Multioutput switching power supply

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a multi-output switching power supply device, and more particularly to a multi-output switching power supply device capable of obtaining an energy saving effect by suppressing a decrease in power efficiency when a part of output circuits are in a no-load state.

【0002】

[Previous technology]

The primary DC power obtained by rectifying the primary DC power, for example, commercial AC power with a diode bridge, is switched at high speed by a switching element, input to the primary winding of the transformer, and induced in the secondary winding. A switching power supply that keeps the output voltage constant by rectifying and smoothing the generated AC power again and outputting it as secondary DC power, and by detecting the output voltage and controlling the switching duty ratio (hereinafter referred to as "switching"). There is a "regulator").

【0003】

By increasing the switching frequency, such a switching regulator has the advantages of being compact and lightweight as a whole despite using a transformer, and having high power efficiency (low loss) and thus generating less heat. Furthermore, one transformer is provided with a plurality of secondary windings, and each transformer is rectified and smoothed to obtain DC power having different voltages and polarities.

【0004】

Therefore, there are various voltages, polarities, and current capacities inside, such as a control unit that has a small current capacity but requires constant voltage, and a drive unit that does not require constant voltage but allows a relatively large current to flow when operating. Many devices use a switching regulator as a power source for devices with different loads.

【0005】

However, switching regulators can certainly obtain high power efficiency of about 80% at rated load, but when used at light loads such as 1/2 or 1/3 of the rating, the power efficiency drops to 50% or less. In many cases. However, when used as a power source for a device, a continuous load such as a control unit generally has a small current capacity, and an intermittent load such as a drive unit has a large current capacity, so that the efficiency is the lowest when the device is in the standby state.

【0006】

Due to the severe power situation that the power supply capacity is not enough to meet the peak power demand as in recent years, or environmental problems such as the regulation of exhaust gas to prevent acid rain and regional warming, energy saving worldwide As laws and regulations are being examined or implemented, improving power efficiency has become a top priority.

【0007】

Therefore, for example, as shown in FIG. 13, the switching regulator 40 for intermittent load and the switching regulator 41 for continuous load are connected in parallel to the smoothing capacitor C4 to which the primary DC power is input, and the switching regulator 40, Of the SWCs (switching control circuits) 42 and 43 that control each of the 41 switching elements, the SWC42 turns its action on or off according to the switch command input from the control unit of the device, and the SWC43 always turns it on. was there.

【0008】

In this way, the continuous load of the control unit of the device connected to the switching regulator 41 is always activated, the switching regulator 40 is always off, and only when the intermittent load of the connected drive unit or the like is activated. When turned on by a switch command, the two switching regulators 40, 41 always operate at or near the rating, resulting in high efficiency.

【0009】

[Problems to be Solved by the Invention]

However, since the proposal shown in FIG. 13 requires at least two switching regulators, high-frequency noise due to switching interferes with each other, and not only wide-band noise extending to the low frequency range is generated, but also the power supply unit As the size increases, the cost increases significantly.

【0010】

Therefore, there is no merit unless it is a high-power device whose efficiency improvement directly affects the power charge (running cost), so it is applied to the power supply device of small and medium-power devices such as household equipment and office equipment. There was a problem that it was difficult to do in terms of initial cost.

【0011】

The present invention has been made in view of the above points, and an object of the present invention is to suppress a decrease in power efficiency even when the load is lower than the rated load at low cost.

【0012】

[Means for solving problems]

In order to achieve the above object, the present invention inputs a primary DC power to a series circuit of a primary winding of a transformer and a switching element, and turns the switching element on and off to turn on and off a plurality of secondary windings of the transformer. A plurality of output circuits that output secondary DC power obtained by rectifying and smoothing the AC power induced in the above by a rectifying and smoothing means, and one of the plurality of output circuits is used as a feedback system output circuit to detect the output voltage. In a multi-output switching power supply device provided with a switching control means for controlling on / off of a switching element so that the detected voltage holds a preset voltage, each of them is as follows.

【0013】

That is, a switch element for interrupting the current is provided between the secondary winding of at least one output circuit of the output circuit excluding the feedback system output circuit and the rectifying and smoothing means.

【0014】

Alternatively, a switch element for interrupting a current in the common line by collectively forming each ground line of an output circuit having the same polarity of an arbitrary number of output voltages among the output circuits excluding the feedback system output circuit as a common line. Is provided.

【0015】

In the above-mentioned multi-output switching power supply device, among a plurality of secondary windings of a transformer, each secondary winding of an arbitrary number of output circuits sharing a common line is grouped together and one end thereof is connected to the common line. It may be one winding with a tap.

【0016】

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a circuit diagram showing an example of a configuration of a switching regulator according to a first embodiment of the multi-output switching power supply device of the present invention. The primary side of the transformer T1 of the switching regulator 1 shown in FIG. 1 is a capacitor C1 for primary DC power connected between the positive and negative input terminals 15 and a transformer T1 connected in parallel to the capacitor C1. It is composed of a series circuit of the next winding Np and a transistor (which may be a FET) Q which is a switching element.

【0017】

The secondary side of the transformer T1 consists of four secondary windings Nsf, Nsa, Nsb, Nsc and a rectifying smoothing circuit connected to each secondary winding, and the smoothed positive output f and output a, respectively. It is composed of four output circuits (not shown, but each with "f, a, b, c") that output output b and negative output c.

【0018】

Of the four output circuits f, a, b, c, the output circuits f and a are for continuous load, the output circuits b and c are for intermittent load, and the secondary windings Nsb, Nsc of the output circuits b and c are used. The ground line connecting the rectifying and smoothing circuit is provided with switches SWb and SWc, which are switch elements that are turned on and off according to a switch command, respectively. The ground line of each output circuit is connected to each other to form a common line downstream of the switch SW if it is provided.

【0019】

The SWC (switching control circuit) 16 that connects the primary side and the secondary side of the transformer T1 detects the output voltage of the output circuit f, which is the feedback system output circuit, and a high-frequency drive pulse with a pulse width corresponding to the detected voltage. Is output to drive the transistor Q, so that the output voltage of the output circuit f is controlled to be a preset voltage.

【0020】

The transistor Q turns on / off the current that is input from the input terminal 15 and flows through the primary winding Np of the primary DC power stored in the capacitor C1 according to the drive pulse input from the SWC16. Therefore, the transformer T1 AC power of a voltage corresponding to the winding ratio with the primary winding Np is induced in each secondary winding Ns of.

【0021】

The configuration of each output circuit is the secondary winding Ns, rectifier diode D1, commutation diode D2, choke (coil) CH, smoothing capacitor C, respectively, except for the presence / absence of switch SW and the presence / absence of polarity and feedback. Since they are the same as each other, the operation will be described, for example, in the output circuit a.

【0022】

The AC power current induced in the secondary winding Nsa when the transistor Q is on charges the smoothing capacitor Ca via the rectifier diode D1a and the choke CHa constituting the choke input type smoothing circuit. A part of the electric power stored in the choke CHa is converted into magnetic energy at the rising edge of the current, and is converted into electric power again when the transistor Q is turned off to charge the smoothing capacitor Ca via the commutation diode D2a. To do.

【0023】

The secondary DC power charged with the smoothing capacitor Ca is supplied to the continuous load connected from the output terminal as a positive output a. The same applies to the other output circuits f, b, and c. However, the output circuit f is a constant voltage output circuit that maintains a constant voltage even if the input voltage or output current fluctuates, but the other output circuits a, b, and c are not affected by the fluctuation of the input voltage. However, it is a quasi-constant voltage output circuit in which the output voltage is slightly affected if the output current fluctuates.

【0024】

The output circuits b and c for intermittent load provided with switches SWb and SWc that turn on / off according to the switch command are shown in Fig. 1 when they are turned on / off at the same time by the same switch command, but they are not necessarily turned on / off at the same time. Needless to say, it is not necessary to do so, but rather it is better to turn it on and off by a switch command that inputs different timings according to the operation of each connected intermittent load.

【0025】

The switches SWb and SWc are always off, and when the intermittent load connected to the output circuits b and c is activated, they are turned on by the switch command input from immediately before the operation to the end of the operation, and the outputs b and c are loaded, respectively. Supply to.

【0026】

Therefore, since the switches SWb and SWc of the output circuits b and c of the switching regulator 1 are always off, for example, during standby, the output circuits f and a of the switching regulator 1 only supply power to the load, and the SWC16 is the same. The transistor Q is driven by outputting a drive pulse having a low duty ratio (narrow pulse width) according to the supplied power.

【0027】

When the intermittent load connected to the output circuits b and c is activated, the switches SWb and SWc are turned on by the switch command input from immediately before the operation to the end of the operation, and the output circuits b and c are activated and respectively. Power the load. The SWC16 changes to output a drive pulse with a high duty ratio (wide pulse width) according to the supply power of the output circuits f and a plus the output circuits b and c.

【0028】

Therefore, the switching regulator 1 operates according to the total power supply, and since no extra power is supplied to the unnecessary output circuit, the loss is minimized, and the power efficiency is reduced even when the load is lower than the rated load. The decrease can be suppressed. Moreover, since only two switches SWb and SWc are added to the conventional switching regulator, the cost increase does not become a problem.

【0029】

Looking only at Fig. 1, even with a conventional switching regulator that does not have switches SWb and SWc, the power supply is zero when the load does not operate, so the loss is only about the leakage current of the smoothing capacitors Cb and Cc, and the effect is not so great. May not seem to be.

【0030】

However, in general, when the load is zero, the output voltage of the rectifying / smoothing circuit rises sharply and becomes unstable. Therefore, a bleeder resistor that always flows a current of about 1/5 to 1/10 of the rated load is connected between each output terminal to prevent the load from becoming zero, and the output voltage rise and instability are prevented.

【0031】

However, in the switching regulator 1 shown in FIG. 1, a continuous load is connected to the output circuits f and a, and when the output circuits b and c are active, the connected intermittent load is operating. The circuit also does not go to zero load when active. Therefore, as shown in the figure, the bleeder resistor is omitted from all the output terminals.

【0032】

In general, for equipment with intermittent load, the standby time is often much longer than the operation time, so a dummy load of about 1/5 to 1/10 of the rated load due to the braider resistance is no longer necessary. As a result, the effect of saving unnecessary power consumption is extremely large.

【0033】

FIG. 2 is a circuit diagram showing an example of a configuration of a switching regulator according to a second embodiment of the present invention. In the switching regulator 2 shown in FIG. 2, the ground lines of the output circuits a, b, and c having the same polarity (positive) to which the intermittent load is connected are collectively used as a common line, and the common line is common to each output circuit. A switch SW is provided.

【0034】

In addition, the polarity of the secondary winding Nsc, rectifier diode D1c, commutation diode D2c, and smoothing capacitor Cc was reversed because the output voltage of the output circuit c changed from negative to positive. Other than that, it is the same as the switching regulator 1 shown in FIG. 1, so the same parts are designated by the same reference numerals and the description thereof will be omitted.

【0035】

The switching regulator 2 is suitable for a device in which only the control unit, which is a continuous load connected to the output circuit f, is operating during standby, and the operator turns on a start switch (not shown) only when it is used. The switch command is input and the common switch SW is turned on. In this case, since the output circuits a, b and c are active at the same time, only the output circuit to which the intermittent load is connected, which operates intermittently during the period when the start switch is turned on, is active or inactive in synchronization with the load. It is impossible to do.

【0036】

However, if such an intermittent load is connected to the output circuit in combination with a load that becomes a continuous load at startup, or if there is no continuous load to be combined in relation to voltage etc., a bleeder resistor is provided between the output terminals of the output circuit. If is provided, the load will not be zero. Thus, even if some loss occurs due to the provision of the bleeder resistor, it is only while the start switch is on, and the loss due to the bleeder resistor does not occur during a longer standby time.

【0037】

FIG. 3 is a circuit diagram showing a modification of the switching regulator 2 shown in FIG. The switching regulator 3 shown in FIG. 3 is obtained by replacing not only the switch SW but also the rectifier diodes D1a, D1b, and D1c of each output circuit in the switching regulator 2 with one common rectifier diode D1. The same parts are designated by the same reference numerals and the description thereof will be omitted.

【0038】

By combining the ground lines of output circuits of the same polarity into a common line like the switching regulator 3, even if they are combined into one rectifier diode D1, the action and effect are the same as those of the switching regulator 2, and the cost is further increased. It can be cheap and easy to configure. It does not matter if the arrangement of the switch SW and the rectifier diode D1 on the common line is reversed.

【0039】

FIG. 4 is a circuit diagram showing another modification of the switching regulator 2 shown in FIG. The switching regulator 4 shown in FIG. 4 has secondary windings Nsa , Nsb , Nsc inside instead of the transformer T1 in which the secondary windings Nsa, Nsb, Nsc used for the switching regulator 2 are independent of each other. The transformer T2 connected in series with the above is used, and the same parts are designated by the same reference numerals and the description thereof will be omitted.

【0040】

Needless to say, each number of turns of the secondary winding of the transformer T2 is set so that the output voltage when connected in series is the output voltage output by each independent winding of the transformer T1. The thickness is also changed.

【0041】

When the ground lines of output circuits of the same polarity are combined into a common line, a transformer T2 with secondary windings connected in series can be used to simplify the circuit on the board without changing the operation and effect. You can also do it. Also, like the switching regulator 3, the switching regulator 4 can combine the rectifying diodes into one.

【0042】

5 to 7 are circuit diagrams showing still other modifications of the switching regulator 2 shown in FIG. The switching regulators 5 to 7, respectively shown in FIGS. 5 to 7, are examples in which the positive output voltage of the switching regulators 2 to 4 shown in FIGS. 2 to 4, respectively, becomes negative.

【0043】

Since the polarities of the output voltage are reversed, the polarities of the secondary winding Ns or Ns', the rectifier diode D1, the commutation diode D2, and the smoothing diode C are reversed. Since it is the same as the switching regulators 2 to 4, the same parts are designated by the same reference numerals and the description thereof will be omitted.

【0044】

8 and 9 are circuit diagrams showing an example of the configuration of the switching regulator according to the third embodiment of the present invention, respectively. In each of the switching regulators 8 and 9 shown in FIGS. 8 and 9, two positive and negative output circuits excluding the output circuit f are grouped together, and switches SWp and SWn for positive output and negative output are provided. The same reference numerals are given to the other same parts, and the description thereof will be omitted.

【0045】

The difference between the switching regulator 8 and the switching regulator 9 is that, as in the case of the switching regulator 2 (Fig. 2) and the switching regulator 4 (Fig. 4), the transformer T3 whose secondary windings are independent of each other is used, or the secondary winding is used. Since the difference is whether to use a transformer T4 in which the wires are connected in series, the switching regulator 8 will be described, and the description of the switching regulator 9 will be omitted.

【0046】

The switching regulator 8 has a positive feedback system output circuit f and two positive output circuits a and b and negative output circuits c and d, respectively, and correspondingly, the transformer T3 has five independent transformers T3. It has secondary windings Nsf, Nsa, Nsb, Nsc, Nsd.

【0047】

Of these secondary windings, the ground lines of the secondary windings Nsa and Nsb of the positive output circuits a and b and the ground lines of the secondary windings Nsc and Nsd of the negative output circuits c and d are, respectively. A switch SWp for positive output and a switch SWn for negative output, which are connected to each other and are turned on / off according to a switch command, are connected in series between the connection point and each smoothing rectifier circuit.

【0048】

FIG. 10 is a circuit diagram for explaining the effect of grouping only the output circuits having the same polarity as each other and providing the switches for the positive output and the switches for the negative output independently. And (B) show the case where the positive and negative switches are provided independently and the case where they are common. For the sake of simplicity, the rectification / smoothing circuit is shown as a half-wave rectification / capacitor input type circuit.

【0049】

(A) and (B) in FIG. 10 consist of secondary windings Nsp and Nsn of a transformer (shown with the primary side omitted), rectifier diodes Dp and Dn, and smoothing capacitors Cp and Cn, respectively. It consists of positive and negative output circuits, and the ground lines of both output circuits are connected to a common common terminal COM, and positive and negative outputs are supplied to the loads Rp and Rn, respectively.

【0050】

Hereinafter, the circuits shown in FIGS. 10A and 10 are referred to as the circuit (A) and the circuit (B), respectively, and the difference between the two circuits is that the circuit (A) has secondary windings Nsp and Nsn. The switches SWp and SWn are provided on the ground line, respectively, and are connected to the common terminal COM at the downstream, while the circuit (B) is the common line at the secondary winding Nsp and Nsn. After that, a common switch SW was provided. That is, the circuit (B) turns on / off the output circuit of different polarity with one switch SW.

【0051】

Both the circuit (A) and the circuit (B) supply DC power to continuous loads Rp and Rn such as a bleeder resistor without any problem while the switches SWp, SWn and SW are on. (A) When the switches SWp and SWn are turned off, if the positive and negative powers charged in the smoothing capacitors Cp and Cn are discharged by the loads Rp and Rn, respectively, no more current will flow.

【0052】

However, in the circuit (B), even if the switch SW is turned off, the power induced in the series circuit of the secondary windings Nsp and Nsn is rectified by the rectifier diodes Dp and Dn, and the smoothing capacitor Cp and Cn series circuit. Since it continues to supply DC power to the series circuit of the load Rp and Rn, the on / off of the common switch SW is completely useless.

【0053】

That is, in the switching regulators 8 and 9 shown in FIGS. 8 and 9, the respective switches operate effectively by providing the switches SWp or SWn together with the output circuits having the same polarity. Further, it is clear from the circuit (A) shown in FIG. 10 (A) that no trouble occurs even if the switches SWp or SWn are turned on and off at independent timings.

【0054】

Further, in the switching regulator 8 or 9, when the operation timings of the loads connected to the output circuits a and b or the output circuits c and d are different from each other, it is perfectly acceptable to divide the switches SWp or SWn into separate switches. There is no problem in controlling the on / off control of three or more output circuits with one switch if the output circuits have the same polarity, as shown in switching regulators 2 to 7.

【0055】

11 and 12 are circuit diagrams showing an example of the configuration when the present invention is applied to a switching regulator in which the rectifying and smoothing circuit on the secondary side of the transformer is a half-wave rectifying / capacitor input type circuit, respectively. The same reference numerals are given to the parts, and the description thereof will be omitted.

【0056】

The switching regulators 10 and 11 shown in FIGS. 11 and 12 are the same except that the output voltages of the output circuits a, b, and c are opposite to each other, and the rectification of the output circuits f, a, b, and c is performed. The switching regulators 2 and 5 shown in FIGS. 2 and 5 except that the smoothing circuit is a half-wave rectifier / capacitor input type circuit consisting only of a rectifier diode and a smoothing capacitor as shown in FIG. 10, respectively. Since they are the same, the description thereof will be omitted.

【0057】

In the switching regulators 1 to 11 described above, the switches SW, SWb, SWc, SWp, and SWn, which are the respective switch elements, are indicated by the symbols of the mechanical switches, but the direction of the current flowing through them is constant in all the switches. Therefore, it goes without saying that it can be easily replaced with a semiconductor switch such as a transistor or FET.

【0058】

[Effect of the invention]

As described above, the multi-output switching power supply device according to the present invention suppresses a decrease in power efficiency even at a low cost and at a load lower than the rated load, and an energy saving effect can be obtained.

[Simple explanation of drawings]

[Figure 1]

It is a circuit diagram which shows an example of the structure of the switching regulator which is 1st Embodiment of the multi-output switching power supply device of this invention.

[Figure 2]

It is a circuit diagram which shows an example of the structure of the switching regulator which is the 2nd Embodiment of this invention.

[Fig. 3]

It is a circuit diagram which shows one modification of the switching regulator shown in FIG.

[Fig. 4]

It is a circuit diagram which shows the other modification of the switching regulator shown in FIG.

[Fig. 5]

It is a circuit diagram which shows the other modification of the switching regulator shown in FIG.

[Fig. 6]

It is a circuit diagram which shows the other modification of the switching regulator shown in FIG.

[Fig. 7]

It is a circuit diagram which shows the other modification of the switching regulator shown in FIG.

[Fig. 8]

It is a circuit diagram which shows an example of the structure of the switching regulator which is the 3rd Embodiment of this invention.

[Fig. 9]

It is a circuit diagram which shows one modification of the switching regulator shown in FIG.

[Fig. 10]

It is a circuit diagram for demonstrating the effect of the switching regulator shown in FIG. 8 and FIG.

[Fig. 11]

It is a circuit diagram which shows the other modification of the switching regulator shown in FIG.

[Fig. 12]

It is a circuit diagram which shows one modification of the switching regulator shown in FIG.

[Fig. 13]

It is a circuit diagram which shows the conventional example of a multi-output switching power supply device.

[Explanation of symbols]

1 ~ 11: Switching regulator (multi-output switching power supply) 16: SWC (Switching Control Circuit; Switching Control Means) C, Cf, Ca ~ Cd: Smoothing capacitor (secondary side) C1: Capacitor (for primary DC power) CH, CHf, CHa ~ CHd: Chalk D1, D1f, D1a ~ D1d: Rectifier diode D2, D2f, D2a ~ D2d: commutation diode Np: Primary winding Ns, Nsf, Nsa ~ Nsd: Secondary winding Q: Transistor (switching element) SW, SWb, SWc, SWp, SWn: Switch (switch element) T1 ~ T4: Transformer