JP4830238B2 - DC / DC converter circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention detects a voltage value output from a power supply to a load, and performs pulse width modulation (hereinafter referred to as PWM) control based on an error voltage signal between the voltage value and a reference voltage value of a reference power supply. In particular, the DC / DC converter circuit is configured to apply a constant voltage to the load. In particular, the DC / DC converter circuit is used to stabilize the power supply voltage of an electronic device connected to a power supply having an unstable voltage value such as a battery. The present invention relates to a DC converter circuit.
[0002]
[Prior art]
First, a conventional DC / DC converter circuit will be described.
FIG. 5 is a diagram showing a conventional DC / DC converter circuit configured to supply a constant voltage to a load resistor.
[0003]
The DC / DC converter circuit is configured as an integrated circuit (IC) 100 having external terminals 101 to 105. Of the external terminals 101 to 105, 101 is supplied with a start signal for the power supply circuit, and 102 and 103 output PWM control signals to the gates of the power MOSs 20 and 30.
[0004]
The power source 10 is, for example, an unstable battery, and its + side terminal is connected to the drain of the power MOS 20, and the source of the power MOS 20 is connected to the drain of the low side power MOS 30 and one end of the inductor 40. The source of the power MOS 30 is grounded, and the other end of the inductor 40 is connected to the resistor R2, the capacitor C1, and the load resistor R1.
[0005]
A pair of resistors R2 and R3 connected in series constitutes a detection resistor circuit, and a capacitor C1 is connected in parallel to the detection resistor circuit, so that a voltage value applied to the load resistor R1 is a capacitor. It is detected as the voltage between terminals of C1. Further, in the IC 100 constituting the converter circuit, the potential at the connection point between the resistors R2 and R3 is taken in from the external terminal 104 to detect the voltage across the load resistor R1. Further, a capacitor C3 for soft start is connected to the external terminal 105.
[0006]
Next, the configuration of the internal circuit of the IC 100 will be described.
The IC 100 is configured to supply a stable constant voltage regardless of the magnitude of the load resistance R1 by alternately turning on and off the pair of power MOSs 20 and 30 based on the detected detection voltage. . That is, the IC 100 is provided with a reference power source 1 that is less affected by temperature changes, and a constant reference voltage value is always input to the + side input terminal of the operational amplifier 2 from here. In the operational amplifier 2, the voltage value detected by the detection resistor circuit of the resistors R2 and R3 externally attached via the external terminal 104 is input to the negative input terminal, and the deviation between these voltage values is used as an error voltage signal. Amplified and output.
[0007]
The oscillation circuit 3 outputs a triangular wave having a predetermined frequency, and its output terminal is connected to the negative side input terminals of the comparators 4 and 9. The comparator 4 has a positive input terminal connected to the output terminal of the operational amplifier 2 and is configured to compare the output voltage of the oscillation circuit 3 with the deviation output of the operational amplifier 2.
[0008]
The output terminal of the comparator 4 is connected to the driver circuit 7 via the AND gate 8, and the power MOS 20 connected to the external terminal 102 is on / off controlled by the output voltage signal of the comparator 4. The output voltage signal of the comparator 4 is inverted from the AND gate 8 by the inverter 5 and supplied to the driver circuit 6, and the power MOS 30 connected to the external terminal 103 is turned on / off by the inverted voltage signal from the inverter 5. Be controlled.
[0009]
On the other hand, the comparator 9 supplies a soft start voltage signal to the external terminals 102 and 103 via the AND gate 8, and its + side input terminal is connected to the soft start capacitor C 3 via the external terminal 105. It is connected. The current source 11 and the NMOS switching device 12 are provided in series between the internal power supply and the ground, and the connection point between the current source 11 and the NMOS switching device 12 is connected to the bi-terminal 105 and the NMOS switching. A soft start start signal is supplied from the external terminal 101 to the gate of the device 12 as a start signal for the power supply circuit.
[0010]
Next, the operation at the time of starting the DC / DC converter circuit described above will be described. FIG. 6 is a timing chart showing voltage waveforms of respective portions of the DC / DC converter circuit before and after the start (T0).
[0011]
6A shows the error voltage signal V2 of the operational amplifier 2, the triangular wave of the oscillation circuit 3, and the voltage signal V105 for soft start applied to the external terminal 105. FIG. FIG. 5B shows the output voltage V9 of the comparator 9, the output voltage V4 of the comparator 4, and the output voltage V8 of the AND gate 8.
[0012]
When the DC / DC converter circuit is started (T0), when the current starts to flow from the power source 10 to the load resistor R1 via the power MOS 20 and the inductor 40, the external terminal 105 is set so that a large current does not suddenly flow through the load resistor R1. Is connected to a capacitor C3 for soft start. In the DC / DC converter circuit, a high voltage signal is applied to the external terminal 101 so that the DC output stop state is maintained. In this stopped state, the NMOS switching device 12 is turned on by the voltage signal of the external terminal 101, so that all the current from the current source 11 flows between the drain and the source, and the drain voltage becomes the ground potential. Accordingly, the + side input terminal of the comparator 9 becomes the ground potential, and the output voltage V9 of the comparator 9 is maintained at the ground potential as shown in FIG. 6B as a timing waveform before the start (T0).
[0013]
Before the DC / DC converter circuit is started (T0), the potential of the load resistor is also the ground potential, and the negative input terminal of the operational amplifier 2 from the external terminal 104 is also the ground potential. On the other hand, since a constant potential is supplied from the reference power supply 1 to the + side input terminal of the operational amplifier 2, as shown in FIG. 6A, the error voltage signal V2 of the operational amplifier 2 becomes a high potential. The output voltage V4 of the comparator 4 is maintained at a high potential.
[0014]
Thus, in the stop state in which the output voltage V8 of the AND gate 8 is maintained at the ground potential, the power MOS 20 is maintained in the off state via the driver circuit 7, and the power MOS 30 is maintained in the on state via the inverter 5 and the driver circuit 6. Therefore, the DC / DC converter circuit is maintained in a stopped state.
[0015]
To start the DC / DC converter circuit, the soft start start signal applied to the external terminal 101 as the start signal may be switched to the ground potential. That is, when the soft start start signal becomes the ground potential, the NMOS switching device 12 is turned off, and the current from the current source 11 charges the soft start capacitor C3. Therefore, according to the capacitance value of the capacitor C3, the voltage signal V105 increases linearly with the passage of time in the external terminal 105, and the output voltage V9 of the comparator 9 is equal to the ground potential as shown in FIG. The waveform repeats alternately with a high potential.
[0016]
In this way, the pair of power MOSs 20 and 30 are alternately controlled on and off, and the voltage across the load resistor R1 gradually becomes higher, so that it is detected via the detection resistors R2 and R3. The voltage also increases. As a result, since the error voltage signal V2 shown in FIG. 6A gradually decreases from the high potential side, the on / off of the pair of power MOSs 20 and 30 is controlled by the soft start voltage signal V105 and the error voltage signal V2. And is controlled by a low voltage. Therefore, immediately after the start (T0), the voltage is controlled by the soft start voltage signal V105, the amount of current flowing through the load resistor R1 can be adjusted, and the soft start can be performed. Thereafter, the two voltage signals V105 and V2 intersect. After the cross point time, the timing is determined by the error voltage signal V2 of the operational amplifier 2.
[0017]
[Problems to be solved by the invention]
However, in the conventional DC / DC converter circuit, the amount of initial current flowing from the power supply 10 via the power MOS 20 and the inductor 40 immediately after startup is determined by the capacitor C3 externally attached to the external terminal 105, and therefore the resistance of the load resistor R1. There is a problem that the time until the output voltage becomes stable differs depending on the value.
[0018]
FIG. 7 is a diagram illustrating a difference in time from the start time (T0) to the cross point according to the magnitude of the load resistance R1. FIG. 4A shows a cross point time T1a at light load, and FIG. 4B shows a cross point time T1b at heavy load.
[0019]
Here, the output voltage waveform of the oscillation circuit 3 and the charging voltage waveform in the capacitor C3 have the same magnitude regardless of the magnitude of the load resistor R1. Accordingly, the timing at which the power MOSs 20 and 30 are turned on / off immediately after startup is the same for both light and heavy loads, and the charging current flowing through the inductor 40 is also equal.
[0020]
As a result, when the load is light, the voltage rise of the load resistor R1 is fast, but on the contrary, the rise is slow when the load is heavy. That is, the error voltage signal of the operational amplifier 2 is obtained by amplifying the difference between the voltages detected by the series circuit of the detection resistors R2 and R3 of the voltage between the terminals of the reference power source 1 and the load resistor R1 having a constant voltage. If R1 is a light load, the voltage between the terminals of the load resistor R1 approaches the voltage value of the reference power supply 1 as fast as that. Therefore, the cross-point times T1a and T1b at which the error voltage signal V2 intersects the soft-start voltage signal V105 are , T1a <T1b.
[0021]
An object of the present invention is to provide a DC / DC converter circuit capable of equalizing the rising speed of a DC voltage applied to a load resistor regardless of the size of the load resistor.
[0022]
[Means for Solving the Problems]
In order to achieve the above object, a voltage value output from a power supply to a load is detected, and pulse width modulation (PWM) control is performed based on an error voltage signal between the voltage value and a reference voltage value of a reference power supply. Thus, a DC / DC converter circuit configured to apply a constant voltage to the load is provided. The DC / DC converter circuit includes a first operational amplifier that calculates the error voltage signal, and a voltage follower configuration that outputs an output current signal of a certain magnitude to the first operational amplifier when the operation starts. A second operational amplifier and a second operational amplifier on the output side of the second operational amplifier for soft start at power- on, and a predetermined value corresponding to the magnitude of the output current signal with respect to the first operational amplifier And a capacitor circuit that provides a reference voltage value that increases linearly with an inclination .
[0023]
In the DC / DC converter circuit described above, the reference voltage supplied to the + side input terminal of the first operational amplifier is held at the ground potential when the power supply is stopped, and is gradually increased from the ground potential to the rated voltage immediately after startup. I have to.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is a circuit diagram showing a DC / DC converter circuit of the present invention.
[0025]
The integrated circuit (IC) 100 having the external terminals 101 to 104 is supplied with the start signal of the power supply circuit to the external terminal 101 as in the conventional circuit described with reference to FIG. A signal is output to the gates of the power MOSs 20 and 30. The power supply 10 for supplying a DC voltage to the load resistor R1 is, for example, an unstable battery, and its + side terminal is connected to the drain of the power MOS 20, the source of the power MOS 20 is the drain of the low side power MOS 30, and It is connected to one end of the inductor 40. The source of the power MOS 30 is grounded, and the other end of the inductor 40 is connected to the resistor R2, the capacitor C1, and the load resistor R1. Further, the IC 100 detects the voltage between the terminals of the load resistor R1 by taking in the potential at the connection point of the resistors R2 and R3 from the external terminal 104.
[0026]
Next, the configuration of the internal circuit of the IC 100 will be described only in the differences from the conventional circuit shown in FIG.
A second operational amplifier 13 having a voltage follower configuration and a soft start capacitor C2 are connected to the + side input terminal of the first operational amplifier 2 that calculates the error voltage signal. The second operational amplifier 13 has an input signal terminal 13a connected to the positive electrode of the reference power supply 1, an activation control terminal 13b connected to the external terminal 101, a soft start control signal output terminal 13c, and a first operational amplifier. 2 + side input terminals are connected. Further, the comparator 4 has its + side input terminal connected to the output terminal of the first operational amplifier 2, and compares the output voltage of the oscillation circuit 3 with the deviation output of the first operational amplifier 2. The comparison result is directly supplied to the driver circuit 7 and also supplied to the driver circuit 6 via the inverter 5.
[0027]
Next, the operation at the start of the DC / DC converter circuit will be described with reference to FIG.
FIG. 2 is a timing diagram showing signal waveforms at various parts of the second operational amplifier 13. Va is a reference voltage signal of the reference power source 1, Vb is a soft start start signal for stop and start supplied from the external terminal 101, and Vc is an output signal that gradually rises immediately after the start time T 0. When the soft start start signal Vb applied to the start control terminal 13b is at a high potential, the output signal Vc of the operational amplifier 13 is at the ground potential and is in a stopped state.
[0028]
Thereafter, when the soft start start signal Vb reaches the ground potential at time T0, the operational amplifier 13 having the voltage follower configuration starts to operate, and the output signal Vc increases linearly from the ground potential to the magnitude of the reference voltage signal Va. When the potential of the signal Va is exceeded, control is performed so as to return to the reference voltage. The slope of the output signal Vc at this time is determined by the capacitance value of the soft start capacitor C2 and the magnitude of the output signal current I0 of the second operational amplifier 13.
[0029]
In this way, the operational amplifier 13 having the voltage follower configuration constitutes a soft-start operational amplifier that gives the first operational amplifier 2 a reference voltage value that gradually increases with a predetermined slope. Regardless of the magnitude of R1, the rising speed of the load voltage can be controlled to be constant.
(Second embodiment)
FIG. 3 is a circuit diagram showing a DC / DC converter circuit of the present invention.
[0030]
The second embodiment is different from the circuit shown in FIG. 1 in that the capacitor C2 built in for soft start is replaced with an external capacitor C3. That is, the external terminal 105 is provided in the IC 100, and the soft start time immediately after startup is adjusted by changing the capacitance value of the capacitor C3 connected thereto. By using the external capacitor C3, it is possible to set the rising time of the soft start in the range of several tens of milliseconds to several seconds. Since other configurations are the same as those of the above-described embodiment, their description is omitted.
[0031]
Here again, since the operational amplifier 13 for soft start is constituted by the operational amplifier 13 having the voltage follower configuration, the rising speed of the load voltage can be controlled to be constant regardless of the size of the load resistor R1.
[0032]
Note that the operational amplifier 13 having a voltage follower configuration may be configured as shown in FIG. In FIG. 4, an operational amplifier is constituted by a current source I, a resistor R4, a capacitor C4, and MOS transistors M1 to M10, and switching transistors S1 to S6 constitute a switch for switching between start and stop by a soft start control signal. ing.
[0033]
When the start control terminal 13b is at a high potential, the switching transistors S1 and S2 are inverters, so that the drain of S1 is at the ground potential, S4 is in the on state, and the start control terminal 13b is on the gate electrodes of S3, S5, and S6 Is applied, and the operational amplifier 13 is maintained in the stopped state. When the control signal for soft start changes from a high potential to a ground potential, all the switching transistors S3 to S6 are turned off, and the operational amplifier 13 starts operating. At this time, the magnitude of the output signal current I0 from the control signal output terminal 13c for soft start depends on the current value of the current source I by I1, the gate widths Wn and gate lengths Ln of the MOS transistors M1 to M3, and M9. Can be determined as follows.
[0034]
I0 = {(W2 / L2) × (W9 / L9) / (W1 / L1) × (W3 / L3)} × I1
In the above formula, Wn and Ln are the gate width and gate length of the MOS transistor Mn.
[0035]
【The invention's effect】
As described above, according to the DC / DC converter circuit of the present invention, the reference voltage supplied to the + side input terminal of the first operational amplifier is held at the ground potential when the power supply is stopped, By gradually increasing the potential to the rated voltage, the rising speed of the DC voltage applied to the load resistance can be made equal regardless of the magnitude of the load resistance.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a DC / DC converter circuit of the present invention.
FIG. 2 is a timing chart showing signal waveforms of respective parts of a second operational amplifier.
FIG. 3 is a circuit diagram showing another DC / DC converter circuit.
FIG. 4 is a circuit diagram illustrating an example of an operational amplifier having a voltage follower configuration.
FIG. 5 is a diagram showing a conventional DC / DC converter circuit.
FIG. 6 is a timing diagram showing voltage waveforms at various parts of the DC / DC converter circuit before and after startup.
FIG. 7 is a diagram illustrating a difference in time from the start to the cross point according to the magnitude of the load resistance.
[Explanation of symbols]
100: Integrated circuit (IC)
101-104 ... External terminal 10 ... Power source 20, 30 ... Power MOS 20
DESCRIPTION OF SYMBOLS 40 ... Inductor 1 ... Reference power supply 2 ... 1st operational amplifier 3 ... Oscillator circuit 4 ... Comparator 5 ... Inverter 6, 7 ... Driver circuit 13 ... 2nd operational amplifier

Claims (4)

A voltage value output from the power supply to the load is detected, and a pulse voltage modulation (PWM) control is performed based on an error voltage signal between the voltage value and the reference voltage value of the reference power supply, whereby a constant voltage is applied to the load. In the DC / DC converter circuit adapted to apply
A first operational amplifier for computing the error voltage signal;
When the operation is started, a second operational amplifier having a voltage follower configuration that outputs an output current signal having a constant magnitude to the first operational amplifier;
A reference voltage which is provided on the output side of the second operational amplifier for soft start when power is turned on and linearly increases with a predetermined slope corresponding to the magnitude of the output current signal with respect to the first operational amplifier. A capacitor circuit to give a value ;
A DC / DC converter circuit comprising:   2. The DC / DC converter circuit according to claim 1, wherein the capacitor circuit is formed in an integrated circuit integrally with the first and second operational amplifiers.   2. The DC / DC converter circuit according to claim 1, wherein the capacitor circuit is formed by an external capacitor with respect to the integrated circuit constituting the first and second operational amplifiers. 2. The DC / DC converter circuit according to claim 1, wherein a soft start start signal is input to the second operational amplifier, and an operation is started by the soft start start signal.

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