Solid state relay

Abstract

To shorten a time from when a control signal is turned off to when a semiconductor switching element is actually turned off.SOLUTION: A photovoltaic coupler 10 receives a first control signal Vctl1 and outputs a second control signal Vctl2 generated in accordance with the first control signal Vctl1. A first semiconductor switching element Q1 includes a control terminal to which the second control signal Vctl2 is applied, and turns on and off in accordance with the second control signal Vctl2. A detection circuit 11 detects whether the voltage of the first control signal Vctl1 has dropped below a predetermined threshold. A discharge circuit 12 discharges the charge of the control terminal when the voltage of the first control signal Vctl1 has dropped below the threshold.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to solid state relays. [Background technology]

[0002] In order to overcome various drawbacks of mechanical relays, such as poor contact of contacts, chattering, operating noise, arcing, etc., solid-state relays consisting only of semiconductor elements have been proposed.

[0003] A solid-state relay includes a semiconductor switching element (e.g., a field-effect transistor) that is turned on and off in response to a control signal. A solid-state relay may include a photocoupler or a photovoltaic coupler to maintain electrical isolation between its primary and secondary circuits.

[0004] For example, Patent Document 1 discloses a switching device including a photovoltaic coupler. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-242157 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, in order to save power, it is required to reduce the on-resistance of semiconductor switching elements. In this case, since the gate capacitance of the semiconductor switching element is large, the gate-source voltage of the semiconductor switching element drops gradually after the control signal is turned off, and it takes time for the semiconductor switching element to actually be turned off after the control signal is turned off. In the case of a field effect transistor, if the gate-source voltage is not large enough, the on-resistance increases. Therefore, when a large current flows in the secondary circuit, the loss of the semiconductor switching element becomes large, and therefore it is outside the safe operating area of ​​the semiconductor switching element. In this case, there is a risk that the semiconductor switching element will be damaged when it is turned off. For this reason, it is required to shorten the time from when the control signal is turned off to when the semiconductor switching element is actually turned off.

[0007] An object of the present disclosure is to provide a solid state relay in which the time from when a control signal is turned off until a semiconductor switching element is actually turned off is shorter than in the past. [Means for solving the problem]

[0008] A solid state relay according to a first aspect of the present disclosure includes: a photovoltaic coupler that receives a first control signal and outputs a second control signal generated in accordance with the first control signal; a first semiconductor switching element having a control terminal to which the second control signal is applied and turned on and off in accordance with the second control signal; a detection circuit that detects whether a voltage of the first control signal has dropped below a predetermined threshold; and a discharge circuit that discharges the control terminal when the voltage of the first control signal falls below the threshold value.

[0009] According to this configuration, the time from when the control signal is turned off until the semiconductor switching element is actually turned off can be shortened compared to the conventional case.

[0010] According to a second aspect of the present disclosure, in the solid state relay according to the first aspect, the detection circuit includes a Zener diode and a second semiconductor switching element, The threshold value is set based on the sum of a breakdown voltage of the Zener diode and a threshold voltage of the second semiconductor switching element.

[0011] According to this configuration, it is possible to detect whether or not the voltage of the first control signal has dropped below a predetermined threshold value.

[0012] According to a third aspect of the present disclosure, there is provided a solid state relay according to the first aspect, the detection circuit includes a comparison circuit having an input terminal to which the first control signal is input and first and second output terminals; The comparison circuit includes: internally isolating the first and second output terminals when a voltage of the first control signal is greater than or equal to the threshold; When the voltage of the first control signal falls below the threshold, the first and second output terminals are shorted.

[0013] According to this configuration, it is possible to detect whether or not the voltage of the first control signal has dropped below a predetermined threshold value.

[0014] According to a fourth aspect of the present disclosure, in the solid state relay according to one of the first to third aspects, The detection circuit includes a first capacitor connected to provide energy to the discharge circuit when a voltage of the first control signal falls below the threshold.

[0015] According to this configuration, even if the voltage of the first control signal drops, a sufficiently large current can be supplied to the discharge circuit.

[0016] According to a solid state relay according to a fifth aspect of the present disclosure, in the solid state relay according to one of the first to fourth aspects, The discharge circuit includes a coupling element that electrically isolates the first semiconductor switching element from the detection circuit.

[0017] According to this configuration, the first semiconductor switching element can be electrically insulated from the detection circuit.

[0018] According to a sixth aspect of the present disclosure, there is provided a solid state relay according to the fifth aspect, The discharge circuit further comprises a second capacitor connected between the coupling element and the detection circuit.

[0019] According to this configuration, when the voltage of the first control signal falls below the threshold value, the charge at the control terminal can be instantly discharged. Effect of the Invention

[0020] According to one aspect of the present disclosure, it is possible to reduce the time from when a control signal is turned off until a semiconductor switching element is actually turned off, compared to the conventional method. [Brief description of the drawings]

[0021] [Figure 1] 1 is a circuit diagram showing a configuration of a solid state relay 1 according to an embodiment. [Diagram 2] 2 is a timing chart illustrating the operation of the solid state relay 1 of FIG. [Diagram 3] FIG. 2 is a circuit diagram showing a configuration of a solid state relay 2 according to a comparative example. [Figure 4] 4 is a timing chart illustrating an operation when the solid state relay 2 in FIG. 3 transitions from on to off. [Diagram 5] 2 is a timing chart illustrating an operation when the solid state relay 1 of FIG. 1 transitions from on to off. [Figure 6] FIG. 11 is a circuit diagram showing a configuration of a solid state relay 1A according to a modified example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment according to one aspect of the present disclosure will be described with reference to the drawings. In each drawing, the same reference numerals denote similar components.

[0023] [Configuration of the embodiment] 1 is a circuit diagram showing the configuration of a solid state relay 1 according to an embodiment. The solid state relay 1 includes a photovoltaic coupler 10, a semiconductor switching element Q1, resistors R1 and R2, a detection circuit 11, and a discharge circuit 12.

[0024] The solid state relay 1 has input terminals P1, P2 connected to a signal source of a control signal Vctl1, and output terminals P3, P4 connected to a DC load device.

[0025] The resistor R1 is connected between the input terminal P1 (or P2) and the photovoltaic coupler 10.

[0026] The photovoltaic coupler 10 receives a first control signal Vctl1 and outputs a second control signal Vctl2 generated in accordance with the first control signal Vctl1. The photovoltaic coupler 10 includes a light-emitting diode on the primary side and an array of multiple photodiodes on the secondary side. When the control signal Vctl1 is input to the primary side of the photovoltaic coupler 10, light generated by the light-emitting diode is incident on the photodiode array, which generates a predetermined voltage in response to the incident light, and this voltage becomes the control signal Vctl2. The voltage of the control signal Vctl2 has a magnitude large enough to drive a discrete MOSFET without an additional power supply.

[0027] In the example of Fig. 1, the semiconductor switching element Q1 is a field effect transistor. The semiconductor switching element Q1 has a gate (i.e., control terminal) g to which a control signal Vctl2 is applied, and a drain d and a source s connected to output terminals P3 and P4 of the solid-state relay 1, respectively. The semiconductor switching element Q1 turns on and off in accordance with the control signal Vctl2. The semiconductor switching element Q1 also has a parasitic capacitance Cgd between the gate and drain, and a parasitic capacitance Cgs between the gate and source.

[0028] The resistor R2 is connected between the gate g and source s of the semiconductor switching element Q1.

[0029] The detection circuit 11 detects whether the voltage of the control signal Vctl1 has dropped below a predetermined threshold value. The detection circuit 11 includes semiconductor switching elements Q11-Q12, resistors $11-R13, a diode D11, Zener diodes ZD11-ZD12, and a capacitor C11. In the example of FIG. 1, the semiconductor switching element Q11 is a field effect transistor, and the semiconductor switching element Q12 is a bipolar transistor. The resistor R11, the Zener diode ZD11, and the resistor R12 are connected in series between the input terminal P1 and a ground conductor. The node between the Zener diode ZD11 and the resistor R12 is connected to the gate of the semiconductor switching element Q11. The diode D11 and the resistor R13 are connected between the input terminal P1 and the drain of the semiconductor switching element Q11. The source of the semiconductor switching element Q11 is grounded. The drain of the semiconductor switching element Q11 is connected to the base of the semiconductor switching element Q12. The emitter of the semiconductor switching element Q12 is grounded, and the collector is connected to a discharge circuit. A Zener diode ZD12 and a capacitor C11 are connected between a node between the diode D11 and the resistor R13 and a ground conductor.

[0030] When the voltage of the control signal Vctl1 falls below the threshold, the discharge circuit 12 discharges the charge on the gate g of the semiconductor switching element Q1 (i.e., draws out the charge). The discharge circuit 12 includes a photocoupler 21, resistors R21-R22, and a capacitor C21. The primary side (light-emitting diode) of the photocoupler 21 is connected between a node between the diode D11 and the resistor R13 and the collector of the semiconductor switching element Q12. A parallel circuit of the resistor R21 and the capacitor C21 is connected in series to the light-emitting diode. The secondary side (phototransistor) of the photocoupler 21 is connected between the gate g of the semiconductor switching element Q1 and the output terminal P4. A resistor R22 is connected in series to the phototransistor.

[0031] [Operation of the embodiment] FIG. 2 is a timing chart for explaining the operation of the solid state relay 1 of FIG. 1. FIG. 2 shows the voltage of the control signal Vctl1, the base-emitter voltage Vbe(Q12) of the semiconductor switching element Q12, the collector current Ic(Q12) of the semiconductor switching element Q12, the gate-source voltage Vgs(Q1) of the semiconductor switching element Q1, and the drain current Id(Q1) of the semiconductor switching element Q1. When the control signal Vctl1 falls below the sum of the breakdown voltage of the Zener diode ZD11 and the threshold voltage of the second semiconductor switching element Q11, the semiconductor switching element Q11 is turned off. This generates a voltage between the base and emitter of the semiconductor switching element Q12, and the semiconductor switching element Q12 is turned on. As a result, a current flows through the light-emitting diode on the primary side of the photocoupler 21, causing it to emit light, which in turn turns on the phototransistor on the secondary side, discharging the charge at the gate g of the semiconductor switching element Q1.

[0032] 3 is a circuit diagram showing a configuration of a solid state relay 2 according to a comparative example. The solid state relay 2 has a configuration in which the detection circuit 11 and the discharge circuit 12 are removed from the solid state relay 1 in FIG.

[0033] Figure 4 is a timing chart that explains the operation of the solid-state relay 2 in Figure 3 when it transitions from on to off. According to Figure 4, even when the control signal Vctl1 transitions from on to off, it takes time for the gate-source voltage Vgs(Q1) of the semiconductor switching element Q1 to decrease due to the gate capacitance of the semiconductor switching element Q1 (see the thick dashed line). It takes td = about 1 millisecond from when the control signal Vctl1 is turned off until the semiconductor switching element Q1 is turned off.

[0034] In general, when a photovoltaic coupler passes a current through the primary side, it generates a voltage on the secondary side, but the current it supplies is very small, on the order of tens to hundreds of microamperes. Therefore, in the configuration of the comparative example, the resistor R2 cannot be made small. If the resistor R2 is made small, it becomes impossible to generate a sufficiently large voltage between the gate and source of the semiconductor switching element Q1. As a result, because the resistor R2 is large, the charge on the gate g of the semiconductor switching element Q1 cannot be discharged quickly.

[0035] Figure 5 is a timing chart that explains the operation of the solid-state relay 1 in Figure 1 when it transitions from on to off. Figure 5 shows that the gate-source voltage Vgs(Q1) of the semiconductor switching element Q1 drops quickly by discharging the charge on the gate g of the semiconductor switching element Q1 (see the thick dashed line). This allows the semiconductor switching element Q1 to be turned off immediately after the control signal Vctl1 is turned off.

[0036] 1, the energy stored in the capacitor C11 can be utilized when a current flows on the primary side of the photocoupler 21. By providing the capacitor C11, even if the voltage of the control signal Vctl1 drops, a sufficiently large current can flow on the primary side of the photocoupler 21. Since the diode D11 is provided between the capacitor C11 and the input terminal P1, the potential of the capacitor C11 does not drop immediately even if the voltage of the control signal Vctl1 drops.

[0037] The capacitor C21 functions as a speed-up capacitor, which can instantly discharge the charge on the gate g of the semiconductor switching element Q1 when the semiconductor switching element Q12 is turned on.

[0038] According to this embodiment, the time from when the control signal Vctl1 is turned off until the semiconductor switching element Q1 is actually turned off can be shortened compared to the conventional method. This makes it difficult for a large current to flow when the on-resistance of the semiconductor switching element Q1 is high, and makes it difficult for the semiconductor switching element to be damaged when it is turned off.

[0039] According to this embodiment, it is possible to prevent the semiconductor switching element Q1 from operating at a low voltage. By appropriately setting the parameters of the Zener diode ZD11, it is possible to easily adjust the voltage at which the semiconductor switching element Q1 is turned off.

[0040] According to this embodiment, the resistor R2 can be made larger than in the past, and the speed at which the semiconductor switching element Q1 is turned on can also be improved.

[0041] Generally, it takes a long time to lower the gate-source voltage due to the Miller effect of the capacitance between the gate and drain of a semiconductor switching element, etc. According to this embodiment, a significant effect is obtained even when the load device operates at a high voltage of, for example, about 400 V.

[0042] [Modifications of the embodiment] FIG. 6 is a circuit diagram showing a configuration of a solid state relay 1A according to a modified embodiment. The solid state relay 1A includes a detection circuit 11A instead of the detection circuit 11 of FIG. 1. The detection circuit 11A includes a comparison circuit 31, a Zener diode ZD31, a diode D31, resistors R31 to R34, and a capacitor C31. The resistor R31 and the Zener diode ZD31 are connected in series between the input terminal P1 and a ground conductor. A node between the resistor R31 and the Zener diode ZD31 is connected to an input terminal IN of the comparison circuit 31. A first output terminal OUT of the comparison circuit 31 is connected to the discharge circuit 12, and a second output terminal GND of the comparison circuit 31 is grounded. The terminals OUT and GND are connected to each other via a resistor R32. The diode D31 and resistors R33 to R34 are connected in series between the input terminal P1 and a ground conductor. The capacitor C31 is connected between a node between the resistors R33 to R34 and a ground conductor. The node between the resistors R33 and R34 is further connected to the discharge circuit 12.

[0043] The comparison circuit 31 may be, for example, an integrated circuit for resetting. A control signal Vctl1 is input to a terminal IN of the comparison circuit 31. When the voltage of the control signal Vctl1 is equal to or higher than a threshold value, the comparison circuit 31 internally insulates the terminals OUT and GND, and when the voltage of the control signal Vctl1 falls below the threshold value, the comparison circuit 31 shorts the terminals OUT and GND.

[0044] The Zener diode ZD31 is provided to protect the comparison circuit 31 from high voltages.

[0045] According to the configuration of FIG. 6, by using the comparison circuit 31, it is possible to compare the voltage of the control signal Vctl1 with the threshold value with higher accuracy than in the case of the solid state relay 1 of FIG.

[0046] [Other embodiments] Although the embodiment of the present disclosure has been described in detail above, the above description is merely an example of the present disclosure in every respect. It goes without saying that various improvements and modifications can be made without departing from the scope of the present disclosure. For example, the following modifications are possible. In the following, the same reference numerals are used for the same components as in the above embodiment, and the description of the same points as in the above embodiment is omitted as appropriate. The following modifications can be combined as appropriate.

[0047] The detection circuit 11 may include another semiconductor switching element, such as a MOSFET, instead of the semiconductor switching element Q12, which is a bipolar transistor.

[0048] Instead of the photocoupler 21, the discharge circuit 12 may include another coupling element that electrically insulates the semiconductor switching element Q1 from the detection circuit 11, such as a photoMOS relay or a transformer.

[0049] The solid-state relay 1 may include other semiconductor switching elements, such as a SiC element, a GaN element, or a thyristor, instead of the semiconductor switching element Q1 which is a field-effect transistor.

[0050] When the solid-state relay 1 is connected to an AC load device, it may include two semiconductor switching elements connected in series with each other instead of one semiconductor switching element Q1. In this case, the sources (or drains) of the two semiconductor switching elements are connected with each other, and the control signal Vctl2 is applied to the gates of the two semiconductor switching elements.

[0051] [Summary of the embodiment] An electrical device according to each aspect of the present disclosure may be expressed as follows.

[0052] According to one aspect of the present disclosure, a solid-state relay 1 includes a photovoltaic coupler 10, a first semiconductor switching element Q1, a detection circuit 11, and a discharge circuit 12. The photovoltaic coupler 10 receives a first control signal Vctl1 and outputs a second control signal Vctl2 generated in accordance with the first control signal Vctl1. The first semiconductor switching element Q1 has a control terminal to which the second control signal Vctl2 is applied, and is turned on and off in accordance with the second control signal Vctl2. The detection circuit 11 detects whether the voltage of the first control signal Vctl1 has dropped below a predetermined threshold. The discharge circuit 12 discharges the charge of the control terminal when the voltage of the first control signal Vctl1 has dropped below the threshold.

[0053] According to one aspect of the present disclosure, the detection circuit 11 includes a Zener diode ZD11 and a second semiconductor switching element Q11. The threshold value is set based on the sum of the breakdown voltage of the Zener diode ZD11 and the threshold voltage of the second semiconductor switching element Q11.

[0054] According to one aspect of the present disclosure, the detection circuit 11 includes a comparison circuit 31 having an input terminal to which a first control signal Vctl1 is input and first and second output terminals. The comparison circuit 31 internally isolates the first and second output terminals when the voltage of the first control signal Vctl1 is equal to or higher than a threshold, and shorts the first and second output terminals when the voltage of the first control signal Vctl1 falls below the threshold.

[0055] According to one aspect of the disclosure, the detection circuit 11 includes a first capacitor C11 coupled to provide energy to the discharge circuit 12 when the voltage of the first control signal Vctl1 falls below a threshold value.

[0056] According to one aspect of the present disclosure, the discharge circuit 12 includes a coupling element 21 that electrically isolates the first semiconductor switching element Q1 from the detection circuit 11.

[0057] According to one aspect of the present disclosure, the discharge circuit 12 further includes a second capacitor C21 connected between the coupling element 21 and the detection circuit 11. [Industrial Applicability]

[0058] The present disclosure is applicable to solid state relays. [Explanation of symbols]

[0059] 1,1A solid state relay 10 Photovoltaic Coupler 11,11A Detection circuit 12 Discharge circuit 21 Photocoupler 31 Comparison circuit C11, C21, C31 capacitors Cgd,Cgs Parasitic capacitance D11, D31 Diode Q1, Q11~Q12 Semiconductor switching elements R1~R2, $11~R13, R21~R22, R31~R34 Resistors ZD11~ZD12,ZD31 Zener diodes

Claims

1. a photovoltaic coupler that receives a first control signal and outputs a second control signal generated in accordance with the first control signal; a first semiconductor switching element having a control terminal to which the second control signal is applied and turned on and off in accordance with the second control signal; a detection circuit for detecting whether a voltage of the first control signal has dropped below a predetermined threshold; a discharge circuit that discharges the control terminal when the voltage of the first control signal falls below the threshold value. Solid state relay.

2. the detection circuit includes a Zener diode and a second semiconductor switching element; the threshold value is set based on a sum of a breakdown voltage of the Zener diode and a threshold voltage of the second semiconductor switching element.

2. The solid state relay according to claim 1.

3. the detection circuit includes a comparison circuit having an input terminal to which the first control signal is input and first and second output terminals; The comparison circuit includes: internally isolating the first and second output terminals when a voltage of the first control signal is greater than or equal to the threshold; when the voltage of the first control signal falls below the threshold, the first and second output terminals are shorted; 2. The solid state relay according to claim 1.

4. the detection circuit comprises a first capacitor connected to provide energy to the discharge circuit when a voltage of the first control signal falls below the threshold; 2. The solid state relay according to claim 1.

5. the discharge circuit includes a coupling element that electrically isolates the first semiconductor switching element from the detection circuit. A solid state relay according to any one of claims 1 to 4.

6. the discharge circuit further comprises a second capacitor connected between the coupling element and the detection circuit.

6. The solid state relay according to claim 5.

Images