this embodiment is
Since it is composed of the operational amplifier 43, the diode 44, and the voltage dividing circuit 45 and has a small circuit scale, there is an advantage that it can be easily added to a power supply circuit of a conventional configuration having a soft start function using a capacitor. Further, since the output of the operational amplifier 43 is rectified by the diode 44, the rise of the output voltage Vo (detection voltage Va) is not fed back to the capacitor 27, and the voltage rise rate at the soft start can be made constant. it can. Therefore, even when the input power supply voltage VB fluctuates significantly,
The soft start can be effectively operated, and a high quality switching power supply circuit can be realized.

The present invention is not limited to the embodiment described above and shown in the drawings, and can be modified or expanded as follows, for example. The inrush current is the operational amplifier 3
6 is generated by the voltage difference between the command value used by 6 (the lower voltage of the reference voltage Vr and the terminal voltage Vc) and the detection voltage Va. Therefore, in order to reduce the inrush current, not only the above-mentioned configuration but also a configuration in which the output voltage Vo is fed back and the terminal voltage Vc is controlled according to the voltage (detection voltage Va) may be generally used. In particular, when the output voltage Vo (detection voltage Va) decreases due to a temporary decrease of the input power supply voltage VB, the terminal voltage Vc may be decreased accordingly.

For example, the reference limiting voltage generating means may be composed of the capacitor 27 and its discharging means, and the reference limiting voltage control means may be configured to control the charging current of the capacitor 27. Further, the reference limit voltage generating means is a capacitor 27.
And the charging / discharging means thereof, and the reference limiting voltage control means may control the charging / discharging current of the capacitor 27.

The reference limit voltage control means comprises a comparison circuit for comparing the terminal voltage Vc with the detection voltage Va using the voltage ΔV as an offset voltage, and a discharge circuit for discharging the capacitor 27 based on the comparison result of this comparison circuit. You may. The power-on reset circuit 39 may be provided as needed. It is also applicable to power supply devices such as switching power supply circuits and linear regulators according to other methods. Further, the present invention can be applied not only to vehicle-mounted ECUs but also to power supply devices used in various other devices.

[Brief description of drawings]

FIG. 1 is an electrical configuration diagram of a switching power supply circuit according to an embodiment of the present invention.

FIG. 2 is an operation waveform diagram of the switching power supply circuit.

FIG. 3 is a view corresponding to FIG. 1 showing a conventional technique.

FIG. 4 is a view corresponding to FIG.

[Explanation of symbols]

21 is a switching power supply circuit (power supply device), 27 is a capacitor, 35 is a voltage dividing circuit (voltage detection means), 36 is an operational amplifier (output voltage control means), 37 is a bandgap reference voltage generation circuit (reference voltage generation means), 38 is a constant current circuit (charging means), 39 is a power-on reset circuit (power-on reset means), 42 is a discharge control circuit (reference limit voltage control means), 43 is an operational amplifier (amplification means), 44
Is a diode (rectifying means), and 45 is a voltage dividing circuit (voltage dividing means).

Claims (8)

[Claims] 1. A capacitor comprising: a voltage detection means for outputting a detection voltage according to an output voltage; a reference voltage generation means for outputting a reference voltage according to a target voltage of the output voltage; a capacitor and a charging means for the capacitor. A reference limit voltage generating unit that outputs a reference limit voltage that gradually increases by charging, and an output voltage that controls the output voltage based on a voltage deviation from the detected voltage while limiting the reference voltage using the reference limit voltage. A power supply device comprising: a control unit; and a reference limit voltage control unit that controls the reference limit voltage according to the detected voltage. 2. The reference limit voltage generation means is configured to output a reference limit voltage that gradually increases until it finally becomes equal to or higher than the reference voltage, and the output voltage control means includes the reference voltage and the reference limit voltage. The lower voltage of the voltages is set as a command voltage, and the output voltage is controlled based on a voltage deviation between the command voltage and the detection voltage. Power supply. 3. The power supply device according to claim 1, wherein the reference limit voltage control means controls the reference limit voltage so as to decrease in accordance with the decrease in the detection voltage. 4. The reference limit voltage control means controls the discharge of the capacitor so that the reference limit voltage does not become higher than the detection voltage by a predetermined voltage or more. The power supply device according to. 5. The reference limit voltage control means, when the reference limit voltage is higher than the detected voltage by a predetermined voltage or more, lowers the reference limit voltage to a level at which the reference limit voltage does not reach the state. The power supply device according to claim 4. 6. The reference limit voltage control means, comparing means for comparing the reference limit voltage with the detection voltage using the predetermined voltage as an offset voltage, and discharging the capacitor based on the comparison result of the comparing means. The power supply device according to claim 5, wherein the power supply device comprises a discharging means. 7. The reference limiting voltage control means divides the reference limiting voltage at a predetermined ratio, and a difference between the divided reference limiting voltage output from the dividing means and the detected voltage. The power supply device according to claim 5, wherein the power supply device comprises an amplifying means for amplifying a voltage, and a rectifying means connected between a terminal of the capacitor and an output terminal of the amplifying means. 8. The power supply device according to claim 1, further comprising power-on reset means for discharging the electric charge of the capacitor when an input power supply voltage is applied.