Overshoot-free ramp voltage generation circuit and method and control circuit of switching circuit

Abstract

The invention provides a non-overshoot ramp voltage generation circuit and method and a control circuit of a switching circuit, before a ramp voltage reaches a first threshold voltage, a first current source charges a first capacitor, and after the ramp voltage reaches the first threshold voltage, a first voltage source is switched to charge the first capacitor; the ramp voltage is the voltage of the first capacitor, and the first threshold voltage is smaller than the voltage of the first voltage source. When the ramp voltage is about to reach the voltage of the first voltage source, the charging of the first current source to the first capacitor is closed, and then the first voltage source is connected to charge the first capacitor, so that the ramp voltage with accurate and stable clamping can be generated, the output ramp voltage is not overshoot, and the circuit is simple to realize.

Description

Technical Field

[0001] This invention relates to the field of power electronics, and in particular to a control circuit for a non-overshoot ramp voltage generation circuit, a method for generating such a voltage, and a switching circuit. Background Technology

[0002] In the control circuits of existing switching circuits, ramp voltage with clamping function is often required. For example, ramp voltage generating circuit is often used to generate ramp voltage during the startup process of switching circuit, and ramp voltage generating circuit is also required to generate ramp voltage in normal working loop.

[0003] like Figure 1 The diagram shows a schematic of a prior art ramp voltage generation circuit. In this circuit, the ramp voltage is generated by charging the first capacitor C1 with the first current source I1, and the first voltage source Vclamp clamps the ramp voltage through operational amplifier U1 and diode D1. However, during the clamping process, due to the excessively rapid increase rate of the ramp voltage, the response speed and stability of the ramp voltage generation circuit are difficult to coordinate, resulting in the ramp voltage exhibiting the following characteristics: Figure 2 As shown in the waveform, it can be seen that the ramp voltage Vramp does not stop increasing when it reaches the voltage of the first voltage source Vclamp. Instead, it reaches a maximum value and is then pulled back to the voltage of the first voltage source Vclamp. This results in inaccurate clamping of the ramp voltage Vramp and overshoot. Summary of the Invention

[0004] The purpose of this invention is to provide a ramp voltage generation circuit, method, and control circuit for a switching circuit that prevents overshoot, thereby enabling accurate ramp voltage clamping without overshoot.

[0005] In a first aspect, the present invention provides an overshoot-free ramp voltage generating circuit for generating a ramp voltage, comprising a first current source, a first capacitor, and a first voltage source, wherein the first current source charges the first capacitor until the ramp voltage reaches a first threshold voltage; after the ramp voltage reaches the first threshold voltage, the circuit switches to the first voltage source to charge the first capacitor; wherein the ramp voltage is the voltage of the first capacitor, and the first threshold voltage is less than the voltage of the first voltage source.

[0006] Preferably, it further includes: a control unit, configured to output a first control signal based on the ramp voltage and the first threshold voltage; and a switching unit, configured to receive the first control signal and control the first capacitor to switch from being charged by the first current source to being charged by the first voltage source when the ramp voltage reaches the first threshold voltage.

[0007] Preferably, the control unit includes a timing circuit for determining the moment when the ramp voltage reaches the first threshold voltage based on the current information of the first current source, the parameter information of the first capacitor, and the first threshold voltage, so as to output the first control signal.

[0008] Preferably, the control unit further includes: a current detection circuit for detecting the current of the first current source to output a first detection signal characterizing the current information of the first current source; the timing circuit receives the first detection signal and obtains the current information of the first current source based on the first detection signal.

[0009] Preferably, the control unit includes: a comparison circuit, a first input terminal receiving a ramp signal characterizing the ramp voltage, a second input terminal receiving a reference signal, comparing the ramp signal and the reference signal to output a comparison signal; the control unit outputs the first control signal according to the comparison signal.

[0010] Preferably, the switching unit includes a first switch and a second switch, the first switch being connected between the first current source and the first capacitor, and the second switch being connected between the first capacitor and the first voltage source; the first control signal controls the first switch to turn off when the ramp voltage reaches the first threshold voltage, and the second switch to turn on when the ramp voltage reaches the first threshold voltage, so that the first capacitor switches from being charged by the first current source to being charged by the first voltage source when the ramp voltage reaches the first threshold voltage.

[0011] Preferably, the switching unit includes a first selection switch, which is connected between the first capacitor and the first current source and the first voltage source; the first control signal controls the first selection switch to disconnect the connection between the first capacitor and the first current source and connect the connection between the first capacitor and the first voltage source when the ramp voltage reaches the first threshold voltage, so that the first capacitor switches from being charged by the first current source to being charged by the first voltage source when the ramp voltage reaches the first threshold voltage.

[0012] Preferably, it further includes an impedance unit, through which the first voltage source charges the first capacitor after the ramp voltage reaches the first threshold voltage.

[0013] Secondly, the present invention also provides a method for generating an overshoot-free ramp voltage, applied to an overshoot-free ramp voltage generating circuit, the overshoot-free ramp voltage generating circuit including a first current source, a first capacitor, and a first voltage source for generating a ramp voltage, the method including: the first current source charging the first capacitor until the ramp voltage reaches a first threshold voltage; after the ramp voltage reaches the first threshold voltage, switching to the first voltage source to charge the first capacitor; wherein, the ramp voltage is the voltage of the first capacitor, and the first threshold voltage is less than the voltage of the first voltage source.

[0014] Preferably, determining that the ramp voltage reaches the first threshold voltage includes: determining the moment when the ramp voltage reaches the first threshold voltage based on the current information of the first current source, the parameter information of the first capacitor, and the first threshold voltage; or, comparing the ramp signal characterizing the ramp voltage with a reference signal to obtain a comparison result, and determining that the ramp voltage reaches the first threshold voltage based on the comparison result.

[0015] Thirdly, the present invention also provides a control circuit for a switching circuit, including the overshoot-free ramp voltage generation circuit described above, wherein the control circuit generates a switching control signal based on the ramp voltage, and the switching control signal is used to control the switching action of the power switching transistor in the switching circuit.

[0016] The present invention provides a ramp voltage generation circuit, method, and control circuit for a switching circuit without overshoot. Before the ramp voltage reaches a first threshold voltage, a first current source charges a first capacitor. After the ramp voltage reaches the first threshold voltage, the circuit switches to a first voltage source to charge the first capacitor. The ramp voltage is equal to the voltage of the first capacitor, and the first threshold voltage is less than the voltage of the first voltage source. By turning off the charging of the first capacitor by the first current source when the ramp voltage is about to reach the voltage of the first voltage source, and then connecting the first voltage source to charge the first capacitor, a clamped and stable ramp voltage can be generated, preventing overshoot in the output ramp voltage. Furthermore, the circuit implementation is simple. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a ramp voltage generation circuit in the prior art.

[0018] Figure 2 This is a schematic diagram of a ramp voltage waveform in the prior art;

[0019] Figure 3 This is a schematic diagram of the circuit structure of the overshoot-free ramp voltage generation circuit according to the first embodiment of the present invention;

[0020] Figure 4This is a schematic diagram of the circuit structure of the overshoot-free ramp voltage generation circuit according to the second embodiment of the present invention;

[0021] Figure 5 This is a schematic diagram of the circuit structure of the overshoot-free ramp voltage generation circuit according to the third embodiment of the present invention;

[0022] Figure 6 This is a schematic diagram of the circuit structure of the overshoot-free ramp voltage generation circuit according to the fourth embodiment of the present invention;

[0023] Figure 7 This is a schematic diagram of the circuit structure of the overshoot-free ramp voltage generation circuit according to the fifth embodiment of the present invention;

[0024] Figure 8 According to Figure 3 A schematic diagram of the circuit structure after the ramp voltage reaches the first threshold voltage;

[0025] Figure 9 This is a schematic diagram of the ramp voltage waveform in this invention. Detailed Implementation

[0026] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the present invention.

[0027] To provide the public with a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the invention, but those skilled in the art can fully understand the invention without these details.

[0028] The invention is described in more detail below by way of example with reference to the accompanying drawings. It should be noted that the drawings are simplified and use non-precise proportions to facilitate and clearly illustrate the embodiments of the invention.

[0029] Figure 3 This is a schematic diagram of the circuit structure of the overshoot-free ramp voltage generation circuit of the present invention. Figure 3 As shown, the overshoot-free ramp voltage generation circuit may include a first current source I1, a first capacitor C1, and a first voltage source Vclamp, wherein the first current source I1 is connected to the power supply voltage VDD, and the first capacitor C1 and the first voltage source Vclamp are both connected to the reference ground.

[0030] The first current source I1 charges the first capacitor C1 until the ramp voltage Vramp reaches the first threshold voltage V1. After the ramp voltage Vramp reaches the first threshold voltage V1, the charging of the first capacitor C1 can be switched to the first voltage source Vclamp. Here, the ramp voltage Vramp is the voltage of the first capacitor C1, and the first threshold voltage V1 is less than the voltage of the first voltage source Vclamp.

[0031] It should be noted that I1 shown in the text description and accompanying drawings of this invention can refer to the first current source element or the current of the first current source; Vclamp shown in the text description and accompanying drawings of this invention can refer to the first voltage source element or the voltage of the first voltage source.

[0032] For example, the ramp voltage Vramp can be the positive terminal voltage of the first capacitor C1, or it can be the voltage across the first capacitor C1. The first threshold voltage V1 can be slightly less than the voltage of the first voltage source Vclamp. For example, the first threshold voltage V1 can be set to 90% of the voltage of the first voltage source Vclamp. The value of the first threshold voltage V1 can be set according to the specific circuit conditions, and the present invention does not limit it.

[0033] In this embodiment, the overshoot-free ramp voltage generation circuit may further include a control unit 101 and a switching unit 102. The switching unit 102 is connected between the first capacitor C1 and the first current source I1 and the first voltage source Vclamp.

[0034] The control unit 101 is used to output a first control signal based on the ramp voltage Vramp and the first threshold voltage V1. The switching unit 103 is used to receive the first control signal and control the first capacitor C1 to switch from being charged by the first current source I1 to being charged by the first voltage source Vclamp when the ramp voltage Vramp reaches the first threshold voltage V1.

[0035] In this embodiment, the overshoot-free ramp voltage generation circuit may further include an impedance unit 103. The impedance unit 103 may consist of one or more impedance elements. One end of the impedance unit 103 is connected to the switching unit 102, and the other end is connected to the first voltage source Vclamp. When the switching unit 103 receives a first control signal, it may also control the first capacitor C1 to switch from being charged by the first current source I1 to being charged by the first voltage source Vclamp through the impedance unit 103 when the ramp voltage Vramp reaches the first threshold voltage V1.

[0036] It should be noted that the first current source I1 in this invention can be an ideal current source or a current source with output impedance. The first voltage source Vclamp in this invention can be an ideal voltage source or a voltage source with output impedance. When the first voltage source Vclamp is a voltage source with output impedance, if the impedance is set appropriately, the impedance unit 103 does not need to be set in the circuit. That is, when it is determined that the ramp voltage Vramp reaches the first threshold voltage V1, the first capacitor C1 is controlled to be charged only by the first voltage source Vclamp, and the first voltage source Vclamp does not need to charge the first capacitor C1 through an external impedance element.

[0037] In this embodiment, the switching unit 102 may include a first switch K1 and a second switch K2. The first switch K1 is connected between the first current source I1 and the first capacitor C1, and the second switch K2 is connected between the first capacitor C1 and the first voltage source Vclamp. When the switching unit 102 receives a first control signal, the first control signal can control the first switch K1 to turn off when the ramp voltage Vramp reaches the first threshold voltage V1, and the second switch K2 to turn on when the ramp voltage Vramp reaches the first threshold voltage V1, so that the first capacitor C1 switches from being charged by the first current source I1 to being charged by the first voltage source Vclamp when the ramp voltage Vramp reaches the first threshold voltage V1.

[0038] Specifically, before the ramp voltage Vramp reaches the first threshold voltage V1, the first control signal can control the first switch K1 to turn on and the second switch K2 to turn off, so that the first current source I1 charges the first capacitor C1; when the ramp voltage Vramp reaches the first threshold voltage V1 and after that moment, the first control signal can control the first switch K1 to turn off and the second switch K2 to turn on, so that the first voltage source Vclamp charges the first capacitor C1.

[0039] In another embodiment, such as Figure 4 As shown, the switching unit 102 may also include a first selection switch S. Exemplarily, the first selection switch S can be a single-pole double-throw switch. The first selection switch S is connected between the first capacitor C1 and the first current source I1 and the first voltage source Vclamp. When the switching unit 102 receives a first control signal, the first control signal can control the first selection switch S to disconnect the connection between the first capacitor C1 and the first current source I1 and connect the connection between the first capacitor C1 and the first voltage source Vclamp when the ramp voltage Vramp reaches the first threshold voltage V1, so that the first capacitor C1 switches from being charged by the first current source I1 to being charged by the first voltage source Vclamp when the ramp voltage Vramp reaches the first threshold voltage V1.

[0040] Specifically, before the ramp voltage Vramp reaches the first threshold voltage V1, the first control signal can control the first selection switch S to turn on the connection between the first capacitor C1 and the first current source I1, and to turn off the connection between the first capacitor C1 and the first voltage source Vclamp; when the ramp voltage Vramp reaches the first threshold voltage V1 and after that time, the first control signal can control the first selection switch S to turn off the connection between the first capacitor C1 and the first current source I1, and to turn on the connection between the first capacitor C1 and the first voltage source Vclamp.

[0041] like Figure 5 As shown, the control unit 101 may include a timing circuit 1011. Exemplarily, the timing circuit 1011 may be implemented using an analog-to-digital converter (ADC).

[0042] In this embodiment, the timing circuit 1011 can determine the moment when the ramp voltage Vramp reaches the first threshold voltage V1 based on the current information of the first current source I1, the parameter information of the first capacitor C1, and the first threshold voltage V1, and output a first control signal so that the switching unit 102 switches according to the received first control signal at the moment when the ramp voltage Vramp reaches the first threshold voltage V1, switching the charging of the first capacitor C1 from the first current source I1 to the first voltage source Vclamp. The current information of the first current source I1 can be known in advance, and the parameter information of the first capacitor C1 can be the capacitance value C of the first capacitor C1.

[0043] Specifically, the timing circuit 1011 can calculate the charging rate based on the current information of the first current source I1 and the capacitance C of the first capacitor C1, and then obtain the time when the ramp voltage Vramp reaches the first threshold voltage V1 based on the charging rate and the first threshold voltage V1.

[0044] In another embodiment, such as Figure 6 As shown, the control unit 101 may further include a timing circuit 1011 and a current detection circuit 1012. The current detection circuit 1012 may be connected to the positive terminal of the first capacitor C1 or to the first current source I1.

[0045] The current detection circuit 1012 can be used to detect the current of the first current source I1 and output a first detection signal characterizing the current information of the first current source I1. The timing circuit 1011 can receive the first detection signal and obtain the current information of the first current source I1 based on the first detection signal. By detecting the current of the first current source I1 to obtain the current information of the first current source I1, the current information of the first current source I1 can be determined more accurately.

[0046] In another embodiment, such as Figure 7 As shown, the control unit 101 may include a comparison circuit U2. Exemplarily, the comparison circuit U2 may be a comparator. The first input terminal of the comparison circuit U2 may receive a ramp signal Va characterizing the ramp voltage Vramp, and the second input terminal may receive a reference signal Vref. The comparison circuit U2 compares the ramp signal Va and the reference signal Vref to output a comparison signal. The control unit 101 may output a first control signal based on this comparison signal.

[0047] It should be noted that the first input terminal of the comparator circuit U2 can also directly receive the ramp voltage Vramp, in which case the second input terminal receives the first threshold voltage V1. In this case, the first input terminal can be connected to the positive terminal of the first capacitor C1 or the first current source I1. The comparator circuit U2 obtains the comparison result by comparing the ramp voltage Vramp and the first threshold voltage V1. Alternatively, the first input terminal of the comparator circuit U2 can be connected to the positive terminal of the first capacitor C1 or the first current source I1 through a voltage divider resistor. In this case, the first input terminal receives the ramp signal Va, which characterizes the ramp voltage Vramp, and the second input terminal receives the reference signal Vref. The comparator circuit U2 obtains the comparison result by comparing the ramp signal Va and the reference signal Vref.

[0048] The output of the comparator circuit U2 can be directly connected to the switch unit 102 to output a first control signal to control the switching of the switch unit 102; the output of the comparator circuit U2 can also be connected to the switch unit 102 after passing through a delay module. The comparator circuit U2 outputs a comparison signal, which is then output as a first control signal after passing through the delay module to control the switching of the switch unit 102.

[0049] Figure 7 The diagram shows that the positive input terminal of the comparator circuit U2 is connected to the positive terminal of the first capacitor C1 or the first current source I1, the negative input terminal receives the reference signal Vref, and the output terminal is connected to the switching unit 102.

[0050] like Figure 3 and Figure 8 As shown, the switching unit 101 consists of a first switch K1 and a second switch K2. The following is a combination of... Figure 3 , Figure 8 and Figure 9 The working principle of the overshoot-free ramp voltage generation circuit provided by this invention is explained in detail below:

[0051] Before time TI, the first switch K1 is turned on and the second switch K2 is turned off, allowing the first current source I1 to charge the first capacitor C1, generating a ramp voltage Vramp. At time T1, when the ramp voltage Vramp reaches the first threshold voltage V1, the first switch K1 turns off and the second switch K2 turns on, disconnecting the connection to the first current source I1 and connecting a voltage source with output impedance. This voltage source Vclamp then charges the first capacitor C1, clamping the ramp voltage Vramp. This can be implemented using a digital-to-analog converter (DAC), which has an output impedance, and the voltage of the first voltage source Vclamp is adjustable.

[0052] During the period from time T1 to T2, the ramp voltage Vramp will reach the voltage of the first voltage source Vclamp through RC charging. The transition slope of the ramp voltage Vramp from the first threshold voltage V1 to the voltage of the first voltage source Vclamp can be smoothed by adjusting the internal resistance of the first voltage source Vclamp. Therefore, at time T2, the ramp voltage Vramp smoothly rises from the first threshold voltage V1 to the voltage of the first voltage source Vclamp.

[0053] Depend on Figure 9 As can be seen from the waveform of the ramp voltage shown, the ramp voltage Vramp can be accurately clamped without overshoot by the ramp voltage generation circuit provided by this invention. Moreover, from time T1 to time T2, the ramp voltage Vramp can smoothly transition from the first threshold voltage Vref to the voltage of the first voltage source Vclamp.

[0054] The overshoot-free ramp voltage generation circuit provided by this invention can be applied in the control circuit of a switching circuit. In one embodiment, it can be used to control the output voltage to rise slowly during the startup process of the switching circuit. For example, the ramp voltage generated by the overshoot-free ramp voltage generation circuit and the output voltage feedback signal can be transmitted to the input of a comparator or operational amplifier to obtain a switching control signal. Since the ramp voltage clamping is accurate and does not overshoot, an accurate output voltage can be obtained during the startup process of the switching circuit, and the obtained output voltage will not overshoot, making the system work stably. In another embodiment, it can be used in the loop control during the normal operation of the switching circuit. For example, the ramp voltage generated by the overshoot-free ramp voltage generation circuit, the inductor current feedback voltage, the reference voltage, and the bias voltage can be used as signal inputs in the circuit loop and input to the input of a multi-terminal comparator to generate a switching control signal for controlling the main power switch, thereby obtaining a stable and accurate output voltage.

[0055] This invention also provides a method for generating ramp voltage without overshoot. The working principle of this method can be found in the description of the ramp voltage generation circuit without overshoot described in the above embodiments, and will not be elaborated further here. Furthermore, the ramp voltage generation method provided by this invention does not place high demands on the circuit specifications.

[0056] Although the embodiments are described and illustrated separately above, some common technologies are involved. Those skilled in the art can replace and integrate them between the embodiments. If there is any content not explicitly described in one embodiment, then another embodiment that is described can be referred to.

[0057] The embodiments described above do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the above embodiments should be included within the scope of protection of this technical solution.

Claims

1. A ramp voltage generation circuit without overshoot, used to generate a ramp voltage, characterized in that, Includes a first current source, a first capacitor, and a first voltage source. The first current source charges the first capacitor until the ramp voltage reaches the first threshold voltage. After the ramp voltage reaches the first threshold voltage, the voltage source is switched to charge the first capacitor. Wherein, the ramp voltage is the voltage of the first capacitor, and the first threshold voltage is less than the voltage of the first voltage source.

2. The overshoot-free ramp voltage generation circuit according to claim 1, characterized in that, Also includes: The control unit is configured to output a first control signal based on the ramp voltage and the first threshold voltage; A switching unit is configured to receive the first control signal and, based on the first control signal, control the first capacitor to switch from being charged by the first current source to being charged by the first voltage source when the ramp voltage reaches the first threshold voltage.

3. The overshoot-free ramp voltage generation circuit according to claim 2, characterized in that, The control unit includes: A timing circuit is used to determine the moment when the ramp voltage reaches the first threshold voltage based on the current information of the first current source, the parameter information of the first capacitor, and the first threshold voltage, so as to output the first control signal.

4. The overshoot-free ramp voltage generation circuit according to claim 3, characterized in that, The control unit further includes: A current detection circuit is used to detect the current of the first current source and output a first detection signal characterizing the current information of the first current source. The timing circuit receives the first detection signal and obtains the current information of the first current source based on the first detection signal.

5. The overshoot-free ramp voltage generation circuit according to claim 2, characterized in that, The control unit includes: The comparator circuit has a first input terminal that receives a ramp signal representing the ramp voltage, and a second input terminal that receives a reference signal. The ramp signal and the reference signal are compared to output a comparison signal. The control unit outputs the first control signal based on the comparison signal.

6. The overshoot-free ramp voltage generation circuit according to claim 2, characterized in that, The switching unit includes a first switch and a second switch, wherein the first switch is connected between the first current source and the first capacitor, and the second switch is connected between the first capacitor and the first voltage source; The first control signal controls the first switch to turn off when the ramp voltage reaches the first threshold voltage, and the second switch to turn on when the ramp voltage reaches the first threshold voltage, so that the first capacitor switches from being charged by the first current source to being charged by the first voltage source when the ramp voltage reaches the first threshold voltage.

7. The overshoot-free ramp voltage generation circuit according to claim 2, characterized in that, The switching unit includes a first selection switch, which is connected between the first capacitor and the first current source and the first voltage source. The first control signal controls the first selection switch to disconnect the first capacitor from the first current source and connect the first capacitor to the first voltage source when the ramp voltage reaches the first threshold voltage, so that the first capacitor switches from being charged by the first current source to being charged by the first voltage source when the ramp voltage reaches the first threshold voltage.

8. The overshoot-free ramp voltage generation circuit according to claim 1, characterized in that, It also includes impedance units, After the ramp voltage reaches the first threshold voltage, the first voltage source charges the first capacitor through the impedance unit.

9. A method for generating overshoot-free ramp voltage, characterized in that, An overshoot-free ramp voltage generation circuit is applied, the overshoot-free ramp voltage generation circuit including a first current source, a first capacitor, and a first voltage source, for generating a ramp voltage, the method including: The first current source charges the first capacitor until the ramp voltage reaches the first threshold voltage. After the ramp voltage reaches the first threshold voltage, the voltage source is switched to charge the first capacitor. Wherein, the ramp voltage is the voltage of the first capacitor, and the first threshold voltage is less than the voltage of the first voltage source.

10. The method for generating overshoot-free ramp voltage according to claim 9, characterized in that, Determining that the ramp voltage reaches the first threshold voltage includes: The moment when the ramp voltage reaches the first threshold voltage is determined based on the current information of the first current source, the parameter information of the first capacitor, and the first threshold voltage. Alternatively, the ramp signal characterizing the ramp voltage can be compared with a reference signal to obtain a comparison result, and the ramp voltage can be determined to have reached the first threshold voltage based on the comparison result.

11. A control circuit for a switching circuit, characterized in that, Including the overshoot-free ramp voltage generation circuit as described in any one of claims 1-8, The control circuit generates a switching control signal based on the ramp voltage, and the switching control signal is used to control the switching action of the power switching transistor in the switching circuit.

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