JPS5849091B2 - AC/DC switching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention connects a first capacitor 4 to one end 3 of an input terminal which is selectively connected to an AC power supply 1 or a DC power supply 2, and connects the other end of the first capacitor 4 to the input terminal. A parallel circuit of a diode bridge 7 and an AC relay 10 is inserted and connected between the other end 6, and a parallel circuit of a discharge resistor 8 and a second capacitor 9 is inserted and connected between the midpoints of the diode bridge 7. The purpose of this device is to have an AC/DC detection function, and to prevent malfunctions caused by AC relay chattering when DC voltage is turned on and incorrect polarity of DC input voltage. An object of the present invention is to provide an AC/DC switching device that prevents this.

Conventionally, an AC/DC switching device having a circuit configuration shown in FIG. 3 has been provided.

That is, a series circuit in which a diode 12 is connected in series to a parallel circuit of a resistor 13 and a capacitor 11 is connected in parallel to an AC relay 10, and when a DC voltage with the polarity shown in the figure is applied to the input terminal, the capacitor 14 The charging current flows through the capacitor 11 and the diode 12, and the divided voltage by the capacitors 14 and 11 is applied to the AC relay 10. Since the AC relay 10 is set lower than the voltage, the AC relay 10 does not operate.

Note that although the charging current of the capacitor 14 also flows through the AC relay 10, the impedance of the AC relay 10 with respect to the charging current that flows immediately after the application of the DC voltage is much larger than the impedance of the capacitor 11.
Most of the charging current flows through the capacitor 11, and the voltage divided by the capacitors 14 and 11 is applied to the AC relay 10.

Next, when the AC power supply 1 is connected to the input terminal instead of the DC power supply 2, and an AC voltage with the polarity shown in the figure is selectively applied to the input terminal, the DC current half-wave rectified by the diode 12 charges the capacitor 11. However, when the current is reversed, the current is cut off by the diode 12 and no longer flows through the capacitor 11.

In this way, the alternating current that has passed through the capacitor 14 is asymmetrically positive and negative, but most of it flows to the alternating current relay 10.
It operates by AC excitation of 0.

However, in such a conventional example, if the DC power supply 2 is incorrectly connected and a DC voltage with the opposite polarity to that shown in the figure is applied, the AC relay 10 has a drawback that it malfunctions for a short time due to the charging current of the capacitor 14. .

In order to eliminate this drawback, a resistor 13 is installed as shown in FIG.
A parallel circuit of a capacitor 11 and a series circuit of a diode 12 were made anti-parallel and connected in parallel to an AC relay 10, but when an AC voltage is applied, the charge in each capacitor 11 is Since the current flows through the AC relay 10, the current flowing through the AC relay 10 decreases, resulting in deterioration of the AC relay 10's touching and opening characteristics.

15 is a relay contact of the AC relay 10.

The present invention can be provided in view of the above-mentioned points, and will be explained in detail below with reference to Examples.

FIG. 1 is a diagram showing one embodiment of the present invention. When the DC power supply 2 is applied to the input terminal with the polarity shown in the figure, the charging current of the l-th capacitor 4 is transferred to the first diode 16 of the diode bridge 7.
, the charging current flows through the second capacitor 9 and the second diode 17, and when the DC power supply 2 is applied to the input terminal with the polarity opposite to that shown in the figure, the charging current flows through the third diode 18 of the diode bridge 7, the second capacitor 9, and the second diode 17. The current flows through the four diodes 19, and the divided voltage from the first and second capacitors 4 and 9 is applied to the AC relay 10.
Since this divided voltage is set below the voltage of the AC relay 10 as in the conventional example, the AC relay 10 does not operate.

Next, when the AC power supply 1 is applied to the input terminal, a part of the AC flows through the series circuit of the first diode 16, the second capacitor 9, and the second diode 17, and the series circuit of the third diode 18 and the second diode 17.
The current flows through the series circuit of the capacitor 9 and the fourth diode 19, but since the direction of the current flowing through the second capacitor 9 is the same, the second capacitor 9 maintains its charged state and the current flowing through the series circuit is only a small amount. It becomes a little,
Most of the AC flows to AC relay 10 and AC relay 1
0 works normally.

In this way, when the DC power supply 2 is applied to the input terminal, the AC relay 10 does not operate, and when the AC power supply 2 is applied, the AC relay 10 operates, thereby enabling detection control of AC and DC.

20 is a resistor connected in parallel to the input terminal.

FIG. 2 shows an application example of the present invention, and is a circuit diagram of a two-wire emergency lighting device with a separate power supply.

In the figure, A is an inverter circuit that converts direct current to alternating current, B is the above-described circuit of the present invention, 21 is a commercial ballast, 22 is a lamp, 23 is a lighting tube, and 15 is a relay contact of the AC relay 10. .

Here, when AC power supply 1 is connected to the input side, AC relay 1
0 operates, each relay contact 15 is turned to the NO contact side shown in the figure, and the lamp 22 is lit by the lighting tube 23 and the commercial ballast 21.

Next, when the AC power source 1 is switched and connected to the DC power source 2 on the input side, no current flows through the AC relay 10, and each relay contact 15 instantaneously returns to the NC contact side opposite to that shown in the drawing.

Therefore, the DC power supply 2 is connected to the diode 2 of the inverter circuit A.
The high frequency power is supplied to the lamp 22 from the output winding of the inverter transformer 24, and the lamp 22 maintains the lighting state.

Here, when DC is turned on, the AC relay 10 does not cause chattering due to the DC step voltage, so the commercial ballast 2
Burnout of the commercial ballast due to direct current flowing into the relay contact 15 and welding due to arcing when switching the relay contact 15 to direct current do not occur.

As described above, the present invention connects a first capacitor to one end of an input terminal that is selectively connected to an AC power supply or a DC power supply, and connects a diode bridge between the other end of this first capacitor and the other end of the input terminal. By inserting and connecting a parallel circuit with an AC relay and connecting a parallel circuit with a discharge resistor and a second capacitor between the midpoints of the diode bridge, by reducing the discharge resistance, you can switch from AC input to DC input. , the charge in the second capacitor is instantly discharged through the discharge resistor, and the charging current of the first capacitor due to the application of DC input is no longer blocked from flowing into the second capacitor, and the charging current does not flow to the AC relay but instead flows into the second capacitor. This voltage flows into the second capacitor and has the effect of shortening the switching time of the AC relay from on to off.Moreover, when AC input is applied, the voltage applied to the second capacitor every half cycle of the AC power supply is in the same direction. As a result, the second capacitor maintains its charged state, and therefore the current flowing into the diode bridge can be made small.
Most of the current can flow through the AC relay, reducing power loss. Furthermore, due to the symmetry of the diode bridge, the current flowing through the AC relay has a positive and negative symmetrical waveform, which prevents buzzing and cracking of the AC relay. In addition, the charging current of the first capacitor will not flow to the AC relay due to the difference in polarity of the DC input, and short-term malfunction of the AC relay when switching from AC input to DC input is prevented. This has the effect of making it possible.

[Brief Description of the Drawings] Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is a circuit diagram of an application example of the above, and Figs. 3 and 4 are circuit diagrams showing conventional examples of the above, respectively. , 1 is an AC power supply, 2 is a DC power supply, 3 is one end of an input terminal, 4 is a first capacitor, 6 is the other end of an input terminal, 7 is a diode bridge, 8 is a discharge resistor, 9 is a second capacitor, 10 is a It is an AC relay.

Claims (1)

[Claims] 1 A first capacitor is connected to one end of an input terminal that is selectively connected to an AC power source or a DC power source, and a diode bridge and an AC relay are connected in parallel between the other end of this first capacitor and the other end of the input terminal. An AC/DC switching device characterized in that a circuit is inserted and connected, and a parallel circuit of a discharge resistor and a second capacitor is inserted and connected between the midpoints of a diode bridge.