TWI547071B - An abnormality detection device for power switch - Google Patents

Description

Power switch abnormality detecting device

The present invention relates to an abnormality detecting device for a power switch, and more particularly to a related art according to whether a power switch and a temperature-dependent on-impedance are abnormal, as a basis for generating an abnormal alarm.

Power switch refers to a transistor that can withstand large current, has small leakage current, and has better saturation conduction and cut-off characteristics under certain conditions. One of the most common power switches currently used is gold oxide half field effect transistor (MOSFET). . Since the power switch has the above characteristics, it is often applied to a power supply device, such as an exchange power supply. Referring to FIG. 7, an existing switched power supply includes a rectifier circuit 81 and a power factor correction circuit 82. And the DC-to-DC conversion circuit 83 and the like; 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 supply loop, and the DC-DC conversion circuit 83 includes A transformer T1, a pulse width modulation controller U1 and a power switch S2, a control terminal of the pulse width modulation controller U1 is connected to the power switch S2, and the power switch S2 is connected to the primary side of the transformer T1.

As can be seen from the above, the switching power supply fully utilizes the power switch as a switching element to adjust the power factor of the power supply and perform power conversion. Since the conventional pulse width modulation controller U1 adopts a hard switching of the power switch S2, the voltage and current waveforms of the switching terminals overlap each other and are not equal to zero, so that the power switch S2 may be greatly changed when turned on or off, except In addition to electromagnetic interference, the power switch S2 is easily damaged due to frequent switching and large fluctuations. In order to improve the problem of hard switching, the technology of soft switching has been developed. The so-called soft switching is mainly the overlapping area of voltage and current when the power switch is switched off, and even the overlap area is zero, and the switching loss is Zero, specific techniques include zero current switching (ZCS) or zero voltage switching (ZVS).

Although the problem of the conventional PWM switch for the hard switching of the power switch S2 is solved by the soft switching technology. However, also in the power factor correction circuit 82 of the switching power supply, based on the circuit characteristics, the PFC controller still performs hard switching on the control of the power switch S1, and the power switch S1 frequently operates under hard switching, except for loss. In addition, it may also 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 the operating characteristics and abnormalities.

Therefore, the main object of the present invention is to provide an abnormality detecting device for a power switch, which uses the impedance variation related to the temperature of the power switch as a basis for judging whether the power switch is abnormal, so as to monitor the working state of the power switch at any time, thereby ensuring the use of the power switch. Equipment stability.

A main technical means for achieving the foregoing objective is that the abnormality detecting device of the power switch is connected to a current path of a power switch, and comprises: a voltage dividing circuit having a voltage dividing node; a differential pressure switch, Connected between the voltage dividing node of the voltage dividing circuit and the current path of the power switch; thereby, 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 dividing node The voltage is less than a second set value. 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 when the voltage of the voltage dividing node is greater than or equal to the second set value, an abnormal alarm may be generated.

The invention mainly utilizes the corresponding relationship between the temperature of the power switch and its on-resistance, and determines whether the voltage on the current path of the power switch is greater than a set value to further analyze whether the impedance is abnormally increased, and further, whether the power switch is temperature or not. The judgment basis of the abnormality; the above technology can effectively monitor the working state of the power switch and maintain the stability of the system.

With respect to the abnormality detecting device of the power switch of the present invention, as shown in FIG. 1 , the abnormality detecting device of the power switch is connected to a current path of a power switch S1, and includes: a partial pressure The circuit 10 has a voltage dividing 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 half field effect transistor (MOSFET), and more specifically, an N-type metal oxide half field effect transistor (NMOS). It should be noted that the aforementioned N-type MOS half-field effect transistor is only an example, and is not intended to limit the component type of the power switch S1.

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

The voltage dividing circuit 10 includes a first resistor R1 and a second resistor R1. The first resistor R1 and the second resistor R2 are connected in series with each other to form the voltage dividing node X, and the first resistor R1. The end of the second resistor R2 is connected to the source of the power switch S1 and is grounded; the voltage dividing circuit 10 is divided by the DC power source Vcc, the first resistor R1 and the second resistor R2. The pressure formula determines a second set value V2 which is a constant value, that is, a normal voltage value that can be measured at the voltage dividing node X when the differential pressure switch 20 is turned off.

The voltage dividing circuit 10, that is, the voltage dividing node X formed by connecting the first resistor R1 and the second resistor R2 in series, is connected to the drain of the power switch S1 through the differential pressure switch 20, and in the embodiment, the The differential pressure switch 20 is a diode, and the diode is connected to the voltage dividing node X of the voltage dividing circuit 10 by an anode, and the cathode thereof is connected to the drain of the power switch S1, that is, the dividing voltage of the voltage dividing circuit 10 The pressure node X is connected in the forward direction to the drain of the power switch S1 through the diode.

Under the foregoing architecture, when the power switch S1 is turned on, the voltage Vds (ie, the voltage on the current path) between the 汲 and the source of the power switch S1 is small, and the differential pressure switch 20 is turned on, so the voltage dividing circuit The voltage Vx on the 10-divide node X is pulled down and is smaller than the second set value V2. The equivalent circuit at this time is as shown in FIG. 2A, and the voltage Vx on the voltage dividing node X of the voltage dividing circuit 10 is as follows: Formula: , Vf = forward voltage of the differential pressure switch 20

However, when the temperature of the power switch S1 rises, its conduction resistance Rds also increases at a fixed current (see the characteristic diagram of FIG. 3). When the temperature of the power switch S1 continues to rise, its on-resistance Rds follows. If it is increased, its voltage Vds (汲 source current Ids × on-resistance Rds) increases accordingly, 俟 is greater than a first set value V1, and the differential pressure switch 20 is turned off (the equivalent circuit is as shown in FIG. 2B). When the voltage dividing circuit 10 determines that the voltage Vx is equal to the second set value V2, an abnormality alarm can be generated; at this time, the voltage dividing circuit 10 divides the voltage on the node X as: Vx = V2 = Vcc × R2/(R1+R2)

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

The voltage Vx of the voltage dividing node X of the voltage dividing circuit 10 can be obtained by a digital controller in a sampling manner, and the digital controller simultaneously controls the conduction of the power switch S1. 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. Periodically conducting, sampling the voltage dividing node of the voltage dividing circuit 10 during each conduction period of the power switch S1. When the sampled voltage dividing node X voltage Vx is equal to the second set value V2, a digital controller can generate a Abnormal alert.

Referring to FIG. 5, it is a further preferred embodiment of the present invention. The basic structure is substantially the same as that of the previous embodiment. The differential pressure switch 20' is still a diode, and the difference lies in: the diode. The cathode is connected to the voltage dividing node X of the voltage dividing circuit 10, and the anode is connected to the drain of the power switch S1.

In the foregoing embodiment, 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 on-resistance Rds is normal, the 汲 and source voltages Vds are not greater than the forward voltage of the diode, and the voltage Vx of the voltage dividing circuit 10 of the voltage dividing circuit 10 does not reach the second setting. For the value V2, the sampling controller will not generate an abnormal alarm; if the temperature of the power switch S1 rises abnormally, the on-resistance Rds is relatively increased, and the 汲 and source voltages Vds are larger than the forward voltage of the diode, resulting in partial voltage division. The voltage Vx of the voltage divider node X increases, and when it is greater than the second set value V2, the sampled controller immediately generates an abnormal alarm.

Referring to FIG. 6, when the power switch S1 is used in the power factor correction circuit 82, the foregoing digital controller may be a PFC controller in the power factor correction circuit 82, and the abnormality detecting device 1 of the present invention and the power switch S1, respectively. The bungee and the source are connected to the PFC controller, and the PFC controller is further connected to an alarm module (Alarm) to generate an abnormality alarm when detecting that the voltage Vx of the voltage dividing node X is greater than or equal to the second set value V2. When the power switch S1 is used in a DC-to-DC conversion circuit, the aforementioned digital controller may be a pulse width modulation controller in the DC-to-DC conversion circuit.

It can be seen from the above that the present invention mainly utilizes the relationship between the temperature of the power switch and its on-resistance, and determines whether the voltage on the current path of the power switch is greater than a set value for further analysis of whether the on-resistance is abnormally increased, and further As a basis for determining whether or not the power switch temperature abnormality alarm is generated, the operating characteristics of the power switch can be monitored at any time, and an alarm is generated in time for an abnormal situation to ensure the stability of the system and avoid damage.

1‧‧‧Anomaly detection device
10‧‧‧voltage circuit
20,20'‧‧‧ differential pressure switch

1 is a 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. Figure 3 is a graph showing the relationship between the temperature and the on-resistance of the power switch. Figure 4 is a waveform diagram of the present invention for sampling a voltage dividing circuit with a digital controller. Figure 5 is a circuit diagram of still another preferred embodiment of the present invention. Figure 6 is a circuit diagram of the present invention applied to an exchange power supply. Figure 7 is a circuit diagram of a known switched power supply.

10‧‧‧voltage circuit

20‧‧‧ differential pressure switch

Claims (10)

An abnormality detecting device for a power switch is connected to a current path of a power switch, comprising: a voltage dividing circuit having a voltage dividing node, and the voltage dividing node is connected to a digital controller; a differential pressure switch Connected between the voltage dividing node of the voltage dividing circuit and the current path of the power switch; thereby, 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 dividing node The voltage is less than a second set value. 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 when the voltage of the voltage dividing node is greater than or equal to the second set value, an abnormal alarm may be generated. . The abnormality detecting device for the power switch according to claim 1, wherein the differential pressure opening relationship is constituted by a diode. The abnormality detecting device of the power switch according to claim 2, wherein an anode of the differential pressure switch is connected to a voltage dividing node of the voltage dividing circuit, and a cathode thereof is connected to a current path of the power switch. The device of claim 3, wherein the voltage dividing circuit comprises a first resistor and a second resistor, wherein the first resistor and the second resistor are connected in series with each other to form the voltage dividing node. The other end of the first resistor is connected to the DC power source, and the other end of the second resistor is connected to the source of the power switch and grounded. The abnormality detecting device for the power switch according to claim 4, wherein the voltage dividing circuit determines the second set value according to the voltage dividing formula by the DC power source, the first resistor and the second resistor. The abnormality detecting device of the power switch according to claim 5, wherein the first set value is a forward voltage of the differential pressure switch. An abnormality detecting device for a power switch according to claim 1, wherein the power is related to a MOSFET, and the drain and the source constitute the current path. The abnormality detecting device for the power switch according to any one of claims 1 to 7, wherein the digital controller generates a driving signal to drive the power switch, and the voltage dividing circuit is in each conducting period of the power switch The voltage divider node samples. The abnormality detecting device of the power switch according to any one of claims 1 to 7, wherein the digital controller is a PFC controller. The abnormality detecting device for the power switch according to any one of claims 1 to 7, wherein the digital controller is a pulse width modulation controller.