electrical circuit

Abstract

The present application provides an electrical circuit having an intrinsically safe explosion-proof structure that can increase the capacitance of the circuit while suppressing the influence on the function of the circuit. The electrical circuit includes: a plurality of functional blocks (2-1 to 2-3, 3-1 to 3-6) that are circuits for realizing a prescribed function; Zener diodes (D1 to D8) that are provided in parallel with a circuit capacitance (Cs2, Cs4 to Cs6) among circuit capacitances (Cs1 to Cs10) connected to a power supply line or a signal line of each of the plurality of functional blocks (2-1 to 2-3, 3-1 to 3-6), the circuit capacitance (Cs2, Cs4 to Cs6) being connected to a power supply line on a boundary line that separates the entire electrical circuit into a voltage side higher than a Zener voltage and a voltage side below the Zener voltage or a signal line on the boundary line; and current limiting resistors (Rp1 to Rp4) that are inserted in series at a more upstream side than the Zener diodes (D1 to D8) of the power supply line on the boundary line or the signal line on the boundary line.

Description

Technical Field

[0001] This invention relates to an electrical circuit, and more particularly to an electrical circuit with an intrinsically safe explosion-proof structure. Background Technology

[0002] In intrinsically safe explosion-proof structures, in order to meet necessary conditions, the allowable capacitance value of the circuit is limited, as shown in equation (1).

[0003] The total capacitance value of Co≧Ceff (=Cs×α)…(1)

[0004] The permissible capacitance value Co is the permissible capacitance value relative to the voltage (e.g., 30V) required to meet the intrinsic safety explosion-proof requirements (hereinafter referred to as the 30V permissible capacitance value Co, etc.). The circuit capacitance value Cs is the actual capacitance value mounted on the circuit. The reduction rate α is the proportion of capacitance reduction caused by the current-limiting resistor (described later) (α < 1). The larger the resistance value, the smaller the reduction rate α. The effective capacitance value Ceff is the capacitance value of the circuit capacitance value Cs after reflecting the reduction rate α caused by the current-limiting resistor.

[0005] To ensure both circuit functionality and intrinsic safety (explosion protection), the following design is required: energy suppression using safety holding components, increasing the circuit capacitance Cs by limiting voltage or current. One method for suppressing voltage is using a Zener diode as a safety holding component (Patent Document 1). By flexibly utilizing the Zener diode, the voltage can be limited based on the Zener voltage, thus allowing for consideration of the application range based on the Zener voltage value. By reducing the voltage, the allowable capacitance Co increases, thereby increasing the circuit capacitance Cs.

[0006] Another method for suppressing current is to use a current-limiting resistor (hereinafter referred to as the limiting resistor) connected in series with the capacitor as a safety holding component to limit the discharge current (Patent Document 2). In this method, equation (2) can be applied, thereby reducing the effective capacitance value Ceff and increasing the circuit capacitance value Cs.

[0007] Ceff=Cs×α…(2)

[0008] However, the use of safety-maintaining components may lead to functional loss or an increase in circuit size. For example, Zener diodes generate leakage current. Therefore, increasing the number of Zener diodes increases the overall current consumption of the circuit, especially in the case of two-wire products, which can sometimes affect the output current. Furthermore, as is characteristic of Zener diodes, the smaller the difference between the operating voltage and the Zener voltage during normal operation, the greater the leakage current. Therefore, if the Zener voltage is brought closer to the operating voltage to increase the allowable capacitance value, the leakage current increases significantly, and the overall current consumption of the circuit also increases.

[0009] On the other hand, limiting resistors can also affect the function of filter circuits or the stability of power supply circuits. In particular, regarding the output capacitors of power supply circuits, large capacitance values ​​are sometimes required to counter noise or cope with load variations and reduce ripple. However, if limiting resistors are used, it will have an adverse effect on stability. Therefore, sometimes large limiting resistor values ​​cannot be used, and the effective capacitance value Ceff cannot be significantly reduced.

[0010] As a specific example of an existing circuit, assume Figure 4 The structure shown. In Figure 4 In this diagram, 1 is the external power supply and safety retainer for voltage Vsup; 2-1 to 2-3 and 3-1 to 3-6 are functional blocks that implement the specified functions. Functional blocks 3-1 to 3-6 of functional blocks 2-1 to 2-3 and 3-1 to 3-6 are circuits that implement functions such as sensing, calculation, control, and communication. Functional blocks 2-1 to 2-3 are power supply circuits that supply voltages +V1, +V2, and +V3 respectively. Due to the limitations of the safety retainer, the maximum voltage of the external power supply and safety retainer 1 is 30V, and the maximum current is 100mA. Figure 4 In this case, the circuit capacitance value is set as CsX (X = 1, 2, ..., 10).

[0011] exist Figure 4 In the structure, since there is no countermeasure based on safety retaining parts, in order to meet the necessary conditions for intrinsic safety and explosion protection, equation (3) needs to be satisfied. Examples of permissible capacitance values ​​Co relative to voltage are shown in Table 1.

[0012] Co≧Cs1+Cs2+Cs3+Cs4+Cs5+Cs6+Cs7+Cs8+Cs9

[0013] +Cs10…(3)

[0014] [Table 1]

[0015] Voltage [V] Permissible capacitance [μF] 5.0 100 5.1 88 5.2 79 5.3 71 5.4 65 5.5 58 5.6 54 5.7 50 5.8 46 5.9 43 6.0 40 6.5 25 6.6 22 6.7 19.6 6.8 17.9 6.9 16.8 7.0 15.7 7.1 14.6 7.2 13.5 7.3 12.7 7.4 11.9 7.5 11.1 29.5 0.071 29.6 0.070 29.7 0.069 29.8 0.068 29.9 0.067 30.0 0.066 30.2 0.065 30.4 0.064 30.6 0.0626 30.8 0.0616 31.0 0.0605

[0016] Since the allowable capacitance value Co of 30V is very small (0.066μF = 66nF according to Table 1), there is a high possibility that the circuit capacitance value CsX required to ensure the function of functional blocks 3-1 to 3-6 is insufficient.

[0017] Therefore, the structure for taking countermeasures using a Zener diode with a safety retention component is shown below. Figure 5 Since Zener diodes D1 to D8 can be used to limit the voltage based on the Zener voltage Vza, the design can satisfy all of equations (4) and (5).

[0018] 30V allowable capacitance value Co≧Cs1+Cs3…(4)

[0019] Vza allowable capacitance value Co≧Cs1+Cs2+Cs3+Cs4+Cs5+Cs6+Cs7

[0020] +Cs8+Cs9+Cs10…(5)

[0021] Compared to the case where no countermeasures are taken, the Zener voltage Vza is less than 30V, so the allowable capacitance value Co can be increased, which can increase the circuit capacitance value CsX relative to the Zener voltage Vza. However, if leakage current is considered, the circuit capacitance value CsX required to ensure functionality may sometimes be insufficient due to the limitation that the number of Zener diodes cannot be increased or that the Zener voltage Vza needs to be higher than the circuit's operating voltage.

[0022] Next, the structure for taking countermeasures using a limiting resistor relative to the capacitor will be shown. Figure 6 In the middle. By adding limiting resistors R1, R2, R8, and R10, the reduction rates αr1, αr2, αr8, and αr10 can be considered for capacitors Cs1, Cs2, Cs8, and Cs10 respectively, so the design is to satisfy all of equations (6) and (7).

[0023] The allowable capacitance value for 30V is Co≧Cs1·αr1+Cs3…(6)

[0024] Vza allowable capacitance value Co≧Cs1·αr1+Cs2·αr2+Cs3+Cs4+Cs5

[0025] +Cs6+Cs7+Cs8·αr8+Cs9+Cs10·αr10…(7)

[0026] That is, by reducing the effective capacitance value Ceff of a portion of the capacitor through a limiting resistor, the circuit capacitance value CsX can be increased. However, considering the loss of circuit function, it is difficult to insert a limiting resistor in series with the output capacitor of the filter section or power supply circuit. Therefore, sometimes the circuit capacitance value CsX required to ensure function is insufficient.

[0027] As mentioned above, in existing methods, the required circuit capacitance value CsX may become insufficient, thus requiring further improvement. Specifically, a method that can increase the circuit capacitance value CsX is desired. In other words, a method that, while providing the same circuit capacitance value CsX, can suppress the impact on circuit function and reduce the effective capacitance value Ceff is desired.

[0028] [Existing technical documents]

[0029] [Patent Literature]

[0030] [Patent Document 1] International Publication No. WO2019 / 082578

[0031] [Patent Document 2] Japanese Patent Application Publication No. 07-095221 Summary of the Invention

[0032] [The problem the invention aims to solve]

[0033] The present invention was made to solve the aforementioned problem, and its purpose is to provide an electrical circuit with an intrinsically safe explosion-proof structure that can increase the circuit capacitance value while suppressing the influence on circuit function.

[0034] [Technical means to solve the problem]

[0035] The electrical circuit of the present invention is characterized by comprising: a plurality of functional blocks for implementing a predetermined function; a Zener diode, which is provided in parallel with the circuit capacitors connected in the respective power lines or signal lines of the plurality of functional blocks, namely, the circuit capacitors connected in parallel to the power lines or signal lines on the boundary line separating the electrical circuit as a whole into a voltage side higher than the Zener voltage and a voltage side lower than the Zener voltage; and a current limiting resistor, which is inserted in series on the power lines or signal lines on the boundary line upstream of the Zener diode.

[0036] In another example of the electrical circuit structure of the present invention, the boundary line is set such that the circuit capacitance values ​​are approximately equally separated on both sides.

[0037] In another example of the electrical circuit structure of the present invention, the current limiting resistor is inserted at a position that satisfies the specified specifications of the functional block directly upstream of the Zener diode.

[0038] Furthermore, in one structural example of the electrical circuit of the present invention, when the functional block directly upstream of the Zener diode is a power supply circuit, the value Rp of the current limiting resistor that is connected in series to the input power line of the power supply circuit satisfies Rp≦(V1-V2-Vdrop) / I when the input voltage of the power supply circuit is set to V1, the output voltage of the power supply circuit is set to V2, the difference between the input voltage and the output voltage required for the power supply circuit to output a specified voltage is set to Vdrop, and the current flowing in the current limiting resistor is set to I.

[0039] [The effects of the invention]

[0040] According to the present invention, by providing a Zener diode in parallel with the circuit capacitor connected to the power line or signal line on the boundary line separating the electrical circuit as a whole into a voltage side higher than the Zener voltage and a voltage side lower than the Zener voltage, and then inserting a current limiting resistor in series on the power line or signal line on the boundary line upstream of the Zener diode, an electrical circuit with an intrinsically safe explosion-proof structure that can increase the circuit capacitance value while suppressing the influence on the circuit function can be realized. Attached Figure Description

[0041] Figure 1 This is a diagram illustrating a system structure example when intrinsically safe explosion-proof measures are not taken.

[0042] Figure 2 This is a diagram illustrating an example of the system structure of an embodiment of the present invention.

[0043] Figure 3 This is a diagram illustrating the boundary lines of an embodiment of the present invention.

[0044] Figure 4 This is a diagram showing an example of an existing circuit that is an intrinsically safe explosion-proof structure.

[0045] Figure 5 This diagram illustrates an example of an existing circuit that utilizes Zener diodes for intrinsically safe explosion protection.

[0046] Figure 6 This diagram illustrates an example of an existing circuit that utilizes a Zener diode and a current-limiting resistor to address intrinsically safe explosion protection.

[0047] Explanation of icon numbers

[0048] 2-1~2-3, 3-1~3-6: Functional blocks

[0049] 100: External power supply

[0050] 101: On-site equipment

[0051] 102: Safety Retainer

[0052] D1~D8: Zener diodes

[0053] Cs1~Cs10: Circuit capacitors

[0054] Rp1~Rp4: Current limiting resistors Detailed Implementation

[0055] [Principles of the Invention]

[0056] This invention combines safety-maintaining components (Zener diode and limiting resistor) with a prescribed circuit structure. The proposed structure reduces the impact on circuit function by configuring the Zener diode and limiting resistor as a circuit structure that appropriately limits the energy of the capacitor. Compared to existing methods, it increases the circuit capacitance value CsX (while providing the same circuit capacitance value CsX, it suppresses the impact on circuit function and reduces the effective capacitance value Ceff).

[0057] Specifically, for the circuit as a whole, it is configured to use Zener diodes to interrupt the voltage, and limiting resistors are applied to all of the Zener diodes, which also serve as limiting resistors for the total capacitance of the high-voltage side (upstream side) or low-voltage side (downstream side) based on the interruption line, thereby increasing the circuit capacitance.

[0058] [Example]

[0059] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The system structure without intrinsically safe explosion-proof measures is illustrated below. Figure 1 The system structure of this embodiment, which incorporates intrinsically safe explosion-proof measures, is illustrated in [the following text]. Figure 2 In. Figure 1 , Figure 2 In the diagram, 100 is the external power supply, 101 is the field machine (electrical circuit) including multiple functional blocks 2-1 to 2-3 and 3-1 to 3-6 as circuits to perform the specified functions, 102 is a safety holder that limits the supply of voltage and current, for example, exceeding 30V and 100mA, to the field machine 101, and R100 is the load resistor.

[0060] Functional blocks 3-1 to 3-6, and functional blocks 2-1 to 2-3 and 3-1 to 3-6 respectively, are circuits that implement functions such as sensing, calculation, control, and communication. Functional blocks 2-1 to 2-3 are power supply circuits that supply power voltage to functional blocks 3-2 to 3-6. A circuit capacitor Cs1 is inserted between the power line and ground of the field machine 101 connected from the external power supply 100 via the safety retainer 102. A circuit capacitor Cs2 is inserted between the power line or signal line and ground of functional block 3-1.

[0061] Functional block 2-1, serving as the power supply circuit, generates voltage V1 (Vsup > V1) based on the voltage Vsup supplied from the external power supply 100. A circuit capacitor Cs3 is inserted between the output voltage V1 line and the ground line of functional block 2-1. Functional block 2-2, serving as the power supply circuit, generates voltage V2 (V1 > V2) based on the voltage V1 supplied from functional block 2-1. A circuit capacitor Cs4 is inserted between the output voltage V2 line and the ground line of functional block 2-2. Functional block 2-3, serving as the power supply circuit, generates voltage V3 (V1 > V3) based on the voltage V1 supplied from functional block 2-1. A circuit capacitor Cs5 is inserted between the output voltage V3 line and the ground line of functional block 2-3.

[0062] A circuit capacitor Cs6 is inserted between the power line or signal line and the ground line in functional block 3-2. Circuit capacitors Cs7 to Cs10 are inserted between the power line or signal line and the ground line in functional blocks 3-3 to 3-6 respectively. D1 to D8 are Zener diodes, and Rp1 to Rp4 are current-limiting resistors. The following is a detailed description of this embodiment.

[0063] (a) For the overall circuit of field machine 101, a boundary line is defined that can be separated into a voltage side (upstream side) with a voltage side (downstream side) with a voltage higher than the Zener voltage of the Zener diode, and the Zener diode is configured in parallel with the circuit capacitor located at the boundary line.

[0064] In this embodiment, the Zener diodes are configured such that their circuit capacitance values ​​are approximately equally spaced on both sides of the boundary line, maximizing their effectiveness. For example, in Figure 2 In the example case, the circuit capacitance value CsX is 10 times that of Cs1 to Cs10. If we consider the tendency for the value of Cs3 to increase with larger load currents, then... Figure 3 As shown, a boundary line 200 is set to separate circuit capacitors Cs1 and Cs3 from other circuit capacitors Cs2, Cs4 to Cs10. Figure 3 In the example, the Zener diode's Zener voltage is set to, for example, 5.8V, the output voltage V1 of functional block 2-1 is set to 7V, the output voltage V2 of functional block 2-2 is set to 4V, the output voltage V3 of functional block 2-3 is set to 3.3V, and functional blocks 3-1 and 3-2 are set to operate at voltages below 3V. Furthermore, in Figure 3 In subsequent diagrams, the external power supply 100 and the safety retainer 102 will be combined into one, and... Figure 5 , Figure 6 Similarly, it is recorded as external power supply and safety retainer 1.

[0065] By setting the boundary line 200, such as Figure 3As shown, Zener diodes D1 and D2 are connected in parallel with the circuit capacitor Cs2 of the power line or signal line connected to the boundary line 200 of functional block 3-1. Zener diodes D5 and D6 are connected in parallel with the circuit capacitor Cs4 of the power line connected to the boundary line 200 of functional block 2-2. Zener diodes D7 and D8 are connected in parallel with the circuit capacitor Cs5 of the power line connected to the boundary line 200 of functional block 2-3. Furthermore, Zener diodes D3 and D4 are connected in parallel with the circuit capacitor Cs6 of the power line or signal line connected to the boundary line 200 of functional block 3-2.

[0066] (b) Next, configure limiting resistors for all installed Zener diodes. Ideally, this should be configured to meet the specified power supply specifications of the functional block located directly upstream (in front of) the Zener diode (so that the voltage drop across the limiting resistor has no effect on the function of the functional block), and a large resistor value should be used.

[0067] exist Figure 2 In the example, for the power or signal lines of functional block 3-1, a limiting resistor Rp1 is inserted in series upstream of Zener diodes D1 and D2. The value of the limiting resistor Rp1 only needs to be set to a value that has no effect on the function of functional block 3-1.

[0068] Additionally, a limiting resistor Rp2 is connected in series with the input power line directly upstream of functional block 2-2. Since functional block 2-2 is a power supply circuit, the limiting resistor Rp2 is inserted in a way that always satisfies the value Rp2 ≦ (V1 - V2 - Vdrop2) / I2. V1 is the input voltage of functional block 2-2 (the output voltage of functional block 2-1), V2 is the output voltage of functional block 2-2, Vdrop2 is the difference between the voltage V1 and the voltage V2 required for functional block 2-2 to output the specified voltage V2, and I2 is the current flowing through the limiting resistor Rp2.

[0069] Additionally, a limiting resistor Rp3 is connected in series with the input power line directly upstream of functional block 2-3. Since functional block 2-3 is a power supply circuit, the limiting resistor Rp3 is inserted to always satisfy the value Rp3 ≦ (V1 - V3 - Vdrop3) / I3. V3 is the output voltage of functional block 2-3, Vdrop3 is the difference between the voltage V1 and the voltage V3 required for functional block 2-3 to output the specified voltage V3, and I3 is the current flowing in the limiting resistor Rp3.

[0070] Additionally, for the power or signal lines of functional block 3-2, a limiting resistor Rp4 is inserted in series upstream of Zener diodes D3 and D4. The value of the limiting resistor Rp4 should be set to a value that has no effect on the function of functional block 3-2.

[0071] The effects of this embodiment will now be explained. First, the combined resistance of the configured limiting resistors Rp1 to Rp4 is calculated. When the ignition source is upstream of the boundary line, this combined resistance limits the total capacitance on the downstream side; when the ignition source is downstream of the boundary line, it limits the total capacitance on the upstream side. Therefore, when the ignition source is upstream of the boundary line, the reduction rate of the combined resistance can be applied to the total capacitance value on the downstream side; when the ignition source is downstream of the boundary line, the reduction rate of the combined resistance can be applied to the total capacitance value on the upstream side. For both the upstream and downstream cases where the ignition source is upstream of the boundary line, if the allowable capacitance value Co ≥ the effective capacitance value Ceff, then the necessary conditions for intrinsically safe explosion-proof are met.

[0072] For example, in this embodiment, when the combined resistance of limiting resistors Rp1 to Rp4 is large, the effect of limiting resistors Rp1 to Rp4 on the capacitor can be greatly enhanced as described below, and the circuit capacitance value CsX can be significantly increased.

[0073] 30V allowable capacitance value Co≧Cs1+Cs3…(8)

[0074] Vza allowable capacitance value Co≧Cs1+Cs3+(Cs2+Cs4+Cs5+Cs6)

[0075] +Cs7+Cs8+Cs9+Cs10)×αtotal…(9)

[0076] Vza allowable capacitance value Co≧(Cs1+Cs3)×αtotal+(Cs2+Cs4)

[0077] +Cs5+Cs6+Cs7+Cs8+Cs9+Cs10)…(10)

[0078] As mentioned above, the 30V allowable capacitance value Co is the allowable capacitance value for 30V, and the Vza allowable capacitance value Co is the allowable capacitance value for the Zener voltage Vza. Equation (9) is for the case where the ignition source is located upstream of the boundary line, and Equation (10) is for the case where the ignition source is located downstream of the boundary line. αtotal is the reduction rate corresponding to the combined resistance of the limiting resistors Rp1 to Rp4.

[0079] In this embodiment, using specific numerical values, we will compare the effective capacitance value Ceff with existing circuits when providing the same circuit capacitance value CsX. A lower effective capacitance value Ceff allows for a greater increase in the circuit capacitance value CsX, which is an advantage.

[0080] Here, the circuit capacitance values ​​are set as follows: Cs1 is 30nF, Cs2 is 1μF, Cs3 is 10μF, Cs4 is 5μF, Cs5 is 5μF, Cs6 is 1μF, Cs7 is 300nF, Cs8 is 300nF, Cs9 is 300nF, and Cs10 is 300nF. Additionally, the following values ​​are set: Figure 6 In the existing circuit shown, the limiting resistor R1 is set to 10Ω, R2 to 20Ω, R8 to 33Ω, and R10 to 33Ω. In this embodiment, the limiting resistors Rp1 to Rp4 are each set to 2.8kΩ. The combined resistance of limiting resistors Rp1 to Rp4 is Rp1 / / Rp2 / / Rp3 / / Rp4 = 700Ω.

[0081] Without safety retaining parts Figure 4 In the case of the structure, in order to meet the necessary conditions for intrinsic safety and explosion protection, it is necessary to satisfy equation (11).

[0082] 30V allowable capacitance value Co≧Cs1+Cs2+Cs3+Cs4+Cs5+Cs6+Cs7

[0083] +Cs8+Cs9+Cs10=23.23μF…(11)

[0084] Using Zener diodes to take countermeasures Figure 5 In the case of the structure, in order to meet the necessary conditions for intrinsic safety and explosion protection, equations (12) and (13) need to be satisfied.

[0085] The allowable capacitance value for 30V is Co≧Cs1+Cs3=10.03μF…(12)

[0086] Vza allowable capacitance value Co≧Cs1+Cs2+Cs3+Cs4+Cs5+Cs6+Cs7

[0087] +Cs8+Cs9+Cs10=23.23μF…(13)

[0088] Countermeasures were taken using Zener diodes and limiting resistors. Figure 6 In the case of the structure, in order to meet the necessary conditions for intrinsic safety and explosion protection, it is necessary to satisfy equations (14) and (15).

[0089] The allowable capacitance value for 30V is Co≧Cs1·αr1+Cs3=10.02μF…(14)

[0090] Vza allowable capacitance value Co≧Cs1·αr1+Cs2·αr2+Cs3+Cs4+Cs5

[0091] +Cs6+Cs7+Cs8·αr8+Cs9+Cs10·αr10

[0092] =22.49μF…(15)

[0093] Based on the resistance values, the reduction rate αr1 corresponding to resistor R1 is 0.74, the reduction rate αr2 corresponding to resistor R2 is 0.57, and the reduction rates αr8 and αr10 corresponding to resistors R8 and R10 are 0.49.

[0094] In this embodiment, in order to meet the necessary conditions for intrinsically safe explosion protection, equations (16) to (18) must be satisfied.

[0095] The allowable capacitance value for 30V is Co≧Cs1+Cs3=10.03μF…(16)

[0096] Vza allowable capacitance value Co≧Cs1+Cs3+(Cs2+Cs4+Cs5+Cs6)

[0097] +Cs7+Cs8+Cs9+Cs10)×αtotal=10.54μF

[0098] …(17)

[0099] Vza allowable capacitance value Co≧(Cs1+Cs3)×αtotal+(Cs2+Cs4)

[0100] +Cs5+Cs6+Cs7+Cs8+Cs9+Cs10)=13.59μF

[0101] …(18)

[0102] Based on the resistance value, the reduction rate αtotal corresponding to the combined resistance of limiting resistors Rp1 to Rp4 is 0.039. According to equations (17) and (18) of this embodiment, it can be seen that the effective capacitance value Ceff (the value on the right side of the equation) can be reduced and the circuit capacitance value CsX can be increased relative to any of equations (11), (13), and (15).

[0103] In this embodiment, an example of an electrical circuit is given using a field machine as an example, but it is not limited to this. This invention can be applied to any electrical circuit that requires intrinsic safety and explosion protection.

Claims

1. An electrical circuit, characterized in that, include: Multiple functional blocks constitute the circuitry for achieving the specified functions; A Zener diode, and circuit capacitors connected in parallel with the circuit capacitors of the power lines or signal lines of the respective power lines or signal lines of the plurality of functional blocks, namely, circuit capacitors connected in parallel with the power lines or signal lines on the boundary line separating the electrical circuit as a whole into a voltage side higher than the Zener voltage and a voltage side lower than the Zener voltage; and A current-limiting resistor is inserted in series on the power line or signal line on the boundary line, more upstream of the Zener diode.

2. The electrical circuit according to claim 1, characterized in that, The boundary line is set such that the circuit capacitance values ​​are approximately equally separated on both sides.

3. The electrical circuit according to claim 1, characterized in that, The current-limiting resistor is inserted at a position that meets the specified specifications of the functional block directly upstream of the Zener diode.

4. The electrical circuit according to claim 1, characterized in that, When the functional block directly upstream of the Zener diode is a power supply circuit, the value Rp of the current limiting resistor, which is connected in series with the input power line of the power supply circuit, satisfies the following conditions: Rp≦(V1-V2-Vdrop) / I when the input voltage of the power supply circuit is set to V1, the output voltage of the power supply circuit is set to V2, the difference between the input voltage and the output voltage required for the power supply circuit to output a specified voltage is set to Vdrop, and the current flowing in the current limiting resistor is set to I.

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