JPH07274495A - Switching regulator - Google Patents

Abstract

PURPOSE:To perform the phase compensation without increasing ripple by adding a pass controller to the resistor for phase compensation of a low-range filter for smoothing. CONSTITUTION:A capacitor 44 is connected in parallel with the resistor 44 for phase compensation of a low-range filter LPF4 for smoothing, and the value of this capacitor is made so that the capacitance may be equal with the resistance value of a resistor 43 with the medium frequency on logarithm graduation between the switching frequency and the frequency at the time when the open loop gain of a control system is 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator, and more particularly to a switching regulator having a phase compensation circuit in a control loop system for stabilizing an output voltage.

[0002]

2. Description of the Related Art Conventionally, this type of switching regulator generally has a circuit configuration shown in FIG. In FIG. 2, the voltage V ₁ of the DC power supply 1 is pulse-converted by the main transistor 12 and the main transformer 3, and the converted pulse is rectified by the diodes 5 and 6, and is converted by the coil 131, the capacitor 132, and the resistor 133. It is smoothed by the constituted low-pass filter LPF13, becomes the output voltage V ₂ , and is supplied to the load 7. In order to stabilize the output voltage V ₂ , the output voltage V ₂ is input to the error amplifier 8 forming a loop control system, compared with the reference voltage here, and the difference is detected and amplified. The increased error component is input to the pulse width modulation circuit 9, and the pulse width of the switching pulse generated here is modulated. The modulated switching pulse is input to the drive circuit and powered up, and drives the main transistor 12 via the driver transformer 11.

That is, the error voltage of the output voltage V ₂ is detected by this loop control system, and the error voltage is controlled by changing the width of the switching pulse. For example, when the output voltage V ₂ changes in the high direction, the switching pulse width becomes narrow and the output voltage V ₂ is controlled in the low direction to be stabilized.

In this control loop system, it is necessary to provide a sufficient stabilizing condition for the oscillation phenomenon. For example, the input side of the error amplifier 8 is cut and the open loop gain measured from the cut end is used. Looking at the stabilization condition with the phase characteristic, when the open loop gain of this loop control system is 1 or more, the phase delay of the loop control system must be suppressed to 180 degrees or less.

The phase characteristic of this control loop system is approximately LPF1.
3 coil 131 and capacitor 132.
(The resistor 133 will be described later, but is 0 Ω here.) The constants of the coil 131 and the capacitor 132 have a minimum value determined by the switching frequency, the duty ratio, and the minimum load current, but in reality, from the ripple suppression of the output voltage V _2. A value considerably larger than this minimum value is determined. However, there is a limit to this maximum value from the response speed of the control loop system with respect to input voltage or load fluctuation. In the coil 131 and the capacitor 132 whose constant values are determined in this way, when the constant values are L and C, respectively,

[0006]

Then, a phase delay of 90 degrees occurs, and when the frequency rises above this frequency f ₁ , the phase delay further increases to a maximum of 180 degrees. That is, at this time, the phase delay in the LPF 13 becomes 180 degrees.

Therefore, at a frequency where the phase delay is 180 degrees, the open loop gain becomes unstable in the oscillation region when it is 1 or more. Therefore, the gain of the error amplifier 8 and the resistance and the capacitor of the feedback circuit are set to 1 or less. Adjust the value or, as shown in Figure 2, LPF 13 condenser 132
A resistor 133 having a small resistance value is inserted in series with and the phase delay is prevented from being 180 degrees at the maximum.

The effect of this resistor 133 is described in the reference material, Japanese Patent Application Publication No. Showa 57-85113. The phase characteristic of the LPF 13 at this time becomes the curve (C) shown in FIG. That is,

[0010]

There is a phase delay of 90 degrees at the resistor 133.
If is 0Ω, it becomes the curve of (b) as described above.
Although it reaches 0 degrees, when the resistor 133 is rΩ, f ₂ = 1
A phase delay of 135 degrees occurs at / 2πrC, and reaches 90 degrees when the frequency further increases. Therefore, by properly selecting the resistance value r, the phase delay can be 180 degrees or less at any frequency.

[0012]

As described above, in the conventional example, in order to prevent the phase rotation by the smoothing low-pass filter, the error amplifier of the loop control circuit is phase-compensated, or the capacitor of the low-pass filter is used. A small resistor for phase compensation is inserted in series. Therefore, in the former case, the number of parts will increase and adjustment will take time,
Further, in the latter, there is a problem that the ripple of the output voltage increases due to the ripple voltage generated across the minute resistor.

[0013]

SUMMARY OF THE INVENTION A switching regulator of the present invention is a low frequency band composed of a switching circuit for converting an input voltage into a pulse, a diode for rectifying the pulse, and a coil and a capacitor for smoothing the rectified output. In a switching regulator including a filter and a loop control circuit for stabilizing the output voltage of the low-pass filter, the low-pass filter includes a phase compensation resistor connected in series with the capacitor, and a parallel resistor connected to the resistor. And a connected capacitor for ripple compensation.

The capacitance value of the capacitor is set so that the capacitance is equal to the resistance value of the resistor at an intermediate frequency on the exponential scale between the switching frequency and the frequency when the open loop gain of the control loop system is 1. You may.

[0015]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of this embodiment. In Figure 1, the voltage V ₁ of the DC power source 1 is pulsed converted by the main transistor 12 and the main transformer 3, the transformed pulse is rectified by the diode 5, 6, a coil 41 and a capacitor 42 resistor 43 Is smoothed by the low-pass filter LPF4 composed of the output voltage V ₂ and the load 7
Is supplied to. In order to stabilize the output voltage V ₂ , the output voltage V ₂ is input to the error amplifier 8 forming a loop control system, compared with the reference voltage here, and the difference is detected and amplified. The increased error component is input to the pulse width modulation circuit 9, and the pulse width of the switching pulse generated here is modulated. The modulated switching pulse is input to the drive circuit and powered up, and drives the main transistor 13 via the driver transformer 11.

That is, the output voltage V ₂ is voltage-controlled by detecting the error voltage in the loop control system and changing the error voltage in the switching pulse. For example, when the output voltage V ₂ changes in the high direction, the switching pulse width becomes narrow and the output voltage V ₂ is controlled in the low direction to be stabilized.

In the LPF 4, the resistor 43 and the capacitor 44 are the low pass filter coil 41 and the capacitor 42.
This is to prevent the phase rotation due to and to compensate the phase characteristic of the control loop. The difference from the conventional example shown in FIG. 2 is that this capacitor 44 is connected in parallel to a resistor 43 having a minute resistance value. The capacitor 44 is for suppressing the ripple voltage generated at both ends of the resistor 43 inserted for phase compensation.

The capacitance value C ₂ is the switching frequency f for suppressing the ripple with respect to the resistance value r of the resistor 43.
When ₀ is the capacitance (1/2 [pi] f ₀ C ₂₎ and sufficiently small, and the control loop system of the open loop gain capacitance for frequency f ₂ the phase compensation of 1 vicinity (1
/ 2πf ₂ C ₂ ) is set to a value that is sufficiently large. That is, r >> 1 / 2πf ₀ C ₂ and r << 1/2
Since it is πf ₂ C ₂ , it suffices that the capacitance be equal to r at the intermediate frequency on the logarithmic scale of f ₀ and f ₂ . Therefore,

[0019]

And is calculated by this equation. on the other hand,
As described with reference to FIG. 2, the resistance value r of the resistor 43 is normally determined by r = 1 / 2πf ₂ C as the phase compensation is performed at the frequency f ₂ near the open loop gain 1.

In the resistor 43 and the capacitor 44 thus determined, when the constant value of the coil 41 of the low pass filter is L and the constant value of the capacitor 42 is C, the phase characteristic of the control loop system is shown in FIG. On the street. In the region where the frequency rises and is controlled by L and C of the low pass filter,

[0022]

Then, the phase delay becomes 90 °, and the resistor 43,
If the capacitor 44 is not provided and the frequency is further increased, the phase delay reaches 180 degrees as shown by the curve (b) and becomes unstable. When the resistor 43 is inserted, the curve becomes like (C), and when f ₂ = 1 / 2πrC, the phase is compensated for around 135 degrees, and when the frequency further rises, it reaches 90 degrees.

When the capacitor 44 is further added, the curve (a) is obtained, and the curve is intermediate between the curves (b) and (c). That is, the phase is fully compensated at f ₂ , and the frequency rises to the maximum, approaching 180 degrees at the switching frequency f ₀ or higher. On the other hand, the gain characteristic usually has the characteristic shown in FIG.
_{Since the} gain is 1 at ₂ and is 1 or less in the attenuation region near the switch frequency f ₀ , there is no problem even if the phase becomes 180 degrees in this region.

The normal switching frequency f ₀ is several tens KH
z~ is several hundred KHz, the frequency f ₂ when the open-loop gain 1 is set to f _0/100 to 500. Therefore, since C _{2 of} the capacitor 44 is also determined as described above, the ripple voltage at the frequency f ₀ generated at both ends of the resistor 43 is sufficiently suppressed, and the ripple of the output voltage V ₂ is not increased. Absent.

[0026]

As described above, in the switching regulator of the present invention, a capacitor is added in parallel to the resistance for phase compensation connected in series with the capacitor of the low pass filter, and its constant value is set appropriately. By doing so, there is an effect that sufficient phase compensation is performed at a frequency where the open loop gain is close to 1 without increasing the ripple of the output voltage, and the control loop is stabilized.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a characteristic diagram showing the phase characteristic of FIG.

FIG. 4 is a characteristic diagram showing the gain characteristic of FIG.

[Explanation of symbols]

 1 DC power supply 2 Input capacitor 3 Main transformer 4 LPF 5,6 Diode 7 Load 8 Error amplifier 9 Pulse width modulator 10 Drive circuit 11 Driver transformer 41 Coil 42,44 Capacitor 43 Resistor

Claims (2)

[Claims] 1. A low-pass filter including a switching circuit for converting an input voltage into a pulse, a diode for rectifying the pulse, a coil for smoothing the rectified output, and a capacitor, and stabilizing the output voltage of the reduction filter. In the switching regulator including a loop control circuit for, the low-pass filter comprises a resistor for phase compensation connected in series with the capacitor, and a capacitor for ripple compensation connected in parallel with the resistor. Characteristic switching regulator. 2. The capacitance value of the capacitor is set so that the capacitance becomes equal to the resistance value of the resistor at an intermediate frequency on a logarithmic scale between the switching frequency and the frequency when the open loop gain of the control loop system is 1. The switching regulator according to claim 1, wherein: