Current detection type co sensor detection jig circuit

Abstract

The utility model discloses a kind of current detection type CO sensor detection tooling circuit, comprising: power supply circuit, carbon monoxide detection circuit and control circuit;Power supply circuit is powered for carbon monoxide detection circuit and control circuit, carbon monoxide detection circuit output end is connected to control circuit first input end;Power supply circuit includes: first voltage-stabilizing module, second voltage-stabilizing module, control switch type current output module and current voltage conversion module, first voltage-stabilizing module input end is connected into direct-current power supply, first voltage-stabilizing module output end is connected to second voltage-stabilizing module input end.The current detection type CO sensor detection tooling circuit of this band solves the problem that the output current size when power supply module cannot test power supply module for carbon monoxide detection module in prior art.

Description

Technical Field

[0001] This utility model relates to the field of CO monitoring, specifically to a CO sensor detection tooling circuit with current detection. Background Technology

[0002] Chinese patent discloses a carbon monoxide alarm circuit with application number CN202323190620.X. This carbon monoxide alarm circuit includes: a control module, a carbon monoxide detection module, a power supply module, and an alarm module. The power supply module supplies power to the control module, the carbon monoxide detection module, and the alarm module. The first input / output terminal of the control module is connected to the carbon monoxide detection module, and the second input / output terminal of the control module is connected to the alarm module. The power supply module includes: an input voltage unit and a current limiting unit. The input terminal of the input voltage unit receives voltage, and the output terminal of the input voltage unit is connected to the input terminal of the current limiting unit. The current limiting unit restricts the input voltage unit to only receive a positive power supply. The first and second output terminals of the current limiting unit are the first and second output terminals of the power supply module.

[0003] Although this carbon monoxide alarm circuit can solve the problem of not being able to limit the input of opposite voltage in the existing technology, the following drawback still exists: the discharge test module can test the voltage at which the power supply module supplies power to the carbon monoxide detection module, but it cannot test the output current when the power supply module supplies power to the carbon monoxide detection module. Utility Model Content

[0004] This invention provides a current-detection CO sensor detection fixture circuit, which solves the problem in the prior art that the output current cannot be tested when the power supply module supplies power to the carbon monoxide detection module.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This utility model discloses a detection fixture circuit for a CO sensor with current detection, including: a power supply circuit, a carbon monoxide detection circuit, and a control circuit; the power supply circuit supplies power to the carbon monoxide detection circuit and the control circuit, and the output terminal of the carbon monoxide detection circuit is connected to the first input terminal of the control circuit; the power supply circuit includes: a first step-down voltage regulator module, a second step-down voltage regulator module, a control switch-type current output module, and a current-to-voltage conversion module; the input terminal of the first step-down voltage regulator module is connected to a DC power supply, the output terminal of the first step-down voltage regulator module is connected to the input terminal of the second step-down voltage regulator module, the output terminal of the second step-down voltage regulator module is connected to the input terminal of the control switch-type current output module, the control terminal of the control switch-type current output module is connected to the first output terminal of the control circuit, the voltage output terminal of the control switch-type current output module is connected to the second input terminal of the control circuit, the output terminal of the control switch-type current output module is connected to the input terminal of the current-to-voltage conversion module, the first output terminal of the current-to-voltage conversion module is connected to the third input terminal of the control circuit, the second output terminal of the current-to-voltage conversion module supplies power to the power supply terminal of the carbon monoxide detection circuit; the output terminal of the second step-down voltage regulator module supplies power to the control circuit.

[0007] Preferably, the current-to-voltage conversion module includes: a current-to-voltage conversion execution unit and a follower unit. The input terminal of the current-to-voltage conversion execution unit is the input terminal of the current-to-voltage conversion module, the first output terminal of the current-to-voltage conversion execution unit is the first output terminal of the current-to-voltage conversion module, and the second output terminal of the current-to-voltage conversion execution unit is the second output terminal of the current-to-voltage conversion module. The power supply terminal of the follower unit is connected to the output terminal of the second buck regulator module, and the output terminal of the follower unit is connected to the input terminal of the current-to-voltage conversion execution unit.

[0008] Preferably, the current-to-voltage conversion execution unit includes: resistors R7, R8, R12, and R13, capacitor C8, and current-to-voltage converter U3A. The first terminal of resistor R7 is the input terminal of the current-to-voltage conversion execution unit, the second terminal of resistor R7 is connected to the non-inverting input terminal of current-to-voltage converter U3A, the inverting input terminal of current-to-voltage converter U3A is connected to the first terminal of resistor R8, the second terminal of resistor R8 is the second output terminal of the current-to-voltage conversion execution unit, the inverting input terminal of current-to-voltage converter U3A is connected to the first terminal of resistor R13 and the first terminal of capacitor C8, the second terminals of capacitor C8 and resistor R13 are both connected to the output terminal of current-to-voltage converter U3A, the output terminal of current-to-voltage converter U3A is connected to the first terminal of resistor R12, and the second terminal of resistor R12 is the second output terminal of the current-to-voltage conversion execution unit.

[0009] Preferably, the follower unit includes: resistor R9, resistor R10, resistor R11, and follower U3B. The first end of resistor R10 is the power supply terminal of the follower unit, the second end of resistor R10 is grounded through resistor R11, the second end of resistor R10 is connected to the non-inverting input terminal of follower U3B, the inverting input terminal of follower U3B is connected to the output terminal of follower U3B, the output terminal of follower U3B is connected to the first end of resistor R9, the second end of resistor R9 is the output terminal of the follower unit, and the output terminal of the follower unit is connected to the second end of resistor R7.

[0010] Preferably, the control switch current output module includes: resistor R4, resistor R5, resistor R6, capacitor C7, fuse FU1, and PMOS transistor Q1. The first end of resistor R4 is the input terminal of the control switch current output module, and the first end of resistor R4 is connected to the drain of PMOS transistor Q1. The gate of PMOS transistor Q1 is connected to the second end of resistor R4 and the first end of resistor R5. The second end of resistor R5 is the control terminal of the control switch current output module. The source of PMOS transistor Q1 is connected to the first end of fuse FU1, the first end of resistor R6, and the positive terminal of capacitor C7. The second end of resistor R6 and the negative terminal of capacitor C7 are grounded.

[0011] Preferably, the first buck regulator module includes: capacitors C1, C2, C3, and C4; resistors R1, R2, and R3; inductor L1; and a buck regulator chip U1. The first terminal of capacitor C1 is connected to the first terminal of resistor R1 and the IN pin of buck regulator chip U1. The GND pin of buck regulator chip U1 and the second terminal of capacitor C1 are grounded. The BST pin of buck regulator chip U1 is connected to the first terminal of capacitor C3. The second terminal of capacitor C3 is connected to the SW pin of buck regulator chip U1 and the first terminal of inductor L1. The second terminal of inductor L1 is connected to the first terminal of resistor R2, the positive terminal of capacitor C2, and the positive terminal of capacitor C4. The second terminal of resistor R2 is connected to the negative terminal of capacitor C2, the first terminal of resistor R3, and the FB pin of buck regulator chip U1. The second terminal of resistor R3 is grounded, the negative terminal of capacitor C4 is grounded, and the second terminal of inductor L1 is the output terminal of the first buck regulator module.

[0012] Preferably, the second buck regulator module includes: capacitor C5, capacitor C6, and buck regulator chip U2. The first terminal of capacitor C5 is connected to the input terminal of buck regulator chip U2, which is the input terminal of the second buck regulator module. The output terminal of buck regulator chip U2 is connected to the first terminal of capacitor C6, which is the output terminal of the second buck regulator module. The second terminals of capacitors C5 and C6 are both grounded.

[0013] Preferably, the carbon monoxide detection circuit includes: a carbon monoxide sensor MQ, resistors R14, R15, R16, R17, R18, and R19, capacitors C8 and C9, and an NPN transistor Q2. The first terminal of the carbon monoxide sensor MQ is the power supply terminal of the carbon monoxide detection circuit. The first terminal of the carbon monoxide sensor MQ is connected to the second terminal of the carbon monoxide sensor MQ. The third terminal of the carbon monoxide sensor MQ is connected to the first terminal of resistor R14. The second terminal of resistor R14 is the output terminal of the carbon monoxide detection circuit. The second terminal of resistor R14 is connected to the positive terminal of capacitor C8, and the negative terminal of capacitor C8 is grounded. The first terminal of resistor R14 is connected to the first terminals of resistors R15 and R16. The second terminal of resistor R15 is connected to the emitter of NPN transistor Q2, and the emitter of NPN transistor Q2 is grounded. The second terminal of resistor R16 is connected to the collector of NPN transistor Q2. The base of NPN transistor Q2 is connected to the first terminal of resistor R17, and the second terminal of resistor R17 is connected to the second output terminal of the control circuit.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The first step-down voltage regulator module receives a 12V input and reduces it to 5V. The second step-down voltage regulator module reduces the 5V to 3.3V. The control module operates at 3.3V. The control switch current output module controls whether the current output from the second step-down voltage regulator module flows to the current-to-voltage conversion module. The control switch current output module operates under the control of the first output terminal of the control module. The current-to-voltage conversion module converts the current output from the control switch current output module into the sensor operating voltage, which is the voltage required for the carbon monoxide sensor to operate. This enables the carbon monoxide sensor to operate at its operating voltage. The first output terminal of the current-to-voltage conversion module is connected to the third input terminal of the control circuit, allowing the control module to know the precise value of the sensor operating voltage. This facilitates the determination of the relationship between the output value of the carbon monoxide detection circuit and the sensor operating voltage, ultimately determining whether the carbon monoxide sensor is functioning correctly and achieving the detection of carbon monoxide.

[0016] Other advantages, objectives and features of this invention will be partly apparent from the following description, and partly understood by those skilled in the art through study and practice of this invention. Attached Figure Description

[0017] Figure 1 This is the circuit diagram for the carbon monoxide detection circuit.

[0018] Figure 2 This is the circuit diagram for the first step-down voltage regulator module.

[0019] Figure 3 This is a circuit diagram of the second step-down voltage regulator module, the control switch-type current output module, and the current-to-voltage conversion module. Detailed Implementation

[0020] To make the technical means, creative features, achieved objectives and functions of this utility model clearer and easier to understand, the utility model will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0021] like Figures 1 to 3 As shown, this utility model discloses a detection fixture circuit for a CO sensor with current detection, including: a power supply circuit, a carbon monoxide detection circuit, and a control circuit; the power supply circuit supplies power to the carbon monoxide detection circuit and the control circuit, and the output terminal of the carbon monoxide detection circuit is connected to the first input terminal of the control circuit; the power supply circuit includes: a first step-down voltage regulator module, a second step-down voltage regulator module, a control switch-type current output module, and a current-to-voltage conversion module. The input terminal of the first step-down voltage regulator module is connected to a DC power supply, the output terminal of the first step-down voltage regulator module is connected to the input terminal of the second step-down voltage regulator module, the output terminal of the second step-down voltage regulator module is connected to the input terminal of the control switch-type current output module, the control terminal of the control switch-type current output module is connected to the first output terminal of the control circuit, the voltage output terminal of the control switch-type current output module is connected to the second input terminal of the control circuit, the output terminal of the control switch-type current output module is connected to the input terminal of the current-to-voltage conversion module, the first output terminal of the current-to-voltage conversion module is connected to the third input terminal of the control circuit, the second output terminal of the current-to-voltage conversion module supplies power to the power supply terminal of the carbon monoxide detection circuit; the output terminal of the second step-down voltage regulator module supplies power to the control circuit.

[0022] The control circuit includes a control chip with a minimum system. The control chip can be a PY32F002BF15P model, or other models of control chips.

[0023] In this application, the current-to-voltage conversion module includes a current-to-voltage conversion execution unit and a follower unit. The input terminal of the current-to-voltage conversion execution unit is the input terminal of the current-to-voltage conversion module, the first output terminal of the current-to-voltage conversion execution unit is the first output terminal of the current-to-voltage conversion module, and the second output terminal of the current-to-voltage conversion execution unit is the second output terminal of the current-to-voltage conversion module. The power supply terminal of the follower unit is connected to the output terminal of the second buck regulator module, and the output terminal of the follower unit is connected to the input terminal of the current-to-voltage conversion execution unit. The follower unit increases the zero-point reference voltage at the input terminal of the current-to-voltage conversion execution unit. The current-to-voltage conversion execution unit converts the current into the sensor operating voltage.

[0024] The current-to-voltage conversion execution unit includes: resistors R7, R8, R12, and R13, capacitor C8, and a current-to-voltage converter U3A. The first terminal of resistor R7 is the input terminal of the current-to-voltage conversion execution unit. The second terminal of resistor R7 is connected to the non-inverting input terminal of the current-to-voltage converter U3A. The inverting input terminal of the current-to-voltage converter U3A is connected to the first terminal of resistor R8. The second terminal of resistor R8 is the second output terminal of the current-to-voltage conversion execution unit. The inverting input terminal of the current-to-voltage converter U3A is connected to the first terminals of resistor R13 and capacitor C8. The second terminals of capacitor C8 and resistor R13 are both connected to the output terminals of the current-to-voltage converter U3A. The output terminal of the current-to-voltage converter U3A is connected to the first terminal of resistor R12. The second terminal of resistor R12 is the second output terminal of the current-to-voltage conversion execution unit. The current-to-voltage converter U3A mainly converts the current into the sensor's operating voltage.

[0025] The follower unit includes resistors R9, R10, and R11, as well as follower U3B. The first terminal of resistor R10 is the power supply terminal for the follower unit. The second terminal of resistor R10 is grounded through resistor R11. The second terminal of resistor R10 is connected to the non-inverting input terminal of follower U3B. The inverting input terminal of follower U3B is connected to the output terminal of follower U3B. The output terminal of follower U3B is connected to the first terminal of resistor R9. The second terminal of resistor R9 is the output terminal of the follower unit, which is connected to the second terminal of resistor R7. Follower U3B increases the zero-point reference voltage at the second terminal of resistor R7.

[0026] The control switch-type current output module includes: resistors R4, R5, and R6, capacitor C7, fuse FU1, and PMOS transistor Q1. The first terminal of resistor R4 is the input terminal of the control switch-type current output module and is connected to the drain of PMOS transistor Q1. The gate of PMOS transistor Q1 is connected to the second terminal of resistor R4 and the first terminal of resistor R5. The second terminal of resistor R5 is the control terminal of the control switch-type current output module. The source of PMOS transistor Q1 is connected to the first terminal of fuse FU1, the first terminal of resistor R6, and the positive terminal of capacitor C7. The second terminal of resistor R6 and the negative terminal of capacitor C7 are grounded. Fuse FU1 provides overvoltage protection, and PMOS transistor Q1 functions as a switch.

[0027] The first buck regulator module includes: capacitors C1, C2, C3, and C4; resistors R1, R2, and R3; inductor L1; and buck regulator chip U1. The first terminal of capacitor C1 is connected to the first terminal of resistor R1 and the IN pin of buck regulator chip U1. The GND pin of buck regulator chip U1 and the second terminal of capacitor C1 are grounded. The BST pin of buck regulator chip U1 is connected to the first terminal of capacitor C3. The second terminal of capacitor C3 is connected to the SW pin of buck regulator chip U1 and the first terminal of inductor L1. The second terminal of inductor L1 is connected to the first terminal of resistor R2, the positive terminal of capacitor C2, and the positive terminal of capacitor C4. The second terminal of resistor R2 is connected to the negative terminal of capacitor C2, the first terminal of resistor R3, and the FB pin of buck regulator chip U1. The second terminal of resistor R3 is grounded, the negative terminal of capacitor C4 is grounded, and the second terminal of inductor L1 is the output terminal of the first buck regulator module. The step-down regulator chip U1 converts 12V voltage to 5V voltage. Capacitors C1, C2, C3, and C4, resistors R1, R2, and R3, and inductor L1 all play a role in voltage regulation.

[0028] The second buck regulator module includes capacitors C5 and C6, and a buck regulator chip U2. The first terminal of capacitor C5 is connected to the input terminal of buck regulator chip U2, which is the input terminal of the second buck regulator module. The output terminal of buck regulator chip U2 is connected to the first terminal of capacitor C6, and the output terminal of buck regulator chip U2 is the output terminal of the second buck regulator module. The second terminals of both capacitors C5 and C6 are grounded. Buck regulator chip U2 reduces the 5V voltage to 3.3V, and capacitors C5 and C6 function as voltage regulators.

[0029] The carbon monoxide detection circuit includes: a carbon monoxide sensor MQ, resistors R14, R15, R16, R17, R18, and R19, capacitors C8 and C9, and an NPN transistor Q2. The first terminal of the carbon monoxide sensor MQ is the power supply terminal of the carbon monoxide detection circuit. The first terminal of the carbon monoxide sensor MQ is connected to the second terminal of the carbon monoxide sensor MQ. The third terminal of the carbon monoxide sensor MQ is connected to the first terminal of resistor R14. The second terminal of resistor R14 is the output terminal of the carbon monoxide detection circuit. The second terminal of resistor R14 is connected to the positive terminal of capacitor C8, and the negative terminal of capacitor C8 is grounded. The first terminal of resistor R14 is connected to the first terminals of resistors R15 and R16. The second terminal of resistor R15 is connected to the emitter of NPN transistor Q2, and the emitter of NPN transistor Q2 is grounded. The second terminal of resistor R16 is connected to the collector of NPN transistor Q2. The base of NPN transistor Q2 is connected to the first terminal of resistor R17. The second terminal of resistor R17 is connected to the second output terminal of the control circuit. The carbon monoxide sensor MQ changes its resistance based on the change in carbon monoxide concentration, therefore the voltage at the second terminal of resistor R14 will also change.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model and are not intended to limit it. Although this utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this utility model without departing from the spirit and scope of the technical solutions of this utility model, and all such modifications or substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A detection fixture circuit for a CO sensor with current detection, characterized in that, include: Power supply circuit, carbon monoxide detection circuit, and control circuit; The power supply circuit provides power to the carbon monoxide detection circuit and the control circuit. The output terminal of the carbon monoxide detection circuit is connected to the first input terminal of the control circuit. The power supply circuit includes: a first buck regulator module, a second buck regulator module, a control switch current output module, and a current-to-voltage conversion module. The input terminal of the first buck regulator module is connected to a DC power supply. The output terminal of the first buck regulator module is connected to the input terminal of the second buck regulator module. The output terminal of the second buck regulator module is connected to the input terminal of the control switch current output module. The control terminal of the control switch current output module is connected to the first output terminal of the control circuit. The voltage output terminal of the control switch current output module is connected to the second input terminal of the control circuit. The output terminal of the control switch current output module is connected to the input terminal of the current-to-voltage conversion module. The first output terminal of the current-to-voltage conversion module is connected to the third input terminal of the control circuit. The second output terminal of the current-to-voltage conversion module supplies power to the carbon monoxide detection circuit. The output of the second step-down voltage regulator module supplies power to the control circuit.

2. The detection fixture circuit for a CO sensor with current detection according to claim 1, characterized in that, The current-to-voltage conversion module includes a current-to-voltage conversion execution unit and a follower unit. The input terminal of the current-to-voltage conversion execution unit is the input terminal of the current-to-voltage conversion module, the first output terminal of the current-to-voltage conversion execution unit is the first output terminal of the current-to-voltage conversion module, and the second output terminal of the current-to-voltage conversion execution unit is the second output terminal of the current-to-voltage conversion module. The power supply terminal of the follower unit is connected to the output terminal of the second step-down regulator module, and the output terminal of the follower unit is connected to the input terminal of the current-to-voltage conversion execution unit.

3. The detection fixture circuit for a CO sensor with current detection according to claim 2, characterized in that, The current-to-voltage conversion execution unit includes: resistors R7, R8, R12, and R13, capacitor C8, and current-to-voltage converter U3A. The first terminal of resistor R7 is the input terminal of the current-to-voltage conversion execution unit. The second terminal of resistor R7 is connected to the non-inverting input terminal of current-to-voltage converter U3A. The inverting input terminal of current-to-voltage converter U3A is connected to the first terminal of resistor R8. The second terminal of resistor R8 is the second output terminal of the current-to-voltage conversion execution unit. The inverting input terminal of current-to-voltage converter U3A is connected to the first terminal of resistor R13 and the first terminal of capacitor C8. The second terminals of capacitor C8 and resistor R13 are both connected to the output terminal of current-to-voltage converter U3A. The output terminal of current-to-voltage converter U3A is connected to the first terminal of resistor R12. The second terminal of resistor R12 is the second output terminal of the current-to-voltage conversion execution unit.

4. The detection fixture circuit for a CO sensor with current detection according to claim 3, characterized in that, The follower unit includes: resistors R9, R10, and R11, and follower U3B. The first end of resistor R10 is the power supply terminal of the follower unit, the second end of resistor R10 is grounded through resistor R11, the second end of resistor R10 is connected to the non-inverting input terminal of follower U3B, the inverting input terminal of follower U3B is connected to the output terminal of follower U3B, the output terminal of follower U3B is connected to the first end of resistor R9, the second end of resistor R9 is the output terminal of the follower unit, and the output terminal of the follower unit is connected to the second end of resistor R7.

5. The detection fixture circuit for a CO sensor with current detection according to claim 4, characterized in that, The control switch current output module includes: resistor R4, resistor R5, resistor R6, capacitor C7, fuse FU1, and PMOS transistor Q1. The first end of resistor R4 is the input terminal of the control switch current output module. The first end of resistor R4 is connected to the drain of PMOS transistor Q1. The gate of PMOS transistor Q1 is connected to the second end of resistor R4 and the first end of resistor R5. The second end of resistor R5 is the control terminal of the control switch current output module. The source of PMOS transistor Q1 is connected to the first end of fuse FU1, the first end of resistor R6, and the positive terminal of capacitor C7. The second end of resistor R6 and the negative terminal of capacitor C7 are grounded.

6. The detection fixture circuit for a CO sensor with current detection according to claim 5, characterized in that, The first buck regulator module includes: capacitors C1, C2, C3, and C4; resistors R1, R2, and R3; inductor L1; and buck regulator chip U1. The first terminal of capacitor C1 is connected to the first terminal of resistor R1 and the IN pin of buck regulator chip U1. The GND pin of buck regulator chip U1 and the second terminal of capacitor C1 are grounded. The BST pin of buck regulator chip U1 is connected to the first terminal of capacitor C3. The second terminal of capacitor C3 is connected to the SW pin of buck regulator chip U1 and the first terminal of inductor L1. The second terminal of inductor L1 is connected to the first terminal of resistor R2, the positive terminal of capacitor C2, and the positive terminal of capacitor C4. The second terminal of resistor R2 is connected to the negative terminal of capacitor C2, the first terminal of resistor R3, and the FB pin of buck regulator chip U1. The second terminal of resistor R3 is grounded, the negative terminal of capacitor C4 is grounded, and the second terminal of inductor L1 is the output terminal of the first buck regulator module.

7. The detection fixture circuit for a CO sensor with current detection according to claim 6, characterized in that, The second buck regulator module includes: capacitor C5, capacitor C6, and buck regulator chip U2. The first terminal of capacitor C5 is connected to the input terminal of buck regulator chip U2, which is the input terminal of the second buck regulator module. The output terminal of buck regulator chip U2 is connected to the first terminal of capacitor C6, which is the output terminal of the second buck regulator module. The second terminals of capacitors C5 and C6 are both grounded.

8. The detection fixture circuit for a CO sensor with current detection according to any one of claims 1 to 7, characterized in that, The carbon monoxide detection circuit includes: a carbon monoxide sensor MQ, resistors R14, R15, R16, R17, R18, and R19, capacitors C8 and C9, and an NPN transistor Q2. The first terminal of the carbon monoxide sensor MQ is the power supply terminal of the carbon monoxide detection circuit. The first terminal of the carbon monoxide sensor MQ is connected to the second terminal of the carbon monoxide sensor MQ. The third terminal of the carbon monoxide sensor MQ is connected to the first terminal of resistor R14. The second terminal of resistor R14 is the output terminal of the carbon monoxide detection circuit. The second terminal of resistor R14 is connected to the positive terminal of capacitor C8, and the negative terminal of capacitor C8 is grounded. The first terminal of resistor R14 is connected to the first terminals of resistors R15 and R16. The second terminal of resistor R15 is connected to the emitter of NPN transistor Q2, and the emitter of NPN transistor Q2 is grounded. The second terminal of resistor R16 is connected to the collector of NPN transistor Q2. The base of NPN transistor Q2 is connected to the first terminal of resistor R17. The second terminal of resistor R17 is connected to the second output terminal of the control circuit.

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