JPH0582149B2 - - Google Patents

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.

The switching regulator is equipped with a feedback circuit that detects the DC output voltage and compares it with a reference voltage, and controls the conduction width of the switching element based on the comparison result. It is equipped with a filter. 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 has, for example, the configuration shown in FIG. 3, where 31 is a power rectifier circuit, 32 is a transformer,
33 is a drive circuit, 34 is a comparator, 35 is a sawtooth wave generator, 36 is an error amplifier, 37 is a load, Q11
is a transistor, D11 and D12 are diodes,
C11 to C16 are capacitors, L11 and L12 are reactors, FL11 and FL12 are filters, and R1
1 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,
A transistor Q11 serving as a switching element is controlled by a drive circuit 33 to turn on and off the current flowing through the primary winding of the transformer 32. The voltage induced in the secondary winding of the transformer 32 is rectified by diodes D11 and D12, and smoothed by a filter FL11 consisting of a reactor L11 and a capacitor C11, and a filter FL12 consisting of a reactor L12 and a capacitor C12. , 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 + terminal of the error amplifier 36, and the signal of the difference from the reference voltage Vr is sent to the + terminal of the comparator 34.
A pulse width modulated signal is applied to the terminal and compared with the sawtooth wave signal from the sawtooth wave generator 35, and the pulse width is narrowed when the DC output voltage becomes higher than the set value. 33 to control the conduction width of transistor Q11.
That is, by detecting the DC output voltage, the transistor Q1
A feedback circuit that controls the conduction width of 1 stabilizes the DC output voltage.

This feedback circuit includes a filter for smoothing the DC output voltage, and this filter causes a phase delay of 180 degrees, making the operation of the switching regulator unstable. For this purpose, a phase compensation circuit including resistors R14 and R15 and a capacitor C13 is connected to the error amplifier 36 to compensate for the phase delay caused by the filter. Further, capacitors C15 and C16 are connected between the output terminal of the DC output voltage and the housing to bypass noise components.

Furthermore, when ripples in the DC output voltage cannot be removed by a single-stage filter, two-stage connected filters FL11 and FL12 are provided as shown. In this case, the resonance frequencies ₀₁ and ₀₂ of the filters FL11 and FL12 are the same as those of the reactors L11 and L12.
inductance and capacitors C11 and C12
By selecting the capacitance of , the relationship of ₀₁ < ₀₂ is established. For example, the resonance frequency ₀₁ is set so that the low frequency component caused by full wave rectification in the power rectifier circuit 31 is removed by the filter FL11, and the high frequency component caused by the switching of the transistor Q11 is removed by the filter FL12. , its resonant frequency ₀₂ will be set.

In this way, two-stage connected filters FL11 and FL1
2, 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 between the stages of the two-stage connected filters FL11 and FL12, A phase compensation circuit consisting of a capacitor C14 is connected between the positive terminal of the error amplifier 36 and the + terminal of the error amplifier 36. In other words, the delay caused by filter FL12 is reduced by capacitor C.
The lead compensation is performed by a phase compensation circuit consisting of 14 components.

[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, reactors L11 and L12 that constitute filters FL11 and FL12 are connected only to one wire side of the output circuit. Therefore, common mode noise caused by switching of the transistor Q11 or the like can be attenuated by the reactors L11, L12 and the capacitor C15 on the side to which the reactors L11, L12 are connected. 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 performs AC feedback from the first stage filter to the error amplifier via the auxiliary transformer,
This 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 a switching regulator that stabilizes the DC output voltage, reactors 1a, 1b, 2a, 2b are connected to both lines of the output circuit of the DC output voltage, respectively.
A two-stage connected filter 5, 6 is provided, with capacitors 3, 4 connected between both wires, and a DC cutoff capacitor 7 is connected between the two stages of the two-stage connected filters 5, 6. , the primary winding of an auxiliary transformer 8 is connected, and the secondary winding of this auxiliary transformer 8 is connected to a terminal of a comparator circuit 10 which applies a detected value of the DC output voltage via an AC feedback capacitor 9. be.

[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 smoothed by filters 5 and 6 and converted into DC. 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,
First stage filter 5 of two-stage connected filters 5 and 6
Regarding the phase delay caused by the above, a phase compensation circuit is provided in the comparator circuit 10, as in the conventional case.

Then, between the stages of the two-stage connected filters 5 and 6,
The primary winding of an auxiliary transformer 8 is connected via a DC cutoff capacitor 7, and an AC feedback capacitor 9 is connected to its 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, 1b, 2 are connected to both lines of the output circuit.
By connecting a and 2b, common mode noise in both lines can be prevented.

〔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, and 11
12 is a main transformer; 13 is a drive circuit that controls the conduction width of transistor Q1; 14 is a power supply rectifier circuit;
is a comparator, 15 is a sawtooth wave generator, 16 is an error amplifier, 17 is an auxiliary transformer, 18 is a load, D1,
D2 is a diode, C1 to C7 are capacitors, R
1 to R5 are resistances, L1a, L1b, L2a, L2
b is reactor, FL1 is reactor L1a,L
1b and capacitor C1, FL
2 is reactor L2a, L2b and capacitor C2
Vr is the reference voltage, and Vcc is the 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 comparator circuit 10 shown in FIG. 1 includes a drive circuit 13, a comparator circuit 14, a sawtooth wave generator 15, and an error amplifier 16, and the reactors L1a, L1b, L2a, and L2b are connected to the core. It consists of a coil that shares the same voltage and is 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.

Also, reactors L1a, L1b and capacitor C1
A filter FL1 consisting of a reactor L2a,
Filter FL consisting of L2b and capacitor C2
The primary winding of the auxiliary transformer 17 is connected between the stages of the two-stage connection with 2 through a capacitor C4 with a relatively large capacity for DC cutoff, and the secondary winding is connected through a capacitor C5 for AC feedback. + of error amplifier 16
Connect the terminals. 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 dividing the DC output voltage, and the resistor R
An AC component is fed back to the DC output voltage divided by 1 and R2 via the auxiliary transformer 17 and the capacitor 5, and the phase delay caused by the filter FL2 can be compensated for.

〔Effect of the invention〕

As explained above, the present invention provides a reactor 1a, a
1b, 2a, and 2b are connected, and capacitors 3 and 4 are connected between the two lines to form a two-stage connected filter 5,
6, and an auxiliary transformer 8 is connected between the stages of the filters 5 and 6 via a DC cutoff capacitor 7.
The primary winding is connected to the secondary winding, and the secondary winding is connected to the detection voltage application terminal of the comparator circuit 10 via the AC feedback capacitor 9. By performing AC feedback through transformer coupling, the comparator circuit 10 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, reactor 1 is installed on both lines of the output circuit.
By connecting a, 1b, 2a, 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 drawings]

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, 1b, 2a, 2b are reactors, 3, 4
1 is a capacitor, 5 and 6 are filters, 7 is a DC cutoff capacitor, 8 is an auxiliary transformer, 9 is an AC feedback capacitor, and 10 is a comparison circuit.

Claims (1)

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