JPH01238456A - Phase compensating circuit for switching regulator - Google Patents

Abstract

PURPOSE:To compensate the delay of phase, by effecting AC feedback by transformer coupling. CONSTITUTION:The phase compensating circuit of a switching regulator detects a DC output voltage to compare it with a reference voltage through a comparing circuit 10 and controls the width of conduction of a switching element based on the result of the comparison. On the other hand, the phase compensating circuit controls a current, rectified by an electric power source rectifying circuit and conducted through the primary winding of a main transformer, to maintain the DC output voltage constant. In this case, reactors 1a-2b are connected to respective wires of an output circuit and the filters 5, 6 of two-stage connection, to which capacitors 3, 4 are connected, are provided while the primary winding of an auxiliary transformer 3 is connected between the stages through a capacitor 7 for DC cutting-off. Further, the terminals of the comparing circuit 10 for adding the detecting value of the DC output voltage through a capacitor 9 for AC feedback are connected to the secondary winding of the auxiliary transformer 8. According to this method, the AC feedback is effected and common mode noise is prevented by the connection of the reactors 1a-2b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a phase compensation circuit for a switching regulator that compensates the phase of a feedback circuit and reduces common mode noise.

A switching regulator is equipped with a feedback circuit that detects its DC output voltage, compares it with a reference voltage, and controls the conduction width of the switching element based on the comparison result, and is also equipped with a filter to smooth the DC output voltage. It is something that Therefore, when this filter enters the path of the feedback circuit described above, its phase lag becomes a problem, and it is necessary to compensate for this phase lag. For this purpose, a phase compensation circuit is provided.

[Conventional technology]

The phase compensation circuit of a conventional switching regulator is
For example, it has the configuration shown in FIG. 3, where 31 is a power rectifier circuit, 32 is a transformer, 33 is a drive circuit, and 34
is a comparator, 35 is a sawtooth wave generator, 36 is an error amplifier,
37 is a load, Qll is a transistor, Dll, D12 is a diode, C11 to C16 are capacitors, Lll, L
12 is a reactor, FLII, FL12 is a filter, R
11 to R15 are resistors, Vr is a reference voltage, and VCC is an operating voltage of the error amplifier 36.

For example, a full-wave rectified DC voltage is applied to the primary winding of the transformer 32 by the power rectifier circuit 31, and the transistor Qll as a switching element is controlled by the drive circuit 33 to turn on the current flowing to the primary winding of the transformer 32. , off control is performed. The voltage induced in the secondary winding of the transformer 32 is rectified by diodes Dll and D12, and smoothed by a filter FLII made up of a reactor Lit and a capacitor C1l and a filter FL12 made up of a reactor L12 and a capacitor CI2. , a DC output voltage is applied to the load 37.

This DC output voltage is divided by resistors R11 and R12 and applied to the child terminal of the error amplifier 36, and the reference voltage Vr
is applied to the child terminal of the comparator 34 and compared with the sawtooth signal from the sawtooth generator 35, and if the DC output voltage becomes higher than the set value, the pulse width becomes narrower. Such a pulse width modulated signal is applied to the drive circuit 33 to control the conduction width of the transistor Qll. That is, the DC output voltage is stabilized by a feedback circuit that detects the DC output voltage and controls the conduction width of the transistor Qll.

This feedback circuit includes a filter for smoothing the DC output voltage, and this filter allows the phase to be 1.
This results in a delay of 80 degrees, and the operation of the switching regulator is said to be unstable. Therefore, the error amplifier 36 has
A phase compensation circuit consisting of resistors R14 and R15 and a capacitor C13 is connected to compensate for the phase delay caused by the filter.

Also, capacitor CL5. C16 is connected between the output terminal of the DC output voltage and the housing to bypass noise components.

In addition, if the ripple in the DC output voltage cannot be removed by a single-stage filter, a two-stage connected filter F is used as shown in the figure.
LII and FL12 are provided.

In this case, filter FLI1. Resonant frequency of FLL2' O1+ f O! is reactor Lll, L12
By selecting the inductance of and the capacitance of the capacitors C1l and C12, the relationship f61<fog is established. For example, the resonant frequency f is set so that the low frequency component caused by full-wave rectification in the power rectifier circuit 31 is removed by the filter FLII. Set l and transistor Qll
Filter FL12 filters high frequency components due to switching of
The resonant frequency rot will be set so that it is removed by.

When the two-stage connected filters FLII and FL12 are provided in this way, the phase delay caused by the filter FL12 cannot be compensated for only by the phase compensation circuit connected between one terminal and the output terminal of the error amplifier 36, so the two-stage connection is necessary. filter F
A phase compensation circuit consisting of a capacitor C14 is connected between the stages LII and FL12 and the child terminal of the error amplifier 36.

That is, the delay caused by filter FL12 is reduced by capacitor C14.
Advance compensation is performed by a phase compensation circuit consisting of:

[Problem to be solved by the invention]

In the conventional example described above, in order to perform phase compensation by the phase compensation circuit consisting of the capacitor C14, it is necessary to make the potential of the ground side output terminal of the DC output voltage and the ground potential of the error amplifier 36 the same. be. Therefore, the filter FLI
The accelerators Lll and L12 that make up I and FL12 are:
Connected to only one wire side of the output circuit. Therefore, common mode noise caused by switching of transistor Qll, etc., on the side where reactors Lll and LL2 are connected,
These handles Lll, L12 and capacitor C15
It can be attenuated by

However, since there is no such effect on the ground side, there is a drawback that common mode noise cannot be attenuated.

An object of the present invention is to provide a phase compensation circuit that can sufficiently attenuate the common mode noise as described above.

[Means to solve the problem]

The phase compensation circuit of the switching regulator of the present invention includes:
AC feedback is provided from the first stage filter to the error amplifier via an auxiliary transformer, and will be explained with reference to FIG.

The DC output voltage is detected and compared with a reference voltage by the comparator circuit 10, and the conduction width of the switching element is controlled based on the comparison result, and the current that is rectified by the power rectifier circuit and sent to the primary winding of the main transformer is controlled. , in the switching regulator I/- which makes the DC output voltage constant, reactors 1a, Ib, 2 are connected to both lines of the DC output voltage output circuit, respectively.
a, 2b are connected, and a two-stage connected filter 5.6 is provided with a capacitor 3.4 connected between both lines, and a DC-blocking capacitor 7 is installed between the stages of this two-stage connected filter 5.6.
The primary winding of the auxiliary transformer 8 is connected to the secondary winding of the auxiliary transformer 8 via the AC feedback capacitor 9, and the detected value of the DC output voltage is connected to the terminal of the comparator circuit 10. This is what I did.

[Effect]

The conduction width of the switching element connected to the primary winding of the main transformer is controlled, the voltage induced in the secondary winding of the main transformer is rectified by a rectifier circuit, and the rectified output is passed to the filter 5.
．． 6 to obtain a DC output voltage, this DC output voltage is divided by resistors and compared with a reference voltage by a comparison circuit 10, and the DC output voltage is made constant by controlling the switching element based on the comparison result. In addition,
Regarding the phase delay caused by the first stage filter 5 of the filters 5 and 6 of the two-stage contact tE, as in the conventional case, the comparator circuit 10
A phase compensation circuit is provided inside.

The primary winding of the auxiliary transformer 8 is connected between the stages of the two-stage connected filter 5.6 via the DC cutoff capacitor 7, and the AC feedback capacitor 9 is connected to the secondary winding. , to compensate for the phase delay caused by the filter 6.

In this case, since AC feedback is performed via the auxiliary transformer 8, AC feedback can be performed even if the potential of the ground side output terminal of the DC output voltage and the ground potential of the comparator circuit 10 are not the same potential.

Also, reactors 1a, lb, 2a, 2b are connected to both lines of the output circuit.
By connecting the two lines, common mode noise can be prevented on both lines.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a circuit diagram of an embodiment of the present invention, in which 11 is a power rectifier circuit, 12 is a main transformer, 13 is a drive circuit that controls the conduction width of transistor Q1, 14 is a comparator, and 15 is a sawtooth wave generator. 16 is an error amplifier, 17 is an auxiliary transformer,
18 is a load, Di.

D2 is a diode, 01 to C7 are capacitors, R1-R
5 is a resistor, L1a, Llb, L2a, L2b are reactors, FLI is reactors L1a, L1b and capacitor C
1, FL2 is a reactor L2a, L
2b and a capacitor C2, Vr is a reference voltage, and VCC is an operating voltage of the error amplifier 16.

A phase compensation circuit consisting of resistors R4 and R5 and a capacitor C3 connected between one terminal and the output terminal of the error amplifier 16 is the same as in the conventional example. Further, since the operation of making constant the DC output voltage applied to the load 18 is the same as that of the conventional example, a redundant explanation will be omitted.

The comparison circuit 10 in FIG. 1 includes a drive circuit 13, a comparator 14, a sawtooth wave generator 15, and an error amplifier 16, and also includes reactors L1a, Llb, and L2a.
, L2b are composed of coils sharing a core, and are connected to both lines of the DC output voltage output circuit, and capacitors C1 and C2 are connected between the two lines. By connecting reactors to both lines of the output circuit in this way, common mode noise on both lines can be removed.

In addition, a capacitor C4 with a relatively large capacity for DC cutoff is installed between the stages of the two-stage connection of the filter FLI, which is made up of reactors L1a, Llb, and capacitor CI, and the filter FL2, which is made up of reactors L2a, L2b, and capacitor C2.
The primary winding of the auxiliary transformer 17 is connected through the auxiliary transformer 17, and the + terminal of the error amplifier 16 is connected to the secondary winding through the AC feedback capacitor C5. That is, a series circuit of the secondary winding of the auxiliary transformer 17 and the capacitor 5 is connected to both ends of the resistor R1 for voltage division of the DC output voltage, and the DC output voltage divided by the resistors R1 and R2 is connected to the auxiliary transformer. 17 and the capacitor 5, the AC component is fed back to the filter F.
It is possible to compensate for the phase delay caused by L2.

〔Effect of the invention〕

As described above, the present invention provides a reactor la for both lines of the DC output voltage output circuit.

Connect lb, 2a, 2b and connect capacitor 3 between both lines.
, 4 to form a two-stage connected filter 5゜6,
In addition, the primary winding of the auxiliary transformer 8 is connected between the stages of the filter 5.6 via a capacitor 7 for DC cutoff, and the comparator circuit 10 is connected to the secondary winding of the auxiliary transformer 8 via a capacitor 9 for AC feedback. The comparator circuit 10 is connected to the detection voltage application terminal, and performs AC feedback through transformer coupling.
It is possible to compensate for the phase delay caused by the second-stage filter 6 even if the ground potential of the output terminal and the potential of the output terminal of the DC output voltage are made different.

Also, reactors 1a+lb and 2 are connected to both lines of the output circuit, respectively.
By connecting a and 2b, there is an advantage that common mode noise in both lines can be removed and a stabilized DC output voltage can be applied to the load.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the present invention, FIG. 2 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a circuit diagram of a conventional example. 1a, lb, 2a, 2b are reactors, 3.4 is a capacitor, 5.6 is a filter, 7 is a DC blocking capacitor,
8 is an auxiliary transformer, 9 is an AC feedback capacitor,
10 is a comparison circuit. Patent Applicant: Fujitsu Denso Co., Ltd. Representative Patent Attorney: Shoji Aitani Representative Patent Attorney: Hiroshi Watanabe

Claims (1)

[Claims] In a switching regulator, a DC output voltage is detected and compared with a reference voltage by a comparison circuit (10), and the conduction width of a switching element is controlled based on the comparison result to keep the DC output voltage constant. reactors (1a, 1b, 2a, 2) are connected to both lines of the DC output voltage output circuit.
b) and a capacitor (3, 4) between the two lines.
A two-stage connected filter (5, 6) is provided, and the two
The primary winding of an auxiliary transformer (8) is connected between the stages of the stage-connected filters (5, 6) via a DC-blocking capacitor (7), and the secondary winding of the auxiliary transformer (8) is A phase compensation circuit for a switching regulator, characterized in that the voltage is connected via an AC feedback capacitor (9) to a terminal of the comparison circuit (10) to which the detected value of the DC output voltage is added.