JPS63113615A - Direct current power unit - Google Patents

Abstract

PURPOSE:To suppress the heat loss of a transistor (TR) by inserting the front stage of a constant voltage circuit which has a smoothing capacitor on its input side and turning off this switch when the input voltage to a constant voltage circuit exceeds a specific value. CONSTITUTION:The input voltage Vi to the constant voltage circuit 7 is smaller than a reference value Vs in a power-up section right after the power source is turned on, so Vi<=Vs and a comparator 11, therefore, operates and generates an output to turn on the switch 10 through a driving TR 15. Consequently, DC electric power is supplied from a rectifier 3 to the constant voltage circuit 7 and the input voltage Vi increases gradually. Then when Vi>Vs, the comparator 11 judges that and turns off the driving TR 15. The switch 10 is, however, held on because of the characteristics of a thyristor and turned off for the 1st time when a source voltage Va reaches a zero point and a current is ceased. Then, the input voltage Vi drops gradually and the switch 10 is turned on when Vi<=Vs to supply electric power through the switch 10. Consequently, generated heat is reduced greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a DC power supply device that can be suitably applied particularly when the difference between input voltage and output voltage is large.

(Prior art) Conventionally, the fourth power supply device has been used as a power supply device for a controller using a microcomputer, etc. used to control an air conditioner, etc.
The circuit configuration shown in the figure is known. This kind of power supply device is for d, c, microcomputer etc.
5V power supply and d, c, 1 for driving relays etc.
They often have two power supply systems, including a 2V power supply, and FIG. 4 shows such an example.

The DC power supply shown in FIG. 4 has a first system that outputs d, c, and 12V from the transformer 2 through a single-phase bridge rectifier 3, a smoothing capacitor 4, and a transistor type constant voltage circuit 5, and Single-phase full-wave rectifier circuit configured by sharing a part of 3, smoothing capacitor 6
and d, c, 5 through the transistor type constant voltage circuit 7.
and a second system that outputs V. Rectifier 3 is 4
It consists of a set of diodes 3A, 3B, 3C, 3D,
A single-phase bridge-connected rectifier circuit is configured for the first system, and a diode 3A is used for the second system.

3B and the intermediate tap of the secondary winding of the transformer 2 cooperate to form a single-phase aftereffect type rectifier circuit. The transistor type constant voltage circuit 5 of the first system includes a transistor 5A inserted in series in the load current circuit, a capacitor 5B connected in parallel to the output terminal, and a collector of the transistor 5A to limit the base current. It consists of a resistor 5C connected between the bases and a Zener diode 5D for keeping the base voltage of the transistor 5A constant. The transistor type constant voltage circuit 7 of the second system has the same circuit configuration as the transistor type constant voltage circuit 5 of the first system. 7A.

It consists of a capacitor 7B, a resistor 7C, and a Zener diode 7D. In the circuit of FIG. 4, a full-wave rectified voltage with a type voltage 2e between both terminals of the secondary winding of the transformer 2 is applied to both ends of the smoothing capacitor 4, and a full-wave rectified voltage of a voltage e between the center tap and the winding ends is applied to both ends of the smoothing capacitor 4. A rectified voltage is applied across smoothing capacitor 6.

As shown in FIG. 5, the constant voltage circuit 5.6 has a relatively high AC voltage ((a) in the figure; V), so the input voltage of the constant voltage circuit ((b) in the figure: V,) is relatively high. Even if is relatively high,
Furthermore, as shown in Fig. 6, even if the AC voltage (Fig. 6 (a): V) is relatively low, and the input voltage of the constant voltage circuit (Fig. 6 (b): Vt) is relatively low, the It acts so that a nearly constant output voltage (V in FIGS. 5(b) and 6(b)) is obtained. The voltage corresponding to the difference between the input voltage vI and the output voltage V is the transistor 5A.

7A is borne as collector-emitter voltage vcE.

(Problems to be Solved by the Invention) In a DC power supply device having two systems as shown in FIG. % fluctuation range accuracy is required, but in the case of air conditioners and the like, the AC side electric sign often drops instantaneously to about 70% of the rated value due to the starting current of the compressor motor.

In order to maintain the output voltage value within a ±10% fluctuation range even under such circumstances, the primary side voltage of the transistor 7A, that is, the input terminal V of the constant voltage circuit 7, and the secondary control voltage, that is, the output voltage V. It is normal to deal with this by making the collector-emitter voltage VcE of the transistor 7A sufficiently large, which corresponds to the difference.

However, since the transistor 7A has a loss corresponding to the product of the voltage Voo and the load current, the voltage V. E
As the amount of heat increases, the amount of heat generated increases, which not only requires a means for dissipating the heat, such as a large heat sink, but also causes a decrease in the reliability of the entire device.

By the way, for example, the transistor 7A in the constant voltage circuit 7 is composed of a Darlington connection circuit, and the voltage is V. -The saturation value is 1.5V, that is, the rated output voltage of the constant voltage circuit 7 is 5■
Furthermore, it is assumed that the AC power supply voltage can drop to 70% of the rated value in the downward direction, and up to 110% in the upward direction. Assuming that the rate of increase in the transformer secondary voltage is expected to be about 5%, the maximum value of the input voltage of the constant voltage circuit 7 is V1ff111! Nijite V, -5X (1+0.3)X (110,7)
ff1 Xl, IXl, 05-10. 7 (V) must be taken into account. This is the voltage V that is borne by the transistor 7A. If you look at it as 0, then 10, 7-5. 0
-5. 7 (V), which is 114% of the output voltage of 5V. The loss corresponding to the value obtained by multiplying this voltage by the load current becomes the heat source of the transistor 7A.

Therefore, an object of the present invention is to reduce the heat generation of the constant voltage transistor in the constant voltage circuit and to provide a more reliable DC power supply device.

[Structure of the Invention] (Means for Solving the Problems) The DC power supply device of the present invention includes a rectifier that rectifies alternating current, a switch connected in series to the output side of the rectifier, and a switch connected to the output side of the switch. A smoothing capacitor provided, a transistor type constant voltage circuit connected to the smoothing capacitor, and a switch control means for controlling the switch to turn on only when the terminal voltage of the smoothing capacitor is below a predetermined value. It is something.

(Function) According to the present invention, the switch provided on the input side of the smoothing capacitor, that is, the constant voltage circuit, is on when the capacitor voltage is below a predetermined value, but is off when the capacitor voltage is above a predetermined value, and turns all input terminals into a negative voltage. To celebrate.

In other words, in the region where the input voltage of the constant voltage circuit is high, and therefore the difference between the input voltage and the output voltage is large, and the burden voltage of the transistor would be large if there were no switch, the switch bears the entire input voltage, so the transistor Large losses can be avoided, thereby significantly reducing heat generation.

(Example) FIG. 1 shows an embodiment of the present invention.

Here, circuit components that are the same as those in FIG. 4 are denoted by the same reference numerals. The feature of this circuit is that a switch 10 is inserted in series on the input side of the smoothing capacitor 6 and the constant voltage circuit 7, and the switch 10 is controlled to be turned on or off by the output of the comparator 11. switch 10
consists of a photoresist and a light emitting diode. The voltage (for example, 7 V) of the Zener diode 13 connected between the output terminals of the first system via the resistor 12 is input as a reference value V to the first input terminal of the comparator 11, and The terminal voltage of the smoothing capacitor 6, that is, the input terminal (2) of the constant voltage circuit 7 is input to the terminal. The comparator 11 outputs an H signal when V5≦V, turns on the drive transistor 5 via the resistor 14, and the output voltage of the constant voltage circuit 5 causes the light emitting diode in the switch 10 to emit light via the resistor 16. This turns on the switch 10 made of photosyrisk. In the figure, a protective low resistance 9 is connected in series to the switch 10.

The circuit of FIG. 1 will be explained with reference to FIG.

First, in the power-up period t1 immediately after the power is turned on, the input terminal V of the constant voltage circuit 7 is at the basic value V.
Since Vs is below, that is, V≦V, the Vs comparator 11 outputs an operating output, and the switch 10 is turned on (ON) L through the drive transistor 15, and the DC power is regulated from the rectifier 3 through this. The input voltage V1 is supplied to the voltage circuit 7 and gradually increases. When vl>Vs, the comparator 11 determines this and turns off the drive transistor 5. However, the switch 10 remains on due to the characteristics of cyrisk, and turns off only when the power supply voltage (2) reaches the zero point and the current becomes zero. Thereafter, the input voltage V gradually decreases, and when V1≦VS, the switch 10 is turned on according to the process described above, and power is supplied via the switch 10 again. The left half of Figure 2 shows the operation mode when the power supply voltage ■ is at or above the rated voltage.
This shows the average level of On the other hand, the right half of FIG. 2 shows the operating mode when the power supply voltage V 2 is relatively low, and the operating principle is, of course, no different from that when the voltage is high as already described. In this case, although the number of times the drive transistor 5 is turned on and off increases, the switch 10 almost always remains on, and the result is the same as if the switch 10 were not provided. In other words, the present invention can be said to function effectively particularly when the power supply voltage is relatively high.

FIG. 3 shows a modified embodiment of the invention.

In this embodiment, the rectifier circuit of the second system is not a single-phase full-wave type, but the rectifier 3 of the single-phase bridge connection is used in common with the first system, and the rectifier circuit of the second system is The feature is that a switch 20 consisting of a transistor that is directly driven by the operational output of the comparator 11 is inserted in series on the input side of the comparator 11. The basic principle of this circuit configuration is the same as that of the circuit shown in FIG. No intermediate tap is required for the second secondary winding.

In any of the embodiments, in a region where the input voltage vl exceeds the reference value ■, the switch 10 or the switch 20 is turned off to suppress the increase in the voltage borne by the transistor 7A.
Thereby, heat loss of the transistor 7A can be suppressed.

A simple calculation of the voltage burden on the transistor 7A is as follows. Assume that the voltage reference value input to the comparator 11 is 7V. The maximum value of voltage V is set to 10 as before.
．． 7V, and if the minimum value is 7V, the average value of voltage V is approximately (10,7+7.0)/2-8.9 (V),
Therefore, the burden voltage of transistor 7A, ie cE
average is 8.9-5. 0-3. 9 (V), which is lower than the above-mentioned 5.7V to 6896V, and the heat loss also decreases by this amount.

Note that the switches 10 to 20 operate on or off, that is, either the burden voltage or the load current is substantially zero, so even if they are configured with semiconductor switches, the heat loss is mainly from the on to the off state. , or only occurs within a short switching time from off to on, and the heat generated can be almost ignored.

[Effects of the Invention] In the present invention, a switch is inserted before a constant voltage circuit having a smoothing capacitor on the input side, and this switch is turned off when the input voltage of the constant voltage circuit exceeds a predetermined value. Therefore, the voltage load on the constant voltage transistor in the constant voltage circuit, particularly in the high input terminal region, can be reduced without deteriorating the constant voltage characteristics, and thereby the heat loss generated by the transistor can be suppressed. Therefore, the heat sink for the transistor can be made smaller, the heat sink can be simplified, and the reliability of the entire device can be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit connection diagram showing an embodiment of the present invention, FIG. 2 is a time chart for explaining the operation of the circuit in FIG. 1,
FIG. 3 is a circuit connection diagram showing another embodiment of the present invention, FIG. 4 is a circuit connection diagram of a conventional DC power supply device, and FIGS.
6b) and FIGS. 6(a) and 6(b) are voltage waveform diagrams for explaining the operation of the circuit of FIG. 4. 2... Transformer, 3... Rectifier, 4, 6... Smoothing capacitor, 5, 7... Transistor type constant voltage circuit,
7A...transistor, 10.20...switch,
11... Comparator, 13... Zener diode. Applicant's agent: Sato - Yukan Figure 1 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] A rectifier that rectifies alternating current, a switch connected in series to the output side of this rectifier, a smoothing capacitor provided to the output side of this switch, a transistor type constant voltage circuit connected to this smoothing capacitor, and the smoothing A DC power supply device comprising switch control means that turns on the switch only when the terminal voltage of the capacitor is below a predetermined value.