JPH01107619A - Relay contact fusion detection circuit - Google Patents

Abstract

PURPOSE:To detect relay contact fusion, by inputting a signal outputted from a relay to switch the load driven by an AC power source and a signal to drive the relay so that it may be on a low level when it is not driven into a charge- discharge circuit and by comparing its output with the reference voltage. CONSTITUTION:A relay contact state signal Sp is outputted by dividing the voltage across the contact 3a of a relay 3 to control a load 2 switchingly driven by an AC power source 1 with resistances R1 and R2. A relay drive control circuit 4 to output a relay drive signal Sc is composed of a comparator IC1, a pull-up resistance R4, bias resistances R5 and R6 and a driving transistor Tr. Both signals, the relay contact state signal Sp and relay drive control signal Sc, are inputted in the form of taking an OR theory with diodes D1 and D2 into a charge-discharge circuit 5, the output signal Sj of which is compared with the reference voltage Vref in a comparator IC2, and its result is outputted as a relay contact fusion signal Sd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a contact welding detection circuit for a relay that controls switching of a load driven by an AC power source.

[Conventional technology and its problems]

First, the function of the relay contact welding detection circuit will be explained. The relay contact is made (Make) even though the relay drive control circuit is not outputting a drive signal to the relay.
If a welding condition occurs, the load whose switching is controlled by the relay will continue to be energized, which may lead to a fatal situation depending on the type of load. Therefore, at the time of welding, a circuit is provided that performs a protective operation, such as stopping energization to the load, and a signal is generated to the circuit to notify that welding has occurred.

Next, the configuration of the conventional circuit will be explained based on FIG. 3. The voltage across the contact 3a of the relay 3 that controls the switching of the load 2 driven by the AC power source 1 is connected to a resistor R+,
A circuit that divides the voltage with Rz and rectifies it with a diode D1, an inverting comparator IC that compares and inverts the relay contact state signal S generated by the circuit with respect to the reference voltage V P @ tl, and when the relay 3 is driven A drive control circuit 4 that outputs a relay drive control signal Sc at a low level, an inverting comparator IC with the relay drive control signal Sc on the cathode side, and a diode connected so that the output of the inverting comparator IC is on the anode side. D, inverting comparator IC.

Discharging resistor R, charging resistor Ri connected to the output side of
, a charging/discharging circuit 5 consisting of a capacitor C, and a comparison circuit 6 consisting of a comparator ICI and a pull-up resistor R1 that compares the output signal SJ of the charging/discharging circuit 5 with a reference voltage Vrstt.
It is composed of.

Next, the operation of the conventional circuit will be explained. Relay contact status signal S is low level when relay contact 3a is closed;
At the time of break, the signal is a half-wave rectified waveform having the same frequency as the power supply voltage. Relay drive control signal Sc
is low level when relay 3 is driven, and high when not driven (
High) level.

Here, the relay drive control signal Sc and the relay contact state signal S
The output state of the relay contact welding detection signal S4 for the combination of , will be explained.

When the relay 3 is driven (the relay drive control signal Sc is at a low level), the inverting comparator output signals S and I are always at a low level regardless of the relay contact state signal S. The potential at that time is VL%, the potential of the output signal S of the charge/discharge circuit 5 is VJs
If the potential of the pull-up destination of the charging resistor R3 is VCC, then (2) is expressed by the following equation.

R.

Here, the charging resistor R1, so that VJ < V-rg,
Since the discharge resistor R8 and the reference voltage Vr@IN are set, the relay contact welding detection signal S4 becomes low level.

Relay contact status signal S when relay 3 is not driven (relay drive control signal S is high level) and relay contact 3a is broken (relay contact status signal S is a half-wave rectified waveform)
, and the reference voltage ■7. The relationship between □ is shown in Figure 4 (a), the inverting comparator output signal SN is shown in Figure 4 (b), and the relationship between the charging/discharging circuit output signal SJ and the reference voltage V rstz is shown in Figure 4 (C).
The relationship between the charging resistor R1 and the discharging resistor R1 in the charging/discharging circuit 5 shown in FIG. The charging/discharging circuit output signal SJ repeats charging and discharging at a potential lower than the reference voltage Vr+ert, so the relay contact welding detection signal S4 becomes a low level.

When relay 3 is not driven (relay drive control signal Sc is high level) and relay contact 3afJ'Make) (relay contact status signal S is low level), that is, when the relay contact is welded, the output of the inverting comparator ICs is open. The capacitor C is charged to a potential of Vcc via the charging resistor R8, and the output SJ of the charging/discharging circuit and the relay contact welding detection signal S4 both become high level. Based on these, the relay contact welding signal S4 becomes high level only when the relay contact is welded, and the welding state of the relay contact can be detected. However, the circuit configuration is complex and the number of parts is large, which increases the cost and requires mounting design. It is an object of the present invention to provide a relay contact welding detection circuit which has a simple circuit configuration, a small number of parts, a low cost, and an easy implementation design.

[Means for solving problems]

The present invention has been made to solve the above-mentioned problems, and includes a relay contact state signal output from a circuit that resistively divides the voltage across the contacts of a relay that controls switching of a load driven by an AC power source, and A relay drive control signal that is at a low level when not driven is input to a charging/discharging circuit through a diode, and a comparison circuit compares the signal output from the charging/discharging circuit with a preset reference voltage, This device is characterized by outputting a relay contact welding detection signal.

The present invention will be explained in detail below with reference to FIG.

The relay contact status signal S, is output by dividing the voltage across the contact 3a of the relay 3, which controls the switching of the load 2 driven by the AC power supply 1, using resistors R, Rt, and is low when the relay contact 3a is closed. At level and break, it becomes a sinusoidal waveform signal with the same frequency as the power supply voltage. The relay drive control circuit 4 that outputs the relay drive control signal Sc is composed of a comparator IC, a pull-up resistor R4, a bias resistor R%, and a Rh% drive transistor T. When driven, it is at a high level, and when not driven, it is at a low level. Both the relay contact state signal S and the relay drive control signal Sc are input to the charging/discharging circuit 5 in the form of OR logic by the diodes Dr and Dt. The charging/discharging circuit 5 is composed of a capacitor C to which a pull-up voltage Vcc is applied and a charging resistor R8, and the output signal S of the charging/discharging circuit 5 is a signal connected to the diodes D+ and Dt. The comparator IC in the next stage compares it with a reference voltage 1°■ and outputs the result as a relay contact welding detection signal S4.

Here, the output state of the relay contact welding detection signal S4 with respect to the combination of the relay drive control signal Sc and the relay contact state signal S will be explained.

When the relay 3 is driven (the relay drive control signal Sc is at a high level), the capacitor C is discharged along the path R4→D,→C, regardless of the relay contact status signal S. Therefore, both the charging/discharging circuit output signal S and the relay contact welding detection signal S4 are at a high level.

When relay 3 is not driven (relay drive control signal Sc is low level) and relay contact 3a is broken (relay contact status signal S is a sine waveform), capacitor C is connected to load 2→RI−
4D, discharging through the →C route and charging through the C→R1 route are repeated. Here, if the resistance of load 2 is RL, then RL
+RI (Due to the relationship of R3, the charging time constant is much larger than the discharging time constant, and the charging/discharging circuit output signal SJ holds a potential higher than the reference voltage V rat of the comparator ■C8. Therefore, the relay contact welding detection signal S4 also becomes high level.The states of the relay contact state signal S and the charging/discharging circuit output signal SJ at that time are shown in FIGS. 2(a) and (b), respectively.

When the relay 3 is not driven (the relay drive control signal Sc is low level) and the relay contact 3a is made (the relay contact status signal S is low level), that is, when the relay contact is welded,
The capacitor C is in a charging state on the C-4R8 path, and the charging/discharging circuit output signal S.

Both the relay contact welding detection signal S4 and the relay contact welding detection signal S4 become low level.

From these, only when relay contacts are welded, relay contact welding 1F (
The welded state of the relay contact can be detected because the signal t S a becomes low level.

[Effects of the Invention] As explained above, the present invention provides a relay contact state signal output from a circuit that resistively divides the voltage across the contacts of a relay that controls switching of a load driven by an AC power source, and The relay drive control signal, which sometimes becomes a low level, is input to the charging/discharging circuit through a diode, and the signal output from the charging/discharging circuit is compared with a preset reference voltage by a comparison circuit, and the relay contact is welded. Since it is characterized by outputting a detection signal, compared to conventional relay contact welding detection circuits, one comparator can be omitted, reducing the number of parts and reducing costs, as well as simplifying mounting design. This has significant industrial effects such as ease of use.

[Brief explanation of the drawing]

Figure 1 is a relay contact welding detection circuit diagram of the present invention, Figure 2 (
a) and (b) are diagrams respectively showing the relay contact status signal and charging/discharging circuit output signal when the relay is not driven and the relay contact is broken, Figure 3 is a conventional relay contact welding detection circuit diagram, and Figure 4 ( Figures 1, 2, and 3 are diagrams showing a relay contact state signal, an inverting comparator output signal, and a charging/discharging circuit output signal when the relay is not driven and the relay contact is broken, respectively. 1 - AC power supply, 2 ~Load, ゛3~Relay, 38~Relay one contact, 4~Relay one drive control circuit, 5~Charging/discharging circuit, 6~Comparison circuit, 7~Relay one contact welding detection circuit.

Claims (1)

[Claims] A circuit that resistively divides the voltage across the contacts of a relay that switches and controls a load driven by an AC power supply, and outputs a relay contact status signal, a relay drive control signal that is at a low level when the relay is not driven, and a diode. A relay contact welding detection circuit characterized in that the signal is input to a charging/discharging circuit through the charging/discharging circuit, the signal output from the charging/discharging circuit is compared with a preset reference voltage by a comparison circuit, and a relay contact welding detection signal is output.