JPS59144364A - Switching power source - Google Patents

Abstract

PURPOSE:To improve the responding speed by controlling a pulse width modulator by the output of a current detector without using a delay/advance element compensation, thereby increasing the band of a control system. CONSTITUTION:A switching power source turns ON and OFF an input voltage 9 by a switch 6, and outputs and output voltage 8 stabilized through smoothing filters 13, 14. In a feedback control system of this device, the voltage 8 is inputted to a voltage detector 1 having a reference voltage 2, an adder 3 and an error voltage amplifier 4, thereby controlling the ON/OFF time of a pulse width modulator 5 for stabilizing the voltage. A current (g) of a smoothing inductor 13 is further detected by a current detector 21 in addition to the above feedback, and a loop for feeding back to the modulator 5 through a feedback path (h) is provided. In this manner, the phase delay of 180 deg. produced at LC filters 13, 14 is compensated, thereby performing the widening of the control system.

Description

[Detailed description of the invention] This invention relates to improvements in switching power supplies.

A switching power supply in which the control system that traps the output voltage at a constant level has been widened to a wider band without sacrificing its stability, thereby reducing output interference and preventing peaks that become maximum at additional frequencies. It is intended to provide a device t.

Figure 1 shows a book diagram of the feedback control system for voltage stabilization of a conventional general switching power supply. In Figure 2, *tll is the voltage detection circuit, (2) is the reference voltage, and 13) is an adder, and (4) is an error voltage amplifier.

(5) is a pulse modulation circuit, (6) is a switch, (7)
is the smoothing filter, 18) is the output voltage, and (9) is the input voltage.

A is an error signal, 2 ports are a control signal, C is an on/off signal, 2 is a switch output voltage, and E is a feedback path.

First, the principle of voltage stabilization of a general switching power supply will be explained based on FIG. For convenience of explanation,
The operation of the switch (6) will be explained in order.

The switch (6) is composed of a switching device, a transistor, a transformer, an inductor, a rectifier diode, etc. The switch is turned on and off depending on the input voltage (9) and the switch (6). The switch output voltage is determined by the configuration of the switch. The on/off signal (3) is a digital signal, and the switch (2) voltage is a pulse voltage, so it is passed through a smoothing filter (7).
) to obtain a DC output voltage (81).

In order to prevent fluctuations in the output voltage (8) due to the input voltage (9), the load connected to the output voltage (8), or the environmental temperature, all output voltages (8) are detected and returned to ON/OFF signals. R'ff: Multiply the return side (goods) system plan.

The configuration of the feedback control system is as follows.

The output voltage 18) passes through the voltage return path and is then sent to the voltage detection circuit (
1) is input.

The voltage detection circuit (1) has a reference voltage (2), an adder 13) 1
m difference voltage amplifier (4)), the output voltage (8) is sent to the adder I3), and the error signal A, which is the difference from the reference voltage (2), is then input to the error voltage amplifier (71i). 4) The width is increased and becomes 1fil. The control signal port enters the pulse medium 5 mother@fa15) and becomes a digital on/off signal. Here, if we increase the ratio of the time for instructing OFF to ON and OFF signals as the output voltage (8) rises, the output voltage (8) will change depending on the fluctuation of the input voltage (9) or Variations in the load connected to the output voltage (8), some layers are independent of variations in the characteristics of each element due to changes in environmental temperature.

I can be kept almost constant. The extent of this is determined by the characteristics of the elements that make up the feedback control system.

Each element of the switching power supply has a frequency characteristic M shown in FIG. 2, considering minute displacement from a certain constant operating state.

In FIG. 2, element σ0) is the characteristic of the error voltage amplifier (4) and is usually the characteristic of a first-order lag element, K11i is the DC gain, and Tl is the time constant.

Element C is the characteristic of the pulse width modulation circuit 15), which converts the control signal into a switching duty signal.

Here, the duty signal is the amount obtained by dividing the on instruction time by the sum of the on instruction time and the off instruction time in the on and off signals. Element a21 is the characteristic of switch +61,
This is the voltage Vin of the input voltage (9) and the step-up ratio N of the transformer. Furthermore, M-density also includes a dead time element of approximately M switching frequency.51 Since it can be ignored at frequencies lower than the normal switching frequency, the description thereof will be omitted here. [131 is a smoothing inductor, circle is a smoothing capacitor, and these are the Chikuo filter (7) in Figure 1? It consists of

A switching power supply must be equipped with a smoothing filter (7Ht) consisting of a smoothing inductor 1131 and a smoothing capacitor.
is an important constraint when designing control systems. The conventional control system design method and system will be described below.

In Figure 2, the round-trip transmission of the system in the 1' direction is...
It is expressed as ・・・・・・・・・+11. Here, L is the inductance of the smoothing inductor a3), and C is the capacitance of the smoothing capacitor I]41. - 10,000, output impedance Z (SJ is defined as the ratio of the variation of the output voltage (8) and the variation of the load current (151) in the third section. Here, Zc is the smoothing capacitor (141
impedance, Zlj: the resistance value of the resistive load (161) connected to the smoothing inductor (the impedance of 131, the output voltage is 18).

- Represents a parallel connection of dances.

The output impedance is an index that shows the fluctuation of the output voltage (8 points) when the negative current (151) changes, and characteristics that are low and have little dependence on frequency are preferable.

Therefore, in the design of the power supply, -cyclic transfer stroke number T (S)
must be made sufficiently large to reduce the output impedance.

By the way, as a premise that one or more arguments can be established.

This feedback control system is unstable; 1. Don't cry,
The women's beauty, which is covered by the automatic control theory, must be adjusted.

Several methods are known that are mathematically equivalent to the stability condition, but for convenience of explanation, we will explain it here according to the so-called Bode's method. According to Bode's method, it is a condition of stability that one phase does not exceed 1800 when the absolute value force S1 of the one-cycle transmission number T (S) of the control system becomes S1. - The frequency at which the absolute value of SJ is 1 is called the 1st frequency, which coincides with the upper limit λ of the band of the control system. Also, the phase at the crossover frequency and 1800 is called the phase margin, and is one of the indicators of stability.

According to the above-mentioned equation (1), the loop transmission of the control system of the switching power supply w! The J number T (S) always includes a second-order delay element due to the LC filter, and at frequencies above the resonance frequency of the LC filter, the phase delay of T (S) is in principle 180°. The band of element [01 is sufficiently wide ((T
Even if I is small, the phase margin is extremely small and 7i is not suitable for practical use.

Therefore, the conventional method has been to use lag/lead compensation, in which all lag/lead elements are inserted as forward elements in the system shown in FIG. FIG. 4 shows an example of the configuration of the delay/advance element. 117+ in FIG.

(I& is a resistor #fi91. f20+ is a capacitor. FIG. 5 shows the frequency characteristics of the lag/lead element shown in FIG. 4.

Fig. 5(a)/I'i is a custom-made diagram expressed on a logarithmic scale. Fig. 5(b) is a phase characteristic diagram in which only the frequency is expressed on a semi-logarithmic scale. We will use this scale to indicate all of the 1 phase.The frequency range where the phase advances from 0 to 1 in Figure 5 (b) is the LC smoothing filter. (7) Resonant frequency f
If we design the lagging lead g element in the fourth section so that it matches x and insert rC in the system, the -cyclic transfer function T (S) is expressed as shown in Fig. 6 (a
)(b) Gain 1 phase characteristic. For comparison, see Figure 6.
ct('rH(s) when dJ has no lag/lead element
shows the gain 1 phase characteristics of . In the figure, fx indicates the resonance frequency of the LC, and fc indicates the crossover frequency. As is clear from FIG. 6, due to the effect of the delay/lead element, the phase from fx to fc is advanced by 180 degrees, resulting in a 0 phase margin and a stable system. At this time, the output impedance has the shape shown in Figure 7 based on the above-mentioned equation (2).

By the way, the crossover frequency fc of the control system of the switching power supply cannot be made as high as desired.

When the crossover frequency mantissa approaches the switching frequency, the switching frequency component occurring in the output voltage
The tuple voltage is likely to cause single oscillation or disturbance in the control system. ! According to theory and experience, the practical upper limit of the crossover frequency is generally about a few tenths of the switching frequency, and the best one is 1710 to 1/20.
It can only be raised to a certain extent. Further, in general, the resonance frequency fx of the smoothing filter is often about a fraction of the crossover frequency fc. This Vifx, f decrease K
This is because a large smoothing inductor (1: (+) becomes necessary, which increases the size of 1M x 9 price.If you try to increase the inverse VCfx, you need to make the smoothing capacitor circle smaller, and if fc -, then the output voltage ( 8) will increase, and if the smoothing inductor (I3) is made smaller, the current of the switching element will increase.

Therefore, the lagging/lead elements must be designed so that the value of the round transfer internal number T (SJ) at [resonance frequency]X is several times higher than the peak due to resonance.
The characteristic of lower frequency than x is the zero point of the delay element (there are two zero points tI'i, but the higher frequency one)!
At around 7 of 2Q d B/decade, the gain decreases with frequency, and from there to another zero point of the lag/lead element, the gain takes a minimum value.

Therefore, when trying to reduce the output impedance by increasing the DC gain of T (S), in order to increase the value of T (87 to several times K) at the zero point 1 = j of the slow Therefore, it is necessary to lower the poles of the lagging element (there are two poles, but the one with the lowest frequency), which slows down the response of the output voltage.

In addition, above a describes the case where each element of the control system remains unchanged, but 2
For example, in the case of a stock where the value Vin of input voltage (9) fluctuates, the gain of 1' (8) changes, so the maximum VinK
Since the above design must be performed for the input voltage V
When in decreases and fc, the total number of circular transmission poles T (S
The gain of J decreases. The biggest problem in this case is
The output impedance is custom-made and is 1 in the frequency range where the gain of the lagging element is minimal. In Equation (2), 16 minimum values occur in the denominator of the stem and the denominator (which changes in a complicated manner to the absolute value of 1+T (SJ)), and a peak-like maximum value of 1K presses on the output impedance.

``@'fc As the polar circumference number decreases, the response speed also decreases.

The characteristics of the number of transfer strokes T (S) and the output impedance Z (S) are shown in Fig. 8 (aJ, (b) K), respectively.
show.

As mentioned above, compensation for control systems using lagging/lead elements, which has been conventionally practiced, reduces the output impedance and
There is a limit to the improvement in response speed, the response is generally slow, and the output impedance fluctuates depending on the operating conditions, with the drawbacks that it is particularly likely to reach a maximum value.

Furthermore, the output impedance at a higher frequency than the lossover frequency fc matches the impedance Zc of the FJ Heisei condenser and is not directly related to the configuration of the control system.

The switching power supply according to the present invention eliminates the above-mentioned performance limitations and drawbacks, and its purpose is to satisfy the stability condition of the loop gain without using lagging element compensation, reduce the output impedance, and further reduce the input voltage fluctuation. Eliminate the maximum value of output impedance by suppressing the influence of
This achieves an improvement in response speed.

Hereinafter, this invention will be explained in detail with reference to the drawings.

FIG. 9 shows an embodiment of the present invention. In FIG.
is the same as in FIG. 1, and 1211 is a current detection circuit. 9th
The frequency characteristics of each element of the switching power supply shown in the figure are
It becomes figure 0. +81 in Figure 10. (101~(
16j is the same characteristic of the stray current detection circuit (20) as in FIGS. 2 and 3.

G is the current of the smoothing inductor (131), and T is the current return path.

In this method, the entire feedback circuit for the output voltage f81 of the conventional method shown in FIG. A local feedback loop (minor) that feeds back to the on and off signals through the L
What is the 180° phase delay occurring in the C filter? il
The objective is to achieve a wide band and high efficiency control system, and to obtain a low and constant output impedance characteristic with a maximum value and a fast response speed.

In order to explain this principle, we will extract only the LC filter part from FIG.
λ and the transfer number G2 (S) from the inductor current to the output voltage (8) are determined as follows.

, 1iIL G2 (SJ = RL
(4) The frequency characteristics of 1+5CRL G1(S)+02(S) are shown in FIGS. 12 and 13.

The number of minor loop transfer strokes TM(S) that can be formed by the current feedback path in Fig. 10 is TM(SJ == K 3 X K2 X
It is expressed as (N, Vin) Moreover, the closed-loop transfer number GM [S) of the entire minor loop becomes. The frequency characteristics of GM(S) are shown in FIG. 14(a).

Minor, due to the loop effect l), Gz (SJ
has a flat characteristic up to the crossover frequency fc, and the nine phase delay becomes 0. The gain Gy of this flat part is approximately equal to TM (S) >> 1 in the above-mentioned equation (5). Therefore, 3 must be set to a value such that the loop gain of the entire loop at the frequency is exactly crossed. If TM(S) >
If >1 cannot be achieved, the gain of the forward element of the minor loop (eg, 2) needs to be increased.

In any case, the DC stability of the output voltage (8) is better if the feedback path includes a filter that blocks the DC component. The shape of Gy(S) when done in this way is the first
Section 4 (b) Show K. fp is the shielding T of the DC blocking filter
It is the frequency.

In this case, the number of transfer strokes T (S) for the entire loop is expressed as follows. FIG. 15 shows the frequency characteristics of 1(s). Figure 15 (12) can be peeled off, (b) shows phase gold. This system has sufficient phase margin and is stable. The LC smoothing filter (7) in FIG.

It is the product of Gl (S) and G2 (S), each of which is a first-order lag.

In total, it becomes a second-order delay element with a phase delay of 180 degrees, and if it returns as it is, it becomes unstable, but as implemented in this invention, it is minor. By providing a loop, Gl(S) transforms into GM(S), which has flat characteristics up to the total crossover frequency fc, and by making the phase delay total O, the phase delay of the entire system becomes 02 (SJ by qo
The system becomes stable with only O present.

Figure 15 (CJ (dJ) shows the gain 1 phase characteristic of T (S) when using the conventional lag/lead compensation for comparison.The system of this invention has higher gain and response. fast.

Next, in Fig. 10, the output impedance Z' fSJ
The result is a linear expression.

Frequency below the wave number fF (15) Frequency tuning above the wave number fF Below the continuous frequency of the filter of the minor and loop, it is the same as the case without the minor and the loop. , t1
Figure 6(a) shows the circumferential M-kin characteristic of the output impedance z(3). For comparison, FIG. 16(b) shows a custom-made output impedance in the case of using the conventional pre-decreasing method, but the present invention can even achieve a low impedance.

Furthermore, in this invention, the input voltage vin is included in the minor loop.

The effect of fluctuations in Vin is minor, and due to the loop effect, a minor loose closed-loop current (GM) does not appear in SJ. You can get sex,
Bandwidth can be expanded to the maximum. In addition, the output impedance is stable, and there is no peaking of the total pressure like in the past.

As described above, this invention provides band 4 of the open system of a switching power supply.
．． By increasing the gain and suppressing the effects of long-term fluctuations, it is possible to speed up the response of the switching circuit and achieve low a-impedance over all frequencies, improving the performance of switching power supplies. Effective in expanding usage.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional general switching power supply device, Fig. 2 is a block diagram showing the frequency characteristics of each element,
Figure 3 is a block diagram that focuses on the frequency characteristics of the output impedance, Figure 4 is a circuit diagram showing a lagging element, Figure 5 is a schematic diagram showing the frequency characteristics of a lagging element, and Figures 16 to 28 are A schematic diagram showing the frequency characteristics of a conventional method and its effects. FIG. 9 is a block diagram of the switching power supply device of the present invention, FIG. 10 is a block diagram showing the frequency behavior of each element,
Figure 11 is a circuit diagram explaining the LC filter, Figure 12~
A schematic diagram showing the frequency characteristics of the 13th FiLC filter, and FIGS. 14 to 16 are schematic diagrams for explaining the present invention in detail. In the figure (11 is the voltage detection circuit, (2) is the reference voltage, (3
j is an adder, (4) is an error voltage amplifier, (5) is a pulse width modulation circuit, (6) is a switch, (7) is a smoothing filter, (8j is an output voltage, (9) is an input voltage, The side is the frequency characteristic of the error voltage amplifier (4), (1υ is the frequency characteristic of the pulse width modulation circuit (5), 1121 is the frequency characteristic of the switch (6), uJ is the smoothing inductor, U4+ is the smoothing capacitor, 1151 is Kaiga Toryu, u6) is Resistance Kanka,
1171ull is a resistor, U (support) (4) is a capacitor, 1211 is a surge detection circuit, and 4 is the frequency characteristic of the #L production circuit 4. Note that the same or corresponding parts in FIG. 9 are designated by the same reference numerals. Agent Shin Kuzuno - Figure 11, Figure 12, Figure 13. 7. Figure 15

Claims (1)

[Scope of Claims] A switch that turns on and off an input voltage, a switching power supply circuit that obtains an output voltage by smoothing the signal turned on and off by the switch with an LC filter, and an LC filter of the switching power supply circuit. and a current detection circuit that detects the current in the inductor. the switching power supply circuit; and a voltage detection circuit that detects the output voltage of the switching power supply port circuit. a pulse width modulation circuit that receives the outputs of the current detection circuit and the voltage detection circuit and controls the on/off time of the switch; Switching power supply with special features.