Dual boost cold start circuit and cold start circuit system

Abstract

The application discloses a double-BOOST cold starting circuit and a cold starting circuit system, which comprises a third isolation diode D3, a fourth isolation diode D4, a fifth isolation diode D5, a sixth isolation diode D6, a seventh isolation diode D7, an eighth isolation diode D8, a third capacitor C3, an electromagnetic relay RLY1 and a relay driving circuit for driving the electromagnetic relay RLY1. The double-BOOST cold starting circuit and the cold starting circuit system provided by the application realize multi-path power taking of an auxiliary power supply in the simplest way, ingeniously solve the battery cold starting function and effectively reduce the implementation cost.

Description

Technical Field

[0001] This invention relates to the field of uninterruptible power supply technology, and in particular to a dual-boost cold start circuit and cold start circuit system. Background Technology

[0002] Uninterruptible power supplies (UPS) can continuously supply power to loads during short power outages and have been widely used in various fields.

[0003] To ensure power reliability, uninterruptible power supply (UPS) systems require multiple power supply modes for auxiliary power, including AC input, bypass input, battery, and DC bus. The DC bus voltage is stable and power factor corrected, effectively reducing harmonic interference when used as auxiliary power input. However, the battery voltage differs significantly from the DC bus voltage, leading to topology limitations that could cause the battery negative terminal and neutral (N) to share a ground. Furthermore, the UPS system needs to support battery cold starts; therefore, the battery must be connected directly or indirectly to the auxiliary power input. Currently, commercially available UPS systems cannot simultaneously support DC bus power supply when using battery power.

[0004] Therefore, an economical solution is needed to draw power from both the battery and the DC bus simultaneously.

[0005] The above information is provided as background information only to aid in understanding this disclosure and does not constitute an assertion or admission that any of the above content can be used as prior art relative to this disclosure. Summary of the Invention

[0006] This invention provides a dual-boost cold start circuit and cold start circuit system to overcome the shortcomings of the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In a first aspect, embodiments of the present invention provide a dual-boost cold start circuit, the circuit comprising a third isolation diode D3, a fourth isolation diode D4, a fifth isolation diode D5, a sixth isolation diode D6, a seventh isolation diode D7, an eighth isolation diode D8, a third capacitor C3, an electromagnetic relay RLY1, and a relay drive circuit for driving the electromagnetic relay RLY1; wherein,

[0009] The positive terminal of the third isolation diode D3 is electrically connected to the positive terminal of the DC bus, and the negative terminal of the third isolation diode D3 is electrically connected to the positive terminal of the third capacitor C3.

[0010] The positive terminal of the fifth isolation diode D5 is electrically connected to the positive terminal of the battery, and the negative terminal of the fifth isolation diode D5 is electrically connected to the positive terminal of the third capacitor C3.

[0011] The positive terminal of the seventh isolation diode D7 is electrically connected to the L line of the mains input, and the negative terminal of the seventh isolation diode D7 is electrically connected to the positive terminal of the third capacitor C3.

[0012] The positive terminal of the eighth isolation diode D8 is electrically connected to the L line of the bypass input, and the negative terminal of the eighth isolation diode D8 is electrically connected to the positive terminal of the third capacitor C3.

[0013] The positive terminal of the fourth isolation diode D4 is electrically connected to the negative terminal of the third capacitor C3, and the negative terminal of the fourth isolation diode D4 is electrically connected to the neutral (N) line of the mains input.

[0014] The positive terminal of the sixth isolation diode D6 is electrically connected to the negative terminal of the third capacitor C3, and the negative terminal of the sixth isolation diode D6 is connected to the negative terminal of the battery through the normally closed terminal of the electromagnetic relay RLY1.

[0015] Furthermore, in the dual-BOOST cold start circuit, the third capacitor C3 is the primary-side input electrolytic capacitor of the switching transformer T1 in the auxiliary power supply.

[0016] Furthermore, in the dual-BOOST cold start circuit, the auxiliary power supply also includes a third MOSFET switch Q3 and a primary-side current-limiting sampling resistor R1;

[0017] The positive terminal of the third capacitor C3 is connected to the positive terminal of the primary side of the switching transformer T1, and the negative terminal of the third capacitor C3 is grounded.

[0018] The drain of the third MOSFET switch Q3 is connected to the negative terminal of the primary side of the switching transformer T1, the source of the third MOSFET switch Q3 is connected in series with the primary side current-limiting sampling resistor R1 and then grounded, and the gate of the third MOSFET switch Q3 is left floating.

[0019] Furthermore, in the dual-boost cold start circuit, the third MOSFET switch Q3 is an N-channel MOSFET switch.

[0020] Furthermore, in the dual-boost cold start circuit, the relay drive circuit is controlled by a DSP.

[0021] Secondly, embodiments of the present invention provide a dual-BOOST cold start circuit system, the system comprising a first thyristor S1, a second thyristor S2, a third thyristor S3, a first PFC inductor L1, a second PFC inductor L2, a first IGBT single transistor Q1, a second IGBT single transistor Q2, a first power diode D1, a second power diode D2, a first capacitor C1, a second capacitor C2, and the dual-BOOST cold start circuit as described in the first aspect above;

[0022] The negative terminal of the first thyristor S1 is electrically connected to the positive terminal of the first power diode D1 through the first PFC inductor L1, and the positive terminal of the first thyristor S1 is electrically connected to the L line of the mains input.

[0023] The negative terminal of the first power diode D1 is electrically connected to the positive terminal of the DC bus;

[0024] The negative terminal of the second thyristor S2 is electrically connected to the L line of the mains input, and the positive terminal of the second thyristor S2 is electrically connected to the negative terminal of the second power diode D2 through the second PFC inductor L2.

[0025] The positive terminal of the second power diode D2 is electrically connected to the neutral (N) line of the AC power input through the second capacitor C2;

[0026] The first capacitor C1 is electrically connected between the positive terminal of the DC bus and the N line of the mains input;

[0027] The negative terminal of the third thyristor S3 is electrically connected between the negative terminal of the first thyristor S1 and the first PFC inductor L1, and the positive terminal of the third thyristor S3 is electrically connected to the positive terminal of the battery.

[0028] The negative electrode of the battery is electrically connected between the positive electrode of the second thyristor S2 and the second PFC inductor L2.

[0029] The drain of the first IGBT single transistor Q1 is electrically connected between the first PFC inductor L1 and the positive terminal of the first power diode D1, the source of the first IGBT single transistor Q1 is electrically connected to the N line of the mains input, and the gate of the first IGBT single transistor Q1 is floating.

[0030] The drain of the second IGBT Q2 is electrically connected to the neutral (N) line of the AC input, the source of the second IGBT Q2 is electrically connected between the second PFC inductor L2 and the negative terminal of the second power diode D2, and the gate of the second IGBT Q2 is left floating.

[0031] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0032] The present invention provides a dual-BOOST cold start circuit and cold start circuit system, which realizes multiple auxiliary power sources in the simplest way and cleverly solves the battery cold start function, effectively reducing the implementation cost. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a circuit diagram of a dual-BOOST cold start circuit provided in Embodiment 1 of the present invention;

[0035] Figure 2 This is a circuit diagram of the auxiliary power supply in Embodiment 1 of the present invention;

[0036] Figure 3 This is a circuit diagram of a dual-BOOST cold start circuit system provided in Embodiment 2 of the present invention;

[0037] Figure 4 This is a schematic diagram of the control timing and waveforms of the battery cold start process in Embodiment 2 of the present invention. Detailed Implementation

[0038] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0039] In the description of this invention, it should be understood that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intermediate component present simultaneously. When a component is considered to be "set" on another component, it can be directly set on the other component or there may be an intermediate component present simultaneously.

[0040] Furthermore, terms such as “long,” “short,” “inner,” and “outer” indicate orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings. They are used only for the purpose of describing the present invention and are not intended to indicate or imply that the device or component referred to must have this specific orientation or operate in a specific orientational configuration. Therefore, they should not be construed as limitations of the present invention.

[0041] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0042] Example 1

[0043] In view of the deficiencies in the existing technology, the applicant, based on years of practical experience and professional knowledge in the design and manufacturing of this field, and in conjunction with the application of theoretical principles, has actively conducted research and innovation in order to create a technology that can solve the deficiencies in the existing technology. After continuous research, design, and repeated prototype production and improvement, this invention with practical value has finally been created.

[0044] Please refer to Figure 1 This invention provides a dual-boost cold start circuit, comprising a third isolation diode D3, a fourth isolation diode D4, a fifth isolation diode D5, a sixth isolation diode D6, a seventh isolation diode D7, an eighth isolation diode D8, a third capacitor C3, an electromagnetic relay RLY1, and a relay drive circuit for driving the electromagnetic relay RLY1; wherein,

[0045] The positive terminal of the third isolation diode D3 is electrically connected to the positive terminal of the DC bus (DC bus BUS+), and the negative terminal of the third isolation diode D3 is electrically connected to the positive terminal of the third capacitor C3.

[0046] The positive terminal of the fifth isolation diode D5 is electrically connected to the positive terminal of the battery, and the negative terminal of the fifth isolation diode D5 is electrically connected to the positive terminal of the third capacitor C3.

[0047] The positive terminal of the seventh isolation diode D7 is electrically connected to the L line of the mains input, and the negative terminal of the seventh isolation diode D7 is electrically connected to the positive terminal of the third capacitor C3.

[0048] The positive terminal of the eighth isolation diode D8 is electrically connected to the L line of the bypass input, and the negative terminal of the eighth isolation diode D8 is electrically connected to the positive terminal of the third capacitor C3.

[0049] The positive terminal of the fourth isolation diode D4 is electrically connected to the negative terminal of the third capacitor C3, and the negative terminal of the fourth isolation diode D4 is electrically connected to the neutral (N) line of the mains input.

[0050] The positive terminal of the sixth isolation diode D6 is electrically connected to the negative terminal of the third capacitor C3, and the negative terminal of the sixth isolation diode D6 is connected to the negative terminal of the battery through the normally closed terminal of the electromagnetic relay RLY1.

[0051] It should be noted that the power supply for each circuit is isolated from each other through a corresponding isolation diode, and the relay drive circuit is controlled by a DSP.

[0052] In this embodiment, the third capacitor C3 is the primary input electrolytic capacitor of the switching transformer T1 in the auxiliary power supply.

[0053] The auxiliary power supply is a switching power supply, and the third capacitor C3 is located in the auxiliary power supply as follows: Figure 2 As shown. In Figure 2 In this context, the auxiliary power supply also includes a third MOSFET switch Q3 and a primary-side current-limiting sampling resistor R1;

[0054] The positive terminal of the third capacitor C3 is connected to the positive terminal of the primary side of the switching transformer T1, and the negative terminal of the third capacitor C3 is grounded.

[0055] The drain of the third MOSFET switch Q3 is connected to the negative terminal of the primary side of the switching transformer T1, the source of the third MOSFET switch Q3 is connected in series with the primary side current-limiting sampling resistor R1 and then grounded, and the gate of the third MOSFET switch Q3 is left floating.

[0056] In this embodiment, the third MOSFET switch Q3 is an N-channel MOSFET switch.

[0057] The present invention provides a dual-boost cold start circuit that achieves multiple auxiliary power sources in the simplest way and cleverly solves the battery cold start function, effectively reducing the implementation cost.

[0058] Example 2

[0059] Please refer to Figure 3 , Figure 3 This is a circuit diagram of a dual-BOOST cold start circuit system provided in Embodiment 2. The system includes a first thyristor S1, a second thyristor S2, a third thyristor S3, a first PFC inductor L1, a second PFC inductor L2, a first IGBT single transistor Q1, a second IGBT single transistor Q2, a first power diode D1, a second power diode D2, a first capacitor C1, a second capacitor C2, and the dual-BOOST cold start circuit described in Embodiment 1 above.

[0060] The negative terminal of the first thyristor S1 is electrically connected to the positive terminal of the first power diode D1 through the first PFC inductor L1, and the positive terminal of the first thyristor S1 is electrically connected to the L line of the mains input.

[0061] The negative terminal of the first power diode D1 is electrically connected to the positive terminal of the DC bus;

[0062] The negative terminal of the second thyristor S2 is electrically connected to the L line of the mains input, and the positive terminal of the second thyristor S2 is electrically connected to the negative terminal of the second power diode D2 through the second PFC inductor L2.

[0063] The positive terminal of the second power diode D2 is electrically connected to the neutral (N) line of the AC power input through the second capacitor C2;

[0064] The first capacitor C1 is electrically connected between the positive terminal of the DC bus and the N line of the mains input;

[0065] The negative terminal of the third thyristor S3 is electrically connected between the negative terminal of the first thyristor S1 and the first PFC inductor L1, and the positive terminal of the third thyristor S3 is electrically connected to the positive terminal of the battery.

[0066] The negative electrode of the battery is electrically connected between the positive electrode of the second thyristor S2 and the second PFC inductor L2.

[0067] The drain of the first IGBT single transistor Q1 is electrically connected between the first PFC inductor L1 and the positive terminal of the first power diode D1, the source of the first IGBT single transistor Q1 is electrically connected to the N line of the mains input, and the gate of the first IGBT single transistor Q1 is floating.

[0068] The drain of the second IGBT Q2 is electrically connected to the neutral (N) line of the AC input, the source of the second IGBT Q2 is electrically connected between the second PFC inductor L2 and the negative terminal of the second power diode D2, and the gate of the second IGBT Q2 is left floating.

[0069] It should be noted that, Figure 3 The first capacitor C1 and the second capacitor C2 are the positive and negative bus of the DC bus, respectively. The two bus terminals are from the same battery pack, the AC power is the input AC mains power, and the system is a dual-boost boost circuit.

[0070] When there is mains power input or bypass input, the system's DSP self-test is completed. After detecting that the mains power or bypass is normal, the electromagnetic relay RLY1 is directly activated to the normally open terminal through the relay drive circuit. At this time, the negative terminal of the battery is disconnected from the negative terminal of the third capacitor C3. Then the rectifier of the UPS system is soft-started, and the DC bus BUS+ gradually increases. When the voltage of the DC bus BUS+ is greater than the voltage after rectification of the mains power and bypass, the auxiliary power supply is powered by the DC bus BUS+ due to the isolation effect of the isolation diode. The relay drive circuit continues to work until the auxiliary power supply of the whole machine is de-energized.

[0071] In this embodiment, the battery cold start process is as follows: Figure 4As shown. When neither mains power nor bypass power is available, and a battery cold start is required, the user can activate the auxiliary power supply via a button. In this case, the auxiliary power supply is powered by the battery. After power-on, the rectifier begins to start.

[0072] In the first phase, T1-T2, only S3 is activated. BAT charges C1 and C2 through the path S3-L1-D1-C1-C2-D2-L2. The voltage of C1 and C2 is evenly distributed, each being half of the battery voltage. C3 is the battery voltage. Due to the isolation provided by D3 and D4, the auxiliary power supply is directly powered by the battery.

[0073] In the second stage, from T2 to T4, Q1 is controlled with a fixed duty cycle of 0.25, Q2 is normally closed, charging the positive bus (C1). When Q1 is chopping, the BOOST circuit has a strong capability, while the auxiliary power supply has a weak capability. The BOOST circuit will charge C3 through the S3-L1-D1-D3-C3-D4-Q2-L2 loop. The voltage increase of C3 due to the BOOST is approximately the voltage of the positive bus (C1). In other words, the voltage of C3 is approximately the sum of the battery voltage and the voltage of the positive bus.

[0074] In the third stage, T4-T5, the boost circuit operates in a closed-loop control, causing the bus voltage to rise rapidly until the target voltage value is reached. Without control at this point, electrolytic capacitor C3 would fail due to overvoltage caused by the rapid rise in positive bus voltage. Therefore, at time T3, the normally closed terminal of RLY1 is disconnected, ensuring that C3 only follows the positive bus voltage. Time T3 is controlled within the T2-T4 time interval, with T3 controlled by a delay from time T2. If the delay is too short, prematurely disconnecting RLY1 would result in insufficient power supply, preventing the second stage from completing. Considering compatibility with different battery cell counts, a 300ms delay is used to control the relay's on / off state. After T3, C3 is powered by the positive bus until the positive bus is de-energized.

[0075] The present invention provides a dual-BOOST cold start circuit system that achieves multiple auxiliary power sources in the simplest way and cleverly solves the battery cold start function, effectively reducing the implementation cost.

[0076] Thus far, the description of the above embodiments has been provided for illustrative and descriptive purposes. This is not intended to be exhaustive or limiting of the present disclosure. Individual elements or features of particular embodiments are generally not limited to those particular embodiments, but may be interchanged and used in selected embodiments where applicable, even if not specifically shown or described. In many respects, the same elements or features may also be varied. Such variations are not considered a departure from this disclosure, and all such modifications are intended to be included within the scope of this disclosure.

[0077] Example embodiments are provided so that this disclosure will become thorough and will fully convey the scope to those skilled in the art. Numerous details, such as examples of specific parts, apparatus, and methods, are set forth to provide a thorough understanding of embodiments of this disclosure. It will be apparent to those skilled in the art that the specific details are not required, and the example embodiments may be implemented in many different forms, neither of which should be construed as limiting the scope of this disclosure. In some example embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.

[0078] Technical terms are used herein for the purpose of describing specific exemplary embodiments only and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a” and “the” as used herein may also refer to the plural forms. The terms “comprising” and “having” are inclusive and therefore specify the presence of the stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or additional having of one or more other features, integrals, steps, operations, elements, components, and / or combinations thereof. Unless expressly indicated in order of execution, the method steps, processes, and operations described herein are not to be construed as necessarily requiring performance in the specific order discussed and shown. It should also be understood that additional or optional steps may be employed.

[0079] When an element or layer is described as "on," "joined with," "connected to," or "linked to" another element or layer, it may be directly on, joined to, connected to, or linked to another element or layer, or there may be an element or layer in between. Conversely, when an element or layer is described as "directly on," "directly joined with," "directly connected to," or "directly linked to" another element or layer, there may not be an element or layer in between. Other terms used to describe element relationships should be interpreted in a similar manner (e.g., "between" and "directly between," "adjacent" and "directly adjacent," etc.). The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or parts, these elements, components, regions, layers, and / or parts are not limited by these terms. These terms may be used only to distinguish one element, component, region, or part from another element, component, region, or part. Unless the context clearly indicates otherwise, the use of terms such as “first,” “second,” and other numerical terms herein does not imply sequence or order. Therefore, the terms “first element,” “component,” “region,” “layer,” or “part” discussed below may be used in the context of “second element,” “component,” “region,” “layer,” or “part” without departing from the teachings of this exemplary embodiment.

[0080] Spatial relative terms, such as “inside,” “outside,” “below,” “under,” “lower,” “above,” “upper,” etc., may be used herein for descriptive purposes to describe the relationship between one element or feature and one or more other elements or features as shown in the figure. Spatial relative terms may refer to different orientations of the device other than those depicted in the figure. For example, if the device in the figure is rotated, an element described as “below other elements or features” or “below the element or feature” will be oriented “above other elements or features.” Therefore, the example term “below” can encompass both upward and downward orientations. The device may be oriented in other ways (rotated 90 degrees or other orientations) and interpreted using the spatial relative descriptions herein.

Claims

1. A dual-BOOST cold start circuitry, characterized by, The system comprises a first thyristor S1, a second thyristor S2, a third thyristor S3, a first PFC inductor L1, a second PFC inductor L2, a first IGBT single tube Q1, a second IGBT single tube Q2, a first power diode D1, a second power diode D2, a first capacitor C1, a second capacitor C2, and a double BOOST cold start circuit; The negative electrode of the first thyristor S1 is electrically connected with the positive electrode of the first power diode D1 through the first PFC inductor L1, and the positive electrode of the first thyristor S1 is electrically connected with the L line of the power input; The negative electrode of the first power diode D1 is electrically connected with the positive electrode of the DC bus; The negative electrode of the second thyristor S2 is electrically connected with the L line of the power input, and the positive electrode of the second thyristor S2 is electrically connected with the negative electrode of the second power diode D2 through the second PFC inductor L2; The positive electrode of the second power diode D2 is electrically connected with the N line of the power input through the second capacitor C2; The first capacitor C1 is electrically connected between the positive electrode of the DC bus and the N line of the power input; The negative electrode of the third thyristor S3 is electrically connected between the negative electrode of the first thyristor S1 and the first PFC inductor L1, and the positive electrode of the third thyristor S3 is electrically connected with the positive electrode of the battery; The negative electrode of the battery is electrically connected between the positive electrode of the second thyristor S2 and the second PFC inductor L2; The drain electrode of the first IGBT single tube Q1 is electrically connected between the first PFC inductor L1 and the positive electrode of the first power diode D1, the source electrode of the first IGBT single tube Q1 is electrically connected with the N line of the power input, and the gate electrode of the first IGBT single tube Q1 is suspended; The drain electrode of the second IGBT single tube Q2 is electrically connected with the N line of the power input, the source electrode of the second IGBT single tube Q2 is electrically connected between the second PFC inductor L2 and the negative electrode of the second power diode D2, and the gate electrode of the second IGBT single tube Q2 is suspended; The double BOOST cold start circuit comprises a third isolation diode D3, a fourth isolation diode D4, a fifth isolation diode D5, a sixth isolation diode D6, a seventh isolation diode D7, an eighth isolation diode D8, a third capacitor C3, an electromagnetic relay RLY1, and a relay driving circuit for driving the electromagnetic relay RLY1; The positive electrode of the third isolation diode D3 is electrically connected with the positive electrode of the DC bus, and the negative electrode of the third isolation diode D3 is electrically connected with the positive electrode of the third capacitor C3; The positive electrode of the fifth isolation diode D5 is electrically connected with the positive electrode of the battery, and the negative electrode of the fifth isolation diode D5 is electrically connected with the positive electrode of the third capacitor C3; The positive electrode of the seventh isolation diode D7 is electrically connected with the L line of the power input, and the negative electrode of the seventh isolation diode D7 is electrically connected with the positive electrode of the third capacitor C3. The positive electrode of the eighth isolation diode D8 is electrically connected with the L line of the bypass input, and the negative electrode of the eighth isolation diode D8 is electrically connected with the positive electrode of the third capacitor C3; The positive electrode of the fourth isolation diode D4 is electrically connected with the negative electrode of the third capacitor C3, and the negative electrode of the fourth isolation diode D4 is electrically connected with the N line of the mains input; The positive electrode of the sixth isolation diode D6 is electrically connected with the negative electrode of the third capacitor C3, and the negative electrode of the sixth isolation diode D6 is connected with the negative electrode of the battery through the normally closed end of the electromagnetic relay RLY1; The third capacitor C3 is an electrolytic capacitor for inputting the primary side of the switching transformer T1 in the auxiliary power supply; The relay driving circuit is controlled by the DSP.

2. The dual-BOOST cold start circuitry of claim 1, wherein, The auxiliary power supply further comprises a third MOSFET switch Q3 and a primary side current limiting sampling resistor R1; The positive electrode of the third capacitor C3 is connected with the positive electrode of the primary side of the switching transformer T1, and the negative electrode of the third capacitor C3 is grounded. The drain electrode of the third MOSFET switch Q3 is connected with the negative electrode of the primary side of the switching transformer T1, the source electrode of the third MOSFET switch Q3 is connected with the primary side current limiting sampling resistor R1 in series and then grounded, and the gate electrode of the third MOSFET switch Q3 is suspended.

3. The dual-BOOST cold start circuitry of claim 2, wherein, The third MOSFET switch Q3 is an N-channel MOSFET switch.

Images