JPS6243015A - Switching circuit - 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 (Industrial Application Field) The present invention relates to a switch circuit that includes contacts and connects and disconnects the current of an inductive load such as a relay by opening and closing the contacts.

(Prior art) Conventional switch circuits that protect contacts by preventing arc discharge from occurring at the contacts connect a capacitor (bypass capacitor) in parallel to the contacts, and when the contacts open, the current at the contacts There is a device that bypasses this via a bypass capacitor.

FIG. 9 is a circuit diagram of an example of a conventional switch circuit employing such a system. In Fig. 9, Es is a DC power supply, St is a contact that opens and closes to interrupt the current to the load, C is a bypass capacitor that bypasses the contact current when contact Sl opens, and R is contact S1.
L is an inductive load such as a relay, and L is an inductive load such as a relay.

The switch circuit having such a configuration operates as follows.

That is, when the contact S1 is closed, the capacitor C and the contact S1 form a closed circuit via the current limiting resistor R. Therefore, before the contact Sl opens, the charge in the capacitor C has been discharged within this closed circuit. From this state, the contact Sl begins to open.

Along with this, the voltage drop at the contact Sl increases.

As the voltage drop increases, the amount of load current (2) flowing into the inductive load decreases through contact Sl, and the amount flowing through bypass capacitor C increases, and load current I increases. All of this will pass through capacitor C. Then, the capacitor C is charged by the load current ■, and the contact S1 is opened by the time the voltage at the contact St increases.

By the way, the breakdown voltage of the contact St (contact breakdown voltage) increases as the contact Sl opens. On the other hand, the voltage applied to contact Sl (
The contact voltage () also increases as the amount of charge of the capacitor C increases. In this case, if the resistance value of the current limiting resistor R is sufficiently small, the contact voltage V is expressed by the following equation (1).

V=(1/C)xt...(1) However, in equation (1), ■ is the current value of load current ■, C
is the capacitance value of capacitor C, and t is time.

FIG. 1θ is a graph showing the relationship between the contact voltage and the contact breakdown voltage, with voltage on the vertical axis and time on the horizontal axis. The solid line shown in this graph shows the contact voltage V, and the broken line shows the contact breakdown voltage of the contact Sl. In FIG. 1O, the relationship is such that the contact voltage V is smaller than the contact breakdown voltage, but with such a relationship, arc discharge will not occur.

Therefore, in such a case, the purpose of contact protection will be achieved.

In this way, the charge stored in the capacitor C when the contact S1 is opened is discharged along the path of the capacitor C→contact Sl→current limiting resistor R when the contact Sl is closed next time. (However, → indicates the direction in which the discharge current advances. The same applies hereinafter.) The maximum current at this time is determined by Es/R. However, Es is the voltage value of the DC power source Es, and R is the resistance value of the current limiting resistor R.

(Problem to be Solved by the Invention) By the way, in such a switch circuit, in order to have the relationship between the contact breakdown voltage and the contact voltage as shown in Fig. 10 to prevent arc discharge, the capacitance of the capacitor C must be adjusted. It is necessary to make it larger.

Capacitors with larger capacitances generally have larger sizes.

However, a large-sized capacitor does not have good frequency characteristics, so when the contact St starts to open, the load current I does not move instantaneously to the capacitor C1, and therefore the contact S1 cannot be sufficiently protected.

Further, in a capacitor having a large capacity, when the contact Sl is closed, the amount of charge to be discharged becomes large, and therefore, a long time is required for the discharge. Furthermore, since the discharge current flows through the contact St, the contact St is likely to be damaged.

Further, there is no effect of preventing arc discharge caused by a chattering phenomenon when the contact Sl is closed.

The present invention has been made in view of these circumstances.

(Means for Solving the Problems) In the present invention, a transistor is connected in parallel with a main contact through which a load current flows, and the transistor is driven by a circuit section that turns the transistor on or off. An auxiliary contact that is alternately turned on with the main contact is connected between the base and emitter of the transistor, and when the auxiliary contact is on, the transistor is turned off regardless of the operation of the circuit section. The main contact and the auxiliary contact have a transfer contact structure with a common movable contact. With this transfer contact structure, when a contact opens or closes, the transistor is turned on for a short period of time after the contact starts moving and just before it fully opens or closes, during which arc discharge would occur in a normal contact, and the load current that should flow through the contact bypass with a transistor to prevent arc discharge at the contacts.

Further, since the transistor is only energized for a very short time when the contacts are opened and closed, the load is small.

(Example) FIG. 1 is a circuit diagram of Example 1 of the present invention. In Figure 1, Es is a DC power supply, C is a capacitor, DI and D2 are diodes, R is a resistor, Tr is a transistor as a semiconductor switching element, Z is an arrester for overvoltage prevention, F is a fuse, and L is a relay, etc. It is an inductive load. Sl is a main contact connected in parallel to the collector and emitter of the transistor Tr, and S2 is an auxiliary contact. The main contact Sl and the auxiliary contact S2 have a common movable contact, and both contacts S
1 and S2 are transfer contacts. Note that the transistor Tr may be replaced with an element having the same function as the transistor Tr.

In such a configuration, a case will be described in which the main contact S1 is opened. When the main contact Sl begins to open, the voltage drop across the main contact Sl increases.

Along with this, the capacitor C is connected in the path from fuse F to capacitor C to diode DI to the base of transistor Tr.
Charging current begins to flow. This charging current becomes a base current for the base of the transistor Tr. In this way, when the base current 1b flows through the base of the transistor Tr, a current with a current amplification factor β times that of the transistor Tr flows through the collector of the transistor Tr. Then,
The load current I flows through its base and collector at a ratio of 1:β. Since the voltage (2) across the main contact Sl is equal to the charging voltage of the capacitor C, the voltage V is given by the following equation (2).

V=(Ib/C)Xt - (1/(1+β)C)t...(2) Here, C
is the capacitance of capacitor C, and Ib is the base current value. Therefore, when formula (2) is compared with formula (1) above, assuming that the rate of change of voltage V is the same, the capacitance of capacitor C in the example is (! +β) can be reduced to -.

When the main contact S+ is fully opened, the auxiliary contact S2, which is a transfer contact with the main contact Sl, is turned on.

When the auxiliary contact S2 is turned on, the base and emitter of the transistor Tr are short-circuited, and the transistor Tr is turned off. transistor T
When r is turned off, all of the load current I flows through capacitor C. Therefore, capacitor C is rapidly charged.

Due to this charging, the voltage V rapidly rises and reaches the limit voltage of the arrester Z. There is already a sufficient amount of contacts Sl, and the withstand voltage is sufficiently high, so there is no risk of boiling and discharging. Since the voltage drop across the arrester Z is greater than the voltage of the DC power supply Es, the load current I gradually decreases and finally reaches zero.

The charge stored in the capacitor C is then discharged through the path of the capacitor C, the fuse F, the main contact Sl, the resistor R, and the diode D2 when the main contact Sl is closed. Since the capacitance of the capacitor C is small, it can be discharged within a short time. In this case, the fuse F is the transistor T
When a short-circuit failure occurs in r, this transistor Tr is disconnected from the circuit. The current rating of the fuse F is smaller than the load current I.

In normal operation, the energization time of fuse F is very short. Therefore, the fuse F will not melt due to the discharge. Furthermore, if the fuse F blows out, it will no longer be effective in preventing the occurrence of arc discharge. However, in this case, the main contact St can function as a normal contact to connect and disconnect the load current (2).

When the transistor Tr is replaced with a field effect transistor, no gate current flows through the field effect transistor, so the capacitor C is hardly charged from when the main contact Sl begins to open until when the auxiliary contact S2 is turned on. Therefore, voltage V is kept at a constant low voltage. Therefore, it is more effective in preventing arc discharge. Since the capacitance of the capacitor C only needs to be very small, the discharge of the capacitor C when the main contact S1 is closed is extremely short and has the effect of preventing arc discharge even against the chattering phenomenon of the main contact S1. It becomes like this. When a field effect transistor is used as the transistor Tr, a normally-off type transistor that shuts off when the gate voltage is zero is suitable.

FIG. 2 is a circuit diagram of a second embodiment of the present invention, and parts corresponding to those in FIG. 1 are given the same reference numerals.

In FIG. 2, the DC power supply Es and the load are not shown. Embodiment 2 shown in FIG. 2 has a terminal TI in the circuit of FIG.
, T2 and T3 are added. The operation when main contact S1 is opened is similar to the circuit of FIG.

FIG. 3 shows the operating circuit of the second embodiment when the main contact Sl is closed. That is, at the moment when the main contact Sl closes, the electric charge stored in the capacitor C causes a current +1 to flow through the path of capacitor C - fuse F -> main contact S1 - diode D2 -> terminal T2 - terminal Tl -> resistor R -> capacitor C. . This current i1 causes the turns ratio of the transformer T (terminal TI
- a current 12 is induced from terminal T2 to terminal T3 according to the turns ratio between T2 and terminals T2-T3). Induced current 12
flows to the base of the transistor Tr.

This induced current 12 turns on the transistor Tr. Even if the main contact S1 is at an instantaneous level, the current 11 and the load current I flow through the transistor Tr, so the voltage V is kept at a low voltage. This prevents arc discharge at the main contact St due to a chattering phenomenon when the main contact Sl is closed.

FIG. 4 is a circuit diagram of Embodiment 3 of the present invention, which is characterized in that windings T4-T5 are added to the circuit of FIG. 2, and the collector current of the transistor Tr flows through these windings. have Windings T4-T5 and windings T2-T3 constitute a current positive feedback circuit of transistor Tr. Due to the action of this positive feedback circuit, the transistor Tr can self-maintain the on state.

When the main contact S1 is opened, the charging current of the capacitor C flows to the base of the transistor Tr, as described above, thereby triggering the positive feedback circuit formed by the winding. This trigger causes the load current I to rise until the auxiliary contact S2 closes.
is bypassed.

This keeps the voltage of the main contact Sl at a low voltage.

When the main contact S1 closes, the discharge current of the capacitor C flows and the positive feedback circuit is triggered. This prevents the occurrence of arc discharge due to the chattering phenomenon of the main contact St. Since the capacitor C only needs to trigger the positive feedback circuit, it may have a smaller capacitance than the capacitor C in the circuit of FIG. 1 or 2.

FIG. 5 is a circuit diagram of Embodiment 4 of the present invention, in which the transformer T
The windings Tl-T3 supply the base current of the transistor Tr, and the windings T4-T5 pass the collector current, thus forming a current positive feedback circuit similar to the circuit shown in FIG. Capacitor C also triggers the positive feedback circuit in the same way as in Figure 2, and resistor R
1 also acts as a trigger. Winding T6-T7 is the main contact Sl
The current flowing through generates a magnetomotive force in the direction opposite to that of the windings T4-T5, which has the effect of resetting the magnetic flux of the transformer T and increasing the utilization rate of the iron core.

FIGS. 6 and 7 respectively show the operating circuit of the fourth embodiment shown in FIG. Here, N1 is the winding T4-T5. T
The number of turns of 6-T7, N, is the number of turns of winding Tl-T3.

FIG. 8 shows the change in the magnetic flux of the iron core of the transformer T, with the vertical axis representing the magnetic flux and the horizontal axis representing the number of turns×magnetizing current. When closing the main contact Sl, the auxiliary contact S2 is first opened. As a result, the base current of the transistor Tr is supplied through the resistor R1. This supply triggers the positive feedback circuit, resulting in the operating circuit shown in FIG. The transistor Tr is kept in the on state, the voltage (2) is small, the capacitor C is discharged, and the load current I flows through the transistor Tr. The magnetic flux Φ of the transformer T is initially at B° in FIG. 8, and after being triggered, it moves to B'-B-C with time.

Note that the voltage of the winding TI-T3 (number of turns N2) is the sum of the voltage drop of the diode DB and the base voltage of the transistor Tr, and the voltages of the other windings follow the turns ratio.

If is the magnetizing current of the transformer T, from Ic to If
The current excluding Ib is transmitted to the secondary winding as Ib according to the turns ratio.

When the movable contact reaches the main contact Sl and the main contact Sl closes, the operating circuit becomes as shown in FIG. The relationship between the currents in the figure is expressed by the following formula (
3) is given by

Ic=A/B...(3) However, A=1-1f B=2+N! /N rβlc: Collector current N of transistor Tr,: Number of turns N of winding T4-T5! :@Number of turns of wire T6-T7 ■r: If the exciting current β of the transformer T converted to the winding T6-T7 is N, /N, and the iron core is not saturated, the exciting current 1F is small, and the load current I flows almost equally into Is and Ic. Since the voltage across the winding is opposite to that in FIG. 6, the magnetic flux moves from point 0 to point A in FIG. This movement eventually saturates the iron core. That is, the operating point is A
It becomes a point. As a result, the excitation current 1f increases and
is equal to

At this point, no current is transmitted to the winding Tl-T3, and the transistor Tr is turned off. After this turning off, all current flows through the contact S1, and the magnetic flux becomes a negative saturated magnetic flux.

When opening the contact S1, the contact S1 first begins to open, the voltage drop increases, and a charging current flows through the capacitor C.

This triggers the positive feedback circuit to form the operating circuit of FIG. In this state, transistor Tr is turned on and bypasses load current I. The voltage V is kept at a low voltage until the contact Sl is completely opened, and no arc discharge occurs at the contact Sl. During this time, the magnetic flux of the transformer T moves from point A to point B in FIG. When the contact Sl is sufficiently opened and the contact S2 is closed, the transistor Tr is turned off, the capacitor C is charged, the voltage ■ becomes the arrester voltage, and the load current I decreases to zero. The magnetic flux of the transformer T moves from point B to point B' in FIG. 8 and stops.

In this way, the transformer T in FIG.
Since the magnetic flux that has moved from point A in the figure to point 0 is reset to point A during the operation period in FIG. 7, the utilization rate of the iron core is good and the iron core can be made smaller.

(Effects of the Invention) As described above, according to the present invention, the transistor driving section is connected in parallel with the main contact, and the transistor is turned on by the charge/discharge current of the capacitor due to the voltage of the contact, or by the transformer that provides positive feedback to the transistor. In addition, an auxiliary contact, which forms a transfer contact together with the main contact, is connected between the base and emitter of the transistor to turn off the transistor, effectively preventing arc discharge that occurs at the contact. This makes it possible to extend the life of the contacts. Note that those using capacitor charging and discharging are suitable for relatively small current circuits, and those using a transformer are suitable for relatively large current circuits.

[Brief explanation of the drawing]

1 to 8 show each embodiment of the present invention, FIG. 1 is a circuit diagram of the first embodiment, FIG. 2 is a circuit diagram of the second embodiment, and FIG.
The figure is a circuit diagram for explaining the operation of the second embodiment, FIG. 4 is a circuit diagram for the third embodiment, FIG. 5 is a circuit diagram for the fourth embodiment, and FIGS. 6 and 7 are respectively for explaining the operation of the fourth embodiment. FIG. 8 is a graph of the relationship between magnetic flux and excitation current in Example 4. FIG. 9 is a circuit diagram of the conventional example, and FIG. 10 is a graph for explaining the operation of the conventional example. In each figure, the symbol Es is a DC power supply, L is a load, Sl is a main contact, S2 is an auxiliary contact, C is a capacitor, Tr is a transistor, and Z is an arrester.

Claims (5)

[Claims] (1) A main contact connected between a load and a power source, a semiconductor switch element connected in parallel with the main contact, and a circuit section for turning on and off the semiconductor switch element, the circuit section comprising: When opening the main contact, the increase in the voltage drop of the main contact drives the semiconductor switch element to conduct the load current, the main contact opens in a no-current state, and after the contact opening operation is completed, the semiconductor switch element A switch circuit characterized in that the occurrence of arc discharge accompanying the opening operation of a main contact is prevented by driving a switch element off. (2) The semiconductor switch element is composed of a transistor or an element having an equivalent function (hereinafter referred to as a transistor), and an auxiliary contact that is turned on alternately with the main contact is connected between the base and emitter of the transistor. 2. The switch circuit according to claim 1, wherein when the main contact is completely open, the auxiliary contact is closed to short-circuit between the base and emitter of the transistor to turn off the transistor. (3) The switch circuit according to claim 2, comprising a capacitor to which a main contact voltage is applied, and the charging current or discharging current of the capacitor is configured to be the base current of the transistor. (4) The positive feedback circuit is triggered by a circuit that positively feeds back the collector current of the transistor to its base side, and a resistor that leads the charging current or discharging current of the capacitor or the collector voltage to the base, and the transistor is activated. The switch circuit according to claim 3, which is turned on. (5) The positive feedback circuit is configured with a transformer, the main contact current is passed through one winding of the transformer, and the winding is configured so that the polarity of the magnetomotive force is opposite to the magnetomotive force due to the collector current. 5. The switch circuit according to claim 4, wherein the change in magnetic flux of the iron core of the transformer caused by the positive feedback is reset by the current of the main contact.