A DC-AC modified sine wave inverter with output short circuit protection circuit

Abstract

The invention discloses a DC-AC modified wave inverter with an output short-circuit protection circuit, which comprises a boost unit, the boost unit is used to convert an input voltage; a rectifier unit, whose input end is connected to the output end of the boost unit; a full-bridge inverter unit, whose input end is connected to the output end of the rectifier unit, and the full-bridge inverter unit is used to invert the voltage output by the rectifier unit into an AC voltage; an MCU programming output control unit, whose input end is connected to the output end of the full-bridge inverter unit, and whose output end is connected to a switch tube in the full-bridge inverter unit, and also comprises: a short-circuit protection unit, whose input end is connected to the output end of the rectifier unit, and whose output end is connected to the full-bridge inverter unit; the short-circuit protection unit is used to drive its input end and output end to be turned on or off according to the load voltage change of the output end of the full-bridge inverter unit, so as to control the opening and closing of the switch tube in the full-bridge inverter unit, and has a simple structure and a fast response speed.

Description

Technical Field

[0001] The invention relates to a DC-AC modified wave inverter with an output short-circuit protection circuit. Background Art

[0002] A modified sine wave inverter is a device that converts direct current (DC) into alternating current (AC). Because it is cheaper than a sine wave, it is used in many practical applications. The circuit diagram of a commonly used modified sine wave inverter is shown in the attached figure. Figure 1 As shown, because the frequency of the correction wave is generally 50 / 60HZ, when the load at its output end is short-circuited, if the switch tube (MOSFET tube) of the inverter circuit cannot be turned off in time during the high-voltage period of the output square wave pulse, the MOSFET tube in the inverter circuit will be in a continuous high-current working state and is easily damaged; or when the inverter is started, the output end will output a large current, and the connected load (such as light bulbs, motors, induction cookers, etc.) has a very small resistance in the cold state. At this time, it is equivalent to a short circuit at the load end. If the protection threshold is not selected properly, it is also easy to damage the MOSFET tube in the inverter circuit. The general processing method is to control the closure of the corresponding MOSFET tube after making a judgment through the microprocessor chip (MCU), but it has the disadvantage of a long detection cycle causing a delay in judgment, which can easily cause the MOSFET tube to be damaged due to the energy carried exceeding the specification parameters. Summary of the invention

[0003] The purpose of the present invention is to address the deficiencies of existing modified sine wave inverters and to provide a DC-AC modified sine wave inverter with an output short-circuit protection circuit.

[0004] The present invention proposes a DC-AC modified wave inverter with an output short-circuit protection circuit, comprising: a boost unit, the boost unit is used to convert an input voltage; a rectifier unit, whose input end is connected to the output end of the boost unit; a full-bridge inverter unit, whose input end is connected to the output end of the rectifier unit, and the full-bridge inverter unit is used to invert the voltage output by the rectifier unit into an AC voltage; an MCU programming output control unit, whose input end is connected to the output end of the full-bridge inverter unit, and whose output end is connected to a switch tube in the full-bridge inverter unit, and is used to control the on and off of the switch tube in the full-bridge inverter unit; it is characterized in that it also includes: a short-circuit protection unit, whose input end is connected to the output end of the rectifier unit, and whose output end is connected to the full-bridge inverter unit; the short-circuit protection unit is used to drive its input end and output end to be turned on or off according to the load voltage change at the output end of the full-bridge inverter unit, thereby controlling the on and off of the switch tube in the full-bridge inverter unit.

[0005] Preferably, the short-circuit protection unit includes a voltage divider unit and a short-circuit switch unit, one end of the voltage divider unit is connected to the output end of the rectifier unit, and the other end is connected to the negative pole of the bus of the DC-AC modified wave inverter output short-circuit protection circuit, and the input end of the short-circuit switch unit is connected to the voltage divider unit.

[0006] Preferably, the voltage dividing unit comprises a resistor R85, a resistor R86, a resistor R87 and a resistor R29 connected in series in sequence, one end of the resistor R85 is connected to the output end of the rectifier unit, and one end of the resistor R29 is connected to the negative electrode of the bus.

[0007] Preferably, the short-circuit switch unit includes a resistor R14, a resistor R28, a transistor Q18, a resistor R89, a diode D14, a resistor R88, a transistor Q16, a resistor R83, a resistor R84, a diode D4, a transistor Q17 and a diode D12; one end of the resistor R14 is connected to a node between the resistor R87 and the resistor R29, and the other end thereof and one end of the resistor R28 are both connected to the base of the transistor Q18; the other end of the resistor R28 is connected to the cathode of the bus; the collector of the transistor Q18 is connected to a high potential through the resistor R89, and its emitter is connected to the cathode of the bus; the emitter of the transistor Q16 is connected to the cathode of the bus through the resistor R88 is connected to a high potential, and its collector is connected to the negative electrode of the bus; the anode of the diode D14 is connected to the node between the collector of the transistor Q18 and the resistor R89, and its cathode is connected to the collector of the transistor Q16 and to the base of the transistor Q17; the base of the transistor Q16 is connected to the collector of the transistor Q17, the cathode of the diode D4 and the cathode of the diode D12 through the resistor R83, and the anodes of the diode D4 and the diode D12 are respectively connected to the gates of the switching tubes on the half bridge in the full-bridge inverter unit; the base of the transistor Q17 is connected to the negative electrode of the bus through the resistor R84, and its emitter is connected to the negative electrode of the bus.

[0008] Preferably, the short-circuit switch unit also includes a capacitor C40 and a capacitor C38, one end of the capacitor C40 is connected to the base of the transistor Q18, and the other end is connected to the negative electrode of the bus; one end of the capacitor C38 is connected to the collector of the transistor Q16, and the other end is connected to the negative electrode of the bus.

[0009] The beneficial effects of the present invention include: by setting a short-circuit protection unit in the modified sine wave inverter, when a short circuit occurs at the load end of the full-bridge inverter unit or returns to normal, the short-circuit protection unit can quickly control the closing and opening of its own input and output ends according to the change of voltage, and then control the closing and opening of the switch tube in the full-bridge inverter unit connected thereto to finally achieve the purpose of protecting the modified sine wave inverter; and the structure is simple, the cost is low, and the response speed is fast. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a circuit principle block diagram of an existing modified sine wave inverter.

[0011] Figure 2 The invention discloses a circuit principle block diagram of a modified sine wave inverter.

[0012] Figure 3 yes Figure 2 Circuit diagram of the short-circuit protection unit in the modified sine wave inverter. DETAILED DESCRIPTION

[0013] The present invention will be further described in detail below in conjunction with specific implementations and with reference to the accompanying drawings. It should be emphasized that the following description is merely exemplary and is not intended to limit the scope of the present invention and its application.

[0014] This embodiment provides a DC-AC modified sine wave inverter with an output short-circuit protection circuit. Figure 2 and Figure 3 As shown, it includes: a boost unit for converting the input voltage; a rectifier unit, whose input end is connected to the output end of the boost unit, converting the AC power output by the boost unit into DC power; a full-bridge inverter unit, which converts the above DC power into high-frequency AC power by changing the switching cycle of the corresponding MOSFET tube in its bridge arm; an MCU programming output control unit, whose input end is connected to the output end of the full-bridge inverter unit, and whose output end is connected to control the switch tube in the full-bridge inverter unit, used to control the opening and closing of four MOSFET tubes in the full-bridge inverter unit and detect whether the input and output of the full-bridge inverter unit are normal; and also includes a short-circuit protection unit for timely shutting off the MOSFET tube when a short-circuit abnormality occurs in the load at the output end of the inverter. The input end of the short-circuit protection unit is connected to the output end of the rectifier unit, and the output end is connected to the full-bridge inverter unit; the short-circuit protection unit drives its input end and output end to be turned on or off according to the load voltage change at the output end of the full-bridge inverter unit, thereby controlling the opening and closing of the MOSFET tube in the full-bridge inverter unit.

[0015] Specifically, the short-circuit protection unit includes a voltage divider unit and a short-circuit switch unit, one end of the voltage divider unit is connected to the output end of the rectifier unit, the other end is connected to the negative pole of the bus of the DC-AC modified wave inverter output short-circuit protection circuit, and the input end of the short-circuit switch unit is connected to the voltage divider unit. The voltage divider unit is used to adjust the voltage at the input end of the short-circuit switch unit, and specifically, it includes a resistor R85, a resistor R86, a resistor R87 and a resistor R29 connected in series in sequence, one end of the resistor R85 is connected to the output end of the rectifier unit, and one end of the resistor R29 is connected to the negative pole of the bus.

[0016] Specifically, the short-circuit switch unit includes a resistor R14, a resistor R28, a transistor Q18, a resistor R89, a diode D14, a resistor R88, a transistor Q16, a resistor R83, a resistor R84, a diode D4, a transistor Q17 and a diode D12; one end of the resistor R14 is connected to a node between the resistor R87 and the resistor R29, and the other end thereof and one end of the resistor R28 are both connected to the base of the transistor Q18; the other end of the resistor R28 is connected to the negative electrode of the bus; the collector of the transistor Q18 is connected to a high potential through the resistor R89, and its emitter is connected to the negative electrode of the bus. The emitter of transistor Q16 is connected to a high potential through resistor R88, and its collector is connected to the negative electrode of the bus; the anode of diode D14 is connected to the node between the collector of transistor Q18 and resistor R89, and its cathode is connected to the collector of transistor Q16 and the base of transistor Q17; the base of transistor Q16 is connected to the collector of transistor Q17, the cathode of diode D4 and the cathode of diode D12 through resistor R83, and the anodes of diode D4 and diode D12 are respectively connected to the gates of MOSFET tubes on the half bridge in the full-bridge inverter unit (such as Figure 3 The base of transistor Q17 is connected to the negative pole of the bus through resistor R84, and its emitter is connected to the negative pole of the bus. Among them, diodes D14, D4 and diode D12 play a role in stabilizing the current flow and preventing the MOSFET tubes on the half bridge in the full-bridge inverter unit from malfunctioning.

[0017] Furthermore, in order to filter out high-frequency signals, the short-circuit switch unit also includes capacitor C40 and capacitor C38, one end of capacitor C40 is connected to the base of transistor Q18, and the other end is connected to the negative electrode of the bus; one end of capacitor C38 is connected to the collector of transistor Q16, and the other end is connected to the negative electrode of the bus.

[0018] The working principle of the modified sine wave inverter output short-circuit protection circuit of the present invention is as follows: when the load at the output end of the inverter is abnormally short-circuited, the potential of the voltage-dividing unit immediately becomes low, the potentials at both ends of the resistor R14 in the short-circuit switch unit become low, and the transistor Q18 stops working. At this time, the voltage-stabilized power supply (+5V) supplies power to the base of the transistor Q17 through the resistor R89 ​​and the diode D14, so that the transistor Q17 enters the conducting state, and then the base potential of the transistor Q16 is pulled down, and then turned on, maintaining the base high potential of the transistor Q17. After the transistors Q16 and Q17 are turned on, the gate potential of the MOSFET tube on the half bridge in the full-bridge inverter unit is pulled down, causing the MOSFET tube to stop working, so as to effectively protect the MOSFET tube when an abnormality occurs in the inverter circuit. When the short circuit at the output end of the inverter is released, the potential of the voltage divider unit immediately becomes high, and then the potential at both ends of the resistor R14 becomes high, and the transistor Q18 is turned on. The collector potential of the transistor Q18 immediately becomes low, and then the base potential of the transistor Q17 immediately becomes low and then does not conduct, and the base potential of the transistor Q16 becomes high and then does not conduct. After the transistors Q16 and Q17 are not conducting, the gate potential of the MOSFET tube on the half bridge in the full-bridge inverter unit becomes high and resumes the working state. At this time, the inverter is in a normal working state, and the on and off of the MOSFET tube in the full-bridge inverter unit continues to be controlled by the MCU.

[0019] The present invention sets a short-circuit protection unit in the inverter. When a large current occurs in the inverter circuit due to a short circuit at the load end, the short-circuit protection unit quickly turns off the MOSFET tube in the inverter circuit that is in the on state by turning on and off the corresponding triode according to the voltage change. When the current in the inverter circuit returns to a normal state, the short-circuit protection circuit adjusts the state of the triode according to the potential change to turn on the above-mentioned turned-off MOSFET tube, thereby protecting the inverter. The circuit can realize the short-circuit protection function only by judging the high and low levels, and has a simple structure, low cost and fast response speed.

[0020] Those skilled in the art will appreciate that numerous variations to the above description are possible, and that the examples and figures are intended only to describe one or more specific implementations.

[0021] Although what is considered as exemplary embodiments of the present invention has been described and narrated, it will be appreciated by those skilled in the art that various changes and substitutions may be made thereto without departing from the spirit of the present invention. In addition, many modifications may be made to adapt specific situations to the teachings of the present invention without departing from the central concept of the present invention described herein. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but the present invention may also include all embodiments and their equivalents that fall within the scope of the present invention.

Claims

1. A DC-AC modified sine wave inverter with an output short-circuit protection circuit, comprising: A boost unit, the boost unit is used to convert an input voltage; A rectifier unit, whose input end is connected to the output end of the boost unit; A full-bridge inverter unit, whose input end is connected to the output end of the rectifier unit, and the full-bridge inverter unit is used to invert the voltage output by the rectifier unit into an AC voltage; An MCU programming output control unit, whose input end is connected to the output end of the full-bridge inverter unit, and whose output end is connected to the switch tube in the full-bridge inverter unit, for controlling the on and off of the switch tube in the full-bridge inverter unit; It is characterized in that it also includes: a short-circuit protection unit, whose input end is connected to the output end of the rectifier unit, and whose output end is connected to the full-bridge inverter unit; the short-circuit protection unit is used to drive its input end and output end to be turned on or off according to the load voltage change at the output end of the full-bridge inverter unit, thereby controlling the opening and closing of the switch tube in the full-bridge inverter unit; the short-circuit protection unit includes a voltage divider unit and a short-circuit switch unit, one end of the voltage divider unit is connected to the output end of the rectifier unit, and the other end is connected to the bus negative pole of the output short-circuit protection circuit of the DC-AC modified wave inverter, and the input end of the short-circuit switch unit is connected to the voltage divider unit; The voltage dividing unit includes a resistor R85, a resistor R86, a resistor R87 and a resistor R29 connected in series in sequence, one end of the resistor R85 is connected to the output end of the rectifier unit, and one end of the resistor R29 is connected to the negative electrode of the bus; The short-circuit switch unit includes a resistor R14, a resistor R28, a transistor Q18, a resistor R89, a diode D14, a resistor R88, a transistor Q16, a resistor R83, a resistor R84, a diode D4, a transistor Q17 and a diode D12; One end of the resistor R14 is connected to the node between the resistor R87 and the resistor R29, and the other end thereof and one end of the resistor R28 are both connected to the base of the transistor Q18; the other end of the resistor R28 is connected to the cathode of the bus; the collector of the transistor Q18 is connected to a high potential through the resistor R89, and its emitter is connected to the cathode of the bus; the emitter of the transistor Q16 is connected to a high potential through the resistor R88, and its collector is connected to the cathode of the bus; the anode of the diode D14 is connected to the transistor Q18 At a node between the collector of and the resistor R89, its cathode is connected to the collector of the transistor Q16 and to the base of the transistor Q17; the base of the transistor Q16 is connected to the collector of the transistor Q17, the cathode of the diode D4 and the cathode of the diode D12 through the resistor R83, and the anodes of the diode D4 and the diode D12 are respectively connected to the gates of the switching tubes on the half bridge in the full-bridge inverter unit; the base of the transistor Q17 is connected to the negative electrode of the bus through the resistor R84, and its emitter is connected to the negative electrode of the bus.

2. The DC-AC modified wave inverter with output short circuit protection circuit as claimed in claim 1, characterized in that: The short-circuit switch unit also includes a capacitor C40 and a capacitor C38, one end of the capacitor C40 is connected to the base of the transistor Q18, and the other end is connected to the negative electrode of the bus; one end of the capacitor C38 is connected to the collector of the transistor Q16, and the other end is connected to the negative electrode of the bus.

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