JP2002176770A - Switching power source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control circuit capable of attaining high-speed response to the output voltage and stabilization according to a remote sense method, especially when a load changes. SOLUTION: This switching power source includes a first error amplifier for compensating for a phase, and a second error amplifier for detecting a sudden change in output voltage and conducting a high-speed response. The output voltage detecting position of the second error amplifier is disposed on a load side more than that of the first error amplifier. A resistor or an impedance component which has a value higher than or equal to a fixed value is inserted in between the output voltage detecting positions of the first error amplifier and the second error amplifier. It is thus possible to obtain the switching power supply having a remote sense function which is stable and excellent and capable of eliminating a phase delay in a control loop centered on an amplifier in which the output voltage provides error signals during a steady state for the sudden change in the load.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply, and more particularly, to a control circuit which achieves high-speed response and stabilization of an output voltage by a remote sensing method when a load changes.

[0002]

2. Description of the Related Art Conventionally, as a means for stabilizing fluctuations in output voltage due to fluctuations in the load of a switching power supply, a method has been proposed in which two types of error amplifiers, a phase-compensated error amplifier and a high-speed response error amplifier, are operated in parallel. However, when remote sensing is performed by this method, there is a problem that the phase of a control loop centered on an amplifier that provides an error signal in a steady state is delayed, resulting in unstable operation.

FIG. 6 shows a conventional switching power supply circuit in which two types of error amplifiers, a phase-compensated error amplifier 20 and a high-speed response error amplifier 25, are connected in parallel, and the difference between the output and the synchronization signal is determined by the error amplifier. 13, the pulse width is controlled by comparison. FIG. 8 shows an example in which remote sensing is performed by the circuit of FIG.

As shown in FIG. 9, a load 12 shown in FIG. 8 has wiring resistances 33 and 38 and wiring inductances 34 and 3.
9, a circuit including a delay element is formed on the load side from the output terminal, including a parasitic component such as the bypass capacitor 35. Therefore, when a voltage fluctuation occurs due to a load fluctuation, it cannot be responded at a high speed because the voltage fluctuation is stabilized by the remote sensing method.

In the conventional switching power supply circuit shown in FIG. 8, there is a problem that the phase margin of the control loop of the switching power supply is reduced due to the influence of the delay component and the switching power supply becomes unstable. Is desired.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object the wiring resistance, wiring inductance,
Eliminates the effects of delay components due to bypass capacitors, etc.
It is possible to provide a method capable of improving the instability of the switching power supply and solving the problem at a low cost.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the invention according to the present invention is directed to a switching element under PWM control, a first detection signal corresponding to an output voltage, and a first reference voltage. And outputs a first level error signal, and outputs a second level error signal by comparing a second detection signal corresponding to an output voltage with a second reference voltage. And a second power amplifier.

A phase compensating capacitive element is connected between a detection signal terminal and an output terminal of the first error amplifier, and a PW signal is output using a first level error signal or a second level error signal.
The position where the M control is performed and the second detection signal is collected is closer to the output terminal than the position where the first detection signal is collected, and the position where the first detection signal is collected and the second detection signal are collected. A resistance component is inserted between the positions.

[0009] The fact that the resistance component is a conductor resistance means that the voltage fluctuation is applied to the input side and the output side of the resistor without a phase shift and without generating an extra voltage when the voltage fluctuation occurs. For the detection, the influence of the extra voltage in the first error amplifier can be suppressed, which is effective for eliminating extra delay. The use of the conductor resistance, which is the wiring resistance of the substrate of the power supply, realizes the above-described effects at low cost and with high efficiency.

[0010] Since the second detection signal sampling position and the ground potential of the second reference voltage are wired to the load side of the switching power supply in the form of remote sensing, the voltage at the second detection signal sampling position is determined by the voltage at the second detection signal sampling position. Since the battery is charged and the voltage before the output voltage is changed is held, it is effective to detect a load change with high sensitivity.

A reference voltage source for obtaining the second reference voltage is charged with the output voltage at the position where the second detection signal is sampled, so that a predetermined voltage is obtained and the voltage before the output voltage changes is a certain voltage. Providing a time constant circuit for holding only for a period is effective because an error signal with high sensitivity to a load change can be provided.

When the second error amplifier is composed of two comparators or two high-gain error amplifiers as a reference voltage source for obtaining the second reference voltage, an error signal which is fast with respect to a load change is provided. Is effective because it can be provided stably.

[0013]

FIG. 1 is a block diagram of a switching power supply according to a first embodiment of the present invention. The difference from the conventional switching power supply is that a second error for a high-speed response is provided. The amplifier is such that the plus side of the output voltage detection point is on the load side with respect to the output voltage detection point of the phase error compensated first error amplifier with the resistance component 10 inserted.

FIG. 2 shows operation waveforms of the circuit shown in FIG. 1 when the load changes suddenly. FIG. 2A shows that the load current is changed from t = 0 to t.
The case where the output current fluctuated from the rated output to 1/3 in the period of 1 is shown. The waveform of FIG. 2B shows the conductor resistance component r of the substrate.
The potential drop of 1−r1 × Io is viewed with reference to the plus terminal of the capacitor 9. 2C is a waveform of the voltage Vc of the capacitor 9. The waveform in FIG.
At the output terminal voltage Vo, the waveform becomes the sum of -r1 × Io and Vc.

On the other hand, the operation waveform of the conventional circuit as shown in FIG. 6 is as shown in FIG. In FIG. 7, the capacitor voltage Vc is equal to the output terminal voltage Vo. That is, when the output voltage fluctuation is detected at the same set value Vo + th using the amplifier 25 for high-speed response, the potential drop in FIG. 2 is −r1 × Io.
, The voltage fluctuation of the capacitor voltage Vc can be reduced. Accordingly, the voltage fluctuation of the capacitor voltage Vc due to the load fluctuation is improved.

The change in voltage due to the newly inserted resistance component can be effectively detected if the change in load is usually 10% or more. For example, in a power supply with an output of 5 V, the variation ΔVo of the static output voltage is often, for example, 10 mV or less when the variation ΔIo of the static output current is between 5 A and 10 A. The resistance component r1 in this case is: r1 = (ΔVo / ΔIo) × 0.1 = {10 [mV] / (10−5) [A]} × 0.1 = 0.2 [mΩ]. . . (1) It becomes effective if it is 0.2 [mΩ] or more, in the detection operation.

FIG. 3 is a block diagram of a switching power supply according to a second embodiment of the present invention. The difference from FIG. 1 is that the error amplifier 25 for high-speed response has a resistance component on the minus side of the output voltage detection point. 30 is inserted and located on the load side from the output voltage detection point of the phase-compensated first error amplifier.

The difference from FIG. 1 is that the reference voltage of the error amplifier 25 for high-speed response is generated from the output voltage by using the resistor 26 and the capacitor 27. Thereby, the capacitor 27
An output voltage having a timer characteristic composed of a time constant of the resistor 26 and the capacitor 27 is held as a reference voltage at both ends of the output voltage.

FIG. 4 is a block diagram of a switching power supply according to a third embodiment of the present invention. The difference from FIG. 3 is that the output voltage detection point of the error amplifier 25 for high-speed response is
Load circuit 3 without parasitic elements in the form of remote sensing
6 is in the vicinity. In FIG. 4, the parasitic resistance components 33 and 38 of the wiring of the load substrate correspond to the insertion resistance value r1. The output voltage detection sensitivity of the error amplifier 25 for high-speed response is improved by the potential drop caused by the resistance value r1.
In FIG. 4, the parasitic inductors 34 and 39 also act in the direction of limiting the current in the same manner as the resistance component r1, so that they are effective for improving the sensitivity of the error amplifier 25 and improving the phase delay in the control loop of the power supply. is there.

In FIG. 4, the phase-compensated error amplifier 20 responds with the voltage of the output capacitor 9, so that during normal operation, the wiring resistances 33 and 38 and the wiring inductance 3
The control loop is not affected by delays caused by parasitic elements such as 4, 39 and the bypass capacitor 35. When the load suddenly changes,
An error amplifier 25 for high-speed response efficiently detects a load change in the form of remote sensing, and makes a switching power supply respond quickly.

FIG. 5 is a block diagram of a switching power supply according to a fourth embodiment of the present invention. The difference from FIG. 4 is that the error amplifier 25 for high-speed response is connected to the comparator 42 for overvoltage detection and the low-voltage comparator 42. And a comparator 45 for voltage detection. Therefore, the reference voltage 43 is, for example, 3% higher than the reference voltage 21, and the reference voltage 46 is, for example, 3% lower than the reference voltage 21. However, because of the remote sensing method, the reference voltages 43 and 46 are set higher than the reference voltage 21 by the amount corresponding to the output current Io and the drop (Io × r1) caused by the resistance r1 caused by the wiring resistances 33 and 38. Need to be done.

[0022]

According to the present invention, a first error amplifier for performing phase compensation and a second error amplifier for detecting a sudden change in the output voltage and responding at a high speed are provided, and the output voltage of the first error amplifier is detected. The output voltage detection position of the second error amplifier is arranged on the load side from the position, and the resistance component having a certain value or more is set between the output voltage detection position of the first error amplifier and the output voltage detection position of the second error amplifier. By inserting the switching power supply between them, it is possible to provide an inexpensive switching power supply that has a stable output voltage even when the load suddenly changes and has a good remote sensing function.

[0023]

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment which is a switching power supply according to the present invention.

FIG. 2 is an operation waveform diagram in the circuit of FIG. 1;

FIG. 3 is a circuit diagram of a switching power supply according to a second embodiment of the present invention;

FIG. 4 is a circuit diagram of a switching power supply according to a third embodiment of the present invention;

FIG. 5 is a circuit diagram of a switching power supply according to a fourth embodiment of the present invention.

FIG. 6 is a first circuit example which is a conventional switching power supply.

FIG. 7 is an operation waveform diagram in the circuit of FIG. 6;

FIG. 8 shows a second example of a circuit which is a conventional switching power supply.

FIG. 9 shows a power supply and a load circuit when remote sensing is performed.

[Explanation of symbols]

1. Input power supply 2. Input terminal 3. Input capacitor 4. Main switch 5. Main transformer 6. Secondary side rectifier diode 7. Secondary side flywheel diode 8. Output choke 9. Output capacitor 10.30. 10. Conductor resistance component of power supply board Output terminal 12. Load circuit 13. Comparator 14.19.24.27. Capacitor 15. Constant current supply circuit 16. Constant current discharge circuit 18. Photo coupler 17.22.23.26.40. Resistance element 20. First amplifier (for normal operation) 21.2.43.4.46. Reference voltage source 25. Second amplifier (for sudden load change operation) 28. Primary side control circuit;
Same as-terminal. 29. Secondary-side control circuit; (ground potential is capacitor 9)
Same as-terminal. ) 31. Terminal for remote sensing 33.38. Conductor resistance component of wiring 34.39. Parasitic inductance component of wiring 35. Load bypass capacitor 36. Load circuit; (not including parasitic element) 41.44. Decoupling diode 42.45. Comparator

Claims (6)

[Claims] 1. A switching element under PWM control, a first error amplifier for comparing a first detection signal corresponding to an output voltage with a first reference voltage and outputting an error signal of a first level. And a second error amplifier for comparing a second detection signal corresponding to the output voltage with a second reference voltage and outputting a second level error signal. A phase compensating capacitive element is connected between the signal terminal and the output terminal, and PWM is performed using the first level error signal or the second level error signal.
The position for controlling and sampling the second detection signal is closer to the output terminal than the position for sampling the first detection signal;
A switching power supply characterized in that a resistance component or an inductance component is inserted between a position where the detection signal is sampled and a position where the second detection signal is sampled. 2. The switching power supply according to claim 1, wherein the resistance component comprises a conductor resistance. 3. The switching power supply according to claim 1, wherein the inductance component comprises a parasitic inductance of a conductor. 4. The switching power supply according to claim 1, wherein a position at which the second detection signal is sampled and a ground potential of the second reference voltage are wired to the load side of the switching power supply in the form of remote sensing. Switching power supply characterized by the following. 5. The switching power supply according to claim 1, wherein the reference voltage source for obtaining the second reference voltage is a second reference voltage.
A predetermined constant voltage is obtained by being charged by the output voltage at the position where the detection signal is sampled, and a time constant circuit that holds the voltage before the output voltage changes for a certain period when the output voltage changes is provided. Switching power supply characterized by things. 6. The switching power supply according to claim 1, wherein the second error amplifier comprises two comparators or two high gain error amplifiers.