JPS623451B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching power supply device used in circuits where voltage fluctuations and ripples are relatively tolerated, such as relay indicator light circuits and thyristor gate circuits.

Various types of switching power supply circuits using transistors have been known for a long time, and their use has been increasing in recent years with the development of switching power supply ICs.
An example of this known circuit is shown in FIG. In Figure 1, 1 is an AC power supply, 2 is a rectifier, 3 is a smoothing capacitor, 4 is a transistor, 5 is a control amplifier, 6 is a flywheel diode, 7 is a smoothing reactor, 8 is a voltage detector, and 9 is a smoothing capacitor. , 10
indicates a load, and 11a and 11b indicate terminals. In the above circuit, when the transistor 4 is on, an increasing current flows from the AC power supply 1 to the series circuit of the rectifier 2, the transistor 4, the smoothing reactor 7, the smoothing capacitor 9, and the load 10, and the smoothing capacitor 9 is charged. Next, when the transistor 4 is turned off, the electromagnetic energy of the smoothing reactor 7 causes a current to flow through the smoothing capacitor 9 and the load 10 in a closed circuit passing through the flywheel diode 6 and the smoothing reactor 7 while decreasing. By repeating the above-described on/off operation, the load current, that is, the load voltage, can be set to a desired value.

The control amplifier 5 performs this on/off control.
and voltage detector 8, most of which are currently
It is integrated into an IC. However, in either case, the device is complicated and expensive.

The present invention has been made in view of the above-mentioned points, and allows the load voltage to be controlled even if the control amplifier 5, voltage detector 8, and smoothing reactor 7 are eliminated.

The present invention will be explained below based on the drawings of the embodiments.

FIG. 2 is a circuit diagram showing an embodiment of the present invention, in which the same functional parts as in FIG. 1 are designated by the same reference numerals.
In the figure, 12 represents a resistor, and 13 represents a switching element. FIG. 3 is a diagram showing the characteristics of the switching element 13. FIG. 4 shows a circuit whose characteristics are equivalent to the switching element 13, in which 13a is a thyristor and 13b is a constant voltage diode. Fig. 5 is a waveform diagram of each part for explaining the operation of the circuit shown in Fig. 2. Fig. 5 a shows the output voltage of the rectifier 2, Fig. 5 b
is the base voltage of the transistor 4, FIG. 5c is the collector current of the transistor 4, and FIG. 5d is the voltage of the smoothing capacitor 9. As shown in FIG. 3, the switching element 13 has switching characteristics such that when the applied voltage exceeds a certain value, current flows and the voltage across both ends decreases. The switching element 13 is composed of a thyristor 13a and a constant voltage diode 1 having similar characteristics as shown in FIG.
It is also possible to replace it with 3b. Transistor 4, to which a voltage obtained by rectifying AC power supply 1 is applied, is turned on by a base current flowing through resistor 12, current flows through smoothing capacitor 9 and load 10, and smoothing capacitor 9 is charged. This state is shown in the period _T1 in FIG.

Next, when the voltage slightly dropped by the resistor 12 from the rectified voltage of the AC power supply 1, that is, the base voltage of the transistor 4, reaches the switching voltage of the switching element 13 shown by V ₁ in FIG. A current flows through the switching element 12, and the switching element 13 becomes conductive, and the voltage across the switching element 13 decreases to the saturation voltage shown at _V2 in FIG. 5b. By this time, the smoothing capacitor 9 has been charged to a voltage obtained by subtracting the voltage drop between the base and emitter of the transistor 4 from the base voltage of the transistor 4 immediately before the switching element 13 becomes conductive. is higher than the base voltage of transistor 4. Therefore, no base current flows through transistor 4, and transistor 4 is turned off. Even if the transistor 4 is turned off, the current continues to flow through the load with a slight decrease due to the charged charge of the smoothing capacitor 9. This state is the fifth
This is the period _T2 in the figure. The off state of the transistor 4 continues even if the voltage obtained by rectifying the AC power source 1 reaches its peak value and further drops. The voltage obtained by rectifying the AC power supply 1 drops and the voltage is applied to the switching element 13.
When the voltage becomes lower than the saturation voltage V ₂ , no current flows through the switching element 13, and the switching element 13 becomes non-conductive. Next, when the voltage obtained by rectifying the AC power supply 1 rises again and becomes slightly higher than the voltage of the smoothing capacitor 9, a base current flows through the resistor 12, turning on the transistor 4, and the smoothing capacitor 9 is charged in the same manner as described above. This state is the period _T3 in FIG. By repeating the above steps, the voltage applied to the load 10 is approximately equal to the switching voltage _V1 of the switching element 13, and its ripple has a value determined by the capacitance of the smoothing capacitor 9, the magnitude of the load current, and the frequency of the pulsating current power source.

Although the circuit using the NPN transistor shown in FIG. 2 has been described above, the present invention can also be applied to a circuit using the PNP transistor. Figure 6 is the second
The circuit is constructed to replace the NPN transistor shown in the figure with a PNP transistor (transistor 4'), and its operation is similar to that of the circuit shown in FIG. 2 described above, so a description thereof will be omitted.

The voltage applied to the load of the present invention, that is, the output voltage is the switching voltage of the switching element 13.
It has already been explained that it is determined by V ₁ , but it is also possible to change this. FIG. 7 shows a circuit in which a constant voltage diode 14 and a blocking diode 15 are added to the circuit shown in FIG. By adding a constant voltage diode 14 in series with the switching element 13 as shown in FIG. The value is the sum of the voltage _V1 . Therefore, switching element 13
The smoothing capacitor 9 is charged until it becomes conductive.
The voltage is also the Zener voltage of the constant voltage diode 14 and the switching voltage V ₁ of the switching element 13.
is approximately equal to the sum of That is, the output voltage can be easily changed by adding a constant voltage diode with a different Zener voltage. When the switching element 12 becomes conductive, the blocking diode 15 prevents the base voltage of the transistor 4 from being lower than the emitter voltage of the smoothing capacitor 9, so that no reverse voltage is applied between the base and emitter of the transistor 4. It is for. Further, when the output voltage, that is, the voltage of the smoothing capacitor 9 is higher than the base-emitter reverse breakdown voltage of the transistor 4, it is effective to insert a blocking diode 15 in series with the emitter of the transistor 4.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional switching type power supply circuit, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3 is a diagram showing characteristics of a switching element, and Fig. 4 is a diagram showing a switching element equivalent to the switching element. Diagram showing the circuit, No. 5
The figure is an operation waveform diagram of each part for explaining the operation of the present invention, and FIGS. 6 and 7 are circuit diagrams showing other embodiments of the present invention. 1... AC power supply, 2, 2'... Rectifier, 3, 9
...Smoothing capacitor, 4,4'...Transistor, 5...Control amplifier, 6...Flywheel diode, 7...Smoothing reactor, 8...Voltage detector, 10...Load, 12...Resistance , 13... switching element, 13b, 14... constant voltage diode, 15... blocking diode.

Claims (1)

[Claims] 1. A smoothing capacitor and load are connected via the collector and emitter of a switching transistor from a pulsating power supply using a single-phase rectifier circuit that does not have a smoothing capacitor, and a resistor is placed between the collector and base of the transistor. A switching element is connected between the base of the transistor and the other end of the pulsating current power source, and the transistor is turned off when the instantaneous value of the pulsating current power source reaches a switching voltage of the switching element. Features a power supply circuit.