JP7399551B2 - power circuit - Google Patents

Description

The present invention relates to a power supply circuit, and particularly to a power supply circuit capable of stabilizing output voltage and useful as a motor control circuit.

In order to stabilize the output voltage, the power supply circuit has a circuit that monitors the output voltage.The output voltage is divided and compared with the reference voltage using an error amplifier.If the result of the comparison is different, the error voltage is output. and is transmitted to the primary side via a photocoupler. The error voltage is input to one of the PWM controllers on the primary side, and the duty ratio of the switching operation is adjusted based on a carrier signal such as a sawtooth wave that is input to the other PWM controller, and the switching operation is performed based on this duty ratio. Generally, a feedback loop is formed to keep the output voltage constant (see Patent Document 1).

For example, when the output voltage becomes lower than the reference voltage, an error voltage is generated, and based on this error voltage, a switching operation is performed at a duty ratio adjusted by the PWM controller. As a result, a switching voltage with a high ratio of the ON state of the switching operation is generated, and the output voltage increases and approaches the reference voltage, reducing the error voltage. When the output voltage exceeds the reference voltage, a switching voltage with a high ratio of the OFF state of the switching operation is generated, and the output voltage decreases and approaches the reference voltage, reducing the error voltage. Since a feedback loop is formed in this way, even if some disturbance is applied, the duty ratio is always adjusted and a steady state is maintained.

Patent No. 5593001

By the way, for example, if the input power is too insufficient, the duty ratio becomes 100%, and the switching operation is always performed in the ON state.

At this time, the control that maintains the steady state is out of control, so if there is an integral element using a capacitor in the feedback loop that integrates the error voltage in order to bring the output voltage closer to the reference voltage, the control In this state, when the input power is restored, the capacitor is charged to an excess level compared to its original level, so the capacitor is charged until the output control is restored. There was a problem in that it took time for the voltage to return to an appropriate level, and during that time the output (voltage) remained uncontrollable for a long time.

Also, if the output is overvoltage, for example, if the load of this power supply circuit is a motor, and an external force that accelerates the motor is applied, the motor will function as a generator and the output of the power supply circuit will become the reference voltage. An overvoltage exceeding the voltage may be applied. In such a state, the power supply circuit stops its switching operation, the duty ratio becomes 0%, and the control also goes out of order, resulting in an excessive integration being applied to the capacitor.

When the output overvoltage is resolved from such a state, it takes time for the capacitor to reach a proper charging state, and there is a problem in that control cannot be performed during that time.

Even when the duty ratio reaches 0% or 100%, it takes time for the input voltage to recover or for the abnormality in the output voltage to be resolved, resulting in an uncontrollable state and stability. It was not possible to provide a power supply circuit.

In conventional power supply circuits that attempt to deal with these issues, it is determined that the control range has been exceeded by analog comparison of the output voltage of the error amplifier, and when it is determined that the control range has been exceeded, the phase Most of them operate by forcibly discharging the compensation circuit to maintain it at a predetermined constant voltage, or charging it with a constant current. It is difficult to consistently provide appropriate judgment and optimal operation for the phase compensation circuit in response to fluctuations in component characteristic values due to changes in temperature and over time, and as a result, it takes a long time to return to the switching state. However, the problem of high costs had not been resolved.

This invention determines whether or not the control is off based on the digital state of whether or not the switching operation is being performed, so when an out-of-control state is detected, it can be determined instantly and more reliably. , and the phase compensation circuit section can be quickly disconnected and connected from the feedback loop.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a stable power supply circuit.

In order to solve the above problem, the invention of claim 1 provides a power circuit that performs predetermined processing on an input signal by a switching operation to generate an output signal, and an error amplifier that generates an output value and a reference value of the output signal. A control circuit that generates an error signal by comparing the error signal and the carrier signal, generates a switching signal by determining a duty ratio from the error signal and the carrier signal, and returns the switching signal to the power circuit to form a feedback loop. The power circuit includes a switching circuit section that performs the switching operation, and the control circuit includes a phase compensation circuit section that includes a capacitor and compensates for the phase of the feedback loop; a switching monitor unit that monitors the working ratio, and the switching monitor unit determines whether the working ratio is higher than the upper predetermined value or lower than the lower limit. The phase compensation circuit section is disconnected from the feedback loop when the value falls below a predetermined value (hereinafter referred to as "outside the control range"), and the duty ratio is within a range between the upper predetermined value and the lower limit predetermined value ( (hereinafter referred to as "within a control range"), the phase compensation circuit section is connected to the feedback loop and a switching operation is started under the phase compensation voltage accumulated in the capacitor . .

In the invention of claim 1, the switching monitor section determines whether the switching operation is within the control range based on the switching signal, and when the switching operation is outside the control range, the phase compensation circuit section including the capacitor is connected to the feedback loop. When the switching operation returns to a steady state in which the switching operation is within the control range, the phase compensation circuit section is connected to the feedback loop to start the switching operation under the phase compensation voltage stored in the capacitor .

The invention according to claim 2 is characterized in that, in the invention according to claim 1 , the predetermined value of the upper limit of the working ratio is 100%, and the predetermined value of the lower limit of the working ratio is 0%.

According to the invention of claim 1, in order to determine whether or not the switching operation is within the control range, that is, whether the duty ratio is equal to or higher than a predetermined upper limit value or lower than a predetermined lower limit value, the digital It enables high-speed judgment, and is not affected by variations in component characteristic values, environmental temperature, or changes over time. Overshoot and undershoot of the output voltage can be suppressed, and a stable power supply circuit can be provided. Furthermore, since the return to the steady state within the control range is performed under the phase compensation voltage accumulated in the capacitor , it is possible to return to the steady state in a better state.

According to the second aspect of the invention, since the duty ratio is determined as 100% or 0%, it is suitable for digital control and can be returned to a steady state within the control range more quickly.

The power supply circuit according to the first embodiment is shown together with FIGS. 2 to 4, and this figure is a circuit diagram. It is a graph diagram showing the characteristics of each component when a load is applied in a no-load state with a duty ratio of 0%, (a) is for the power supply circuit of Embodiment 1, and (b) is for the power supply circuit without countermeasures. It is something. It is a graph diagram showing the characteristics of each component when the input voltage is increased in a duty ratio state of 100%, (a) is for the power supply circuit of Embodiment 1, and (b) is for the power supply circuit without countermeasures. It is something. Similar to FIG. 3, it is a graph showing the characteristics of each component when the input voltage is increased in a duty ratio state of 100%, and the time scale of FIG. 3(a) is expanded, and FIG. 3(c) is obtained by multiplying the time width by 4 times from FIG. 3(a), and FIG. 3(c) is obtained by multiplying the time width by 100 times from FIG. 3 is a circuit diagram showing a power supply circuit according to a second embodiment. FIG.

(Embodiment 1)
Hereinafter, the present invention will be explained based on the illustrated embodiment 1. Embodiment 1 is applied to switching regulation as a DC-DC converter, and constitutes a so-called feedback loop that compares the output voltage with a reference voltage and adds and controls a switching operation to the input voltage based on the error voltage. do.

In FIG. 1, a power supply circuit 1 includes a power circuit 10 that transforms an input voltage under switching operation to generate an output voltage, and a power circuit 10 that generates an error voltage by comparing the output voltage and a reference voltage, and also generates an error voltage by comparing the output voltage with a reference voltage. A control circuit 20 is provided, which determines a duty ratio from a voltage and a carrier signal, generates a switching signal, and feeds the switching signal back to the power circuit to form a feedback loop.

The power circuit 10 includes an input terminal 11 to which an input voltage is applied, a switching circuit section 12 that switches the voltage input to the input terminal 11, and an output terminal 14 that rectifies and smoothes the switching voltage and outputs a step-down voltage. have

In the figure, the left side of the power circuit 10 with the switching circuit section 12 as the boundary is referred to as the input side, and the right side with the boundary as the output side. In the control circuit 20, the left side with the photocoupler 24 as described later as the boundary is referred to as the input side, and the right side is referred to as the input side. is called the output side.

In the power circuit 10 , a voltage input from an input terminal 11 is switched by a switching circuit 12 , and the switching voltage is rectified and smoothed by a rectification and smoothing circuit, and then outputted to an output terminal 14 .

The control circuit 20 includes an error amplifier 21 that divides the output voltage applied to the output terminal 14 and compares it with a reference voltage, a phase compensation circuit section 23 that includes a capacitor 22 and compensates and stabilizes the phase of the feedback loop, and a phase compensation circuit section 23 that compensates and stabilizes the phase of the feedback loop. The first photocoupler 24 transmits the error voltage of the amplifier 21 to the input side, and the error voltage of the error amplifier 21 received via the first photocoupler 24 is compared with the sawtooth wave, and the switching circuit section 12 is A PWM controller 25 that operates at a duty ratio within a predetermined value range, a switching monitor unit 26 that determines whether the error voltage of the error amplifier 21 has a duty ratio within a predetermined value range, and a switching monitor unit 26 that operates at a duty ratio within a predetermined value range. and a second photocoupler 27 for determining and disconnecting the phase compensation circuit section 23 from the feedback loop if the duty ratio is not within a predetermined value.

In the first embodiment, the predetermined value of the upper limit of the duty ratio is set to 100%, and the predetermined value of the lower limit of the duty ratio is set to 0%. Therefore, when the capacitor 22 is overcharged, the switching circuit section 12 continues to maintain the ON state at a duty ratio of 100%, and when the capacitor 22 is overdischarged, the switching circuit section 12 continues to be in the ON state at a duty ratio of 0%. The section 12 is kept in the OFF state. Note that if the duty ratio cannot be set to 100% or 0% due to circuit design or component characteristics, the duty ratio may be designed at the maximum or minimum duty ratio within the allowable range.

The above-mentioned control range means that the power supply circuit 1 is controlled within the range between the upper limit predetermined value and the lower limit predetermined value (a range where the duty ratio does not reach 100% and 0%). The term "outside the control range" refers to a state in which the control range has been deviated from, that is, a state in which the duty ratio has reached 100% or 0%.

Next, the operation of the power supply circuit 1 of the first embodiment will be explained.

First, in a state within the control range, as described above, when a voltage within a predetermined value range is applied to the input terminal 11 of the power circuit 10, it is switched by the switching circuit section 12, and the voltage is applied to the output terminal 14 via the rectifying and smoothing circuit. An output voltage is generated.

Further, the control circuit 20 divides the voltage applied to the output terminal 14 and compares it with a reference voltage by the error amplifier 21. As a result, control is performed to increase the duty ratio when the output voltage is lower than the reference voltage, and to decrease the duty ratio when it is higher than the reference voltage.

The obtained error voltage compared by the error amplifier 21 is transmitted to the input side of the power supply circuit 1 via the first photocoupler 24.

The output terminal 14 is connected to a phase compensation circuit section 23 including a capacitor 22 , and the capacitor 22 is charged with the output voltage of the error amplifier 21 .

Further, the subsequent stage of the phase compensation circuit section 23 is connected to the first photocoupler 24 via a switch section 27a on the output side of the second photocoupler 27.

The phase compensation circuit section 23 also performs phase compensation to keep the phase shift within a certain limit so that oscillation does not occur within the feedback loop.

On the input side of the control circuit 20, the error voltage received by the first photocoupler 24 is input to the comparator 25a of the PWM controller 25, and the comparator 25a converts the error voltage into a sawtooth wave (carrier signal) that serves as a reference for the duty ratio. A PWM signal having a duty ratio corresponding to the error voltage is outputted from the PWM controller 25 as a switching signal.

Once the duty ratio is determined, the switching signal is transmitted to the switching circuit section 12 of the power circuit 10, and the switching circuit section 12 performs a switching operation, that is, turns ON and OFF the switching circuit section 12, based on this duty ratio.

Further, the output of the PWM controller 25 is connected to a switching monitor section 26, which detects whether the duty ratio has become 0% or 100%. When the switching monitor unit 26 detects duty ratio=0% or 100%, the output signal is transmitted to the second photocoupler 27 side. Note that in the above state, since the duty ratio is within the control range (other than 0% and 100%), the second photocoupler 27 does not operate.

Next, the operation of the power supply circuit 1 when the duty ratio is 0% (outside the control range) and a load of 10 A is applied from a no-load state will be explained with reference to FIG.

As mentioned above, when the output voltage becomes overvoltage, the duty ratio decreases in an attempt to keep the output voltage at the reference voltage, and when the duty ratio reaches 0%, it goes out of the control range, and the switching circuit section 12 remains in the OFF state. As a result, the capacitor 22 of the phase compensation circuit section 23 becomes over-discharged.

Therefore, when the duty ratio reaches 0%, the second photocoupler 27 operates and turns off the switch section 27a to disconnect the phase compensation circuit section 23 from the feedback loop, thereby cutting off the discharge of the capacitor 22. , the overdischarge is eliminated.

In this state, the output voltage of the error amplifier 21 is compared (sampled) with the reference voltage, and the switching circuit section 12 is maintained in the OFF state because the duty ratio is 0%.

As mentioned above, when the duty ratio is 0%, it means that the output (load) is overvoltage and is outside the control range. When the switching monitor section 26 detects the duty ratio of 0%, the second photocoupler 27 The switch section 27a is turned off and no switching operation is performed.

If a load is applied to the output terminal 14 in this state, the output voltage will drop below the reference voltage, so the error amplifier 21 generates an error voltage in the direction of increasing the duty ratio, that is, increasing the ON state ratio, to the phase compensation circuit section. It is issued immediately without being affected by 23.

This error voltage is then transmitted to the input side of the power supply circuit 1 via the first photocoupler 24.

On the input side of the power supply circuit 1, a switching signal for increasing the duty ratio is generated from the PWM controller 25 and transmitted to the switching circuit unit 12, and a switching operation with a high ON state ratio is started.

Furthermore, when the switching signal of the PWM controller 25 is output to the switching monitor section 26, the switch section 27a is turned on via the second photocoupler 27, and the phase compensation circuit section 23 is connected to the feedback loop. , phase compensation is performed. At this time, by connecting the phase compensation circuit section 23 to the feedback loop, the phase compensation voltage stored in the capacitor 22 is output to the first photocoupler 24, and the switching operation is started under the phase compensation voltage. That will happen.

FIG. 2 is a graph showing changes in the output voltage when the switching circuit unit 12 starts operating. (a) is the output of the power supply circuit of the first embodiment, and (b) is the output of the power supply circuit without countermeasures. Shows changes in voltage.

In the figure, the upper graph shows the output voltage, the middle graph shows the switching state, and the lower graph shows the load current. The straight line portion (left side) of the middle graph indicates a non-switching state, and the slightly wider hatched portion (right side) indicates a switching state.

Further, in the graph diagram, the voltage of the output voltage in the upper graph indicates the difference with respect to the reference voltage.

In the case of the power supply circuit 1 of Embodiment 1 (FIG. 2(a)), the output voltage changed from a minimum value of -440 mV to a maximum value of 120 mV almost at the same time as the load was applied, whereas in the case of no countermeasure. In the power supply circuit, the output voltage varied from a minimum value of -2.2V to a maximum value of 80mV.

As described above, according to the power supply circuit 1 of the first embodiment, the rate of change in the output voltage can be suppressed to about 1/5 compared to the power supply circuit without countermeasures, and the output voltage is more stable. I can understand that.

Next, the operation of the power supply circuit 1 in a state where the input voltage is insufficient will be explained with reference to FIGS. 3 and 4. In FIGS. 3 and 4, the input voltage has returned from 25.6V to 37.6V.

As mentioned above, when the input voltage is insufficient, the duty ratio increases in an attempt to keep the output voltage at the reference voltage, and when the duty ratio reaches 100%, it goes out of the control range, and if this continues, the switching circuit section 12 will not maintain the ON state. As a result, the capacitor 22 of the phase compensation circuit section 23 becomes overcharged.

Therefore, when the duty ratio reaches 100%, the second photocoupler 27 operates to turn off the switch section 27a and disconnect the phase compensation circuit section 23 from the feedback loop, thereby cutting off the charge to the capacitor 22. This will eliminate overcharging.

In this state, the output voltage of the error amplifier 21 is compared (sampled) with the reference voltage, and the switching circuit section 12 is maintained in the ON state because the duty ratio is 100%.

As described above, the duty ratio is 100% when the switching monitor unit 26 detects the duty ratio of 100% while the input voltage decreases and the switching circuit unit 12 maintains the ON state. , the switch section 27a of the second photocoupler 27 is in the OFF state, out of the control range, and no switching operation is performed.

When the input voltage rises in this state, the output voltage momentarily rises above the reference voltage, so the error amplifier 21 sends an error voltage to the phase compensation circuit section 23 in the direction of lowering the duty ratio, that is, increasing the OFF state ratio. It is issued immediately without being affected by

This error voltage is then transmitted to the input side of the power supply circuit 1 via the first photocoupler 24.

On the input side of the power supply circuit 1, the PWM controller 25 receives a signal in the direction of lowering the duty ratio, is transmitted to the switching circuit unit 12, and a switching operation with a high OFF state ratio is started.

Further, when the PWM signal of the PWM controller 25 is output to the switching monitor section 26, the switch section 27a is turned on via the second photocoupler 27, and the phase compensation circuit section 23 is connected to the feedback loop. In operation, phase compensation of the switching operation is performed. At this time, by connecting the phase compensation circuit section 23 to the feedback loop, the phase compensation voltage stored in the capacitor 22 is output to the first photocoupler 24, and the switching operation is started under the phase compensation voltage. That will happen.

3 and 4 are graphs showing changes in the output voltage when the operation of the switching circuit section 12 is started, and FIGS. FIG. 3(b) shows the power supply circuit 1 without countermeasures.

In the figure, the upper graph shows the output voltage, the middle graph shows the switching state, and the lower graph shows the input voltage. The straight line part of the middle graph shows the non-switching state, and the slightly wider hatched part shows the switching state.

In addition, in the middle graph showing the switching state, until the input voltage is restored, the duty ratio is 100%, but since it is in a non-switching state, it is shown as a straight line, and almost at the same time as the input voltage is restored, it becomes the switching state shown by hatching. It is something.

In the case of the power supply circuit 1 of Embodiment 1 (FIG. 3(a)), almost at the same time as the input voltage is increased, the output voltage rises to 2.4V, immediately drops, drops to -360mV, and then rises slightly again. However, once the switching operation started, it returned to the standard value.

On the other hand, in a power supply circuit without countermeasures, the output voltage suddenly rises to 4.24V, then gradually drops to -2.20V, and then rises again when it exceeds the reference value. The switching action started, then dropped slightly and returned to the standard value.

When comparing FIGS. 3A and 3B, the difference is not only the amount of change in the output voltage but also the time required to reach the reference voltage. The power supply circuit 1 of the first embodiment returns to the reference voltage in an instant, but the power supply circuit without countermeasures takes several hundred times as long as the power supply circuit 1 of the first embodiment. I understand. Figures 3(a) and (b) are shown on the same time scale, but Figure 4(a) has a slightly expanded time width (4 times) than Figure 3(a). 4(b) shows the time width further expanded (100 times).

As described above, according to the power supply circuit 1 of the first embodiment, the time required for the output voltage to reach the switching state after the input voltage is restored is several hundred times faster than that of a power supply circuit without countermeasures, and the output voltage is It can be seen that this is a more stable power supply circuit.

(Embodiment 2)
The present invention will be described below based on a second embodiment shown in the drawings.

FIG. 5 is a circuit diagram showing the power supply circuit 2 according to the second embodiment. This second embodiment differs in configuration from the first embodiment in that it includes a sample and hold circuit 30 that holds the phase compensation voltage of the phase compensation circuit section 23 at the time when it deviates from the control range. 1, the same reference numerals are used to omit the explanation.

The second photocoupler 27 is equipped with two switch sections 27a and 27b, and one switch section 27a connects the phase compensation circuit section 23 including the capacitor 22 from the feedback loop, as in the first embodiment. The other switch section 27b is a switch section built into the sample and hold circuit 30.

One end of the sample hold circuit 30 is connected between the capacitor 22 of the phase compensation circuit section 23 and the switch section 27a of the second photocoupler 27, and the other end is connected between the switch section 27a of the second photocoupler 27 and the second photocoupler 27. 1 and the photocouplers 2 and 4 .

Then, when the duty ratio reaches 0% or 100%, the switch section 27a of the second photocoupler 27 is turned OFF and the phase compensation circuit section 23 is disconnected from the feedback loop, and at the same time, the second photocoupler 27 is disconnected from the feedback loop. The switch 27b of 27 is turned off, and the phase compensation voltage accumulated in the capacitor 22 of the phase compensation circuit section 23 is held.

This sampling state is maintained because even if the voltage of the capacitor 22 fluctuates due to self-discharge of the capacitor 22 or leakage current of the switch, when switching control is restored, the switching operation is performed under the sampled and held phase compensation voltage. It is possible to achieve a return state close to the ideal as feedback control, and to suppress overshoot and undershoot of the output voltage. Note that if the delay of the sample and hold circuit 30 is not a problem, the switch section 27a can be omitted.

In this way, according to the power supply circuit 2 of the second embodiment, overshoot and undershoot at the time of recovery of switching control can be suppressed, so that the stability of the power supply circuit 2 can be further increased.

Although the embodiments of this invention have been described above, the specific configuration is not limited to the above embodiments, and even if there are changes in the design within the scope of the gist of this invention, Included in invention. For example, in the first and second embodiments described above, the present invention is applied to a non-insulated power supply circuit, but the present invention is not limited thereto, and can also be applied to an insulated power supply circuit. Furthermore, although the voltage power supply circuit has been described, the present invention can also be applied to a current power supply circuit that controls current.

1 Power supply circuit 2 Power supply circuit 10 Power circuit 12 Switching circuit section 20 Control circuit 21 Error amplifier 22 Capacitor 23 Phase compensation circuit section 26 Switching monitor section 30 Sample hold circuit

Claims (2)

A power circuit generates an output signal by subjecting an input signal to predetermined processing using a switching operation, and an error amplifier generates an error signal by comparing the output value of the output signal with a reference value. a control circuit that determines a duty ratio from a carrier signal to generate a switching signal, and returns the switching signal to the power circuit to form a feedback loop;
The power circuit has a switching circuit section that performs the switching operation,
The control circuit includes a capacitor, and has a phase compensation circuit section that compensates for the phase of the feedback loop, and a switching monitor section that monitors the duty ratio of the switching signal,
The determination of the upper limit predetermined value and the lower limit predetermined value of the duty ratio is performed by the switching monitor unit,
When the duty ratio becomes greater than or equal to a predetermined upper limit value or less than a predetermined lower limit value, the phase compensation circuit section is disconnected from the feedback loop, and the duty ratio is set to be between the predetermined upper limit value and the predetermined lower limit value. connecting the phase compensation circuit section to the feedback loop when the voltage returns within the range, and starting a switching operation under the phase compensation voltage accumulated in the capacitor ;
A power supply circuit characterized by: The predetermined value of the upper limit of the working ratio is 100%, and the predetermined lower limit value of the working ratio is 0%.
The power supply circuit according to claim 1, characterized in that:

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