JPS6036606B2 - switching regulator - Google Patents

Description

[Detailed description of the invention] The present invention relates to switching regulators.

The present invention makes it possible to widen the control range in which the output voltage can be stabilized against load fluctuations without using a large transformer or choke coil required for a switching regulator.
Further, the present invention can further extend the limit of the control range when the load is heavy and the output power is large, and in this sense, the control range can also be extended. Furthermore, in the configuration in which the duty factor of the pulse that drives the switching element is controlled, the variation range of this duty factor can be made smaller, and the load on the drive pulse generation circuit can be reduced. There are various types of switching regulators, and one example of which is shown in FIG. 1 or 2 is known.

In FIG. 1, 1 indicates an input DC voltage source Ei formed by rectifying and smoothing an AC power source, and 2 indicates a switching element, such as a transistor, between the collector of the transistor 3 and the input DC voltage source 1. Next coil 4
a is connected, and the emitter is also grounded. One end of the secondary coil 4b of the transformer 3 is grounded, and the other end is connected to a rectifier circuit consisting of a diode 5 and a capacitor 6, and a load 7 is connected to the output of this rectifier circuit. The output DC voltage Eo supplied to the load 7 is given to a comparison detection circuit 8 and compared with a reference voltage to detect its fluctuation, and from this detection output, for example, the output pulse of the pulse width modulation circuit 9 The duty factor is varied. The output pulse of the pulse width modulation circuit 9 causes the transistor 2 to perform a switching operation. For example, if the output DC voltage Eo rises above a specified value, the pulse width modulation circuit 9 is controlled so that the on period of the transistor 2 is shortened, and the output DC voltage Eo is kept constant.
In addition, in the configuration shown in FIG. 2, the input DC voltage source 1 is connected to the collector of the transistor 2, and the smoothing circuit in which the choke coil 10 and the capacitor 11 are connected in parallel is connected to the emitter of the transistor 2, and the diode 12 is connected to the emitter. has been done.

When transistor 2 is on, capacitor 11
As the transistor 2 is charged, a current flows through the load 7, and when the transistor 2 is off, the energy stored in the choke coil causes a current to flow through the diode 12 and charge the capacitor 11. The output DC voltage (Eo) is stabilized by controlling the switching operation of the transistor 2 by the comparison detection circuit 8 and the pulse width modulation circuit 9. The present invention can be applied to any of these switching regulators, but by taking the configuration shown in FIG. 1 as an example, the output DC voltage (
Let us find the inductance of the transformer 3 required to stabilize Eo).

Generally, the following relationship holds between input and output in a switching regulator. pi=2
...'11 power i = Hatake... ...---'
21ri・Ei・D:N・B〇. (11D) ...(31
However, li: input DC current Pi: input power P.

: Output power: Efficiency N: Number of turns of the primary coil 4a when the winding ratio of the secondary coil 4b of the transformer 3 is set to 1 D: Duty ratio Here, as shown in FIG. If the transistor 2 is turned on even at the ratio D, an excitation current shown in FIG. 3B flows through the primary coil 4a of the transformer 3.

The maximum value of this current is 1〆, the minimum value is 1〆2, the average value of the sawtooth wave is 1〆, (1〆, 1〆〆2=△1〆), the inductance on the primary side of transformer 3 When is L, li=D
・1〆＾・Sakichi skin {41 △M=Three fort soil skin '5'.

The maximum value 1 and the minimum value 1 and 2 of the excitation current are '41
From formula and formula '5), M = 1〆160 + E-gaku T...
・・・Tana・Yu 2=・So-mushi E-Sat-E Sanyazuchi ------'7
'2 It becomes 1D.

Here, since (1so2>0), from the above formula, L>
Three worlds 4Ei2-bi-T = gai-li・Ei2・L1P・T"""[8, 2P.

becomes.

Therefore, {from formula 81, the fluctuation of load '71, that is, the output power P. It is possible to obtain the inductance L required to enable constant voltage control with respect to fluctuations in . Now, if the inductance when the load is the lightest (P.min.) is L, and the inductance device when the load is the heaviest (P.max.) is L2, then (L,>L2). Therefore, the inductance L of the transformer 3 must have a minimum value of L, and P. max. However, it is required not to become saturated. The transformer 3 used in the conventional switching regulator has a constant inductance in the unsaturated range, like a normal transformer, and has a constant inductance of P as shown in FIG. 4A.

min. If the inductance L, is required in
It becomes a constant characteristic at L. As an example, the control range (P.
min. ~P. max. ) is (60W to 120W) and the duty ratio D changes from (0.3 to 0.7). In an attempt to expand this control range, P
. min. If we try to increase the inductance to 15 [W], the required inductance L' will be quadrupled as is clear from equation (2), and a transformer with constant characteristics of 4'' will be required as shown in Figure 4B. . Also, P. max. From equation 81, the inductance at the time of , becomes the value of L. To quadruple the inductance, the secondary had to either quadruple the cross-sectional area of the core or widen the core gap and double the number of turns. As a result, the shape of the transformer becomes large and the cost also increases. The present invention takes the above points into consideration, and as shown in FIG.

The first value peaks in a small range (P.min.) of the output power P. 2nd in a large range (P skin ax.)
A characteristic having a value of L2 is used. In this way, the control range for load fluctuations can be expanded without increasing the size of the transformer 3 or the choke coil 10.

Furthermore, as can be understood by comparing FIG. 4B and FIG. 4C, the slope period of the fall of the change when the inductance L is saturated can be made shorter than before, so P. ma
x. It is possible to further increase the value of , and in this sense also the control range can be expanded. Further, P when the control range is set to, for example, (60 W to 120 W) as in the conventional case, and a transformer having the characteristics shown in FIG. 4C is used. min
．． If we pay attention to the duty ratio D in
} becomes.

However, (K = thousand poisonous works). Therefore, if L can be made four times as much as before as mentioned above, the duty ratio can be reduced to 2.
Since the relationship of the side equation is satisfied even if it is multiplied, P. min.
and P. max. It is possible to reduce the variation width of the duty ratio between the two, and the burden on the pulse width modulation circuit 9 can be lightened. Theoretically, if the inductance can be made large enough, the output voltage can be stabilized against load fluctuations simply by changing the inductance, without changing the duty ratio. Furthermore, the same effects as in the case of load fluctuations described above can be obtained with respect to fluctuations in input DC voltage. Hereinafter, an embodiment of the present invention will be described. In this embodiment, in order to realize a transformer 3 or a choke coil 10 having characteristics as shown in FIG. In parallel to this, a material made of a material different from that of the core is inserted at a distance of 4 mm from the cross-sectional area of the core.

FIG. 5 shows an example of such a core, in which:
20 indicates a core applicable to the present invention as a whole, and 21
22 represents a gap formed in a portion of the core 21, and 23 represents a spacer inserted into this gap 22.

The winding of the transformer or choke coil has a gap of 22
installed near the The surfacer 23 is made of the same material as the core 21, and its cross-sectional area is smaller than the cross-sectional area of the core 21. The fact that such a core 20 exhibits the characteristics shown in FIG. 4C is due to the fact that the core 21 shown in FIG. 6A in which the gap 22 is not formed and the core 21 in which the gap 22 shown in FIG. It can be predicted by combining these DC superposition characteristics. That is, if the gap 22 is not formed, the broken line 2 in FIG.
If the inductance L is large and saturates easily, as shown by 4a, and the gap 22 is formed, the inductance L is small and becomes a characteristic that saturates easily, as shown by the dashed line 240 in FIG. Therefore, in a part of the gap 22, there is a subesa 23 of the same quality as the core 21.
is inserted, solid line 24c similar to Fig. 4C
As shown in , it is a combination of the characteristics of both. Further, this characteristic (solid line 24c) was also confirmed through experiments by the inventor of the present application. Note that the DC superposition characteristic is obtained by determining the inductance L by examining changes in magnetic flux due to a minute AC current while flowing a constant DC current, and the output power P of the switching regulator.

In a strict sense, this is different from the change characteristic of the inductance L (FIG. 4C). However, in a switching regulator, the output power P. is obtained by extracting the energy that was once stored in the inductance element, and the energy (E) stored in the inductance element (L) becomes the tail of (Eg = KyoLF), and therefore (nose 12 =P.-t), so P
. An increase in L means an increase of 1 (input current) since an increase in L is unthinkable. Therefore, the DC superimposition characteristics (L-NI) shown in Fig. 7 and C
The characteristics (LP.) shown in are similar. FIG. 8 shows the configurations of some other examples of transformers or choke coils applicable to the present invention. In the configuration shown in FIG. 8A, the cross-sectional area of the spacer 23 inserted into the gap 22 changes according to the direction of the magnetic path. In the configuration shown in FIG. 8B, the spacer 23 inserted into the gap 22 is made of a magnetic material different from the material of the core 21 (ferrite), such as permalloy. In the configuration shown in FIG. 8C, a spacer 23 made of a material such as permalloy having a magnetic permeability larger than the cross-sectional area of the core 21 and smaller than that of the lower 21 is inserted into the gap 22. . In the configuration shown in FIG. 8D, a permalloy plate 25 is brought into close contact with the outer peripheral surface of the core 21 in which the gap 22 is formed instead of the spacer 23. It is assumed that the core shown in FIG. 8 has the same characteristics as the core shown in FIG. 5.

By appropriately selecting the length of the gap 22, the shape and material of the spacer 23, the change in inductance L with respect to the magnetic field (NI) can be changed in three stages as shown in FIG. 9. Further, since the characteristics can be made according to the specifications of the power supply circuit, there is an advantage that there is no need to manufacture cores of different sizes depending on the specifications of the power supply circuit.

[Brief explanation of drawings]

1 and 2 are connection diagrams of a switching regulator to which the present invention can be applied, FIG. 3 is a waveform diagram used for explaining the same, FIG. 4 is a schematic diagram used for explaining the present invention, and FIG. 5 is a diagram of the present invention. A configuration diagram of a core applicable to the invention, FIG. 6 is a configuration diagram used for explaining the core, and FIG. 7 is a schematic diagram used for explaining its characteristics.
FIG. 8 is a configuration diagram of some examples of cores applicable to the present invention, and FIG. 9 is a schematic diagram showing other examples of core characteristics. 1 is an input DC voltage source, 2 is a switching transistor,
3 is a transformer, 7 is a load, 10 is a choke coil, 21
is a core, 22 is a gap, and 23 is a spacer. 1st
Figure 2 Figure 3 Figure 5 Figure 7 Figure 4 Figure 6 Figure 8 Figure 9

Claims (1)

[Claims] 1. The input DC power supply, the switching element, and the transformer are connected in series with a chiyoke coil, and when the switching element is turned on, a current flows through the winding of the transformer or chiyoke coil to store energy in the transformer or chiyoke coil, and the above-mentioned A switching regulator that flows accumulated energy to a load when a switching element is turned off to obtain an output DC voltage, detects fluctuations in the output DC voltage, and controls the switching element using the detected output. In the controller, the transformer or the chiyoke coil has the characteristic that its inductance takes a first value in a range where the output power is small and takes a second value smaller than the first value in the range where the output voltage is large. Switching regulator using.