JPS60113662A - Switching power source circuit - Google Patents

Abstract

PURPOSE:To increase the range of an input voltage and to reduce a transformer by providing a controller so that the maximum value of the product of a pulse width modulating pulse width and an input voltage does not become larger than the saturated amount of the transformer. CONSTITUTION:An AC voltage induced in the secondary side of a transformer T1 is rectified by a diode D6, and smoothed by a capacitor C2. A comparator U2 receives at one input the output of an operational amplifier U1, and at the other input a triangular wave. The output of a rectifier is divided by resistors R1, R2, and the divided output is applied through a diode D5 to the output line of the comparator U1. A switching transistor Q2 is driven by the output of the comparator U2, and a switching transistor Q1 is driven through a transformer T2. A circuit which has the diodes D5, D6, the capacitor C2 and the resistors R1, R2 is limited so as not to become larger than the saturated value of the transformer T2 at the maximum value of the product of the pulse width modulation pulse width and the input voltage.

Description

[Detailed Description of the Invention] [Technical Field to which the Invention Pertains] The present invention relates to a switching power supply circuit using a pulse width modulation method, and relates to a switching power supply circuit using a pulse width modulation method. The present invention relates to a switching power supply circuit that prevents this from occurring.

[Prior art] A switching power supply using a pulse width modulation method turns on and off the primary side input voltage using a switching circuit using a switching element, and the above-mentioned switching circuit so that the smoothed secondary side DC output is constant. In this type of switching power supply circuit, J'3 (Jl, 1 to magnetic saturation of the lance is 1).
This is a phenomenon that should never occur because it causes overcurrent to flow through the switching circuit such as a helangistor. Therefore, when installing an I-lance, it is necessary to pay sufficient attention to this matter. This will be explained using a single-channel switching power supply circuit as an example.

FIG. 1 is a diagram showing a configuration of a conventional pulse width modulation type switching power supply circuit. In the figure, Jl, Vll) are input terminals, Tit or lance, [1 is the primary winding, L2
is a secondary winding, D+ and D2 are rectifier ties, lj:fl::I, C+ is a smoothing coil, and L and C1 form a smoothing circuit. The output of the smoothing circuit becomes the power supply output youc. Ul is an operational amplifier that receives VOLI[ on one input and a reference voltage vr on the other input; 1 is a pulse width modulation circuit that receives the output of the operational amplifier and outputs a pulse with a width corresponding to the output; 2 is a driving circuit receiving the output of the pulse width modulation circuit, and QI is a switching l-run raster driven by the driving circuit and having an input voltage Vin@J-A.

The operation of the circuit configured as above is summarized as follows. Input voltage (1) is turned on and off by transistors Q1 and Q1, and the changes are transmitted to the secondary side via transistors T1 and T1. The transmitted secondary side AC voltage is connected to diode D+
, D2, and then smoothed by a smoothing circuit consisting of =1 Ill L and capacitor C+, and the DC output vOut is (!7). At this time, the output Vout is This modulated output enters the drive circuit 2, and the drive circuit drives the 1-transistor Q1, thereby applying feedback and stabilizing the output. It is a diagram showing the on/off state of QX.The 1-(level in the diagram shows the on state and the L level shows the on state. The king shows the switching period. During the constant period T, the period is 32111 and +l 11
control. At this time, the output voltage vout is expressed by the following equation.

tolI n2 V 0IJI ------V in < 1 ) 111 Here, nl+'2 is the number of turns of the primary winding L1 and the secondary winding L2, respectively. As the value of the input voltage ■in, use the identification symbol as is, lC,,'A time ton l, 1 ~
It takes time to reset the magnetic flux of the lance.
Therefore, it is usually limited to (t011/block)<0.5.

Let the maximum value of ton be O1l (nlaX).

(1) Formula j, l-, l+ 8. Since n2 is a fixed constant, it can be seen that pulse width control is performed so that vin is constant. Also, the number of volumes is 11, ,
n2 is determined so that the pulse width (O;) is maximized when the input type 1l-vin is minimized.

Figure 3 shows 14 items from 1 to Lance 1! There is a diagram showing the state of the flux. In the diagram, the vertical axis shows the magnetic flux density B, the horizontal axis ta, and the strength of the I!l field 1-1. ΔB is the change in one flux during switching 01 operation. The quantity 'IIoΔB is expressed by the following formula.

Vin. Here, ΔB remains constant regardless of the input voltage V group.During normal operation, V 1-1011 <Vill(max)-1
011(IllaX), and △B is (3n+ax
-[3o) J: sufficiently small.

Here, Vin (river ax) is the maximum II of the input voltage group V
(+, B max is the maximum value of magnetic flux density, BO is the residual magnetic flux density. However, during normal operation, △B is (B
orax -8o), and when the input voltage is high due to 1 sudden load change and 15 overload, and the input voltage is high near the control, V i++ -ton≧V in (max) ・t
On (max) can be considered to be transient.

Therefore, in stage t1 of the transformer, saturation is prevented J
Therefore, V in (max) - ton (max
)(13max -Bo) >-'----n,
It is necessary to determine the number of primary turns, 111, so that -8.

This means that when the input ranges over a wide range, the number of turns 01 of the primary winding L1 increases, resulting in increased copper loss, inability to wrap the winding completely on the given winding frame, and ΔB (3max -
13o) becomes large, resulting in a decrease in usage efficiency.

[Object of the invention] The present invention has been made in view of this connection, and
When J3 is in a transient state such as overload or sudden load change,
By limiting the increase in the voltage-time product of the lance, we have realized a switching power supply circuit that can accommodate a wide range of input voltages and has a smaller lance.

[Structure of the Invention] In order to achieve such an object, the present invention provides a method in which the maximum value of the product (voltage-time product) of the pulse width for pulse width modulation and the input voltage is 1.
It is characterized by a lance saturation fLJ, an unobtrusive J, and a limiting circuit.

[Example code] FIG. 4 is a dimensional electrical diagram illustrating one embodiment of the present invention.

Items that are the same as those in Figure 1 are indicated by incrementing the same numbers.
In the third figure, D6 is a rectifying diode, and C2 is a smoothing capacitor. 1 ~ Lance "The AC voltage induced on the blind secondary side is rectified by diode D6, smoothed by capacitor C2, and converted to DC voltage. U2 connects the output of operational amplifier U1 to one input of triangular waveform. The output of the operational amplifier U is input to the comparator U2 via the backflow prevention diode D3.

On the other hand, the output of the rectifier circuit is divided by resistors R+ and R2, and the divided voltage output is passed through diode D5 to comparator U+.
connected to the output line. Well, diode D
A series circuit of 4 and a voltage ρ is also connected to the output line. The circuit is composed of diodes D3...-D6, capacitor C2, and resistors R+ and R2. The circuit is the same as the conventional circuit shown in FIG. 1 except for the rectifier voltage divider circuit.

The series circuit of die
The lower limit of the true human power is limited. Trans-“2.1-
Together with the transistor Q2, it constitutes a drive circuit for the 1-transistor QI. The operation of the circuit configured as described above will be explained as follows.

The series circuit composed of diode D6 and capacitor C2 is a rectifying and smoothing circuit, and a voltage proportional to the input terminal (II 2 /II + ) ・Vin appears across the capacitor C2 (the diode The forward type Ji precipitation of 211 degrees Celsius). This voltage is divided by resistors R+ and R2, and diode D! The fifth voltage is applied to the current power of the comparator U2 via I. This electric jfb D<, F
i! Similar to the series circuit, the lower limit of the comparator U2 is limited, but the difference from the 16-column circuit is that the level in this case changes in proportion to the input terminal vin.

The discharge time constant determined by capacitor C2, resistor 1<+, and I'<2'c is sufficiently smaller than the fluctuation of input voltage vin, and the delay between lI& of the control system is set sufficiently large. Here, a voltage proportional to the input voltage is taken out from the secondary side of the transformer T1, but if it cannot be taken out accurately due to noise etc., power is supplied to U+, U2, etc. of this circuit. auxiliary power supply circuit (not shown), etc.
You can use 5 wires.

FIG. 5 is a diagram showing operating waveforms. The upper row shows a triangular oscillation waveform applied to the input of the comparator U2, and the ]. rows show the on/off states of transistors Q1 to Q1. In the figure, FQ indicates the limit voltage, EO indicates the output of the operational amplifier U+, and El indicates the divided voltage output of the rectifier circuit described above. and,
The maximum value of these voltages is applied to the positive input of operational amplifier U1. i) In the control state of V, EO>[i,
EO>EQ, EO takes priority and the output is stabilized by feedback control. Now, if control is temporarily lost for some reason and EO becomes low, the pulse width will widen as it decreases, but the positive input of comparator U2 will become Ei from +7° where Ei becomes Ei. It is clamped and the expansion of the pulse width is stopped. Therefore, the voltage-time product applied to the lance 1 is also limited to Vin-ton (Vill). If Ei does not exist, this product (or Vill
・Increase to tall (IIlaX) and -C.

Since 101) and 1111) are inversely proportional to Vin, V
The in-ton (vin) remains constant, and the increase in the magnetic flux of the lance is also limited to a constant value. Here, ton (
vin) This is the pulse width when clamped by C and Ei.

FIG. 6 is a diagram showing the relationship between the input terminal Vin and the duty cycle r. The vertical axis shows the duty (the first axis shows the input voltage V group. ON time for the input voltage vin + 01). In the state [1 shown in J: 1\II, there is a minimum input voltage ζ゛.

f2 is a curve in which the voltage-time product (Vin·tol) reaches a limit when the transformer becomes saturated. In the conventional system, the duty limit is 1) If control is lost when the input voltage is below the may line v1+ax, it is necessary to increase the core size to 12, which exceeds the curve [3]. The duty is controlled according to the input voltage [If a line like the one shown in 4 is used, the duty will not exceed [2].

Effects of the Invention J As described above in detail, according to the present invention, the maximum value of the product (voltage time product) of the pulse width for pulse width modulation and the input voltage does not exceed 1 to the saturation amount of the lance. : By providing such a limiting circuit, it is possible to realize a switching circuit that prevents the l-lance from saturating and the switching element from breaking even under transient conditions using a small l-lance. .

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a conventional device, Fig. 2 is a diagram showing the on/off states of transistors 1 to 3, Fig. 3 is a diagram showing the magnetic flux state of the transformer, and Fig. 4 is a diagram showing an example of the present invention. FIG. 5 is a diagram showing operating waveforms, and FIG. 6 is a diagram showing the relationship between input voltage and duty. 1...Pulse width modulation circuit, 2...Drive circuit, TT. T2...Transformer, D1-D6...Diode, L
・・・Coil, CI, C2...Capacitor, UI・
. . . Ensun's widening device, Q+, C2 . . . 1- transistor, Vill . . . Input voltage, Vr, VQ . . . Parking voltage. Figure 1 I Figure 2 Figure 3 Figure 4 T

Claims (1)

[Claims] Turn on and off the human horn voltage using a switching circuit, transmit the change to the secondary side through the primary to lance, compare the DC output of the secondary side with the base illumination voltage, and set the DC output to a constant value. The pulse width of the pulse signal for turning on and off the input voltage is changed. A switching power supply circuit characterized by having a limiting circuit so that the maximum one shift of the time product does not become larger than the saturation amount of the transformer.