JPH04299069A - Switching regulator - Google Patents

Abstract

PURPOSE:To enhance conversion efficiency and to realize stabilized oscillation by detecting a secondary current, lagging thus detected secondary current and then short-circuiting a diode based on a delay signal. CONSTITUTION:Secondary current I2 is monitored through a resistor R7 and delayed through comparators Com1, Com2 and a transistor Q2 is turned ON upon elapse of a predetermined time after conduction of a diode D3. Consequently, the current I2 begins to flow through the transistor Q2 in the negative direction after the current I2 flowing through the diode D3 goes zero. The current I2 flowing in the negative direction is subsequently cut off when the transistor Q2 is turned OFF by Com1 and Com2. Furthermore, a transistor T1 is provided with reverse bias energy and feeds a current I1. through the diode D3 in the negative direction simultaneously with cut-off of the current I2. At the same time, a voltage for bringing the collector voltage of the transistor Q1 to zero is induced in 1 winding P of the transformer T1 while a voltage for turning Q1 ON is induced in winding B of T1.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] This invention relates to an on-off type self-oscillation switching regulator suitable for use in office machines such as facsimile machines and printers, and power supplies in industrial equipment. This invention relates to a switching regulator that enables stable operation during no-load and light-load conditions.

0002

2. Description of the Related Art There are two types of on-off type switching regulators: a separately-excited type that operates using an external oscillator, and a self-excited type that performs switching operations without a special oscillator.

[0003] In general, the externally excited type has the following characteristics compared to the self-excited type:
It is not used much because it requires a large number of parts and increases costs. The self-oscillating type is RCC (Ringi
This is called the g choke converter) method.

FIG. 4 is a block diagram showing an example of the configuration of essential parts of a conventional RCC type switching regulator. In the figure, Q is a transistor, D is a diode, T is a transformer, C and C0 are capacitors, and R
indicates a resistor, and Vin is the input voltage, Vout
is the output voltage, Vc is the collector voltage of transistor Q, I
c indicates the collector current of transistor Q.

In the conventional RCC type switching regulator shown in FIG.
A rectangular wave is generated on the secondary side (output side) of the converter, and this is converted into a DC voltage. In other words, energy is stored in the inductance (L) of the primary winding of the transformer T while the transistor Q is on, and when the transistor Q is turned off, it is transferred to the smoothing capacitor C and the load through the rectifier diode D. (not shown).

FIG. 5 is a time chart illustrating the operation of the RCC switching regulator shown in FIG. The code of each signal waveform corresponds to the code position in FIG.

A collector voltage as shown by Vc in FIG. 5 is applied to the transistor Q, and Ic (C0
A triangular wave current Ic is generated as shown in (none). In this case, most of the switching losses occur when transistor Q is off.

When a capacitor C0 is inserted in order to reduce the switching loss during off-time, as shown by Ic (with C0) at the bottom of FIG. 5, as a side effect,
Switching loss when turned on increases. As a result, the overall switching losses are not significantly reduced.

FIG. 6 is a block diagram showing a detailed example of the main part configuration of a conventional RCC type switching regulator. In the figure, Q1 is a transistor, PC1 and PC2 are photocouplers, T1 is a transformer, (P), (B), and (S) are their respective windings, and D1
is a diode, ZD is a Zener diode, Amp1
is an amplifier, C1 and C2 are capacitors, R1 to R5
indicates the resistor, I1 is the primary current, I2
indicates the current on the secondary side.

FIG. 6 shows a detailed circuit configuration of the switching regulator shown in FIG. 4 above. Therefore, the basic operation is the same as in FIG.

However, as already mentioned in connection with FIG. 4, the conventional RCC type switching regulator has a problem in that the switching loss increases regardless of the presence or absence of the capacitor C0, resulting in poor conversion efficiency. . Moreover, since it is a self-oscillating type, at light loads,
As the frequency increases, operational instability such as intermittent oscillation tends to occur, which is a disadvantage.

0012

[Problems to be Solved by the Invention] The present invention solves the above-mentioned disadvantages of conventional RCC switching regulators, namely, low conversion efficiency due to large switching loss, and intermittency as the frequency increases during light loads. By solving the problem of operational instability such as oscillation, and by significantly reducing switching loss, conversion efficiency is improved, and by reducing frequency changes in response to load fluctuations, R that enables stable oscillation operation even when
An object of the present invention is to provide a CC type switching regulator.

[0013]

[Means for solving the problems] In this invention, firstly,
a transformer; a switching element on the primary side of the transformer;
In an on-off type self-excited oscillation switching regulator equipped with a diode on the secondary side, there is provided a current detection means for detecting a current flowing in the secondary side, and a signal delay means for delaying a signal detected by the current detection means. , and short circuit means for shorting the diode driven by the signal from the signal delay means.

Second, in the first on-off type self-excited oscillation switching regulator, the current detection means is composed of a resistor.

Thirdly, in the first or second on-off type self-excited oscillation switching regulator, the signal delay means is composed of a comparator.

Fourthly, in the first to third on/off type self-excited oscillation switching regulators, the short circuit means is constituted by a switching element such as a transistor.

[0017]

[Embodiment 1] Next, an embodiment of the switching regulator of the present invention will be described in detail with reference to the drawings. This embodiment corresponds to the inventions of claims to claims 4.

FIG. 1 is a block diagram showing an embodiment of the main structure of a switching regulator according to the present invention. The symbols in the figure are the same as in FIG. 6, and
Q2 is a transistor, D2 and D3 are diodes, Z
D is a Zener diode, Amp1 is an amplifier, C3
~C5 is a capacitor, R6 ~R8 is a resistor, Co
m1 and Com2 indicate comparators.

In the switching regulator of the present invention, in the conventional circuit of FIG. 6 described above, the primary side circuit includes a diode D2, a capacitor C3, and a resistor R6.
are added, and the secondary circuit includes a transistor Q2, capacitors C4 and C5, and resistors R7 and R
8, comparators Com1 and Com2 are added, respectively. Note that the diode D3 on the secondary side corresponds to the diode D1 in FIG.

The basic operation of the present invention is the same as that of the conventional one, and when the transistor Q1 is turned on, a current I1 flows, and energy is stored in the transformer T1. The energy stored in the transformer T1 is released by the current I2 flowing when the transistor Q2 is off, and an output voltage is generated. Therefore, the switching regulator of the present invention can be said to correspond to a modification of the RCC system.

Next, the operation of the switching regulator of the present invention shown in FIG. 1 will be explained.

FIG. 2 is a time chart illustrating the operation of the switching regulator of the present invention. The sign of each signal waveform corresponds to the sign position in FIG. 1, and VQ1 indicates the collector voltage of transistor Q1.

(1) When transistor Q1 is turned on, current I1 increases linearly (I1 in FIG. 2)
. (2) When the base current of transistor Q1 is insufficient, Q1 turns off, but at that moment, the collector of Q1 is kept at 0 (v: volt) by capacitor C3, so switching operation without loss is possible. .

(3) After transistor Q1 is turned off,
Capacitor C3 is charged by current I1, and Q1
The collector voltage increases (VQ1 in FIG. 2), but when it exceeds a certain voltage, current I2 begins to flow through diode D3 on the secondary side. (4) The energy stored in the transformer T1 by the current I1 is released through the current I2, and this I
2 decreases linearly with time (I2 in Figure 2)
.

(5) This current I2 is connected to the resistor R7
and delayed by Com1 and Com2 (+ side input of Com1 and + side input of Com2 in Figure 2).
side input), after a certain period of time when diode D3 conducts,
Turns on transistor Q2 (Com2 in Figure 2)
output becomes the base signal of Q2). (6) Due to the operation in (5) above, diode D3
After the current I2 flowing through becomes “0”, the current I2 starts flowing in the negative direction through the transistor Q2 (
I2 in Figure 2).

(7) After a certain period of time, the negative current I2 flows through the transistor Q2 due to Com1 and Com2.
is cut by turning off (I2 in Figure 2)
. (8) This negative direction current I2 is
Reverse bias energy is applied to the diode D3, and at the same time as I2 is cut off, a negative current I1 is generated through the diode D3 (I1 in FIG. 2).

(9) At the same time as (8) above, a voltage is generated in the (P) winding of the transformer T1 that makes the collector of the transistor Q1 0 (v), and in the (B) winding of T1, A voltage is generated that turns Q1 on.

(10) In short, transistor Q1
Immediately before switching on, the circuit on the primary side is already conducted by diode D3, and here again the voltage 0 (
v) is in the state of switching operation.

(11) Furthermore, even when the transistor Q2 is off, the circuit voltage is maintained at 0 (V) by the capacitor C4, and the circuit voltage is kept at 0 (V) by the capacitor C4, and the circuit voltage is maintained at 0 (V) even when the transistor Q2 is turned off. , 0(v) is possible.

Due to the operations described in (1) to (11) above, in the switching regulator of the present invention, the switching operations of both transistors Q1 and Q2, which are switching elements, are always performed when the circuit voltage is 0 (V). It will be held on. Therefore, in principle, switching losses are reduced and conversion efficiency is improved.

[0031] Furthermore, even when the load is light or there is no load, the switching device has an on time and an off time. That is, when there is no load, the current areas of the currents I1 and I2 in the positive direction and in the negative direction are equal. As a result, there is no extreme decrease in pulse width, so stable oscillation operation is realized. This point is almost the same even when the load is light.

The switching regulator (on-off type switching regulator) of the present invention specifically explained above, that is, the RCC type switching regulator which is a self-oscillation type, has the configuration shown in FIG. However, if we pay attention to its operation, it can be explained as follows.

That is, in the switching regulator of the present invention, in order to detect the secondary side current I2, the resistor R7 is connected, and in order to delay the detection signal,
In this configuration, a transistor Q2 is provided to short-circuit the comparators Com1 and Com2 and the diode D3 driven by the delayed signal. Note that an EFT type transistor can also be used as the transistor Q2. For this configuration,
This will be explained as another example.

[0034]

[Embodiment 2] Next, another embodiment of the switching regulator of the present invention will be described in detail. This embodiment corresponds to the invention of claim 1.

As already mentioned in the embodiment of FIG.
The switching regulator of the present invention uses a resistor R7 to detect the secondary current I2, and comparators Com1 and Co to delay the detection signal.
A transistor Q2 is provided to short m2 and also a diode D3 driven by the delayed signal.

FIG. 3 is a functional block diagram showing an embodiment of the main structure of the switching regulator of the present invention. The symbols in the figure are the same as those in FIG. 1, and 1 indicates a short circuit, 2 indicates a delay circuit, and 3 indicates a current detection circuit. Looking at the function of the switching regulator of the present invention, the resistor R7 in FIG. 1 has a function of detecting the current I2 flowing through the secondary circuit. Therefore, if the current detection circuit 3 has such a function, it is not necessarily necessary to use the resistor R7.

Similarly, the comparators Com1 and Com2 have the function of delaying the detected current I2 and supplying it to the base of the transistor Q2, as shown in FIG. Therefore, it is sufficient to provide a delay circuit 2 having such a delay function.

Furthermore, this transistor Q2 has the function of shorting the diode D3 driven by the delayed signal. Therefore, it is possible to use the short circuit 1 as a circuit having the same function as this transistor Q2.

In this second embodiment, the circuit shown in FIG. 3 is constructed based on this basic recognition. To summarize the above, in an on-off type self-excited oscillation switching regulator that includes a transformer, a switching element on the primary side of the transformer, and a diode on the secondary side, current detection detects the current I2 flowing on the secondary side. Circuit 3 and
The configuration includes a delay circuit 2 that delays the signal detected by the current detection circuit 3, and a shorting circuit 1 that shorts the diode driven by the signal from the delay circuit 2. This second embodiment is the most characteristic configuration of the present invention.

[0040]

Effects of the Invention In the switching regulator of the present invention, the switching operation of the two switching elements can be reduced to 0.
(v), so theoretically no switching loss occurs. Therefore, the conversion efficiency is improved and the device can be made smaller.

Furthermore, since the switching operation is performed at a voltage of 0 (V), short-circuit current due to the parasitic capacitance of the device does not occur, resulting in low noise. Furthermore, even when there is no load, the on/off time has a constant width, so the oscillation is stable, and the control characteristics are also superior to conventional circuits (an effect corresponding to the invention of claim 1).

Furthermore, by using a resistor as a current detection means, a comparator as a signal delay means, and a switching element such as a transistor as a short circuit means, the number of parts is reduced, conversion efficiency is high, and oscillation operation is possible even under no load. Many excellent effects can be achieved, such as being able to realize a self-excited oscillation switching regulator of a stable on/off type (effects corresponding to the inventions of claims 2 to 4).

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the main configuration of a switching regulator of the present invention.

FIG. 2 is a time chart illustrating the operation of the switching regulator of the present invention.

FIG. 3 is a functional block diagram showing an embodiment of the main configuration of the switching regulator of the present invention.

FIG. 4 is a block diagram showing an example of the configuration of essential parts of a conventional RCC switching regulator.

FIG. 5 is a time chart illustrating the operation of the RCC switching regulator of FIG. 4;

FIG. 6 is a block diagram showing a detailed example of the configuration of main parts of a conventional RCC type switching regulator.

[Explanation of symbols]

1 Short circuit 2 Delay circuit 3 Current detection circuit

Claims (4)

[Claims] 1. An on-off self-oscillation switching regulator comprising a transformer, a switching element on the primary side of the transformer, and a diode on the secondary side,
Current detection means for detecting the current flowing to the secondary side, signal delay means for delaying the signal detected by the current detection means, and short circuit means for shorting the diode driven by the signal from the signal delay means. , and a switching regulator. 2. In the on-off type self-oscillation switching regulator according to claim 1, the current detection means comprises:
A switching regulator characterized by being composed of a resistor. 3. The on-off type self-excited oscillation switching regulator according to claim 1 or 2, wherein the signal delay means is comprised of a comparator. 4. The on-off type self-oscillation switching regulator according to claim 1, wherein the short circuit means is comprised of a switching element such as a transistor.