TWI382623B - Over current protection apparatus and method thereof for an amplifier - Google Patents

Description

Overcurrent protection device of amplifier and operation method thereof

The present invention relates to an overcurrent protection device, and more particularly to an overcurrent protection device for use in an audio amplifier.

In recent years, in the midst of the maturity of semiconductor technology and the popularity of portable consumer electronic devices, how to design audio-assisted audio amplifiers has become an important research topic. In general, Class D audio amplifiers are the most efficient of all amplifiers. In addition to traditional linear amplifiers, Class D audio amplifiers require less size than their products. Therefore, it is widely used in various applications requiring high efficiency and small volume.

In general, Class D audio amplifiers include a bridge power circuit to drive a load, such as a speaker. The component of the H-bridge power circuit includes four power transistors that are supplied to the speaker by intermittent turn-off of the power transistors. Once the current flowing through it exceeds the capacity that the power transistor can withstand, an overcurrent fault will occur, which causes many causes of overcurrent faults, such as short circuits or surges. These faults can permanently or severely damage the power transistor, causing damage to the entire audio circuit.

Therefore, how to avoid sudden overcurrents from jeopardizing circuit components must be considered in the design of audio circuits.

Accordingly, it is a primary object of the present invention to provide an overcurrent protection device that prevents sudden overcurrents from damaging circuit components and thereby causing damage to the audio circuitry.

The overcurrent protection device of the audio amplifier of the present invention comprises: a voltage detecting unit for obtaining a complex terminal voltage of the switching element of the audio amplifier; and a differential unit for outputting a voltage difference according to the obtained terminal voltage; And determining whether the voltage difference is greater than a predetermined threshold; and a closing unit, when the voltage difference is greater than a preset threshold, turning off the power of the audio amplifier.

In another embodiment, the present invention provides an overcurrent protection method for an audio amplifier, comprising: obtaining a complex terminal voltage of at least one switching component of the audio amplifier; outputting a voltage difference according to the terminal voltages; and determining whether the voltage difference is greater than one a preset threshold; and when the voltage difference is greater than a predetermined threshold, the power of the audio amplifier is turned off.

Since the overcurrent protection device of the present invention can instantly monitor the terminal voltage of the switching element and immediately cut off the power supply when the terminal voltage exceeds a rated value, it is possible to surely protect each component in the circuit from overcurrent damage.

Referring to Fig. 1, there is shown a system diagram of an overcurrent protection device of the present invention. In a preferred embodiment, the overcurrent protection device 100 is used in an audio amplification circuit 300 to prevent the switching elements 210 and 220 of the audio amplification circuit 300 from being subjected to overcurrent damage. The audio amplifying circuit 300 is, for example, a class D audio amplifier. However, in other embodiments, this overcurrent protection The protection device 100 can also be used for Class A, Class B or Class AB audio amplifiers.

The overcurrent protection device 100 includes a voltage detecting unit 120, a differential unit 130, a determining unit 140, and a closing unit 150. The voltage detecting unit 120 is configured to obtain the terminal voltages S11, S12 or / and S21, S22 of the switching elements 210 or / and 220. In one embodiment, for example, the terminal voltages S11, S12 of the switching elements 210 are obtained. It should be noted that in practical applications, the number of switching elements coupled is not limited to the number of switching elements of the present invention. The differential unit 130 is connected to the voltage detecting unit 120 for outputting a voltage difference Sb according to the terminal voltages S11 and S12 obtained by the voltage detecting unit 120. The determining unit 140 is connected to the differential unit 130 for receiving and determining whether the voltage difference Sb is greater than a predetermined threshold, and sending a control signal Sc, wherein a comparison circuit 141 is configured to compare the voltage difference Sb with a preset threshold. This preset threshold is, for example, a threshold generated by a bandgap circuit that does not vary with supply power and temperature. The closing unit 150 is connected to the determining unit 140 to turn off or maintain the power of the audio amplifying circuit 300 according to the control signal Sc, wherein when the voltage difference Sb is greater than a preset threshold, the turning off unit 150 turns off the power of the audio amplifying circuit 300, and vice versa. When the voltage difference Sb is less than the preset threshold, the closing unit 150 will maintain the power of the audio amplifier circuit 300 in the activated state.

In addition, the overcurrent protection device 100 of the present invention further includes a switching unit 110 for generating a plurality of switching signals Sa for controlling switching of the switching elements 210 and 220, and controlling the voltage detecting unit 120 to obtain the corresponding switching element 210. And the voltage at the end of 220.

2 is a diagram showing a class D audio amplifier according to an embodiment of the invention. An overview of the H-bridge power circuit in the bulk. The H-bridge power circuit 400 includes four power transistors Q1, Q2, Q3, and Q4 and a load L, such as a speaker. When operating, a PWM signal will control the diagonal power transistor switch of the H-bridge power circuit 400 in a symmetrical manner, causing it to be turned on and off intermittently to supply current to the load L. When the power transistors Q1 and Q4 are turned on, the output voltage on the load L is positive; when the power transistors Q2 and Q3 are turned on, the output voltage on the load L is negative.

In one embodiment, the power transistor Q1 is the switching element 210 shown in FIG. 1, and the power transistor Q4 is the switching element 220 shown in FIG. The drain and source terminal voltages of the power transistor Q1 are S11 and S12, respectively, and the drain and source terminal voltages of the power transistor Q4 are S21 and S22, respectively.

Since the resistance value and the maximum withstand current value of the power transistor can be determined according to the process conditions of each power transistor, the maximum voltage that can be withstood by the source and the 汲 terminal of each power transistor can be estimated according to Ohm's law. value. Therefore, the voltage detecting unit 120 of the present invention is used to obtain the drain and source terminal voltages S11, S12 or/and S21, S22 of the power transistor Q1 or/and the power transistor Q4. The voltage difference Sb between the drain and source terminal voltages S11, S12 or / and S21, S22 is calculated via the differential unit 130. Therefore, it is determined whether the voltage difference Sb is greater than a predetermined value.

FIG. 3 is a schematic circuit diagram of a voltage detecting unit and a differential unit according to an embodiment of the invention. The voltage detecting unit 120 includes a switch module 121. The switch module 121 includes a plurality of switch switches W1~Wn and are respectively connected At the two ends of the switching element, that is, the source and the 汲 terminal of the power transistors Q1 to Q4. In one embodiment, the switch W1 is connected to the source terminal of the power transistor Q1 for obtaining the source terminal voltage S12 of the power transistor Q1; the switch W3 is connected to the drain of the power transistor Q1 for obtaining power. The threshold voltage S11 of the crystal Q1; the switch W2 is connected to the source terminal of the power transistor Q4 for obtaining the source terminal voltage S22 of the power transistor Q4; the switch W4 is connected to the drain of the power transistor Q4 for obtaining The extreme voltage S21 of the power transistor Q4. The turn-on or turn-off of the switch W1~Wn is controlled by the switching signal Sa sent by the switching unit 110 to obtain and output the drain and source terminal voltages S11, S12 of the power transistor Q1 or/and the power transistor Q4 or / and S21, S22 to the differential unit 130.

The differential unit 130 includes a differential amplifying circuit 131 coupled to the switch module 121 for receiving the terminal voltages S11, S12, S21, and S22, and calculating the output terminal voltage difference Sb. The differential amplifier circuit 131 has an inverting input terminal A and a non-inverting input terminal B. With the switch module 121, the inverting input terminal A has a lower level of receiving voltages S11, S12, S21, and S22. The bits, that is, the source terminal voltages S12, S22 of the power transistor Q1 and the power transistor Q4. The non-inverting input terminal B receives the higher potentials of the terminal voltages S11, S12, S21, and S22, that is, the 汲 extreme voltages S11 and S21 of the power transistor Q1 and the power transistor Q4. And calculating the output terminal voltage difference Sb, wherein the voltage difference Sb is the power source crystal Q1 or the power transistor Q4 drain source source voltage difference. In addition, the differential amplifying circuit 130 further includes a plurality of resistors R _A and R _B for converting the difference of the terminal voltages into the voltage difference Sb according to the impedance ratio of the resistors.

4 is a flow chart showing an overcurrent protection method in accordance with an embodiment of the present invention. As shown in FIGS. 1 and 4, first in step 410, a plurality of switching signals are generated to the switching element to switch the switching elements. A switching unit 110 generates a plurality of switching signals Sa to control switching of the switching elements 210 and 220. Next, in step 420, the complex terminal voltage of at least one switching element of the audio amplifier is obtained. The voltage detecting unit 120 is configured to obtain the terminal voltages S11, S12 or / and S21, S22 of the switching elements 210 or / and 220. In one embodiment, for example, the terminal voltages S11, S12 of the switching elements 210 are obtained. Next, in step 430, a voltage difference is output according to the terminal voltage. A differential unit 130 is connected to the voltage detecting unit 120, and outputs a voltage difference Sb according to the terminal voltages S11 and S12 obtained by the voltage detecting unit 120. Next, in step 440, it is determined whether the voltage difference is greater than a predetermined threshold. A determining unit 140 is connected to the differential unit 130 for receiving and determining whether the voltage difference Sb is greater than a predetermined threshold, and sending a control signal Sc, wherein a comparison circuit 141 is configured to compare the voltage difference Sb with a preset threshold. , this preset threshold. And, in step 450, when the voltage difference is greater than the preset threshold, the power of the audio amplifier is turned off. The closing unit 150 is connected to the determining unit 140 to turn off or maintain the power of the audio amplifying circuit 300 according to the control signal Sc, wherein when the voltage difference Sb is greater than a preset threshold, the turning off unit 150 turns off the power of the audio amplifying circuit 300, and vice versa. When the voltage difference Sb is less than the preset threshold, the closing unit 150 will maintain the power of the audio amplifier circuit 300 in the activated state.

Wherein, a switch module 121 including a plurality of switch switches W1 W Wn They are respectively connected to the two ends of the switching element to selectively switch the terminal voltages of the switching elements according to a plurality of switching switches W1 to Wn in the switching module 121. A differential amplifying circuit receives a terminal voltage of the switching element and outputs a voltage difference, wherein the differential amplifying circuit is coupled to the switch module.

In summary, the overcurrent protection device of the present invention can instantly monitor the terminal voltage of the switching element and immediately cut off the power supply when the terminal voltage exceeds a rated value, thereby reliably protecting each component in the circuit from overcurrent. damage.

Although the present invention has been described above in terms of a preferred embodiment, it is not intended to limit the invention, and it is obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

300‧‧‧Audio amplification circuit

100‧‧‧Overcurrent protection device

110‧‧‧Switch unit

120‧‧‧Voltage detection unit

121‧‧‧Switch Module

130‧‧‧Differential unit

131‧‧‧Differential Amplifying Circuit

140‧‧‧judging unit

141‧‧‧Comparative circuit

150‧‧‧Close unit

210‧‧‧Switching elements

220‧‧‧Switching elements

400‧‧‧H bridge power circuit

410‧‧‧ generates a plurality of switching signals to the switching element to switch the switching element

420‧‧‧Get the complex terminal voltage of at least one switching element of the audio amplifier

430‧‧‧ Output a voltage difference depending on the terminal voltage

440‧‧‧Check if the voltage difference is greater than a predetermined threshold

450‧‧‧When the voltage difference is greater than the preset threshold, turn off the power of the audio amplifier

S11, S12, S21, S22, Sn1, Sn2‧‧‧ terminal voltage

Sa‧‧‧Switching signal

Sb‧‧‧ voltage difference

Sc‧‧‧ control signal

R _A , R _B ‧‧‧resistance

Q1, Q2, Q3, Q4‧‧‧ power transistors

W1~Wn‧‧‧Toggle switch

L‧‧‧load

The above and other objects, features, advantages and embodiments of the present invention will become more <RTIgt; Functional block diagram of the current protection device.

2 is a schematic diagram of an H-bridge power circuit in a class D audio amplifier according to an embodiment of the invention.

FIG. 3 is a schematic circuit diagram of a voltage detecting unit and a differential unit according to an embodiment of the invention.

4 is a flow chart showing an overcurrent protection method in accordance with an embodiment of the present invention.

300‧‧‧Audio amplification circuit

100‧‧‧Overcurrent protection device

110‧‧‧Switch unit

120‧‧‧Voltage detection unit

121‧‧‧Switch Module

130‧‧‧Differential unit

140‧‧‧judging unit

141‧‧‧Comparative circuit

150‧‧‧Close unit

210‧‧‧Switching elements

220‧‧‧Switching elements

S11, S12, S21, S22‧‧‧ terminal voltage

Sa‧‧‧Switching signal

Sb‧‧‧ voltage difference

Sc‧‧‧ control signal

Claims (21)

An overcurrent protection device for an amplifier, the amplifier having at least one switching element, the overcurrent protection device comprising: a voltage detecting unit for obtaining a plurality of terminal voltages of the switching element; and a differential unit for determining the The terminal voltage outputs a voltage difference; a determining unit is configured to determine whether the voltage difference is greater than a predetermined threshold; and a closing unit, when the voltage difference is greater than the predetermined threshold, the closing unit turns off the amplifier Power supply. The overcurrent protection device of claim 1, further comprising: a switching unit for generating a plurality of switching signals to the switching element to switch the switching element. The overcurrent protection device of claim 2, wherein the voltage detection unit comprises: a switch module connected to the switch component for switching the switch module according to the switching signals to select The terminal voltages of the switching elements are output sexually. The overcurrent protection device of claim 3, wherein the differential unit comprises: a differential amplifier circuit coupled to the switch module for receiving the terminals The voltage is output and the voltage difference is output. The overcurrent protection device of claim 4, wherein the differential amplifier circuit has an inverting input terminal and a non-inverting input terminal, and the inverting input terminal receives the switch module The terminal voltage has a lower level, and the non-inverting input receives a higher level of the terminal voltages. The overcurrent protection device of claim 4, wherein the differential amplifying circuit comprises: a plurality of resistors for converting the difference of the terminal voltages to the voltage difference according to impedance ratios of the resistors. The overcurrent protection device of claim 1, wherein the determining unit comprises: a comparison circuit for comparing the voltage difference with the preset threshold and outputting a determination signal, the closing unit is based on the determining The signal turns off the power to the amplifier. The overcurrent protection device of claim 1, wherein the switching element is a power transistor located at an output stage of the amplifier. The overcurrent protection device of claim 1, wherein the number of the switching elements is four. The overcurrent protection device of claim 1, wherein the amplifier is a class D amplifier. An overcurrent protection method for an amplifier, comprising: obtaining a complex terminal voltage of at least one switching component of the amplifier; outputting a voltage difference according to the terminal voltages; determining whether the voltage difference is greater than a predetermined threshold; and when the voltage When the difference is greater than the preset threshold, the power to the amplifier is turned off. The overcurrent protection method of claim 11, further comprising: generating a plurality of switching signals to the switching element to switch the switching element. The overcurrent protection method of claim 12, further comprising: connecting the switching component by a switch module; switching the switch module according to the switching signals to selectively output the switching component The terminal voltages. The overcurrent protection method according to claim 13, wherein the step of outputting the voltage difference according to the terminal voltages comprises: receiving a voltage of the terminals by a differential amplifying circuit and outputting the voltage Poor, wherein the differential amplifying circuit is coupled to the switch module. The overcurrent protection method according to claim 14, wherein the differential amplifier circuit has an inverting input terminal and a non-inverting input terminal, and the inverting input terminal receives the switch module The terminal voltage has a lower level, and the non-inverting input receives a higher level of the terminal voltages. The overcurrent protection method according to claim 14, wherein the step of inputting the terminal voltages by the differential amplifying circuit and outputting the voltage difference comprises: causing the terminals by an impedance ratio of a plurality of resistors The difference in voltage is converted to this voltage difference. The overcurrent protection method of claim 11, wherein the step of determining whether the voltage difference is greater than the predetermined threshold comprises comparing the voltage difference with the predetermined threshold and outputting a determination signal. The overcurrent protection method according to claim 17, wherein the step of turning off the power of the amplifier is to turn off the power of the amplifier according to the determination signal. An overcurrent protection method according to claim 11, wherein the switching element is a power transistor located at the amplifier The output stage. The overcurrent protection method according to claim 11, wherein the number of the switching elements is four. The overcurrent protection method of claim 11, wherein the amplifier is a class D amplifier.