JP3779542B2 - Switching power supply - Google Patents

Description

[0001]
[Field of the Invention]
The present invention relates to a switching power supply, and more particularly to a control circuit that achieves high-speed response and stabilization of an output voltage by a remote sense method when a load fluctuates.
[0002]
[Prior art]
Conventionally, as a means for stabilizing output voltage fluctuation due to load fluctuation of a switching power supply, there has been proposed a system in which two types of error amplifiers, a phase compensated error amplifier and a fast response error amplifier, are operated in parallel. When remote sensing is performed, there is a problem that the phase of a control loop centering on an amplifier that provides an error signal in a steady state is delayed, resulting in unstable operation.
[0003]
FIG. 6 shows a conventional switching power supply circuit in which two types of error amplifiers, ie, a phase compensated error amplifier 20 and a fast response error amplifier 25 are connected in parallel, and the difference between the output and the synchronization signal is compared by the error amplifier 13. And the pulse width is controlled. FIG. 8 shows an example in which remote sensing is performed using the circuit of FIG.
[0004]
The load 12 in FIG. 8 includes parasitic components such as wiring resistors 33 and 38, wiring inductances 34 and 39, and a bypass capacitor 35 as shown in FIG. 9, and a circuit including a delay element is formed on the load side from the output terminal. Has been. Therefore, when a voltage variation occurs due to a load variation, the remote sensing method stabilizes the voltage variation so that it cannot respond at high speed.
[0005]
In the conventional switching power supply circuit of FIG. 8, there is a problem that the phase margin of the control loop of the switching power supply is lowered due to the influence of the delay component, causing instability of the switching power supply, and a control system that can be solved at low cost is desired. Yes.
[0006]
[Problems to be solved by the present invention]
The present invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to eliminate the influence of delay components due to wiring resistance, wiring inductance, bypass capacitors, etc. in the remote sense method, and to improve the instability of the switching power supply. Thus, a method that can be solved at low cost can be provided.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 compares the switching element under PWM control, the first detection signal corresponding to the output voltage and the first reference voltage, and compares the first reference voltage with the first level. A first error amplifier that outputs an error signal; and a second error amplifier that compares the second detection signal corresponding to the output voltage with a second reference voltage and outputs a second level error signal. Configure the switching power supply.
[0008]
A capacitance element for phase compensation is connected between the detection signal terminal and the output terminal of the first error amplifier, PWM control is performed using the first level error signal or the second level error signal, and the second level The position where the detection signal is collected is closer to the output terminal than the position where the first detection signal is collected, and a resistance component is inserted between the position where the first detection signal is collected and the position where the second detection signal is collected. Has been.
[0009]
The fact that the resistance component is a conductor resistance is to detect voltage fluctuation on the input side and output side of this resistor without causing a phase shift and without generating extra voltage when voltage fluctuation occurs. In addition, it is possible to suppress the influence of the extra voltage in the first error amplifier, which is effective for eliminating the extra delay. In addition, the use of a conductor resistance, which is a wiring resistance of a power supply substrate, realizes the above-described effect at low cost and high efficiency.
[0010]
Since the position where the second detection signal is sampled 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 sense, it is charged by the voltage at the position where the second detection signal is sampled, Since the voltage before the change of the output voltage is held, it is effective in detecting the load fluctuation with high sensitivity.
[0011]
The reference voltage source for obtaining the second reference voltage is charged by the output voltage at the position where the second detection signal is sampled to obtain a predetermined voltage, and the voltage before the output voltage changes is held for a certain period. It is effective to have a time constant circuit that can provide an error signal that is highly sensitive to load fluctuations.
[0012]
If the second error amplifier is two comparators or two high gain error amplifiers as a reference voltage source for obtaining the second reference voltage, a high-speed error signal can be stabilized against load fluctuations. It is effective because it can be provided.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a block circuit 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 the second error amplifier for high-speed response is an output voltage detection point. The plus side is a point on the load side from the output voltage detection point of the first error amplifier phase-compensated by inserting the resistance component 10.
[0014]
FIG. 2 is an operation waveform at the time of sudden load change of the circuit of FIG. FIG. 2A shows a case where the load current fluctuates from the rated output to 1/3 of the output current in the period from t = 0 to t1. The waveform shown in FIG. 2B is obtained by viewing the potential drop −r1 × Io of the conductor resistance component r1 of the substrate with reference to the plus terminal of the capacitor 9. The waveform of FIG. 2C is a waveform of the voltage Vc of the capacitor 9. The waveform in FIG. 2D is the sum of −r1 × Io and Vc at the output terminal voltage Vo.
[0015]
On the other hand, the operation waveform in 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 with the same set value Vo + th using the amplifier 25 for high-speed response, the voltage fluctuation of the capacitor voltage Vc in FIG. 2 can be reduced by the amount of the potential drop −r1 × Io. Accordingly, the voltage fluctuation of the capacitor voltage Vc due to the load fluctuation is improved.
[0016]
The voltage change due to the newly inserted resistance component can be effectively detected if it is usually 10% or more with respect to the load fluctuation. For example, in a power supply with an output of 5 V, when the variation ΔIo of the static output current is between 5 A and 10 A, the variation ΔVo of the static output voltage is often, for example, 10 mV or less. In this case, the resistance component r1 is
r1 = (ΔVo / ΔIo) × 0.1
= {10 [mV] / (10-5) [A]} × 0.1 = 0.2 [mΩ]. . . (1)
If it is 0.2 [mΩ] or more, it works effectively on the detection operation.
[0017]
FIG. 3 is a block diagram of the switching power supply according to the 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 30 inserted on the negative side of the output voltage detection point. In addition, this is a point on the load side from the output voltage detection point of the first error amplifier subjected to phase compensation.
[0018]
1 is different from FIG. 1 in that the reference voltage of the error amplifier 25 for high-speed response is generated from the output voltage using the resistor 26 and the capacitor 27. As a result, an output voltage having timer characteristics composed of the time constants of the resistor 26 and the capacitor 27 is held at both ends of the capacitor 27 as a reference voltage.
[0019]
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 in the form of remote sense and is parasitic. This is in the vicinity of the load circuit 36 that does not include an element. 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 due to the resistance value r1. In FIG. 4, the parasitic inductors 34 and 39 also act in a direction to limit the current in the same way as the resistance component r1 in terms of alternating current, so that it is 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.
[0020]
In FIG. 4, the phase compensated error amplifier 20 responds with the voltage of the output capacitor 9. Therefore, during steady operation, the influence of delay due to parasitic elements such as the wiring resistors 33 and 38, the wiring inductances 34 and 39, and the bypass capacitor 35. The control loop is not affected.
When the load suddenly changes, the error amplifier 25 for high-speed response efficiently detects the load fluctuation in the form of remote sense and makes the switching power supply respond at high speed.
[0021]
FIG. 5 is a block diagram of a switching power supply according to a fourth embodiment of the present invention, which is different from FIG. 4 in that an error amplifier 25 for high-speed response includes an overvoltage detection comparator 42 and a low voltage detection. The comparator 45 of FIG. Therefore, the reference voltage 43 is a value that is 3% larger than the reference voltage 21, and the reference voltage 46 is a value that is 3% smaller than the reference voltage 21, for example. However, since it is a remote sensing method, the reference voltages 43 and 46 are set higher than the reference voltage 21 by an amount corresponding to the drop (Io × r1) due to the output current Io and the resistance value r1 due to the wiring resistors 33 and 38. Need to be done.
[0022]
【The invention's effect】
According to the present invention, the first error amplifier for which phase compensation is performed and the second error amplifier for detecting a sudden change in the output voltage and responding at high speed are provided, and the second error amplifier is connected to the second error amplifier from the output voltage detection position of the first error amplifier. The output voltage detection position of the error amplifier is arranged on the load side, and a resistance component of a certain value or more is inserted between the output voltage detection position of the first error amplifier and the output voltage detection position of the second error amplifier. Therefore, it is possible to provide a low-cost switching power supply having a stable remote sensing function and an output voltage that is stable even when a load suddenly changes.
[0023]
[Brief description of the drawings]
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 of the circuit of FIG. 1. FIG. 3 is a circuit diagram of a second embodiment which is a switching power supply according to the present invention. FIG. 4 is a circuit diagram of a third embodiment which is a switching power supply according to the present invention. FIG. 5 is a circuit diagram of a fourth embodiment which is a switching power supply according to the present invention. FIG. 7 is an operation waveform diagram of the circuit of FIG. 6. FIG. 8 is a second circuit example of a conventional switching power supply. FIG. 9 is a power supply and a load circuit when remote sensing is performed.
1. 1. Input power supply Input terminal 3. Input capacitor 4. 4. Main switch Main transformer 6. Secondary rectifier diode 7. Secondary flywheel diode 8. 8. Output choke Output capacitor 10.30. 10. Conductor resistance component of power supply substrate Output terminal 12. Load circuit 13. Comparator 14.19.24.27. Capacitor 15. Constant current supply circuit 16. Constant current discharge circuit 18. Photocoupler 17.22.23.26.40. Resistance element 20. First amplifier (for steady operation)
21.2.443.46. Reference voltage source 25. Second amplifier (for sudden load change operation)
28. Primary side control circuit; (the ground potential is the same as the negative terminal of the capacitor 3)
29. Secondary side control circuit; (the ground potential is the same as the negative terminal of the capacitor 9)
31. Remote sense terminal 33.38. Conductor resistance component of wiring 34.39. Parasitic inductance component of wiring 35. Load bypass capacitor 36. Load circuit; (not including parasitic elements)
41.44. Decoupling diode 42.45. Comparator

Claims (4)

A switching element that is PWM-controlled, a first error amplifier that compares the first detection signal corresponding to the output voltage with the first reference voltage and outputs an error signal of the first level, and corresponds to the output voltage in the second detection signal and a switching power supply comprising a second error amplifier for outputting a second level error signal by comparing the second reference voltage, a detection signal terminal of the first error amplifier A capacitance element for phase compensation is connected between the output terminals, and the detection signal sampling unit of the second error amplifier is located closer to the output terminal than the detection signal sampling unit of the first error amplifier , and on the output side switching power supply that parasitic resistance and / or parasitic inductance of the base wire having is characterized in that located between the collecting portion detection signal of the first error amplifier of the detection signal collecting unit and the second error amplifier 2. The switching power supply according to claim 1 , wherein the position where the detection signal of the second error amplifier is sampled 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 sense. A switching power supply. 3. The switching power supply according to claim 1 , wherein a reference voltage source for obtaining the second reference voltage is charged by an output voltage at a position where a detection signal of the second error amplifier is sampled. A switching power supply comprising a time constant circuit for holding a voltage before the output voltage changes for a certain period when the output voltage changes. 4. The switching power supply according to claim 1, wherein the second error amplifier comprises two comparators or two high gain error amplifiers.

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