JPH048165A - power supply - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply device for equipment such as a CRT display device that uses a low voltage power supply and a high voltage power supply.

[Prior Art] Television receivers and the like use a low-voltage power supply and a high-voltage power supply as one power supply device, but in the case of a CRT display or the like which consumes a large amount of power, an independent power supply device is used. Recently, a DC to DC converter called a switching regulator has been used as a power supply device, and the self-excitation type is mainly used for low-voltage power supplies, and the separately-excitation type is mainly used for high-voltage power supplies. Conventionally, these two power supplies are used independently. FIG. 4 is a circuit diagram showing an example of a conventional self-oscillation type DC voltage converter. In this figure, one end of the primary winding of a transformer 2 having first to fourth windings is connected to a DC power supply 1, and a switching element for voltage control, for example, a transistor Q1, is connected to the other end, and a resistor R1 is connected to the other end. grounded through. A transistor Q2 for controlling base current is connected to the base of the transistor Q1. On the secondary side of the transformer 2, there is a diode D1. A load 4 is connected via a rectifier circuit 3 consisting of a capacitor C1.

A rectifier circuit 5 consisting of a diode D2 and a capacitor C2 is connected to the tertiary winding of the transformer 2, and a constant voltage circuit consisting of a Zener diode ZDI and a resistor R2 is connected to the output side of the rectifier circuit 5. The rectified tertiary output is voltage-divided by resistors R3 and R4, and the base of transistor Q3 is connected to the midpoint thereof.

The collector of transistor Q3 is connected to one end of resistor R2, and the emitter thereof is connected to the base of transistor Q2. An output terminal 2 of the DC power supply 1 is connected to the base of the transistor Q1 and the collector of the transistor Q2 via a resistor R5. Further, a capacitor C3 forming an automatic oscillation circuit and a resistor R6 for limiting the strength of automatic oscillation are connected in series between the quaternary winding of the transformer 2 and the base of the transistor Q1.

Now, in this self-oscillation type DC voltage converter, when the power is turned on, a base current flows from the DC power supply 1 to the base of the transistor Q1 via the resistor R5, and from the DC power supply 1 passes through the primary winding of the transformer 2 to the transistor Q1. Collector current flows through Q1. This collector current generates a voltage in the fourth winding of transformer 2 that is in reverse phase with the collector voltage, and capacitor C3,
A base current flows through the transistor Q1 via the resistor R6, and the collector current increases. Then, the fourth output of the transformer 2 disappears due to the saturation of the collector current, so the base current of the transistor Q1 decreases and the collector current also decreases. Therefore, a negative voltage is generated in the fourth winding of the transformer 2, and the transistor Ql is rapidly cut off. When the charge of capacitor C3 finishes discharging.

Transistor Q1 becomes conductive in the same manner as when the power is turned on.

Since the current oscillates and current flows intermittently to the primary side of the transformer 2, an output is obtained on the secondary side of the transformer 2. At this time, since the voltage of the transformer 2 is proportional to the turns ratio, the magnitude of the secondary output can be determined from the tertiary output. When the tertiary output increases, the collector voltage of the transistor Q3 becomes higher than the base voltage due to the action of the Zener diode ZD1, so the collector current of the transistor Q3 increases. Since the collector current of the transistor Q3 becomes the base current of the transistor Q2, the collector current of the transistor Q2 flowing from the DC power supply l through the resistor R5 increases, and the collector current of the transistor Q2 increases.
The collector voltage of transistor Q2, ie, the base voltage of transistor Ql, decreases. Therefore, the cut-off period of transistor Q1 becomes longer and the output decreases. In this way, the tertiary output is kept at a constant voltage, and at the same time the secondary output is also kept at a constant voltage.

In this way, conventional self-oscillating DC voltage converters can stably supply power even when there are fluctuations in the input and load.
One pair each is used as a low voltage power supply and a high voltage power supply.

[Problems to be Solved by the Invention] However, in such a conventional self-oscillating type DC voltage converter, the output of the tertiary winding is detected to stabilize the output voltage, but the output voltage is stabilized immediately after the power is turned on. However, since the smoothing capacitor C2 of the tertiary output is not charged and the voltage is low, maximum power is output, which may damage the load 4, making it difficult to use as a high voltage power supply. In a separately excited type DC voltage converter with a built-in oscillation circuit, this problem can be avoided by gradually increasing the oscillation output after the power is turned on, but this increases the complexity of the device and increases the Since there is no output after the power is turned on, there is a problem that the stabilization time of the load equipment becomes longer. Another problem is that a separate power supply is required for the output control circuit including the oscillation circuit.

The present invention has been made in view of the problems of the conventional DC voltage converter, and its technical object is to shorten the start-up and stabilization time of the device.

[Means to solve the problem]

The present invention includes a transformer to which power from a DC power supply is supplied to the primary side, a switching element that connects and connects the transformer, and an output control circuit that controls the conduction time of the switching element. The first method is to rectify the output of the secondary side of the transformer obtained by intermittent operation to obtain direct current.
A power supply device including a second DC voltage converter, wherein the power source of a second output control circuit that controls a second switching element constituting the second DC voltage converter is connected to the first DC voltage converter. It is characterized in that it is supplied from the output of the device.

[Effect]

According to the present invention having the second feature, after the power is turned on, the first DC voltage converter supplies the necessary power to the load, and also supplies power to the output control circuit of the second DC voltage converter. are doing. Then, when the output of the second DC voltage converter increases, the necessary voltage is supplied to the output control circuit by that output or the output of the first DC voltage converter, and the second
The voltage level of the DC voltage converter is controlled.

[Example] Next, a first example of the present invention will be described with reference to FIG. In this figure, first, a first DC voltage converter 10 is provided on the output side of a DC power supply 1.

The first DC voltage converter 10 is an automatic low-voltage DC voltage converter, and has a transformer 2 and transistors Q1 to Q3 as in the conventional example described above.

Since the configuration of each of these circuits is the same as that of the conventional example described above, the same reference numerals are given and detailed explanation will be omitted. In this embodiment, in addition to the DC power supply 1, a second DC voltage converter 20 of a separately excited type and for high voltage is connected. The DC voltage converter 20 is a second voltage converter whose primary end is connected to the DC power supply 1.
A fourth transistor Q4, which is a switching element for controlling current, is connected to the other end of the transformer 21. The secondary side of the transformer 21 is connected to a second load 23 via a rectifier circuit 22 consisting of a diode D3 and a capacitor C4.
connected to. A diode D is connected to the tertiary winding of the transformer 21.
4. A rectifier circuit 24 consisting of a capacitor C5 is connected,
The rectified output is connected to the primary winding of the drive transformer 25, a voltage dividing circuit including resistors R7 and R8, and a constant voltage IC 26. The constant voltage IC 26 supplies driving power to the current control IC 27, and also supplies a reference voltage via a constant voltage circuit including a resistor R9 and a Zener diode ZD2.

A common connection end of the resistors R7 and RB is connected to a comparison input of the current control IC27. The current control IC 27 compares two input voltages (the reference voltage and the voltage divided by the resistors R7 and R8), and controls the base current of the transistor Q5 by changing the output pulse width according to the comparison result.
It is C. Here, the circuit connected to the primary side of the drive transformer 25, the drive transformer 25, and the transistor Q4 are connected to the transformer 21 according to the output voltage of the rectifier circuit 24.
An output control circuit A is configured to control the current on the primary side of the circuit. The output end of the rectifier circuit 5 of the DC voltage converter 10 is
It is connected to the output end (cathode of diode D40) of the rectifier circuit 24 via diode D5. Diode D
5 supplies power to the output control circuit A when the output voltage of the rectifier circuit 5 is higher than the output voltage of the rectifier circuit 24, and supplies power from the rectifier circuit 5 when the output of the DC voltage converter 20 reaches a predetermined value. It constitutes a cutoff means for stopping power supply.

The operation of the power supply device configured in this way will be explained. First, when the DC power supply 1 is turned on, power is supplied to the transformer 2 and the load 4 as in the conventional example described above. At the same time, constant voltage IC2 is applied via diode D5.
6 is supplied with power, and a voltage is also applied to the current control IC 27. The voltage applied to the current control IC 27 at this time may be lower than the normal operating voltage as long as it is higher than the voltage required to start oscillation. Then, when the current control IC 27 starts oscillating, a base current flows through the transistor Q5, and the diode D5. A collector current flows through the transistor Q5 via the drive transformer 25.

Therefore, the current flowing to the secondary side of the transistor Q
4 is energized, a collector current flows from the DC power supply to the transistor Q4 through the second transformer 21, and power is supplied to the secondary and tertiary sides of the second transformer 21. Immediately after the power is turned on, the voltage applied to the comparison input terminal of the current control IC 27 is lower than the specified value because it is supplied from the tertiary winding of the first transformer 2. Therefore, since the comparison voltage is lower than the reference voltage, the oscillation output pulse period or pulse width is changed to lengthen the conduction period of transistor Q5, which acts to increase the output of the second transformer 21. Therefore, the outputs of the secondary and tertiary sides of the second transformer 21 begin to rise, and when the output voltage reaches a predetermined level, the diode D5 is reverse biased and shut off. By this time, the voltage applied to the load 23 has become stable, but as the power supplied to the transistor Q5 increases, the output of the second transformer 21 rapidly increases, similar to a normal separately driven power supply circuit. It is maintained at a constant high pressure.

Therefore, the first
Similar to the conventional example, the DC voltage converter 10 has a period immediately after the power is turned on in which a voltage higher than the normal voltage is outputted, and this is similar to a normal power supply device. The second DC voltage converter 20 can limit its output to a low level until it starts to operate stably, and can output a normal voltage at about the time it starts to operate stably.

In this embodiment, the first DC voltage converter 10 is an automatic type, and the second DC voltage converter 11 is a passive type, but the first DC voltage converter may also be a separately excited type. In this case, a small step-down transformer and a rectifier circuit are required to supply power to the output control circuit.

Further, in FIG. 1, both ends may be short-circuited without using the diode D5. In this case, the output of the second DC voltage converter 20 is used as the output of the first DC voltage converter 10.
output is limited. Therefore, the second DC voltage converter 2
By the time the output of 0 becomes stable, the diode D is connected to the load 4.
A lower voltage will be supplied compared to the case where 5 is used.

Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the first DC voltage converter 10 is the same as the above-mentioned first embodiment, and the same parts in the second DC voltage converter 30 as in the above-described first embodiment are given the same reference numerals. Detailed explanation will be omitted. The second according to this embodiment
The DC voltage converter 30 includes a relay 31 between the diode D4 and the tertiary winding of the second transformer 21. A relay drive circuit 32 is provided to the load 23. The relay drive circuit 32 drives the relay 31 when the voltage level applied to the load 23 is below a reference level, and constitutes a determining means for determining an abnormality in the output of the load.

Further, the relay 31 constitutes a prohibition circuit that cuts off power supply to the output control circuit when an abnormality is determined by the relay drive circuit 32. The other configurations are the same as those of the first embodiment described above.

In the power supply device configured in this way, when the DC type a1 is turned on, no voltage is applied to the second load 23 immediately after the power is turned on, so the relay drive circuit 32 does not operate, and no output is applied to the rectifier circuit 24. . But transistor Q5
is pulse-driven, current also flows through the transistor Q4, and the voltage applied to the load 23 increases. When the voltage reaches a specified value, the relay drive circuit 22 drives the relay 31 and closes its contact. Then, the output of the second transformer 21 is applied to the diode D4, and the same operation as in the first embodiment described above is performed. In the first embodiment, if an abnormality occurs in the second load after reaching a steady state and excessive current flows, the load voltage will drop extremely. Therefore, an excessive current flows through the transistor Q4 in an attempt to return it to a normal voltage, and there is a possibility that the transistor Q4 may be destroyed. However, in this embodiment, the relay drive circuit 32 operates to open the contacts of the relay 31 before the transistor Q4 is destroyed. Therefore, the comparison voltage supplied to the current control IC 27 is reduced, and destruction of the transistor Q4 can be prevented.

In this embodiment, damage to the power supply due to an abnormality in the second load is prevented, but destruction of the load due to an abnormality in the power supply can be prevented by providing a discrimination circuit that similarly determines abnormality in the power output. It is also possible to prevent this.

In each of the embodiments described above, the tertiary output of the second transformer is used as a power source for the output control circuit built in the second DC voltage converter. Since this output is also used as a comparison voltage for stabilizing the secondary output, it is also possible to use the secondary output itself or an output proportional to the secondary output instead of the tertiary output.

For example, the secondary output may be supplied using a photocoupler, a transistor amplifier circuit, a small transformer, and a transistor oscillation circuit.

〔Effect of the invention〕

As explained in detail above, according to the present invention, it is possible to apply an appropriate voltage to the second load immediately after turning on the DC power without applying an excessive voltage, thereby preventing destruction of the equipment serving as the load. be able to. In addition, the output can be increased gradually when the power is turned on, and the stabilization time of the equipment can be shortened. Further, it can be constructed without using a separate power supply for the output control circuit. Furthermore, in addition to such an effect, the invention of claim 2 has the effect that the output can be automatically lowered even when an overload current flows through the load or there is an abnormality in the power supply.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a power supply device according to a first embodiment of the present invention, FIG. 2 is an output characteristic diagram of the first embodiment of the present invention, and FIG. 3 is a diagram of a second embodiment of the present invention. FIG. 4 is a circuit diagram showing an example of a conventional power supply device. 1-------1 DC power supply, 2. 21----One transformer, 35, 22. 2, l-111~-rectifier circuit, 4, 2.3-----load, 25
--- Drive transformer, voltage [C127 ---
----Current control ICl3------Transistor, 10.20 current voltage converter. 26-----Constant Q1~Q 30--------First shift Figure 2 Patent applicant Matsushita Electric Industrial Co., Ltd. Patent attorney Yoshiki Okamoto Power supply switch on Haruma

Claims (5)

[Claims] (1) a transformer to which power from a DC power supply is supplied to the primary side; a switching element that connects and disconnects conduction of the transformer;
and an output control circuit that controls the conduction time of the switching element, and first and second direct currents that obtain direct current by rectifying the output on the secondary side of the transformer obtained by turning on and off the switching element. A power supply device including a voltage converter, wherein the power source of a second output control circuit that controls a second switching element constituting the second DC voltage converter is connected to the first DC voltage converter. A power supply device characterized in that power is supplied from the output. (2) Discrimination means for discriminating an abnormal state of the load or output of the second DC voltage converter, and when the abnormal state is determined by the discrimination means, the output control circuit is transmitted from the second DC voltage converter to its output control circuit. The power supply device according to claim 1, further comprising a prohibition circuit that cuts off the supplied power. (3) The power supply device according to claim 1, wherein the first DC voltage converter is a self-excited DC voltage converter whose switching element is part of an oscillation circuit. (4) A cutoff means for cutting off the power supplied from the first DC voltage converter to the output control circuit of the second DC voltage converter when the output of the second DC voltage converter reaches a predetermined value. The power supply device according to claim 1, characterized in that it has: (5) The first and second DC voltage converters each include a rectifier circuit for supplying power to the second output control circuit, and the cutoff means is configured to provide power to the first and second DC voltage converters. 5. The power supply device according to claim 4, wherein the power supply device is a diode connected between the rectifier circuits.