JPS5914982B2 - switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-channel flyback type switching power supply device that can obtain a plurality of DC outputs.

15 In order to facilitate understanding of the present invention, a conventional switching power supply of this type is shown in the circuit diagrams of FIGS. 1 and 2.

In FIG. 1, two DC outputs are obtained, and one DC output is compared with the reference voltage VRE by an error amplifier 1, and the error output turns the switching transistor Q1 on or off via the control circuit 2. The voltage of one DC output is stabilized by controlling the timing.

When the switching transistor Q1 is "off", the flyback output voltage and the voltage generated at the same time at multiple terminals of the secondary winding of the transformer are proportional to the number of turns, so in the case of Fig. 1, 1 The voltage of one DC output is stabilized, and the voltage of the other DC output is also stabilized. However, there are losses in the transformer windings, rectifier diodes, etc., and variations in the load of the DC output, and it is actually difficult to stabilize the voltage of the other DC output. Further, since the number of turns of the secondary winding is small and the voltage often changes greatly with one turn, it is difficult to obtain the desired voltage.
Furthermore, since the voltages of the two straight 35 outputs rise or fall almost simultaneously, there is a drawback that so-called sequence operation cannot be performed. , C. In FIG. 2, the voltage of the other DC output in FIG. 1 is stabilized using a series regulator.

That is, after obtaining a DC voltage by rectifying the voltage generated in the secondary winding with a diode and storing charge in a capacitor, the error output is obtained by comparing it with the reference voltage VRE2 through the error amplifier 3 via the series transistor Q2. It controls series transistor Q2. In this case, the stability and precision of the voltages of the two DC outputs are improved, which is suitable if the DC output obtained by the series regulator is significantly less than said one DC output. However, if the difference between both DC outputs is small, there is a drawback that the loss due to the series transistor Q2 cannot be ignored. Further, in sequence operation, the DC output obtained by the series regulator has a fast rise, and a slow fall, and cannot be reversed. In this way, Fig. 1 shows a conventional flyback type power supply device.
In Figure 2, there are two DC outputs, but in reality, a multi-channel type that can obtain three or more DC outputs is required.
Furthermore, it is rare to increase only one specific output while decreasing all other outputs.

Therefore, flyback type power supplies generally have a simple circuit configuration, but have various drawbacks when used in multi-channel systems that require DC voltage stability and accuracy. The present invention is a power supply device that eliminates these drawbacks of the conventional flyback type power supply device and makes it possible to actively utilize the advantages thereof.

In the present invention, a series circuit is constructed from a DC power supply, a primary winding of a transformer, and a switching transistor.By turning on the switching transistor, a current flows through the primary winding and energy is stored in the transformer. By turning it off, energy is extracted from the secondary winding of the transformer, rectified and smoothed, and then a plurality of DC outputs are obtained.The first DC output is compared with a reference voltage, and the error output is used to control the switching transistor. In a switching power supply device that stabilizes the voltage of the first DC output by controlling the "on" and "off" timing, at least one of the circuits that can obtain an output other than the first DC output is The DC voltage of the switching transistor is compared with the reference voltage to control each switching transistor based on the error output obtained.
The value divided by the voltage of the DC output is smaller than the value obtained by dividing the number of turns of the secondary winding from which a DC output other than the first DC output is obtained by the voltage of the DC output other than the first DC output. shall be.

The present invention will be explained below with reference to FIG. 3, which is a circuit diagram showing an embodiment of the present invention.

Note that the same parts as in FIGS. 1 and 2 are given the same reference numerals. In Fig. 3, 1 and 3 are difference amplifiers, 2 and 4 are control circuits, 5 and 6 are smoothing circuits, 7 is a DC power supply with a voltage of V, 8 and 9 are output terminals, T is a transformer, Ll, L2 are the primary and secondary windings of the transformer T, 10 and 11 are terminals of the secondary winding L2, Ql and Q3 are switching transistors, Dl and D2 are rectifier diodes, and VREl and VRE2 are reference voltages. be.

DC power supply 7, primary winding Ll. A series circuit is formed by the transistor Q1, and the cathode side of the DC power supply 7 and the transistor Q
Emitter 1 is grounded. Terminal 1 of secondary winding L2
0 is connected to the output terminal 9 via the rectifier diode D2 and the smoothing circuit 6.

Output terminal 9 is connected to the base of transistor Q1 via error amplifier 1 and control circuit 2. Terminal 11 is connected to the collector of transistor Q3 via rectifier diode D1, and emitter is connected to output terminal 8 via smoothing circuit 5. Output terminal 8 is connected to the base of transistor Q3 via error amplifier 3 and control circuit 4. Smoothing circuit 5, 6
consists of a chiyoke coil and a capacitor connected in parallel to both ends, one end of which is grounded. Secondary winding L2 of transformer T
One end of is grounded. The number of turns of the secondary winding L2 is N2l from the ground side at terminal 10, and N22 at terminal 11.
It is.

The number of turns of the primary winding L1 is N1.

Then, the voltage of the first DC output obtained at the output terminal 9 is set to V
2l, and when the voltage of the DC output obtained at the output terminal 8 is V22, the relationship is N22/V22>N2l/V2l. One cycle of continuous operation of the switching power supply device of the present invention constructed as described above will be explained below with reference to the current and voltage waveform diagram of FIG.

In Figure 4, the horizontal axis is the common time axis, and the vertical axis is the primary current 11.
, collector voltage V1 of transistor Q1, secondary current 12
2. Respective changes in the secondary current 121 are shown. First, at time TO, when transistor Q1 turns on, the primary winding L
The primary current 1 flowing through 1 increases linearly and energy is stored in the transformer T. Voltages V2l and V22 are generated at terminals 10 and 11 of the secondary winding L2, but since the rectifier diodes Dl and D2 are in opposite directions, no current is generated.

At time t1, transistor Q1 turns "off" and at the same time transistor Q3 turns "on." A current is generated by voltage V22, and a secondary current 1 is rectified by rectifier diode D1.
22 is smoothed to obtain a DC output voltage V22 at the output terminal 8. Voltage 22 is applied to rectifier diode Dl. transistor Q
3.Although it is higher by the voltage drop due to the smoothing circuit 5, it is almost equal to the voltage V22. The collector voltage V1 of the transistor Q1 is almost equal to zero during the "on" period, but at time t1 the voltage V22 becomes almost equal to the voltage 22 of the DC output, so a voltage of -V22 is induced in the 1N primary winding L1. Since it is added to the voltage N22NlVl, it becomes +-22.

The secondary current N current 122 flows as a current that decreases with time, but because of this, the voltage at the output terminal 8 increases little by little, and at time T2
When a certain voltage exceeding voltage V22 is reached, the error amplifier 3
It is compared with the reference voltage VRE2 to obtain an error output, and the control circuit 4 turns off the transistor Q3.

The secondary current 122 then becomes zero. Note that between time t1 and time T2, the above-mentioned N22/22>N2l/21
According to the relationship, the voltage V2l becomes smaller than the voltage 21 of the first DC output obtained at the output terminal 9, so no current flows to the output terminal 9. When transistor Q3 turns "off" at time T2, the remaining flyback energy in transformer T causes voltage V2l at terminal 10 to change to voltage V2l at the first DC output.
2l, but increases to a voltage higher than the first DC output voltage 21 by the voltage drop of the rectifier diode D2 and the smoothing circuit 6, and the secondary current 121 rectified by the rectifier diode D2 is a current that decreases with time. Flowing. At time T2, the collector voltage V1 of transistor Q1 changes to time t1.
and time T2N, which is 1+- to 12, which is higher than the period of time T2N.

At time T3N2l, the secondary current 121 becomes zero and one cycle ends.

Then, the transistor Q1 is turned on again, returning to the state at time TO and repeating the same operation. In this process, the "on" and "off" timings of transistor Q1 and transistor Q3 are controlled to obtain a stable DC output voltage. According to the present invention, with such a configuration, both the first DC output voltage 21 obtained at the output terminal 9 and the DC output voltage V22 obtained at the output terminal 8 have improved stability and accuracy.

Moreover, since the transistor Q3 only performs a switching operation, the loss is small, and there is no need to set a limit on the power relationship between both outputs. When trying to obtain three DC outputs, the number of turns of the secondary winding at the terminal provided for this purpose is N23, the voltage of the obtained DC output is V23, and the same condition is satisfied by satisfying the condition N237V23>N2l/V2l. All you need to do is configure the circuit.

Regarding the secondary current, if the secondary current flowing in the circuit to obtain the third DC output is I22, it flows from the larger value of N22/V22 and N23/V23, then moves to the smaller value, and finally Secondary current 1 to obtain the first DC output
21 will be played.

Y. If N22/V22-N23/V23, secondary current 122 and secondary current 123 flow simultaneously, and secondary current 121
will be the last. Therefore, in sequence operation, only the first DC output voltage V2l always rises slowly and falls quickly, but the other DC output voltages are divided by the DC output voltage that can obtain the number of turns of the secondary winding. The value can be freely selected depending on the relative value of the value. This holds true even if the number of DC outputs obtained is four or more. FIG. 5 is a circuit diagram showing another embodiment of the present invention.

The same parts as in FIG. 3 are given the same reference numerals. In FIG. 5, unlike FIG. 3, a circuit for obtaining a DC output is commonly connected to the terminal 12 of the secondary winding L2 of the transformer T. In addition, two DC outputs other than the first DC output are obtained, including a rectifier diode D3, a switching transistor Q4, a smoothing circuit 16, an error amplifier 13, and a control circuit 14.
is connected, and the DC output voltage V24 is output to the output terminal 1.
Get 5. The circuit configuration for obtaining the DC output voltage 24 is exactly the same as the circuit configuration for obtaining the DC output voltage 22. Then, the winding of the secondary winding L2 at the terminal 12 is N
If 2O, the value of N2O/V2 is N2O/V22
, N2O/24. Therefore, in FIG. 5, the voltage V2l of the first DC output
If the voltage of each DC output is set higher than the voltage of other DC outputs, three stable DC output voltages can be obtained. As for the sequence operation, the voltages are obtained sequentially from the lowest voltage DC output. terminal 12
It goes without saying that even more DC output can be obtained in the same way by extending the connection point to as shown by the dotted line. In the embodiment shown in FIG. 5, a plurality of different DC outputs can be obtained by using the terminal 12 of the secondary winding L2 in common.

Generally, in a multi-channel switching power supply device, the transformer winding is complicated, but this makes the winding simple and the overall price can be reduced. Furthermore, when the terminal 12 is shared, there is an advantage that the current 120 flowing through the secondary winding L2 can be averaged. FIG. 6 shows the change in the current 120 when the number of DC outputs obtained is four. Time Tl
tThe flow time T2″, T3 in the circuit with the lowest DC output voltage
'', current flows through the circuit with successively higher DC output voltage, and T4'
The flow in the circuit from which the first DC output is obtained becomes zero at time T5'.

Generally, in a flyback type switching power supply, 1
A switching transistor (fifth
The most 2
The secondary current flows through the secondary winding and decreases over time, and
The secondary current flows partially through the secondary winding over time. In the embodiment shown in FIG. 5, since the circuit for obtaining DC output is commonly connected to the terminal 12, the secondary current 128 flows while decreasing relatively slowly and is averaged, reducing the loss in the secondary winding L2. can do. This invention is the first
The number of turns at the terminal of the secondary winding where a DC output other than the first DC output is obtained is divided by the voltage of the first DC output. It is characterized in that it is smaller than the value divided by the voltage of DC outputs other than the first DC output.

Furthermore, switching transistors and error amplifiers are provided in circuits for obtaining DC outputs other than the first DC output, thereby stabilizing the voltage. Therefore, not only can stable and highly accurate DC outputs be obtained, but also losses are reduced, and there is no need to set limits on the relative magnitudes of a plurality of DC outputs. Furthermore, a wide range of sequence operations can be selected. Furthermore, by expanding the idea of the present invention and connecting a circuit for obtaining a DC output to a common terminal of the same secondary winding, the winding of the transformer can be simplified.

Regarding the rectifier diodes, the secondary current is averaged and the difference in maximum current flowing through a plurality of rectifier diodes is reduced, so it is possible to form an integrated circuit with a common anode and separate cathodes. It is clear that these many advantages of the present invention lead to smaller size, higher performance, higher reliability, and lower cost of the switching power supply.

The present invention has a wide range of applications without being limited to the embodiments. For example, in the embodiment, there is one secondary winding, and a circuit for obtaining DC output is connected to another terminal of the same secondary winding or to a common terminal, but a circuit for obtaining DC output is connected to a separate terminal for each of multiple DC outputs. It may be connected to the secondary winding of. Alternatively, only a plurality of desired DC outputs may be taken out from the same secondary winding. These are selected mainly considering sequence operations and do not depart from the scope of the present invention. Furthermore, in the embodiment, all the circuits for obtaining DC outputs other than the first DC output control the respective switching transistors using the error output obtained by comparing with the reference voltage. It goes without saying that if the requirement for accuracy of DC output voltage is low, one part may have the circuit configuration shown in FIGS. 1 and 2.

[Brief explanation of drawings]

1 and 2 are circuit diagrams of a conventional flyback type switching power supply device, FIG. 3 is a circuit diagram showing an embodiment of the switching power supply device of the present invention, and FIG. 4 is a circuit diagram of a conventional flyback type switching power supply device.
FIG.
The figure is a circuit diagram showing another embodiment of the present invention, and FIG. 6 is a current waveform diagram for explaining the operation of FIG. 5. 1, 3, 13: error amplifier, 2, 4, 14: control circuit,
5, 6, 16: Smoothing circuit, 8, 9, 15: Output terminal, 7
: DC power supply, Ql, Q3, Q4: Switching transistor, T: Transformer, L1: Primary winding of transformer T, L
2: Secondary winding of transformer T, 10, 11, 12: Terminals of transformer T.

Claims (1)

[Claims] 1. A series circuit is constructed from a DC power supply, a primary winding of a transformer, and a switching transistor. By turning on the switching transistor, current flows through the primary winding and energy is transferred to the transformer. The energy is extracted from the secondary winding of the transformer by being stored and turned off, rectified and smoothed to obtain a plurality of DC outputs, and the first DC output is compared with a reference voltage and the error output is used to control the switching transistor. In a switching power supply device that stabilizes the voltage of the first DC output by controlling the timing of turning on and off, at least one of the circuits from which an output other than the first DC output is obtained is Each switching transistor is controlled by the error output obtained by comparing each DC output voltage with a reference voltage, and the first DC output voltage of the secondary winding from which the first DC output is obtained is
The value divided by the voltage of the DC output is smaller than the value obtained by dividing the number of turns of the secondary winding from which a DC output other than the first DC output is obtained by the voltage of the DC output other than the first DC output. switching power supply. 2. The number of turns of the secondary winding that provides the first DC output and the number of turns of the secondary winding that provides the first DC output.
2. The switching power supply device according to claim 1, wherein the number of turns of the secondary windings for obtaining a DC output other than the DC output is made equal. 3 Connect the first DC output and the first DC output to the common terminal of the same secondary winding.
2. The switching power supply device according to claim 1, further comprising a circuit connected thereto which can obtain an output other than a DC output. 4 Connect the first DC output and the first DC output to the common terminal of the same secondary winding.
A circuit that provides an output other than the DC output is connected, and the first
The switching power supply device according to claim 1, wherein a difference is provided between the voltages of the outputs other than the DC output.