Power tube overcurrent protection circuit

Abstract

The invention relates to the technical field of semiconductor integrated circuits, in particular to a power tube overcurrent protection circuit, which comprises a power tube current detection circuit used for acquiring an output signal of a power tube control circuit, detecting a drain-source voltage difference of a power tube when the output signal is a logic high level, converting the drain-source voltage difference into a current signal, and outputting the current signal; the current signal is restored to a first voltage value, and the first voltage value is used as a negative phase input signal of the comparator; the drain-source voltage generation circuit is used for acquiring a reference current signal, converting the reference current signal into a second voltage value, and taking the second voltage value as a normal phase input signal of the comparator; the comparator is used for comparing the first voltage value with the second voltage value; and the power tube control circuit is used for controlling the power tube to be turned off. According to the invention, the working current when the power tube is turned on can be detected, various reliability problems caused by series connection of small resistors are avoided, the ground potential of the power tube and the ground potential of the protection circuit can be isolated, and the circuit can be widely applied.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor integrated circuits, and in particular to an overcurrent protection circuit for a power tube. Background Art

[0002] In high-power circuits, power tubes often get damaged due to overcurrent, so some protection circuits are usually needed to shut down the circuit when overcurrent occurs to avoid damage to the power tubes. In these protection circuits, it is usually necessary to detect the output current of the power tubes.

[0003] In the existing current detection circuit, a small resistor is usually connected in series for current detection. However, this detection method has certain disadvantages. In the case of large current, a small resistor connected in series at the source end of the power tube will cause a certain voltage loss and generate a lot of heat, reducing the efficiency of the system. Although the method of detecting the drain-source voltage of the power tube can effectively solve the above problems, in some applications where the power tube is suspended, the potential of the power tube and the protection circuit are different, and there is a problem that the drain-source voltage cannot be directly introduced into the protection circuit. Summary of the invention

[0004] The purpose of the present invention is to provide a power tube overcurrent protection circuit, which can detect the working current when the power tube is turned on and avoid various reliability problems caused by small series resistance. At the same time, it can isolate the ground potential of the power tube from the ground potential of the protection circuit and can be widely used.

[0005] In order to achieve the above object, a power tube overcurrent protection circuit is provided, comprising: a power tube current detection circuit, a drain-source voltage generation circuit, a comparator, and a power tube control circuit; Power tube current detection circuit: used to obtain the output signal of the power tube control circuit, detect the drain-source voltage difference of the power tube when the output signal is at a logic high level, convert the drain-source voltage difference into a current signal, and restore the current signal to a first voltage value, and use the first voltage value as a negative input signal of the comparator; and also used to convert the first voltage value into a current and transmit it between different ground potentials; the ground potential includes AGND and PGND; Drain-source voltage generating circuit: used to obtain a reference current signal, convert the reference current signal into a second voltage value through a MOS tube of the same type and proportionally reduced size as the power tube, and use the second voltage value as a positive input signal of the comparator; Comparator: used to compare the first voltage value with the second voltage value, and output the comparison result to the power tube control circuit; Power tube control circuit: used to obtain a control signal and use it as the first input terminal, and to obtain a comparison result of a comparator and use it as the second input terminal. When the first input terminal and the second input terminal are both at a logic high level, the output signal is at a high level to control the power tube to turn on. Otherwise, the output signal is at a low level to control the power tube to turn off.

[0006] Further, the power tube current detection circuit includes a bias circuit, a voltage-to-current circuit and a current-to-voltage circuit; Bias circuit: used to generate the working current required for the circuit to work; Voltage-to-current circuit: used to collect the drain voltage of the power tube, convert the drain voltage of the power tube into a current signal, and copy the current signal to the current-to-voltage circuit; the ground potential of the voltage-to-current circuit is the same as that of the power tube, both of which are PGND; Current-to-voltage circuit: used to convert the current signal into a first voltage value that can be processed by the comparator and serve as the negative input signal of the comparator; the ground potential of the current-to-voltage circuit is different from the ground potential of the power tube, which is AGND.

[0007] Furthermore, the power tube current detection circuit includes a power tube M1, MOS tubes M2-M9, resistors R1-R6 and a plurality of current sources I B The MOS tubes M3-M7, MOS tube M9, resistors R1-R5 and several current sources I B The voltage-to-current circuit is formed; the plurality of current sources I B For the same current source I B1 , current source I B2 , current source I B3 and current source I B4 , as the bias power supply of the bias circuit; the MOS tube M3, MOS tube M4, current source I B1 , current source I B2 The MOS tube M5, the MOS tube M6, the current source I B3 , current source I B4 The second current mirror is formed; the voltage-to-current circuit includes a MOS tube M8 and a resistor R6.

[0008] Further, the gate of the MOS tube M2 in the voltage-to-current circuit is connected to the gate of the power tube M1, the drain of the MOS tube M2 is connected to the drain of the power tube M1, the source of the MOS tube M2 is connected to the resistor R5, and the resistor R5 is connected to PGND; The gate of the MOS tube M3 is connected to the gate of the MOS tube M4, and the current source I B1The gate of the MOS tube M3 is connected to the drain of the MOS tube M3, the source of the MOS tube M3 is connected to the resistor R1, and the resistor R1 is connected to the resistor R5; the current source I B2 Connected to the drain of the MOS tube M4, the source of the MOS tube M4 is connected to the resistor R2, and the resistor R2 is connected to PGND; The gate of the MOS tube M5 is connected to the gate of the MOS tube M6, and the current source I B3 The gate of the MOS tube M5 is connected to the drain of the MOS tube M5, the source of the MOS tube M5 is connected to the resistor R3, and the resistor R3 is connected to PGND; the current source I B4 connected to the drain of the MOS tube M6, the source of the MOS tube M6 is connected to the resistor R4, and the resistor R4 is connected to the resistor R5; The MOS tube M7 and the MOS tube M8 are a current mirror pair, the gate of the MOS tube M7 is connected to the gate of the MOS tube M8, and the source of the MOS tube M7 and the MOS tube M8 are both connected to the current source I B1 , current source I B2 , current source I B3 and current source I B4 The gate of the MOS tube M7 is connected to its source and connected to the source of the MOS tube M9. The gate of the MOS tube M9 is connected to the drain of the MOS tube M6. The source of the MOS tube M9 is connected to the source of the MOS tube M5.

[0009] Furthermore, the current-to-voltage circuit includes a MOS tube M8 and a resistor R6, the drain of the MOS tube M8 is connected to the resistor R6, the resistor R6 is connected to AGND, and the voltage across the input resistor R6 is used as the first voltage value.

[0010] Furthermore, the drain-source voltage generating circuit includes a MOS tube M10, a reference current source I REF ; The MOS tube M10 is a MOS tube of the same type as the power tube M1, and the width-to-length ratio of the MOS tube M10 is set to 1 / N of the width-to-length ratio of the power tube M1; the reference current source I REF The voltage between the drain and the source of the MOS tube M10 is connected to the drain of the MOS tube M10 . The source of the MOS tube M10 is connected to AGND. The drain-source voltage of the MOS tube M10 is used as the second voltage value.

[0011] Principles and advantages: This solution is applied to the current detection circuit of the power tube in the power circuit and determines whether the power tube current is overcurrent. It can realize the overcurrent protection function of the power tube, avoid using a small series resistor to detect the power tube current, and instead achieve the purpose of power tube current detection by sampling the power tube drain-source voltage difference. It can also realize the conversion of the power tube drain-source voltage difference into current for transmission between different potential circuit modules, solving the problem that when the power tube is located in a suspended ground system, it is impossible to sample the power tube drain-source voltage to the protection circuit module. The system integration, reliability and current detection accuracy are improved, and the overall circuit has the advantages of simple design, flexibility and easy implementation. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A logic block diagram of a power tube overcurrent protection circuit according to an embodiment of the present invention; Figure 2 This is the circuit schematic diagram of the power tube current detection circuit; Figure 3 This is the circuit schematic diagram of the drain-source voltage generating circuit. DETAILED DESCRIPTION

[0013] The following is further described in detail through specific implementation methods: Example A power tube overcurrent protection circuit, basically as follows Figure 1 , Figure 2 , Figure 3 As shown, a power tube current detection circuit, a drain-source voltage generation circuit, a comparator, and a power tube control circuit; A power tube current detection circuit: used to obtain the output signal of the power tube control circuit, detect the drain-source voltage difference of the power tube when the output signal is at a logic high level, convert the drain-source voltage difference into a current signal, and restore the current signal to a first voltage value, and use the first voltage value as a negative input signal of the comparator; and also used to convert the first voltage value into a current and transmit it between different ground potentials; the ground potential includes AGND and PGND; the power tube current detection circuit includes a bias circuit, a voltage-to-current circuit, and a current-to-voltage circuit; Bias circuit: used to generate the working current required for the circuit to work; Voltage-to-current circuit: used to collect the drain voltage of the power tube, convert the drain voltage of the power tube into a current signal, and copy the current signal to the current-to-voltage circuit; the ground potential of the voltage-to-current circuit is the same as that of the power tube, both of which are PGND; Current-to-voltage circuit: used to convert the current signal into a first voltage value that can be processed by the comparator and serve as the negative input signal of the comparator; the ground potential of the current-to-voltage circuit is different from the ground potential of the power tube, which is AGND.

[0014] The power tube current detection circuit includes a power tube M1, MOS tubes M2-M9, resistors R1-R6 and a plurality of current sources I B The MOS tubes M3-M7, MOS tube M9, resistors R1-R5 and several current sources I B The voltage-to-current circuit is formed; the plurality of current sources I B For the same current source I B1 , current source I B2 , current source I B3 and current source I B4 , as the bias power supply of the bias circuit; the MOS tube M3, MOS tube M4, current source I B1 , current source I B2 The MOS tube M5, the MOS tube M6, the current source I B3 , current source I B4 The second current mirror is formed; the voltage-to-current circuit includes a MOS tube M8 and a resistor R6.

[0015] The gate of the MOS tube M2 in the voltage-to-current circuit is connected to the gate of the power tube M1, the drain of the MOS tube M2 is connected to the drain of the power tube M1, the source of the MOS tube M2 is connected to the resistor R5, and the resistor R5 is connected to PGND; The gate of the MOS tube M3 is connected to the gate of the MOS tube M4, and the current source I B1 The gate of the MOS tube M3 is connected to the drain of the MOS tube M3, the source of the MOS tube M3 is connected to the resistor R1, and the resistor R1 is connected to the resistor R5; the current source I B2 Connected to the drain of the MOS tube M4, the source of the MOS tube M4 is connected to the resistor R2, and the resistor R2 is connected to PGND; The gate of the MOS tube M5 is connected to the gate of the MOS tube M6, and the current source I B3 The gate of the MOS tube M5 is connected to the drain of the MOS tube M5, the source of the MOS tube M5 is connected to the resistor R3, and the resistor R3 is connected to PGND; the current source I B4 connected to the drain of the MOS tube M6, the source of the MOS tube M6 is connected to the resistor R4, and the resistor R4 is connected to the resistor R5; The MOS tube M7 and the MOS tube M8 are a current mirror pair, the gate of the MOS tube M7 is connected to the gate of the MOS tube M8, and the source of the MOS tube M7 and the MOS tube M8 are both connected to the current source I B1 , current source I B2 , current source I B3 and current source I B4The gate of the MOS tube M7 is connected to its source and connected to the source of the MOS tube M9. The gate of the MOS tube M9 is connected to the drain of the MOS tube M6. The source of the MOS tube M9 is connected to the source of the MOS tube M5.

[0016] The current-to-voltage circuit includes a MOS tube M8 and a resistor R6. The drain of the MOS tube M8 is connected to the resistor R6. The resistor R6 is connected to AGND. The voltage across the input resistor R6 is used as the first voltage value.

[0017] Drain-source voltage generating circuit: used to obtain a reference current signal, convert the reference current signal into a second voltage value through a MOS tube of the same type and proportionally reduced size as the power tube, and use the second voltage value as a positive input signal of the comparator; The drain-source voltage generating circuit includes a MOS tube M10, a reference current source I REF ; The MOS tube M10 is a MOS tube of the same type as the power tube M1, and the width-to-length ratio of the MOS tube M10 is set to 1 / N of the width-to-length ratio of the power tube M1; the reference current source I REF The voltage between the drain and the source of the MOS tube M10 is connected to the drain of the MOS tube M10 . The source of the MOS tube M10 is connected to AGND. The drain-source voltage of the MOS tube M10 is used as the second voltage value.

[0018] Comparator: used to compare the first voltage value with the second voltage value, and output the comparison result to the power tube control circuit; Power tube control circuit: used to obtain a control signal and use it as the first input terminal, and to obtain a comparison result of a comparator and use it as the second input terminal. When the first input terminal and the second input terminal are both at a logic high level, the output signal is at a high level to control the power tube to turn on. Otherwise, the output signal is at a low level to control the power tube to turn off.

[0019] The power tube control circuit, the power tube and the power tube current detection circuit are connected to PGND, and the power tube current detection circuit, the drain-source voltage generating circuit and the comparator are connected to AGND; and are used to collect the drain-source voltage difference of the power tube located on PGND and process it in the power tube current detection circuit, the drain-source voltage generating circuit and the comparator using AGND.

[0020] In this embodiment, the current source I B It can be any form of current source, and the power tube M1 is the power tube protected by the present invention.

[0021] like Figure 2As shown, CTRL is the gate control signal of the power tube, which is a logic level. When the CTRL signal is a logic high level, the power tube will be turned on. The power tube works in the linear region at this time and can be regarded as a resistor. Assuming the on-resistance of the power tube is RON1, the output current when the power tube is turned on is I OUT , we can find the drain-source voltage V of the power tube DS1 The expression is:

[0022] From the above formula, we can know that the drain-source voltage of the power tube is proportional to the output current. Therefore, by detecting the drain-source voltage of the power tube, we can know the output current of the power tube.

[0023] Figure 2 The MOS tube M2 is a tube with a relatively small width and length, and its size is much smaller than the power tube. The gate of the MOS tube M2 is connected to the gate of the power tube M1. Therefore, when CTRL is at a high level, the MOS tube M2 and the power tube M1 are turned on synchronously. At this time, the drain-source voltage difference of the MOS tube M2 approaches 0, so the source voltage of the MOS tube M2 is approximately equal to the drain voltage of the power tube. At this time, the voltage difference across the resistor R5 is approximately equal to the drain-source voltage of the power tube.

[0024] The source voltage of MOS tube M5 in the power tube current detection circuit can be determined by I CTRL Adding this to IB and multiplying it by the resistance of R3 gives:

[0025] The source voltage of MOS tube M6 in the power tube current detection circuit can be determined by I B4 The voltage drop across resistor R4 plus the voltage across resistor R5 is equal to the drain-source voltage of the power tube:

[0026] The sizes of MOS tubes M3-M6 in the power tube current detection circuit are exactly the same, and the bias current sources of the branches where the four tubes are located are all IB, so the gate-source voltage difference of the four MOS tubes M3-M6 is equal. Therefore, it can be deduced that the source voltages of the two MOS tubes M5 and M6 are equal. Therefore, we have:

[0027] Set R4=R3, simplify to get I CTRL The expression is:

[0028] The width-to-length ratio of the current mirror pair M7 and M8 is the same, so the current in the M8 branch is also I CTRL , set R6 equal to R3, so I CTRLThe voltage generated by the resistor R6 is:

[0029] Therefore, the output of the power tube current detection circuit is equal to V DS1 , that is, the drain-source voltage V of the power tube M1 DS1 .

[0030] like Figure 3 As shown in the figure, it is a drain-source voltage generating circuit. A reference current flows through a normally open proportional MOS tube M10 of the same type as the power tube to generate a V DS10 , since the ratio of M10 on-resistance to M10 on-resistance is inversely proportional to the size of both, and V DS10 by I REF Decide, set different I REF Different V DS10 , thus obtaining different current limit thresholds. Then V DS3 With V DS1 pass Figure 1 The comparator in the circuit is used for comparison to obtain a digital logic signal, which is input into the power tube control circuit so that when overcurrent occurs, the control circuit outputs a low level, thereby shutting down the power tube and realizing the overcurrent protection function.

[0031] The above is only an embodiment of the present invention. The common sense such as the known specific structure and characteristics in the scheme is not described in detail here. The ordinary technicians in the relevant field know all the common technical knowledge in the technical field of the invention before the application date or priority date, can obtain all the existing technologies in the field, and have the ability to apply the conventional experimental means before that date. The ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent. The protection scope required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A power tube overcurrent protection circuit, characterized in that: include: Power tube current detection circuit, drain-source voltage generation circuit, comparator, power tube control circuit; Power tube current detection circuit: used to obtain the output signal of the power tube control circuit, detect the drain-source voltage difference of the power tube when the output signal is at a logic high level, convert the drain-source voltage difference into a current signal, and restore the current signal to a first voltage value, and use the first voltage value as a negative input signal of the comparator; and also used to convert the first voltage value into a current and transmit it between different ground potentials; the ground potential includes AGND and PGND; Drain-source voltage generating circuit: used to obtain a reference current signal, convert the reference current signal into a second voltage value through a MOS tube of the same type and proportionally reduced size as the power tube, and use the second voltage value as a positive input signal of the comparator; Comparator: used to compare the first voltage value with the second voltage value, and output the comparison result to the power tube control circuit; Power tube control circuit: used to obtain a control signal and use it as the first input terminal, and to obtain a comparison result of a comparator and use it as the second input terminal. When the first input terminal and the second input terminal are both at a logic high level, the output signal is at a high level to control the power tube to turn on. Otherwise, the output signal is at a low level to control the power tube to turn off.

2. The power tube overcurrent protection circuit according to claim 1, characterized in that: The power tube current detection circuit includes a bias circuit, a voltage-to-current circuit and a current-to-voltage circuit; Bias circuit: used to generate the working current required for the circuit to work; Voltage-to-current circuit: used to collect the drain voltage of the power tube, convert the drain voltage of the power tube into a current signal, and copy the current signal to the current-to-voltage circuit; the ground potential of the voltage-to-current circuit is the same as that of the power tube, both of which are PGND; Current-to-voltage circuit: used to convert the current signal into a first voltage value that can be processed by the comparator and serve as the negative input signal of the comparator; the ground potential of the current-to-voltage circuit is different from the ground potential of the power tube, which is AGND.

3. The power tube overcurrent protection circuit according to claim 2, characterized in that: The power tube current detection circuit includes a power tube M1, MOS tubes M2-M9, resistors R1-R6 and a plurality of current sources I B The MOS tubes M3-M7, MOS tube M9, resistors R1-R5 and several current sources I B The voltage-to-current circuit is formed; the plurality of current sources I B For the same current source I B1 , current source I B2 , current source I B3 and current source I B4 , as the bias power supply of the bias circuit; the MOS tube M3, MOS tube M4, current source I B1 , current source I B2 The MOS tube M5, the MOS tube M6, the current source I B3 , current source I B4 The second current mirror is formed; the voltage-to-current circuit includes a MOS tube M8 and a resistor R6.

4. The power tube overcurrent protection circuit according to claim 3, characterized in that: The gate of the MOS tube M2 in the voltage-to-current circuit is connected to the gate of the power tube M1, the drain of the MOS tube M2 is connected to the drain of the power tube M1, the source of the MOS tube M2 is connected to the resistor R5, and the resistor R5 is connected to PGND; The gate of the MOS tube M3 is connected to the gate of the MOS tube M4, and the current source I B1 The gate of the MOS tube M3 is connected to the drain of the MOS tube M3, the source of the MOS tube M3 is connected to the resistor R1, and the resistor R1 is connected to the resistor R5; the current source I B2 Connected to the drain of the MOS tube M4, the source of the MOS tube M4 is connected to the resistor R2, and the resistor R2 is connected to PGND; The gate of the MOS tube M5 is connected to the gate of the MOS tube M6, and the current source I B3 The gate of the MOS tube M5 is connected to the drain of the MOS tube M5, the source of the MOS tube M5 is connected to the resistor R3, and the resistor R3 is connected to PGND; the current source I B4 connected to the drain of the MOS tube M6, the source of the MOS tube M6 is connected to the resistor R4, and the resistor R4 is connected to the resistor R5; The MOS tube M7 and the MOS tube M8 are a current mirror pair, the gate of the MOS tube M7 is connected to the gate of the MOS tube M8, and the source of the MOS tube M7 and the MOS tube M8 are both connected to the current source I B1 , current source I B2 , current source I B3 and current source I B4 The gate of the MOS tube M7 is connected to its source and connected to the source of the MOS tube M9. The gate of the MOS tube M9 is connected to the drain of the MOS tube M6. The source of the MOS tube M9 is connected to the source of the MOS tube M5.

5. The power tube overcurrent protection circuit according to claim 4, characterized in that: The current-to-voltage circuit includes a MOS tube M8 and a resistor R6. The drain of the MOS tube M8 is connected to the resistor R6. The resistor R6 is connected to AGND. The voltage across the input resistor R6 is used as the first voltage value.

6. The power tube overcurrent protection circuit according to claim 5, characterized in that: The drain-source voltage generating circuit includes a MOS tube M10, a reference current source I REF ; The MOS tube M10 is a MOS tube of the same type as the power tube M1, and the width-to-length ratio of the MOS tube M10 is set to 1 / N of the width-to-length ratio of the power tube M1; the reference current source I REF The voltage between the drain and the source of the MOS tube M10 is connected to the drain of the MOS tube M10 . The source of the MOS tube M10 is connected to AGND. The drain-source voltage of the MOS tube M10 is used as the second voltage value.

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