CN100518429C - Electronic stabilizer protection circuit with single short-circuit switch - Google Patents

Abstract

The invention discloses a protection circuit of an electronic stabilizer, which comprises: the lamp comprises a short-circuit switch and a connecting circuit, wherein the connecting circuit is electrically connected with a group of filaments of a lamp tube of a fluorescent lamp in series and is electrically connected with a starting circuit and the short-circuit switch. When a voltage of the lamp tube exceeds a preset value, the short-circuit switch is conducted and generates a maintaining current so as to maintain the conducting state of the short-circuit switch and cause a high-voltage coil of an inverter of the ballast to be short-circuited, and the generation of an alternating-current high-voltage power output to the fluorescent lamp is stopped; when a new lamp tube is replaced, the fluorescent lamp can be automatically restarted without turning off or on a power switch of the fluorescent lamp.

Description

Electronic ballast protection circuit with single short circuit switch

technical field

The invention relates to a protection circuit of an electronic ballast.

Background technique

Regarding the prior art, please refer to Fig. 1, which shows the control circuit 1 of the fluorescent lamp disclosed in US Pat. ), which includes a push-pull oscillator circuit with two transistors T1 and T2 (such as 18a and 18b in Figure 1), a series resonant circuit (such as 14 and 14' in Figure 1, each comprising an inductive element <L1 and L1'> and a capacitor <C1 and C1'>) are electrically connected to the fluorescent lamp (3 and 3', which each include two sets of filaments: 6, 7 and 6', 7'), an oscillation trigger circuit (19 It includes an inductor and a capacitor) and two starters (111 and 111'). In order to avoid exposure to a dangerous high voltage connected to the oscillator circuit and the series resonant circuit when removing the load (tube) of the fluorescent lamp, a protection circuit 110 formed by a thyristor TH (thyristor) is provided in the invention , and short at least one transistor (T1) of the push-pull oscillator circuit (18a and 18b) by connecting the protection circuit. The relevant control energy is directly derived from the high-voltage power supply by means of a rectifier D1 and D1', and is connected to the inductance L1 and L1' of the series resonant circuit (such as 14 and 14' in Figure 1), so that the protection circuit 110 The thyristor TH can obtain sufficient and reliable switching energy. Its start-up criterion is a breakdown element ( Such as DIAC1) is determined by the breakdown voltage; it also supplies power to the power supply capacitor C3 in response to the thyristor TH (thyristor). When a lamp tube of the fluorescent lamp (13 and 13') is removed or fails or a fault occurs in the circuit, so that the lamp tube is removed, that is, the load of the circuit is removed, then C3 starts to be charged. When the voltage of C3 rises to the breakdown voltage of DIAC1, the thyristor TH is started. At this time, the base of the transistor T1 is blocked because it no longer receives the control energy, so that the energy of the series resonant circuit (14 and 14') is eliminated. At this time, the thyristor TH is connected to the positive terminal 11 of the DC voltage supply through a resistor R3, so as to provide a holding current to keep the thyristor TH turned on, so as to prevent oscillation. After the circuit has reacted to the fault, it can only be reset by interrupting the input power to the rectifier and operating power supply unit 15 or removing the voltage from the positive and negative terminals 11 and 12 of the DC voltage supply.

In the above-mentioned prior art, after the fault is removed, the power switch must be turned off and on again to cut off the holding current and make the thyristor open to reset the circuit; therefore, it is relatively difficult to operate and use. convenient.

Contents of the invention

The main purpose of the present invention is to provide an electronic ballast protection circuit with a single short-circuit switch (shutdown control switch) and a connecting circuit, and can achieve a relatively simple circuit structure and do not need to be reinstalled after the new lamp tube is reinstalled. Turning off and turning on the power switch of the fluorescent lamp can automatically start the fluorescent lamp due to the conduction of the current.

According to one aspect of the present invention, a protection circuit of an electronic ballast with a single short-circuit switch and a connection circuit, wherein the ballast is an AC/DC conversion circuit for outputting a DC voltage, and an inverter (inverter) is electrically connected to the AC The /DC conversion circuit is used to generate an AC high voltage output to drive a fluorescent lamp, and a starting circuit is used to start the inverter, and the protection circuit is electrically connected to the inverter, and is used to control the voltage of the fluorescent lamp When a predetermined value is exceeded, the inverter stops an oscillation to stop generating the AC high-voltage output, and the fluorescent lamp can be restarted automatically without turning off and on a power switch of the fluorescent lamp after replacing the lamp tube, which Including: a short-circuit switch, which has a control terminal electrically connected to the starting circuit, a first terminal and a second terminal electrically connected to a common ground terminal, and the first terminal and the second terminal are electrically connected in parallel to one of the inverter a high-voltage coil; and a connection circuit having a third end and a fourth end, the third end is electrically connected to an output end of the positive DC voltage of the AC/DC conversion circuit, and the fourth end is electrically connected to the short-circuit switch The first end, the connecting circuit is electrically connected in series to a group of filaments of the fluorescent lamp and electrically connected to the starting circuit and the control end of the short-circuit switch, which is used to make the lamp tube exceed the predetermined value when the voltage of the lamp tube exceeds the predetermined value. The short-circuit switch is turned on and generates a holding current (holding current), which keeps the short-circuit switch in a conductive state, and causes the high-voltage coil of the inverter to be short-circuited to stop generating the AC high-voltage output to the fluorescent lamp, and when When a new lamp tube is replaced properly, the inverter is automatically activated.

According to the above idea, when the lamp tube is removed due to a fault in which the voltage of the lamp tube is higher than the predetermined value, the connecting circuit is disconnected due to the lack of series electrical connection of the group of filaments, resulting in The holding current drops to zero and the short-circuit switch is thus turned off (turn-off), and when the new lamp is installed, the connection is made by electrically connecting a set of filaments of the new lamp in series with the connecting circuit. The circuit is turned on again, and the starting circuit electrically connected to the connection circuit is automatically turned on to start the inverter.

According to the above idea, the short circuit switch is one of a silicon controlled rectifier (SCR) and a combination of a first transistor and a second transistor electrically connected.

According to the above idea, the control terminal of the short-circuit switch is a gate of the SCR, the first terminal is an anode of the SCR, and the second terminal is a cathode of the SCR.

According to the above idea, the first transistor is an NPN transistor and the second transistor is a PNP transistor, wherein a base and a collector of the NPN transistor are respectively connected to a collector and a base of the PNP transistor electrical connection.

According to the above idea, the control end of the short-circuit switch is a connecting node (connecting node) electrically connected to the base of the NPN transistor and the collector of the PNP transistor, and the first end is a connection node of the PNP transistor. an emitter, and the second terminal is an emitter of the NPN transistor.

According to the above idea, the AC/DC conversion circuit is one of a power factor correction (PFC) circuit and a bridge rectifier circuit.

According to another aspect of the present invention, a protection circuit for an electronic ballast, wherein the ballast is an AC/DC conversion circuit having an output terminal, an inverter having a high-voltage coil and electrically connected to the AC/DC conversion circuit to Drive a fluorescent lamp with a set of filaments, and a starting circuit to start the inverter, the protection circuit is electrically connected to the inverter, which includes: a short circuit switch circuit, which has a control terminal electrically connected to the starting circuit, a The first end and a second end are electrically connected to a common ground end, and the first end and the second end are electrically connected to the high voltage coil in parallel; and a connection circuit has a third end and a fourth end, and the third end is electrically connected to the high voltage coil. The output end of the AC/DC conversion circuit is connected, the fourth end is electrically connected to the first end, wherein the connection circuit is electrically connected to the group of filaments in series, and is electrically connected to the starting circuit and the control end.

According to the above idea, when the voltage of the lamp tube exceeds a predetermined value, the short-circuit switch is turned on and generates a holding current (holding current), so that the short-circuit switch remains in the conduction state, and the inverter's The high-voltage coil is short-circuited to stop generating an AC high-voltage output to the fluorescent lamp, and when a new lamp tube is replaced, the inverter is automatically activated.

According to the above idea, the short circuit switch is one of a silicon controlled rectifier (SCR) and a combination of a first transistor and a second transistor electrically connected.

According to the above idea, the control terminal of the short-circuit switch is a gate of the SCR, the first terminal is an anode of the SCR, and the second terminal is a cathode of the SCR.

According to the above idea, the first transistor is an NPN transistor and the second transistor is a PNP transistor, wherein a base and a collector of the NPN transistor are respectively connected to a collector and a base of the PNP transistor electrical connection.

According to the above idea, the control end of the short-circuit switch is a connecting node (connecting node) electrically connected to the base of the NPN transistor and the collector of the PNP transistor, and the first end is a connection node of the PNP transistor. an emitter, and the second terminal is an emitter of the NPN transistor.

According to the above idea, the AC/DC conversion circuit is one of a power factor correction (PFC) circuit and a bridge rectifier circuit.

In the electronic ballast protection circuit with a shutdown control switch and a connection circuit of the present invention, the maintenance current in the present invention flows through the electrodes of the fluorescent lamp tube, so when the lamp tube is removed due to a fault When the maintenance current is interrupted, the inverter can be turned off to stop the oscillation, and after the new lamp tube is reinstalled, the fluorescent lamp can be automatically turned on due to the conduction of the current without having to turn it off again. Turn off and turn on the power switch of the fluorescent lamp, that is, when the voltage of a fluorescent lamp tube exceeds a predetermined value, it will stop the ballast from generating a high-voltage output to the fluorescent lamp, and automatically restart the fluorescent lamp after replacing the lamp tube , a protection circuit with a relatively simple structure. Among them, the fluorescent lamp protection circuit has a relatively simple structure, so its manufacturing, transportation and storage costs are relatively low.

Description of drawings

FIG. 1 shows a schematic circuit diagram of a control circuit and a protection circuit of a fluorescent lamp in the prior art;

Fig. 2 shows the schematic circuit diagram of the electronic ballast with a single short circuit switch in the first preferred embodiment of the present invention;

Fig. 3 shows the schematic diagram of the circuit with a single short-circuit switch electronic ballast and a starting current Is of the first preferred embodiment of the present invention;

4 shows a schematic diagram of a circuit with a single short-circuit switch electronic ballast and a holding current _Ihc according to the first preferred embodiment of the present invention;

Fig. 5 shows the schematic diagram of the circuit with a single short-circuit switch electronic ballast and a first discharge current I _d1 in the first preferred embodiment of the present invention;

6 shows a schematic diagram of a circuit with a single short-circuit switch electronic ballast and a second discharge current I _d2 , a bypass current I _bp and a conduction current I _to according to the first preferred embodiment of the present invention;

FIG. 7 shows a schematic circuit diagram of a second preferred embodiment of the present invention with a single short-circuit switch electronic ballast;

FIG. 8 shows a schematic circuit diagram of a single-short-circuit switch electronic ballast according to a third preferred embodiment of the present invention;

Fig. 9 shows the circuit diagram of the electronic ballast with a single short circuit switch according to the fourth preferred embodiment of the present invention; and

FIG. 10 shows a schematic circuit diagram of an electronic ballast with a single short circuit switch according to a fifth preferred embodiment of the present invention.

Detailed ways

As shown in FIG. 2 , it is a schematic circuit diagram of an electronic ballast 2 with a single short circuit switch according to the first preferred embodiment of the present invention. The electronic ballast 2 includes a power factor correction (PFC) circuit or a bridge rectifier circuit 21, which is used to output a positive DC voltage 211 and a negative DC voltage 212, and an inverter (inverter) 22, which is Electrically connected to the PFC circuit or a bridge rectifier circuit 21 for generating an AC high voltage output to drive a fluorescent lamp 3; a starting circuit 23 (which includes a resistor R1, a group of filaments 31 of the fluorescent lamp, a resistor R9 , a starting capacitor C6, a trigger diode (DIAC) D2 and a metal oxide semiconductor field effect transistor (MOSFET) Q2, please refer to the path of the starting circuit 23 and a starting current _IS shown in Figure 3) for starting the Inverter 22; and a protection circuit 24 (please refer to FIG. 4) electrically connected to the inverter 22, for when a voltage of a lamp tube 32 of the fluorescent lamp 3 exceeds a predetermined value, the inverter 22 Stopping an oscillation to stop generating the AC high voltage output; and the fluorescent lamp 3 can be restarted automatically without turning off and on a power switch of the fluorescent lamp 3 after the lamp tube 32 is replaced. The protection circuit 24 includes: a short-circuit switch 241 (Q3), which has a control terminal electrically connected to the start-up circuit 23, a first terminal and a second terminal electrically connected to a common ground terminal, the first terminal and the second terminal A high-voltage coil T3C of the inverter 22 is electrically connected in parallel; and a connection circuit 242 has a third terminal and a fourth terminal, and the third terminal is electrically connected to the positive DC voltage of the PFC circuit or a bridge rectifier circuit 21 An output end of 211, the fourth end is electrically connected to the first end of the short-circuit switch (it is a silicon-controlled diode (SCR), or a combination of two transistors electrically connected to an NPN and a PNP) 241, the The connection circuit 242 (which includes the resistor R1, the group of filaments 31 of the fluorescent lamp, the resistor R9 and a diode D3, please refer to FIG. 4 ) is electrically connected in series with the group of filaments 31 of the fluorescent lamp 3 and is electrically connected to the starting circuit 23 and The control terminal of the short-circuit switch 241 is used to turn on the short-circuit switch 241 and generate a holding current (holding current) _Ihc when the voltage of the lamp tube 32 exceeds the predetermined value, so that the short-circuit switch 241 Keep the conduction state, and make the high-voltage coil T3C of the inverter 22 be short-circuited to stop generating the AC high-voltage output to the fluorescent lamp 3, and when a new lamp tube 32 is replaced, the inverter 22 is started automatically.

The operation principle of the above-mentioned first preferred embodiment is described as follows. Please refer to FIG. 3, when the electronic ballast 2 is started, the positive DC voltage 211 charges the starting capacitor C6 until the voltage value of the starting capacitor C6 reaches the breakdown voltage value (breakdown voltage) of the DIAC D2, A switch Q2 of the inverter 22 is turned on to form a starting current Is (as shown in FIG. 3 ) to start the fluorescent lamp 3 . And when the fluorescent lamp 3 is in the normal operation state, the voltage value on the starting capacitor C6 will form a first discharge current _Id1 due to the conduction of a bypass diode (bypass diode) D1 and the switch Q2. (the 1st discharging current) to discharge the starting capacitor C6 to a low potential close to zero, and maintain the low potential so as not to turn on the DIAC D2 again (as shown in FIG. 5 ).

Referring to Fig. 6, when the voltage of the lamp tube 32 is higher than the predetermined value, an AC voltage higher than the normal value appears at the connecting node (connecting node) n1 of the group of filaments 31 and a resistor R8 value, on the one hand, the capacitor C8 is charged through the voltage divider circuit composed of the resistor R8 and a resistor R10 and the AC/DC voltage rectifier circuit composed of a diode D5, a resistor R11 and a capacitor C8. When the voltage on C8 is higher than the breakdown voltage of the DIAC D6, the DIAC D6 will be turned on to form a current I _to (turn-on current), and then the short-circuit switch Q3 will be turned on. When the short-circuit switch Q3 is turned on, a high-voltage coil T3C of the inverter 22 electrically connected in parallel is short-circuited and forms a bypass current _Ibp (bypass current) to flow through a diode D4 and the short-circuit switch Q3; The voltage on the starting capacitor C6 will form a second discharging current I _d2 (the ^2nd discharging current), which flows through a diode D3 and the short-circuit switch Q3 to discharge (I _to , I _bp and I _d2 are shown in Figure 6 in detail ) to keep C6 at a low potential close to zero, and then stop the inverter 22 from oscillating and stop generating the AC high voltage output to the fluorescent lamp 3 . At this time, because the short-circuit switch Q3 remains on, a holding current _Ihc is generated between the positive DC voltage 211 and the short-circuit switch Q3, and the short-circuit switch Q3 is kept in a conducting state (the holding current _Ihc flows through The connecting circuit 242 and the short-circuit switch 241 (Q3) are shown in FIG. 4 in detail). Referring to FIG. 4, when the lamp tube 32 is removed, the connection circuit 242 produces an open circuit due to the absence of the series electrical connection of the group of filaments 31, so that the holding current _Ihc drops to zero, and the short circuit switch 241 Therefore be turned off (turn-off); conduction, so that the start-up circuit 23 electrically connected to the connection circuit 242 is automatically turned on (as shown in FIG. 3 in detail), so as to start the inverter 22 .

As shown in Figure 7, it is a schematic circuit diagram of a single short-circuit switch electronic ballast 2 of the second preferred embodiment of the present invention; the biggest difference between it and the first preferred embodiment is that in the first preferred embodiment A capacitor C7 is canceled, and the mode of increasing the capacitance value of C1 (it is about twice the capacitance value of the original C1) is adopted instead, and all the other structures and the principle of operation thereof are the same as those of the first preferred embodiment (see Fig. 7 for details) .

As shown in Figure 8, it is a schematic circuit diagram of a single short-circuit switch electronic ballast 2 of the third preferred embodiment of the present invention; the biggest difference between it and the first preferred embodiment is that in the first preferred embodiment A capacitor C1 is canceled, and the mode of increasing the capacitance value of C7 (it is about twice the capacitance value of the original C7) is adopted instead, and all the other structures and the principle of operation thereof are the same as those of the first and second preferred embodiments (see Figure 8).

As shown in Figure 9, it is a schematic circuit diagram of an electronic ballast 2 with a single short-circuit switch in the fourth preferred embodiment of the present invention; the biggest difference between it and the first preferred embodiment is the change of the connection method of the fluorescent lamp 3 and the capacitors C1/C7 are moved and so on. A group of filaments 31 of the fluorescent lamp 3 is instead electrically connected in series with the positive DC voltage 211 and the resistor R1, and one end of the capacitor C1 is instead coupled to an inductor L1 of the inverter 22 and C1 The other end is instead coupled to another group of filaments 33 of the fluorescent lamp and the resistor R8. Therefore, both the starting current Is and the holding current _Ihc first flow through the group of filaments 31 and then flow through the resistor R1. In addition, the rest of the structure and operating principles of the fourth preferred embodiment of the present invention are the same as those of the first embodiment. It is the same to the third preferred embodiment (see FIG. 9 for details).

As shown in Figure 10, it is a schematic circuit diagram of an electronic ballast 2 with a single short-circuit switch according to the fifth preferred embodiment of the present invention; the biggest difference between it and the first preferred embodiment lies in the change of the connection method of the fluorescent lamp 3 and the capacitors C1/C7 are moved and so on. One group of filaments 33 of the fluorescent lamp 3 is instead coupled to one end of the resistor R8 and the capacitor C1, and the other end of C1 is coupled to an inductor L1 of the inverter 22 and another group of the fluorescent lamp 3 The filament 31 is instead electrically connected in series with the resistor R10 and the negative DC voltage 212 . Therefore, the starting current Is and the holding current _Ihc first flow through the resistor R1 and the rest of the starting circuit 23 and the connecting circuit 242 respectively, and finally flow through the group of filaments 31 . Except for this, the remaining structure and operating principle of the fifth preferred embodiment of the present invention are the same as those of the first to fourth preferred embodiments (see FIG. 10 for details).

It can be seen from the above description that the present invention provides an electronic ballast protection circuit with a single short-circuit switch and a connection circuit, and can achieve a relatively simple circuit structure and do not need to be turned off again after the new lamp tube is reinstalled. The utility model has the advantages of turning off and turning on the power switch of the fluorescent lamp, which can automatically start the fluorescent lamp due to the conduction of the current.

Therefore, even though the present invention has been described in detail by the above-mentioned embodiments and various equivalent changes or substitutions can be made by those skilled in the art, none of these equivalent changes or substitutions departs from the attached specification. Scope of patent application claims.

Claims (14)

1. A protection circuit for an electronic ballast, wherein the ballast is an AC/DC conversion circuit for outputting a DC voltage, and an inverter is electrically connected to the AC/DC conversion circuit to generate an AC high voltage output for Driving a fluorescent lamp, and a starting circuit for starting the inverter, the protection circuit is electrically connected to the inverter, and is used for stopping an oscillation of the inverter when the voltage of the tube of the fluorescent lamp exceeds a predetermined value In order to stop generating the AC high-voltage output, and to automatically restart the fluorescent lamp without turning off and on a power switch of the fluorescent lamp after replacing the lamp tube, the protection circuit includes: A short-circuit switch, which has a control terminal electrically connected to the starting circuit, a first terminal electrically connected to a common ground terminal, and a second terminal, and the first terminal and the second terminal are electrically connected in parallel to a high-voltage line of the inverter circle; and A connection circuit, which has a third terminal and a fourth terminal, the third terminal is electrically connected to an output terminal of the positive DC voltage of the AC/DC conversion circuit, and the fourth terminal is electrically connected to the first terminal of the short-circuit switch At one end, the connecting circuit is electrically connected in series to a group of filaments of the fluorescent lamp and electrically connected to the starting circuit and the control end of the short-circuit switch, which is used to enable the short-circuit switch to be activated when the lamp voltage exceeds the predetermined value. Turn on and generate a holding current, keep the short-circuit switch on, and make the high-voltage coil of the inverter short-circuited to stop generating the AC high-voltage output to the fluorescent lamp, and when a new lamp is replaced When the time is right, the inverter is started automatically. 2. The protection circuit according to claim 1, wherein when the lamp tube is removed due to a fault in which the voltage of the lamp tube is higher than the predetermined value, the connection circuit does not have the set of filaments A series electrical connection creates an open circuit, so that the holding current drops to zero and the short-circuit switch is thereby turned off, and when the new tube is properly installed, since one set of filaments of the new tube is in series with the connecting circuit The electrical connection makes the connecting circuit re-conducted, thereby automatically conducting the starting circuit electrically connected with the connecting circuit to start the inverter. 3. The protection circuit as claimed in claim 1, wherein the short-circuit switch is one of a silicon controlled rectifier and a combination of a first transistor and a second transistor electrically connected. 4. The protection circuit as claimed in claim 3, wherein the control terminal of the short-circuit switch is a gate of the silicon controlled rectifier, the first terminal is an anode of the silicon controlled rectifier, and the first terminal is an anode of the silicon controlled rectifier. The two terminals are a cathode of the silicon controlled rectifier. 5. The protection circuit according to claim 3, wherein the first transistor is an NPN transistor and the second transistor is a PNP transistor, wherein a base and a collector of the NPN transistor are respectively connected to the A collector and a base of the PNP transistor are electrically connected. 6. The protection circuit according to claim 5, wherein the control terminal of the short-circuit switch is a connection node electrically connected to the base of the NPN transistor and the collector of the PNP transistor, and the first terminal is an emitter of the PNP transistor, and the second terminal is an emitter of the NPN transistor. 7. The protection circuit as claimed in claim 1, wherein the AC/DC conversion circuit is one of a power factor correction circuit and a bridge rectification circuit. 8. A protection circuit for an electronic ballast, wherein the ballast is an AC/DC conversion circuit having an output terminal, an inverter having a high-voltage coil and electrically connected to the AC/DC conversion circuit to drive a group of filaments A fluorescent lamp, and a starting circuit to start the inverter, the protection circuit is electrically connected to the inverter, which includes: A short-circuit switch circuit, which has a control terminal electrically connected to the starting circuit, a first terminal and a second terminal electrically connected to a common ground terminal, and the first terminal and the second terminal are electrically connected to the high-voltage coil in parallel; and A connecting circuit has a third end and a fourth end, the third end is electrically connected to the output end of the AC/DC conversion circuit, the fourth end is electrically connected to the first end, Wherein the connecting circuit is electrically connected to the group of filaments in series, and is electrically connected to the starting circuit and the control terminal. 9. The protection circuit as claimed in claim 8, wherein when the voltage of the tube of the fluorescent lamp exceeds a predetermined value, the short-circuit switch is turned on and generates a holding current, so that the short-circuit switch remains on, And the high-voltage coil of the inverter is short-circuited to stop generating an AC high-voltage output to the fluorescent lamp, and when a new lamp tube is replaced, the inverter is automatically started. 10. The protection circuit as claimed in claim 8, wherein the short-circuit switch is one of a silicon controlled rectifier and a combination of a first transistor and a second transistor electrically connected. 11. The protection circuit according to claim 10, wherein the control terminal of the short-circuit switch is a gate of the silicon-controlled rectifier, the first terminal is an anode of the silicon-controlled rectifier, and the first terminal is an anode of the silicon-controlled rectifier. The two terminals are a cathode of the silicon controlled rectifier. 12. The protection circuit according to claim 10, wherein the first transistor is an NPN transistor and the second transistor is a PNP transistor, wherein a base and a collector of the NPN transistor are respectively It is electrically connected with a collector and a base of the PNP transistor. 13. The protection circuit according to claim 12, wherein the control terminal of the short-circuit switch is a connection node electrically connected to the base of the NPN transistor and the collector of the PNP transistor, and the first terminal is an emitter of the PNP transistor, and the second terminal is an emitter of the NPN transistor. 14. The protection circuit as claimed in claim 8, wherein the AC/DC conversion circuit is one of a power factor correction circuit and a bridge rectification circuit.

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