Control circuit and control method of power switch tube

Abstract

The invention discloses a control circuit and a control method for a power switch tube, and the method comprises the steps: setting a reference current signal as a ratio of a voltage difference between a first power end and a second power end of the power switch tube and a reference resistor, and sampling the working current of the power switch tube to obtain a sampling current signal; and the value of the reference current signal is controlled to be consistent with the value of the sampling current signal, so that the conduction internal resistance of the power switch tube is proportional to the resistance value of the reference resistor in the working process. According to the control scheme provided by the invention, the temperature coefficient of the conduction internal resistance of the switch tube can be the same as the temperature coefficient of the reference resistor set in the chip, and the impedance of the conduction internal resistance does not change along with the change of the output voltage, so that the working current of the power switch tube can be kept stable in the working process; the switching regulator is suitable for occasions with high requirements on the current of the power switching tube in the switching regulator.

Description

Technical Field

[0001] The present invention relates to the field of switch driving technology, and more specifically, to a control circuit and a control method for a power switch tube. Background Art

[0002] The power switch tube is the main power device of the switching regulator. During the operation of the switching regulator, the working current of the power switch tube will fluctuate due to various factors. The most important influence is that the on-state internal resistance of the switch tube changes due to changes in temperature or output voltage, which in turn causes the current to change. In some occasions, since the subsequent application equipment is highly sensitive to current, such as in RF working applications, if the current of the power switch tube fluctuates, it may have a greater impact on the subsequent application equipment. Therefore, it is necessary to control the internal resistance of the power switch tube to stabilize the working current of the switch tube.

[0003] like Figure 1 This is an existing method for regulating the on-state internal resistance of a switch tube. By detecting the operating temperature of the switch tube, the driving voltage of the switch tube is adjusted at different temperatures. Due to the different driving voltages, the on-state internal resistance of the switch tube is different, so that the on-state internal resistance of the switch tube can be basically maintained unchanged. However, the shortcomings of this solution are that, on the one hand, the temperature information of the switch tube needs to be tested, and on the other hand, since the voltage regulation is controlled by temperature, such as one temperature corresponds to one voltage, the voltage regulation is limited, generally in a step-like manner, resulting in the current of the switch tube also being in a step-like manner. This regulation method cannot meet the above-mentioned occasions where the subsequent equipment is sensitive to current.

[0004] Therefore, it is necessary to provide an improved technical solution to overcome the above technical problems existing in the prior art. Summary of the invention

[0005] In view of this, an object of the present invention is to provide a control circuit and a control method for a power switch tube, so as to solve the technical problem existing in the prior art that the internal resistance of the power switch tube changes with the output voltage or temperature.

[0006] A control circuit of a power switch tube according to the present application is applied to a switching regulator, and the control circuit includes: a reference current generating circuit, receiving a voltage difference between a first power terminal and a second power terminal of the power switch tube, and used to generate a reference current signal, and the reference current signal is set to be a ratio of the voltage difference between the first power terminal and the second power terminal of the power switch tube and the resistance value of a reference resistor; a sampling current generating circuit, sampling the working current of the power switch tube to obtain a sampling current signal; the output ends of the reference current generating circuit and the sampling circuit generating circuit are both connected to the control end of the power switch tube, and the control circuit controls the reference current signal to be consistent with the value of the sampling current signal, so that during operation, the on-state internal resistance of the power switch tube is proportional to the resistance value of the reference resistor.

[0007] Preferably, the resistance of the on-state internal resistance of the power switch tube is directly proportional to the resistance of the reference resistor.

[0008] Preferably, the reference resistor is arranged in a chip where the control circuit is located, and the impedance temperature coefficient of the on-state internal resistance of the power switch tube varies in accordance with the temperature coefficient of the reference resistor inside the chip.

[0009] Preferably, the control circuit controls the current branch of the reference current signal to be connected in series with the current branch of the sampled current signal.

[0010] Preferably, a series intermediate node of the current branch of the reference current signal and the current branch of the sampled current signal is connected to the control end of the power switch tube.

[0011] Preferably, when the power switch tube is an N-type transistor, the first power tube of the N-type transistor is connected to the output voltage, the second power terminal is connected to the reference ground, and the current branch of the reference current signal and the current branch of the sampling current signal are sequentially connected between the output voltage and the reference ground.

[0012] Preferably, when the power switch is a P-type transistor, the first power tube of the P-type transistor is connected to the power supply voltage, the second power terminal is connected to the output voltage, and the current branch of the sampling current signal and the current branch of the reference current signal are connected between the power supply voltage and the reference ground in sequence.

[0013] Preferably, the reference current generating circuit includes a first operational amplifier circuit, the reference resistor and a first current mirror circuit, the first input terminal of the operational amplifier circuit receives the output voltage, the second input terminal receives the sampling voltage, and the output terminal is connected to the control terminal of the first switch tube, the first switch tube and the reference resistor are connected in series between a first node and a reference ground, and the sampling voltage is the intermediate node voltage of the reference resistor and the first switch tube; the common connection terminal of the current mirror circuit receives the power supply voltage, the first output terminal is connected to the first node, and the second output terminal serves as the output terminal of the reference current generating circuit to output the reference current signal.

[0014] Preferably, the reference current generating circuit includes a first operational amplifier circuit, the reference resistor and a first current mirror circuit, the first input terminal of the operational amplifier circuit receives the output voltage, the second input terminal receives the sampling voltage, and the output terminal is connected to the control terminal of the first switch tube, the reference resistor and the first switch tube are connected in series between the power supply voltage and the first node, and the sampling voltage is the intermediate node voltage of the reference resistor and the first switch tube; the common connection terminal of the current mirror circuit receives the reference ground, the first output terminal is connected to the first node, and the second output terminal serves as the output terminal of the reference current generating circuit to output the reference current signal.

[0015] Preferably, the sampling current generating circuit includes a second current mirror, which is connected to the power switch tube to obtain the sampling current signal by mirror sampling, and the sampling current signal is directly proportional to the operating current of the power switch tube.

[0016] Preferably, the sampling current generating circuit includes a sampling circuit and a third current mirror. The sampling circuit obtains the operating current of the power switch tube through a sampling resistor, and then performs mirror processing through the third current mirror to obtain a sampling current signal that is proportional to the operating current of the power switch tube.

[0017] Preferably, the method comprises the following steps: obtaining a voltage difference value according to a voltage difference between a first power terminal and a second power terminal of the power switch tube, and obtaining a reference current signal according to a ratio of the voltage difference value to a reference resistor; sampling the working current of the power switch tube to obtain a sampled current signal; the reference current signal branch is connected in series with the sampled current signal branch, and a connection node between the two is coupled to the control terminal of the power switch tube.

[0018] Preferably, the on-state internal resistance of the power switch tube is proportional to the resistance value of the reference resistor.

[0019] Preferably, the impedance temperature coefficient of the on-state internal resistance of the power switch tube varies in accordance with the temperature coefficient of the reference resistor inside the chip.

[0020] Preferably, before the power switch tube is started, the reference current signal is greater than the sampling current signal, and the control terminal voltage of the power switch tube is charged high until it reaches the turn-on voltage of the power switch tube.

[0021] Preferably, after the power switch tube is turned on, the sampling current signal gradually increases until the reference current signal is equal to the sampling current signal, the control terminal voltage of the power switch tube remains constant, and the power switch tube enters a stable working state.

[0022] The control circuit of the power switch tube of the present invention is adopted, and the reference current signal is set as the ratio of the voltage difference between the first power terminal and the second power terminal of the power switch tube to the reference resistor, the working current of the power switch tube is sampled to obtain the sampling current signal, and the reference current signal is controlled to be consistent with the value of the sampling current signal, so that during the working process, the on-state internal resistance of the power switch tube is proportional to the resistance value of the reference resistor. The control scheme of the present application can make the on-state internal resistance temperature coefficient of the switch tube the same as the temperature coefficient of the reference resistor set inside the chip, and the impedance of the on-state internal resistance does not change with the change of the output voltage, thereby making the working current of the power switch tube can always remain stable during the working process, and can be suitable for occasions with high current requirements for the power switch tube in the switching regulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A circuit block diagram of a switch tube driving circuit in the prior art;

[0024] Figure 2 A first circuit block diagram of a control circuit for a power switch tube according to the present invention;

[0025] Figure 3 A second circuit block diagram of the control circuit of the power switch tube according to the present invention;

[0026] Figure 4 According to the present invention Figure 2 A circuit diagram of an implementation of a reference current generating circuit in;

[0027] Figure 5 According to the present invention Figure 3 A circuit diagram of an implementation of a reference current generating circuit in;

[0028] Figure 6 A circuit diagram of a sampling current generating circuit according to the present invention;

[0029] Figure 7 A circuit diagram of a sampling current generating circuit according to the present invention;

[0030] Figure 8 It is a comparison diagram of the working waveforms according to the present invention. DETAILED DESCRIPTION

[0031] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made within the spirit and scope of the present invention.

[0032] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0033] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportion, and are only used for the purpose of conveniently and clearly assisting in explaining the embodiments of the present invention.

[0034] refer to Figure 2 is a circuit block diagram of a control circuit of a power switch tube according to the present invention, Figure 3 According to the present invention Figure 2 The first implementation circuit diagram of the control circuit of the power switch tube in FIG. Figure 2 As shown, the control circuit of the power switch tube of the present application is used to control the power switch tube in the switching regulator, such as QM. The switching regulator may also include a load such as a power supply, which is connected to the power switch tube as a post-stage circuit of the power switch tube.

[0035] The control circuit includes a reference current generating circuit 1 and a sampling current generating circuit 2. The reference current generating circuit 1 receives a first power terminal (such as Figure 2 Medium V DD ) and the second power terminal (such as Figure 2 The voltage difference between the first power terminal and the second power terminal of the power switch tube is used to generate a reference current signal Iref, and the reference current signal is set to the ratio of the voltage difference between the first power terminal and the second power terminal of the power switch tube and the resistance value of a reference resistor, such as Iref=V DD / R0, wherein R0 is the resistance of the reference resistor, and the voltage of the reference ground terminal is zero. The sampling current generating circuit 2 samples the working current of the power switch tube to obtain a sampling current signal Isense. The output ends of the reference current generating circuit and the sampling circuit generating circuit are both connected to the control end GATE of the power switch tube, and the control circuit controls the reference current signal to be consistent with the value of the sampling current signal, so that during operation, the on-state internal resistance of the power switch tube is proportional to the resistance of the reference resistor. The resistance of the on-state internal resistance of the power switch tube is in direct proportion to the resistance of the reference resistor, as shown in the following formula:

[0036] Rdson=R0 / K

[0037] Where K is the proportionality coefficient.

[0038] Preferably, the reference resistor is arranged in the chip where the control circuit is located, and the impedance temperature coefficient of the on-state internal resistance of the power switch tube is consistent with the temperature coefficient of the reference resistor inside the chip. As shown in the above formula, the on-state internal resistance of the power switch tube is directly proportional to the resistance value of the reference resistor. In this way, during operation, the on-state internal resistance of the power switch tube is not affected by the change of the output voltage, and when the resistance value of the reference resistor is relatively stable, the on-state internal resistance of the power switch tube is also relatively stable.

[0039] like Figure 2 As shown, the control circuit controls the current branch of the reference current signal to be connected in series with the current branch of the sampling current signal. Furthermore, the series intermediate node of the current branch of the reference current signal and the current branch of the sampling current signal is connected to the control end of the power switch tube. Therefore, according to the magnitude of the current, it can be known that: in the initial state, the power switch tube Q M Not enabled, I OUT =0, then Isense obtained by the sampling current generating circuit is also zero, and in the power switch tube Q M Before starting, the reference current signal Iref is greater than the sampling current signal Isense, and the control terminal voltage of the power switch tube is charged high until it reaches the power switch tube Q M After that, the power switch tube is turned on, and the sampling current signal Isense gradually increases until the reference current signal Iref is equal to the sampling current signal Isense, and the control terminal voltage of the power switch tube remains constant. M Entering a stable working state. According to the control method of the present application, the power switch tube can smoothly enter the working state, and after reaching the stable state, its on-state internal resistance also remains relatively stable and does not change with the output voltage. When the resistance value of the reference resistor is relatively stable, the internal resistance of the power switch tube can also remain stable.

[0040] like Figure 2 As shown in FIG. 1 , the power switch tube is an N-type transistor circuit block diagram, the first power tube of the N-type transistor is connected to the output voltage Vout, the second power terminal is connected to the reference ground, and the current branch of the reference current signal and the current branch of the sampling current signal are connected between the output voltage and the reference ground in sequence. At this time, the reference circuit generation circuit 1 is as shown in FIG. Figure 4As shown, the reference current generating circuit 1 includes a first operational amplifier circuit OPA0, the reference resistor R0 and a first current mirror circuit (composed of switch tubes PM0 and PM1). The first input terminal of the operational amplifier circuit receives the output voltage Vout, the second input terminal receives the sampling voltage, and the output terminal is connected to the control terminal of the first switch tube. The first switch tube and the reference resistor are connected in series between a first node J and a reference ground. The sampling voltage is the intermediate node voltage between the reference resistor and the first switch tube. The common connection terminal of the current mirror circuit receives the power supply voltage, the first output terminal is connected to the first node J, and the second output terminal serves as the output terminal of the reference current generating circuit to output the reference current signal Iref. It can be seen from the above circuit that Iref=Vout / R0. Since the current branch of the reference current signal is connected in series with the current branch of the sampling current signal, Iref=Isense, and

[0041] Isense=Iout / K*Rdson, it can be deduced that Vout / R0=Iout / K, so the impedance of the power switch tube Rdson=Vout / Iout=R0 / K, where K is the current proportional coefficient of the current mirror.

[0042] like Figure 3 As shown, it is a circuit block diagram of a P-type transistor as the power switch tube, the first power tube of the P-type transistor is connected to the supply voltage, the second power terminal is connected to the output voltage, the current branch of the sampling current signal and the current branch of the reference current signal are connected to the supply voltage V DD and the reference ground. At this time, the reference circuit generation circuit is as follows Figure 5 As shown, the reference current generating circuit includes a first operational amplifier circuit OPA0, the reference resistor R0 and a first current mirror circuit (composed of switch tubes NM0 and NM1), the first input end of the operational amplifier circuit receives the output voltage Vout, the second input end receives the sampling voltage, and the output end is connected to the control end of the first switch tube, the reference resistor and the first switch tube are connected in series between the power supply voltage and the first node, and the sampling voltage is the intermediate node voltage of the reference resistor and the first switch tube; the common connection end of the current mirror circuit receives the reference ground, the first output end is connected to the first node J, and the second output end is used as the output end of the reference current generating circuit to output the reference current signal Iref. It can be seen from the above circuit that Iref=(V DD -Vout) / R0. Since the current branch of the reference current signal is connected in series with the current branch of the sampled current signal, Iref=Isense, and

[0043] Isense=(V DD-Vout) / K*Rdson, we can deduce (V DD -Vout) / R0=Iout / K, so the impedance of the power switch tube Rdson=R0 / K.

[0044] Figure 6 A circuit diagram of a sampling current generating circuit according to the present invention; the sampling current generating circuit includes a second current mirror, which is connected to the power switch tube to obtain the sampling current signal through mirror sampling, and the sampling current signal is proportional to the working current of the power switch tube. Figure 6 The second current mirror circuit includes a switch tube Qs, which is in a mirror relationship with the power switch tube QM, and the mirror ratio coefficient is K:1, current mirrors PM2 and PM3, and the PM2 and PM3 ratio coefficients are 1:1; current mirrors NM1 and NM2, and the NM1 and NM2 ratio coefficients are 1:1. The output current Iout is processed by multiple mirrors and the operational amplifier OPA1 to obtain a sampling signal Isense, Isense = Iout / K. The current information of the output current can be accurately obtained through mirror sampling, and the ratio can be enlarged or reduced, which is convenient for the use of the subsequent circuit.

[0045] Figure 7 A circuit diagram of a sampling current generating circuit according to the present invention is provided. The sampling current generating circuit includes a sampling circuit and a third current mirror. The sampling circuit obtains the working current of the power switch tube through a sampling resistor, and then performs mirror processing through the third current mirror to obtain a sampling current signal that is proportional to the working current of the power switch tube. Figure 7 , a sampling circuit and a third current mirror, the sampling circuit includes a sampling resistor Rc, current mirrors PM2 and PM3, the ratio coefficient of PM2 and PM3 is 1:1, current mirrors NM1 and NM2, the ratio coefficient of NM1 and NM2 is 1:1, the output current Iout is sampled and processed by the operational amplifier OPA1, and then the sampling signal Isense is obtained after multiple mirror processing, Isense = Iout / K. The current information of the output current can be accurately obtained through resistor sampling and mirror processing.

[0046] Figure 8 The following is a comparison diagram of the working waveforms according to the present invention. The current of the switch tube in the prior art decreases over time, and the drive voltage is adjusted after temperature detection to stabilize the current of the switch tube. This is repeated, and the current still has certain fluctuations. If the subsequent current is a sensitive device, it will inevitably be affected. However, the working current of the power switch tube in this solution has been well maintained and stable due to the stability of its on-resistance, and the stability effect is good.

[0047] Finally, the present application also proposes a control method for a power switch tube, obtaining a voltage difference based on the voltage difference between the first power end and the second power end of the power switch tube, and obtaining a reference current signal based on the ratio of the voltage difference to the resistance value of a reference resistor; sampling the working current of the power switch tube to obtain a sampling current signal; the reference current signal branch is connected in series with the sampling current signal branch, and the connection node between the two is coupled to the control end of the power switch tube.

[0048] Preferably, during operation, the on-state internal resistance of the power switch tube is proportional to the resistance value of the reference resistor.

[0049] Preferably, the impedance temperature coefficient of the on-state internal resistance of the power switch tube varies in accordance with the temperature coefficient of the reference resistor inside the chip.

[0050] It should be noted that the specific implementation and corresponding illustrations given are merely a way of describing the implementation method of the present invention, and do not limit the specific structure of the implementation scheme of the present invention. Various changes or modifications can be made to these implementation schemes without departing from the principle and essence of the present invention, but these changes and modifications fall within the scope of protection of the present invention.

[0051] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0052] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A control circuit for a power switch tube, applied to a switching regulator, characterized in that: The control circuit comprises: A reference current generating circuit receives a voltage difference between the first power terminal and the second power terminal of the power switch tube to generate a reference current signal, wherein the reference current signal is set to be a ratio of the voltage difference between the first power terminal and the second power terminal of the power switch tube to a reference resistor value; A sampling current generating circuit, sampling the working current of the power switch tube to obtain a sampling current signal; The output ends of the reference current generating circuit and the sampling circuit generating circuit are both connected to the control end of the power switch tube, and the control circuit controls the value of the reference current signal to be consistent with the value of the sampling current signal, so that during operation, the on-state internal resistance of the power switch tube is proportional to the resistance value of the reference resistor.

2. The control circuit according to claim 1, characterized in that: The resistance value of the on-state internal resistance of the power switch tube is directly proportional to the resistance value of the reference resistor.

3. The control circuit according to claim 1, characterized in that: The reference resistor is arranged in the chip where the control circuit is located, and the impedance temperature coefficient of the on-state internal resistance of the power switch tube changes in accordance with the temperature coefficient of the reference resistor inside the chip.

4. The control circuit according to claim 1, characterized in that: The control circuit controls the current branch of the reference current signal to be connected in series with the current branch of the sampling current signal.

5. The control circuit according to claim 4, characterized in that: The series middle node of the current branch of the reference current signal and the current branch of the sampled current signal is connected to the control end of the power switch tube.

6. The control circuit according to claim 4, characterized in that: When the power switch tube is an N-type transistor, the first power tube of the N-type transistor is connected to the output voltage, and the second power terminal is connected to the reference ground. The current branch of the reference current signal and the current branch of the sampled current signal are sequentially connected between the output voltage and the reference ground.

7. The control circuit according to claim 4, characterized in that: When the power switch is a P-type transistor, the first power terminal of the P-type transistor is connected to the supply voltage, and the second power terminal is connected to the output voltage. The current branch of the sampled current signal and the current branch of the reference current signal are connected between the power supply voltage and the reference ground in sequence.

8. The control circuit according to claim 6, characterized in that: The reference current generating circuit comprises a first operational amplifier circuit, the reference resistor and a first current mirror circuit. The operational amplifier circuit has a first input terminal receiving the output voltage, a second input terminal receiving a sampling voltage, an output terminal thereof being connected to a control terminal of a first switch tube, the first switch tube and the reference resistor being connected in series between a first node and a reference ground, and the sampling voltage being a voltage at an intermediate node between the reference resistor and the first switch tube; The common connection terminal of the current mirror circuit receives the power supply voltage, the first output terminal is connected to the first node, and the second output terminal serves as the output terminal of the reference current generating circuit to output the reference current signal.

9. The control circuit according to claim 7, characterized in that: The reference current generating circuit comprises a first operational amplifier circuit, the reference resistor and a first current mirror circuit. The operational amplifier circuit has a first input terminal receiving the output voltage, a second input terminal receiving the sampling voltage, an output terminal thereof connected to the control terminal of the first switch tube, the reference resistor and the first switch tube are connected in series between the power supply voltage and the first node, and the sampling voltage is the intermediate node voltage between the reference resistor and the first switch tube; The common connection terminal of the current mirror circuit receives the reference ground, the first output terminal is connected to the first node, and the second output terminal serves as the output terminal of the reference current generating circuit to output the reference current signal.

10. The control circuit according to claim 4, characterized in that: The sampling current generating circuit comprises a second current mirror, The second current mirror is connected to the power switch tube to obtain the sampling current signal through mirror sampling. The sampling current signal is in direct proportion to the working current of the power switch tube.

11. The control circuit according to claim 4, characterized in that: The sampling current generating circuit comprises a sampling circuit and a third current mirror, The sampling circuit obtains the operating current of the power switch tube through a sampling resistor, and then performs mirror processing through a third current mirror to obtain a sampling current signal that is proportional to the operating current of the power switch tube.

12. A control method for a power switch tube, applied to a switching regulator, characterized in that: Includes steps: Obtain a voltage difference value according to a voltage difference between a first power terminal and a second power terminal of the power switch tube, and obtain a reference current signal according to a ratio of the voltage difference value to a resistance value of a reference resistor; Sampling the operating current of the power switch tube to obtain a sampling current signal; The reference current signal branch is connected in series with the sampling current signal branch, and a connection node between the two is coupled to the control end of the power switch tube.

13. The control method according to claim 12, characterized in that: During operation, the on-state internal resistance of the power switch tube is proportional to the resistance value of the reference resistor.

14. The control method according to claim 12, characterized in that: The impedance temperature coefficient of the on-state internal resistance of the power switch tube varies in accordance with the temperature coefficient of the reference resistor inside the chip.

15. The control method according to claim 12, characterized in that: Before the power switch tube is started, the reference current signal is greater than the sampling current signal, and the voltage at the control terminal of the power switch tube is charged high until it reaches the turn-on voltage of the power switch tube.

16. The control method according to claim 12, characterized in that: After the power switch tube is turned on, the sampling current signal gradually increases until the reference current signal is equal to the sampling current signal, the control terminal voltage of the power switch tube remains constant, and the power switch tube enters a stable working state.

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