JP2001298946A - Direct-current power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC power supply unit that is of small size, lightweight, and simple structure and capable of outputting stable DC voltage to an inductive load, and whose power factor is improved. SOLUTION: An alternating current is full-wave-rectified through a full-wave rectifier DB, and a first inductor L1 is series-connected with the obtained pulsating current. The pulsating current is converted into that of high frequency through a push-pull inverter provided with transistors Tr1 and Tr2, and a second inductor is series-connected with the output of the push-pull inverter. Its output is rectifier, and a direct-current voltage is outputted. To detect idling or no-load running of a direct-current motor as a load, a timer circuit is connected with an overvoltage detection circuit 4 to detect that the state of overvoltage lasts for a certain period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply, and more particularly to an improvement of a DC power supply for supplying a stable DC voltage to an inductive load.

[0002]

2. Description of the Related Art In the case of driving a DC motor having a rated voltage of 15 V, for example, with a commercial power supply, the commercial power supply voltage is conventionally stepped down using a so-called iron-copper type transformer in which a copper wire is wound around an iron core. Some are rectified and converted to direct current for driving. However, this transformer had the disadvantage of being large and heavy.

[0003] In addition, a commercial power supply is converted into a DC voltage by using various switching regulators, converted into a high frequency by a switching section, transformed by using a high frequency transformer, and the transformed output voltage is rectified by high frequency. A method of obtaining a necessary DC power supply has been considered. However, this method has problems such as a large noise (noise), a large inrush current, and a low power factor that prevents harmonics from being suppressed. For this reason, it is necessary to provide a circuit (parts) for each countermeasure, which increases the number of parts and increases the cost. In addition, there is a disadvantage that the size is not reduced even if the weight is light.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a DC power supply having a small, lightweight and simple structure, capable of outputting a stable DC voltage to an inductive load, and having an improved power factor. The purpose is to provide.

[0005]

In order to solve the above-mentioned problems, a DC power supply according to the present invention provides full-wave rectification of an alternating current,
A first inductor is connected in series to the pulsating current, the pulsating current is converted to a high frequency by a push-pull inverter, and a second inductor is connected in series to the output of the push-pull inverter; The output is rectified to output a DC voltage.

[0006]

Embodiments of the present invention will be described below with reference to the drawings.

(Circuit Configuration) FIG. 1 is a circuit diagram of a DC power supply according to one embodiment of the present invention. This DC power supply device includes a rectifier circuit 1, an inverter circuit 2, an output circuit 3, and an overvoltage detection circuit 4. An input side of this circuit may further include an overcurrent protection circuit (such as a fuse), a lightning surge protection circuit (varistor), and a noise prevention circuit (such as a combination of a capacitor and a noise filter).

The rectifier circuit 1 includes a full-wave rectifier DB. The input terminal of the full-wave rectifier DB is connected to the AC power supply, and the output terminals (+,-terminals) are connected to the smoothing circuit 2 side.

The inverter circuit 2 includes a transistor Tr
1 and a push-pull inverter composed of Tr2. One (− side) of the output of the full-wave rectifier DB is connected to both ends of the primary winding of the high-frequency transformer T via the transistors Tr1 and Tr2. The other (+ side) of the output of the full-wave rectifier DB is connected to the middle point of the primary winding of the high-frequency transformer T via a constant current inductor (first inductor) L1. Further, one of the feedback windings of the high-frequency transformer T is connected to the base of the transistor Tr1, and the other is connected to the base of the transistor Tr2.

The output circuit 3 is connected to the secondary winding of the high-frequency transformer T, and includes inductors L2 and L3, a diode D
1, a rectifying unit including D2 and capacitors C3 and C4. In particular, the inductor L2, which is the second inductor of the present invention, may have a smaller inductance than the inductor L1.

The overvoltage detection circuit 4 has a Zener diode Z1 and a capacitor C5 connected in parallel, and a resistor R
3 are connected in series, and both ends thereof are respectively connected to both terminals on the output side. And the Zener diode Z1
Draw terminals from both ends and connect to the timer circuit.

(Operation) Next, the operation of the DC power supply will be described.

The full-wave rectifier DB of the rectifier circuit 1 converts an AC input current into a DC (pulsating current).

In some cases, the output from the full-wave rectifier is smoothed by a large-capacity electrolytic capacitor and input to an inverter circuit.
To about 60%, or a large current flows into the power supply when the power is turned on, which may adversely affect the wiring system. Therefore, in this circuit, the constant current inductor L1 is inserted instead of smoothing by the electrolytic capacitor.

The output voltage of the full-wave rectifier DB is applied to the primary winding of the high-frequency transformer T via the transistors Tr1 and Tr2 of the inverter circuit 2. Since one of the feedback windings of the high-frequency transformer T is connected to the base of Tr1 and the other is connected to the base of Tr2, Tr1 and Tr2 alternately repeat conduction and cutoff. Thus, a sine-wave high-frequency voltage (for example, about 3
0 kHz). A voltage corresponding to the number of turns is generated in the output winding of the high-frequency transformer T, and its waveform is twice the power supply frequency (100 Hz or 120 Hz when a commercial power supply is used).
Hz) having a frequency envelope.

The constant current inductor L1 connected in series to the positive side of the output of the full-wave rectifier DB plays an important role in increasing circuit efficiency and reducing noise. Due to the constant current effect of the inductor on the high frequency, the collector current of the transistor becomes a trapezoidal wave, and the peak current decreases. Accordingly, transistors Tr1 and Tr2 having a small current capacity can be used.
1, the collector-emitter voltage Vce (sa) of Tr2
The power loss due to t) is greatly reduced.

Further, as a reason why high efficiency and high reliability can be obtained, the cutoff of the collector currents of the transistors Tr1 and Tr2 is essentially performed at the time point when Vce is zero on the circuit principle, so that the switching loss is extremely reduced. That it can be made smaller. As a result, the overall efficiency of the inverter 95
% Can be achieved.

Further, the high-frequency voltage and the high-frequency component contained in the current generated in the high-frequency transformer T can be reduced by the constant current inductor L1.
1. At the time when the Tr2 is energized at the same time, the pulsed current flowing from the power supply is absorbed, and as a result, noise can be significantly reduced.

The output circuit 3 rectifies and smoothes a high frequency having a 100 Hz or 120 Hz envelope output from the secondary winding of the high frequency transformer T. Generally, a capacitor is used as a smoothing means. However, since the capacitor is capacitive and its charging voltage is steep, heat generation of the transistor increases. Therefore, in this push-pull inverter, an inductor L2 for reducing a steep charging current is inserted in series between the output terminal and the rectifier circuit to reduce heat generation of the transistor.

The overvoltage detection circuit 4 detects an overvoltage between the output terminals. When the DC motor, which is a load, is idle or has no load, the voltage generated between the output terminals increases.
When the voltage of the Zener diode Z1 exceeds a certain voltage,
Zener diode Z1 conducts. Simply detecting the rise in voltage cannot be distinguished from the high voltage generated at the start of the DC motor. Therefore, by connecting both ends of the zener diode Z1 to the timer circuit, the timer circuit is started when the zener diode Z1 becomes conductive. Then, it is detected whether or not the high voltage state continues for a predetermined time.
After a certain period of time has elapsed since the timer circuit was started, a signal for shutting off the inverter circuit 3 is generated by a signal generator (not shown) to shut off the inverter circuit 3.

In the DC power supply according to the present embodiment, the difference between the output voltage when a load is connected and the output voltage when no load is applied is twice or more (12 V at load, about 32 V at no load, and about 32 V at idle operation. 22V).

[0022]

As described above, according to the DC power supply of the present invention, it is possible to obtain a stable DC voltage with respect to an inductive load with a small, lightweight and simple structure.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a DC power supply device according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 rectifier circuit DB full-wave rectifier 2 inverter circuit L1 constant current inductor (first inductor) Tr1, Tr2 transistor T high-frequency transformer 3 output circuit (smoothing circuit) L2 inductor (second inductor) C3, C4 capacitor 4 overvoltage detection circuit Z1 Zener diode C5 Capacitor

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Katsuo Yamamoto 2-18-19 Hiratsuka, Shinagawa-ku, Tokyo F-term (reference) within SETAC Co., Ltd. 5H006 AA02 BB05 CA01 CA12 CA13 CB01 CB04 CC01 CC08 DA02 DA04 FA01 5H730 AA12 AA18 AA20 AS13 BB25 BB52 CC04 DD02 DD41 EE06 FD01 XX04 XX12 XX23 XX40 XX42

Claims (1)

[Claims] An AC current is full-wave rectified, a first inductor is connected in series to the pulsating current, and the pulsating current is converted to a high frequency by a push-pull inverter. A DC power supply device, wherein a second inductor is connected in series to an output, and the output is rectified to output a DC voltage.