CN105403827A - Power switch abnormality detection device - Google Patents

Abstract

The invention discloses an abnormality detection device of a power switch, which is connected on a current path of the power switch and comprises: a voltage dividing circuit having a voltage dividing node; the voltage difference switch is connected between a voltage division node of the voltage division circuit and a current path of the power switch; when the voltage on the current path is less than a first set value, the differential pressure switch is turned on, so that the voltage of the voltage division node is less than a second set value, and when the voltage on the current path is greater than or equal to the first set value, the differential pressure switch is turned off, and the voltage of the voltage division node is greater than or equal to the second set value, an abnormal alarm can be generated accordingly. The invention mainly judges whether the impedance related to the temperature on the current path is abnormal according to whether the voltage value on the current path of a power switch is more than or equal to a set value when the power switch is conducted, and further the impedance is used as the basis for generating abnormal alarm aiming at the power switch.

Description

Abnormality detection device for power switch

technical field

The invention relates to an abnormality detection device of a power switch, in particular to a related technology for generating an abnormality alarm based on whether the temperature-related conduction resistance of the power switch is abnormal.

Background technique

A power switch refers to a transistor that can withstand a large current, a small leakage current, and has better saturation conduction and cut-off characteristics under certain conditions. One of the most commonly used power switches is a metal oxide semiconductor field effect transistor (MOSFET). ). Because the power switch has the above-mentioned characteristics, it is often used in power equipment, such as a switching power supply. Please refer to FIG. 7. An existing switching power supply includes a rectifier circuit 81, a power factor correction circuit 82 and A DC to DC conversion circuit 83, etc.; wherein: the power factor correction circuit 82 includes an inductor L1, a diode, a power switch S1 and a PFC controller located on the DC power circuit, and the DC to DC conversion circuit 83 includes a transformer T1 . A PWM controller U1 and a power switch S2, a control terminal of the PWM controller U1 is connected to the power switch S2, and the power switch S2 is connected to the primary side of the transformer T1.

From the above, it can be seen that the existing switching power supply fully utilizes the power switch as the switching element to adjust the power factor of the power supply and perform power conversion. Because the traditional pulse width modulation controller U1 adopts hard switching for the power switch S2, the voltage and current waveforms of the switch terminals overlap each other and are not equal to zero, so the power switch S2 will change greatly when it is turned on or off. In addition to causing electromagnetic interference, the power switch S2 is easily damaged due to frequent switching and large fluctuations. In order to improve the problems derived from hard switching, soft switching technology has been developed and published. The so-called soft switching is mainly to reduce the overlapping area of voltage and current when the power switch switches transiently, and even make the overlapping area zero to achieve switching. Losses are zero, specific techniques include zero-current switching (ZCS) or zero-voltage switching (ZVS).

Although the problem derived from the hard switching of the power switch S2 by the traditional pulse width modulation controller is solved by the soft switching technology. However, also in the power factor correction circuit 82 of the switching power supply, based on circuit characteristics, its PFC controller still adopts hard switching for the control of the power switch S1, and the power switch S1 frequently operates under hard switching, in addition to generating losses In addition, it may fail due to abnormal temperature rise. It can be seen that in order to ensure the stable operation of the power switch in the system, it is necessary to monitor its working characteristics and whether it is abnormal or not.

Contents of the invention

Therefore, the main purpose of the present invention is to provide a power switch abnormality detection device, which uses the impedance variation related to the power switch temperature as the basis for judging whether the power switch is abnormal, so as to monitor the working state of the power switch at any time, and then ensure the use of the power switch. device stability.

A main technical means adopted to achieve the aforementioned purpose is to connect the abnormality detection device of the aforementioned power switch to a current path of a power switch, and include:

a voltage divider circuit having a voltage divider node;

a differential pressure switch connected between the voltage dividing node of the voltage dividing circuit and the current path of the power switch;

When the voltage on the current path is less than a first set value, the differential pressure switch is turned on, so that the voltage of the voltage dividing node is less than a second set value, when the voltage on the current path is greater than or equal to the first set value A fixed value, the differential pressure switch is cut off, and when the voltage of the voltage dividing node is greater than or equal to the second set value, an abnormal alarm can be generated accordingly.

The present invention mainly utilizes the corresponding relationship between the temperature of the power switch and its on-resistance which is proportional to its conduction impedance, and further analyzes whether the impedance of the power switch is abnormally increased by judging whether the voltage on the current path of the power switch is greater than a set value. The basis for judging whether the temperature is abnormal; using the above technology can effectively monitor the working status of the power switch and maintain the stability of the system.

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments, but not as a limitation of the present invention.

Description of drawings

Fig. 1 is the circuit diagram of a preferred embodiment of the present invention;

2A and 2B are equivalent circuit diagrams of a preferred embodiment of the present invention;

FIG. 3 is a graph showing the relationship between temperature and on-resistance of the power switch;

Fig. 4 is the waveform diagram that the present invention samples the voltage divider circuit with a digital controller;

Fig. 5 is the circuit diagram of another preferred embodiment of the present invention;

6 is a circuit diagram of the present invention applied to a switching power supply;

FIG. 7 is a circuit diagram of a known switching power supply.

detailed description

Below in conjunction with accompanying drawing, structural principle and working principle of the present invention are specifically described:

Regarding the abnormality detection device of the power switch of the present invention, its one preferred embodiment, please refer to Fig. 1, the abnormality detection device of this power switch is connected on a current path of a power switch S1, and comprises:

A voltage divider circuit 10, having a voltage divider node X;

A differential pressure switch 20 is connected between the voltage dividing node X of the voltage dividing circuit 10 and the current path of the power switch S1.

In this embodiment, the power switch S1 is a metal oxide semiconductor field effect transistor (MOSFET), more specifically, an N-type metal oxide semiconductor field effect transistor (NMOS). It must be noted that: the aforementioned NMOS field effect transistor is just an example, and is not intended to limit the type of the device of the power switch S1.

The power switch S1 has a drain, a source and a gate, the aforementioned current path is formed between the drain and the source, and the drain is connected to the voltage dividing node X of the voltage dividing circuit 10 through the differential pressure switch 20 , its source is grounded, and the gate is used as the control terminal.

The voltage divider circuit 10 includes a first resistor R1 and a second resistor R1, one end of the first resistor R1 and the second resistor R2 are connected in series with each other to form the aforementioned voltage divider node X, and the other end of the first resistor R1 It is connected to a DC power supply Vcc, and the other end of the second resistor R2 is connected to the source of the power switch S1 and grounded; the voltage dividing circuit 10 is composed of the DC power supply Vcc, the first resistor R1 and the second resistor R2 according to the voltage dividing formula Determine a second set value V2, which is a certain value, that is, the normal voltage value that can be measured on the voltage dividing node X when the differential pressure switch 20 is turned off.

The aforementioned voltage divider circuit 10 is the voltage divider node X formed by the series connection of the first resistor R1 and the second resistor R2, which is connected to the drain of the power switch S1 through the differential pressure switch 20. In this embodiment, the voltage divider The differential switch 20 is a diode, the diode is connected to the voltage dividing node X of the voltage dividing circuit 10 with its anode, and its cathode is connected to the drain of the power switch S1, that is, the voltage dividing node X of the voltage dividing circuit 10 is connected through the diode sequentially. The ground is connected to the drain of the power switch S1.

Under the aforementioned architecture, when the power switch S1 is turned on, the voltage Vds between the drain and the source of the power switch S1 (that is, the voltage on the current path) is small, and the differential pressure switch 20 conducts in the forward direction at this time, so the voltage divider circuit The voltage Vx on the 10-divider node X will be pulled down and be smaller than the second set value V2. The equivalent circuit at this time is shown in Figure 2A. The voltage Vx on the 10-divider node X of the voltage divider circuit is as follows:

$\mathrm{Vx}=\frac{\mathrm{Vcc}/R2+(V+\mathrm{Ids}\&Center\; Dot;\mathrm{Rds}\left(\mathrm{on}\right))/\mathrm{Rds}}{\frac{1}{R1}+\frac{1}{R2}+\frac{1}{\mathrm{Rds}\left(\mathrm{on}\right)}},$ Vf=forward conduction voltage of differential pressure switch 20

However, when the temperature of the power switch S1 rises, its on-resistance Rds will also increase at a constant current (please refer to the characteristic curve in Figure 3). When the temperature of the power switch S1 continues to rise, its on-resistance As Rds increases, the voltage Vds (drain-source current Ids×conduction resistance Rds) increases accordingly, and when it is greater than a first set value V1, the differential pressure switch 20 is turned off (the equivalent circuit is shown in Figure 2B), Then when it is judged that its voltage Vx is equal to the second set value V2 on the voltage-dividing node X of the voltage-dividing circuit 10, an abnormal alarm can be generated accordingly; at this moment, the voltage on the voltage-dividing node X of the voltage-dividing circuit 10 is:

Vx=V2=Vcc×R2/(R1+R2)

When the aforementioned differential pressure switch 20 is a diode, the first set value V1 is the forward conduction voltage of the diode, which is about 0.7 volts.

The voltage Vx of the voltage-dividing node X of the aforementioned voltage-dividing circuit 10 can be obtained by a digital controller in a sampling manner, and the digital controller controls the conduction of the power switch S1 at the same time. Please refer to FIG. 4, which is a waveform diagram of the digital controller driving the power switch S1 and sampling the voltage dividing node X of the voltage dividing circuit 10. The digital controller provides a driving signal Vgs to drive the power switch S1 for periodic conduction. When the power switch S1 is turned on, the voltage dividing node of the voltage dividing circuit 10 is sampled. When the sampled voltage dividing node X voltage Vx is equal to the second set value V2, an abnormality will be generated by the digital controller. alarm.

Please refer to FIG. 5 , which is another preferred embodiment of the present invention. Its basic structure is roughly the same as that of the previous embodiment. The differential pressure switch 20 ′ is still a diode. The voltage division node X of the circuit 10 is connected, and the anode is connected to the drain of the power switch S1.

In the foregoing embodiments, the so-called second set value V2 is always greater than the voltage Vx of the voltage dividing node X, and the specific value can be set by the user. That is, when the power switch S1 is turned on, if the conduction resistance Rds is normal, the drain and source voltages Vds are not greater than the forward conduction voltage of the diode, the voltage Vx of the voltage dividing node X of the voltage dividing circuit 10 will not reach the second setting value V2, the sampling controller will not generate an abnormal alarm; once the temperature of the power switch S1 rises abnormally, its conduction resistance Rds will increase relatively, and the drain and source voltage Vds will be greater than the forward conduction voltage of the diode, resulting in a voltage divider circuit 10 The voltage Vx of the voltage dividing node X increases, and when it is greater than the second set value V2, the sampling controller generates an abnormal alarm immediately.

Please refer to FIG. 6, when the aforementioned power switch S1 is used in the power factor correction circuit 82, the aforementioned digital controller can be a PFC controller in the power factor correction circuit 82, and the abnormality detection device 1 of the present invention is connected with the drain of the power switch S1 respectively. Pole, source and PFC controller, the PFC controller is further connected to an alarm module (Alarm), so as to generate an abnormal alarm when the voltage Vx of the voltage dividing node X is detected to be greater than or equal to the second set value V2. When the power switch S1 is used in the DC-to-DC conversion circuit, the aforementioned digital controller can be a pulse width modulation controller in the DC-to-DC conversion circuit.

From the above, it can be known that the present invention mainly utilizes the corresponding relationship between the temperature of the power switch and its conduction resistance, and judges whether the voltage on the current path of the power switch is greater than a set value for further analysis of whether the conduction resistance has abnormally increased. High, and then used as the basis for judging whether to generate an abnormal temperature alarm of the power switch, so that the working characteristics of the power switch can be monitored at any time, and an alarm will be generated in time when an abnormal situation occurs, so as to ensure system stability and avoid damage.

Certainly, the present invention also can have other multiple embodiments, without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding Changes and deformations should belong to the scope of protection of the appended claims of the present invention.

Claims (10)

1. A device for abnormality detection of a power switch, which is connected to a current path of a power switch, is characterized in that it comprises: a voltage divider circuit having a voltage divider node; a differential pressure switch connected between the voltage dividing node of the voltage dividing circuit and the current path of the power switch; When the voltage on the current path is less than a first set value, the differential pressure switch is turned on, so that the voltage of the voltage dividing node is less than a second set value, when the voltage on the current path is greater than or equal to the first set value A fixed value, the differential pressure switch is cut off, and when the voltage of the voltage dividing node is greater than or equal to the second set value, an abnormal alarm can be generated accordingly. 2 . The abnormality detection device for a power switch according to claim 1 , wherein the differential pressure switch is composed of a diode. 3 . The abnormality detection device of the power switch according to claim 2 , wherein the anode of the differential pressure switch is connected to the voltage dividing node of the voltage dividing circuit, and the cathode thereof is connected to the current path of the power switch. 4 . 4. The abnormality detection device of the power switch according to claim 3, characterized in that, the voltage divider circuit includes a first resistor and a second resistor, and the first resistor and the second resistor are connected in series with one end to form the aforementioned The other end of the first resistor is connected to a DC power supply, and the other end of the second resistor is connected to the source of the power switch and grounded. 5 . The abnormality detection device of the power switch according to claim 4 , wherein the voltage divider circuit uses the DC power supply, the first resistor and the second resistor to determine the second set value according to a voltage divider formula. 5 . 6 . The abnormality detection device for a power switch according to claim 5 , wherein the first set value is a forward conduction voltage of the differential pressure switch. 7 . 7 . The abnormality detection device for a power switch according to claim 1 , wherein the power switch is a metal oxide semiconductor field effect transistor, and the current path is formed by a drain and a source. 8. The abnormality detection device for a power switch according to any one of claims 1 to 7, wherein the voltage dividing node of the voltage dividing circuit is connected to a digital controller. 9. The abnormality detection device of the power switch according to claim 8, wherein the digital controller generates a drive signal to drive the power switch, and the voltage divider circuit is connected to the voltage divider during each conduction period of the power switch. The voltage divider node is sampled. 10. The abnormality detection device for a power switch according to claim 8, wherein the digital controller is a PFC controller.