JPH04251563A - Switching regulator - Google Patents

Abstract

PURPOSE:To provide a switching regulator, which stabilizes the output voltage and never lowers the supply efficiency to load. CONSTITUTION:In a switching regulator, which can output, for example, 5V and 12V, the 5V output line is fed back to the primary side so as to elevate the accuracy in output voltage. Moreover, it has certain load between the 12V output line and the 5V output line, and a stabilizing circuit, which is turned on when it becomes above certain voltage, is provided. For the 12V output line where feedback is not applied, the stabilizing circuit is not conducted the range where the voltage rise is allowable, and it does not cause power loss herein. On the other hand, when the voltage rises to a certain value, the stabilizing circuit is conducted and the output current ceases to fall below the certain value, and the output voltage rise is suppressed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator, and more particularly to a switching regulator capable of improving output voltage accuracy.

0002

2. Description of the Related Art Today, switching regulators are widely used as DC stabilized power supplies. FIG. 3 shows an example of switching regulators that can output different voltages. This rectifies and smoothes an AC power source E with an input circuit having a rectifier circuit R and a smoothing capacitor C1, and supplies this as an operating voltage to a series circuit of a transformer T's primary coil NP and a switching transistor Q1. The transformer T has two coils NS1 and NS2 on the secondary side, and outputs DC 5V and 12V smoothed by diodes D1 and D2 and smoothing capacitors C2 and C3, respectively, in response to the operating voltage from the primary side. This is what I did. Furthermore, in a switching regulator, the voltage on the frequently used output side or the output side where the voltage is desired to be stabilized is fed back to the primary side to improve voltage accuracy. In FIG. 3, the voltage on the 5V output side is fed back to the primary side to stabilize the 5V output voltage.

In other words, when the load on the 5V output side is small, the induced voltage has a small duty ratio as shown in FIG. 4(a), but when the load increases, the duty ratio increases as shown in FIG. 5(a). As a result, the duty ratio of the induced voltage increases. By smoothing this induced voltage as shown in FIGS. 4 and 5, (b) and (c), the voltage on the 5V output side is always stabilized regardless of load fluctuations.

0004

However, the change in the duty ratio similarly occurs in the induced voltage on the 12V output side, regardless of the magnitude of the load on the 12V output side. Therefore, if the load on the 12V output side is small, excessive power may be supplied and the voltage may rise too much. This is most noticeable when the maximum load is applied to the 5V output side that is fed back and the duty ratio of the induced voltage is large, and the minimum load is applied to the 12 output side that is not fed back. In the switching regulator shown in Figure 3, when the load on the 5V output side fluctuates, 12
An example of characteristics on the V output side is shown in FIG. As is clear from this characteristic example, there is no load on the 5V output side (output current 0A).
In this case, the voltage on the 12V output side is stable within the range of ±10% of 12V, but if a large load (output current 1.5A) is applied to the 5V output side, the voltage on the 12V output side will drop. Rise. At this time, if the load on the 12V output side is small (output current 0.2A or less), the voltage will be +
It will rise to more than 10%.

Therefore, conventionally, when suppressing the voltage fluctuation on the 12V output side within a range of, for example, ±10%, a dummy resistor RD is connected to the 12V output side circuit as shown in FIG.
This dummy resistor RD prevents the output current on the 12V output side from becoming less than 0.2A. but,
In this case, 12V x 0.2A = 2.4W is always discarded, resulting in poor efficiency.

[0006] The purpose of the present invention is to solve the above-mentioned conventional problems,
It is an object of the present invention to provide a switching regulator that stabilizes the output voltage and does not reduce the supply efficiency to the load.

[0007]

[Means for Solving the Problems] A typical means according to the present invention for solving the above problems has a plurality of output lines on the secondary side, and supplies power from the primary side via a switching circuit and a transformer. In the switching regulator, one of the plurality of output voltages is fed back to the primary side, and one of the plurality of output voltages is fed back to the primary side, and the power is outputted as different voltage values depending on the plurality of output lines. The feature is that a stabilizing circuit is provided between the feedback output line and the output line, which has a constant load and becomes conductive when the voltage exceeds a certain level.

[0008]

[Operation] With the above means, the output voltage is stabilized on the feedback output side. On the other hand, on the output side without feedback, if the voltage is within a permissible range below a certain level, all output current is supplied to the load without being wasted. When the voltage rises above a certain level, such as when the load is light, the stabilizing circuit operates and a certain amount of power is consumed by the stabilizing circuit. Therefore, the output current never falls below a certain level, and the output voltage is always supplied within a certain allowable range.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a switching regulator according to the present invention to which the above-mentioned means is applied will be described in detail with reference to FIG.

In FIG. 1, an AC power source E is connected via a rectifier circuit R to a series circuit of a primary coil NP and a switching transistor Q1 constituting a switching circuit.
Moreover, a smoothing capacitor C1 is connected in parallel to the series circuit of the primary coil NP and the switching transistor Q1. The basic configuration of this primary side is the same as that of the conventional example. On the other hand, the secondary side of the transformer T has two coils NS1 and NS2, and is configured to output different voltage values to a plurality of output lines. In this embodiment, 12V is output between terminals t1 and t0, and 12V is output between terminals t2 and t0.
An example is shown in which 5V is output between 0 and 0.

That is, a smoothing circuit consisting of a diode D1 and a smoothing capacitor C2 is connected to a series circuit of two coils NS1 and NS2, and the voltage induced in the coils NS1 and NS2 is rectified and smoothed to output 12 V DC to the terminal t1. do. Similarly, a smoothing circuit consisting of a diode D2 and a smoothing capacitor C3 is connected to the coil NS2, and the voltage induced in the coil NS2 is rectified and smoothed to output 5 V DC to the terminal t2.

[0012] Also, the terminal that outputs the 5V (hereinafter referred to as ``5V
A feedback circuit consisting of resistors R1 and R2, a shunt regulator TL, a photocoupler PC, and a voltage control circuit A is provided at the terminal t2. As a result, for example, the output voltage of the 5V terminal t2 is set to the reference voltage (5V).
When it becomes higher than , the cathode voltage of the shunt regulator TL decreases, the amount of light emitted by the light emitting diode increases, and the current flowing through the phototransistor increases. In response to this current change, the voltage control circuit A shortens the on time of the switching transistor Q1, reduces the power flowing into the transformer T, and operates to lower the output voltage of the 5V terminal t2. Further, when the output voltage of the 5V terminal t2 becomes lower than the reference voltage, the operation is reversed to that described above. Through this feedback control, the output voltage of the 5V terminal t2 is always held constant.

Furthermore, a terminal that outputs 12V (hereinafter referred to as "12V
There is 1 between t1 (referred to as "terminal") and 5V terminal t2.
Stabilizer circuit B for stabilizing the output voltage of 2V terminal t1
has been established. The configuration of the stabilizing circuit B in this example is (
(circuit surrounded by a broken line in Figure 1), a series circuit of a resistor R3 and a transistor Q2 is connected to a 12V terminal t1 and a 5V terminal t2.
A series circuit of a current limiting resistor R4 and a Zener diode DZ is connected to the 12V terminal t1 and the base of the transistor Q2.

In this stabilizing circuit B, when the output voltage of the 12V terminal t1 rises from 12V to a certain value, the transistor Q2 is turned on. In this embodiment, the output of the 12V terminal t1 is 13.2V (12V+10V). %
), transistor Q2 turns on, and at this time 0.2A flows through resistor R3. That is, the Zener diode DZ becomes conductive when a voltage of 7.4V or more is applied, and the transistor Q2 is used which causes a voltage drop of 0.8V. and resistance R3
=41Ω is connected.

In the above configuration, the output voltage of the 12V terminal t1 when the load on the 5V terminal t2 is small and when it is large will be specifically explained with reference to the characteristic example shown in FIG. First, when the load on the 5V terminal t2 is small (for example, the output current is 0A in Figure 2), the duty ratio of the induced voltage is small (see Figure 4), and the output voltage to the 12V terminal t1 is 12V as shown in Figure 2. Regardless of the size of the load connected to terminal t1, it is stable within the range of 12V±10%. At this time, since the stabilizing circuit B does not operate, no power loss occurs in this circuit B. Therefore, the entire current of the 12V output line is supplied to the load without causing any loss that would occur when a conventional dummy resistor is inserted.

Next, when the load on the 5V terminal t2 is large (for example, the output current is 1.5A in FIG. 2), the duty ratio of the induced voltage becomes large due to the influence of feedback (see FIG. 5). At this time, if the load connected to the 12V terminal t1 is large, the output voltage will be 12V± as shown in Figure 2.
It is stable within 10%, but the output voltage increases when the load is small. However, when the 12V output voltage becomes 13.2V or more, the Zener diode DZ becomes conductive, turning on the transistor Q2, and the resistor R3 and transistor Q
2 circuit becomes conductive. As a result, the resistance R3 becomes (
13.2-5)/41= A current of 0.2A flows. Therefore, even if the load on the 12V terminal t1 is small, the current in the 12V output line will never drop below 0.2A, and as shown in Figure 2.
As shown in , the output voltage of 12V terminal t1 is always 12V.
It becomes stable within a range of ±10%.

By providing the stabilizing circuit B, only when the voltage change of the output line to which no feedback is applied exceeds the permissible range, the same effect as a conventional dummy resistor occurs to stabilize the output voltage and reduce the output voltage. When the voltage change is within the permissible range, there is no power loss and efficient power supply is achieved.

The stabilizing circuit B may be provided between the 12V terminal t1 and the 0V terminal t0 for stabilizing the output voltage. However, in this case, the potential difference (1
2V) increases, the Zener diode DZ
It is necessary to increase the size of the transistor Q2, the resistor R3, and the resistor R3 in accordance with the potential difference. On the other hand, if the stabilizing circuit B is provided between the 5V terminal t2 to which feedback is applied and the 12V terminal t1 as in the embodiment described above, the potential difference (7V) will be reduced.
It is possible to downsize each element of the stabilizing circuit B, which is effective. In addition, since feedback is applied to the 5V output side, the voltage accuracy is high, and the stability circuit B is connected to the 5V output side.
Even if connected to the terminal t2, the output voltage of the 12V terminal t1 is sufficiently guaranteed.

[0019] In the above-mentioned embodiment, examples of output voltage values of 5V and 12V were shown, but the output voltage in the present invention need not be limited to the above values, and may be set to other output voltage values. is of course possible. Further, the feedback circuit does not need to be limited to the circuit of the above-described embodiment as long as it is a circuit that can control the secondary side output by feeding it back to the primary side. Furthermore, the stabilizing circuit also has a constant load, and
It is not necessary to limit the circuit to the circuit of the above-described embodiment as long as the circuit becomes conductive when the output voltage exceeds a certain value.

Furthermore, in the embodiment described above, the output voltage is 5
Although two types of examples, V and 12V, are shown, it is also possible to provide three or more secondary coils and output three or more types of output voltage values. In this case, a stabilizing circuit may be provided between one output voltage terminal to which no feedback is applied and an output voltage terminal to which feedback is applied, or a stabilizing circuit may be provided between all output voltage terminals to which no feedback is applied and one output voltage terminal to which feedback is applied. A stabilizing circuit may be provided between each output voltage terminal.

[0021]

[Effects of the Invention] As described above, the present invention provides a stabilizing circuit between the output voltage terminal that does not feed back and the output voltage terminal that feeds back, so that the output voltage can be stabilized even on the output side where feedback is not applied. It is possible to efficiently supply power by reducing power loss.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a switching regulator according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of the output characteristics of the 12V terminal when the load on the 5V terminal changes.

FIG. 3 is a circuit diagram of a switching regulator according to the prior art.

FIG. 4 is an explanatory diagram showing the induced voltage duty when the load on the 5V terminal is small.

FIG. 5 is an explanatory diagram showing the induced voltage duty when the load on the 5V terminal is large.

FIG. 6 is a graph showing an example of the output characteristics of the 12V terminal when the load of the 5V terminal changes according to the prior art.

[Explanation of symbols]

E is AC power supply, R is rectifier circuit, C1, C2, C3
is a capacitor, T is a transformer, NP is a primary coil, N
S1, NS2 are secondary coils, Q1, Q2 are transistors, R1, R2, R3, R4 are resistors, D1
, D2, and DZ are diodes, TL is a shunt regulator, PC is a photocoupler, A is a voltage control circuit, B is a stabilizing circuit, and t1 and t2 are output terminals.

Claims (1)

[Claims] 1. A switching device having a plurality of output lines on the secondary side and capable of outputting power supplied from the primary side via a switching circuit and a transformer as different voltage values depending on the plurality of output lines. In the regulator, one of the plurality of output voltages is fed back to the primary side, and there is a constant load between at least one other output voltage line and the output voltage line to be fed back, and when the voltage exceeds a certain level, A switching regulator that features a conductive stabilizing circuit.