TWI384734B - Control device for a dc-dc converter and related dc-dc converter - Google Patents

Description

Control device for a DC converter and its associated DC converter

The present invention relates to a control device for a DC-DC converter and its associated DC converter, and more particularly to a control device for properly closing a DC converter by reducing the output voltage of one of the DC converters to mitigate the surge effect and Its associated DC converter.

Electronic devices typically contain different components, each of which may require different operating voltages. Therefore, in an electronic device, it is necessary to pass a DC-to-DC voltage conversion circuit to achieve voltage level adjustment (boost or step-down) and stabilize it at a set voltage value. Many different types of DC-to-DC voltage converters can be extended depending on different power requirements, but they are derived from Buck/Step Down Converter and Boost/Step Up. Converter). As the name suggests, the buck converter reduces the DC voltage at the input to a predetermined voltage level, while the boost converter boosts the DC voltage at the input. Regardless of the buck converter or boost converter, as circuit technology evolves, both have evolved to accommodate different architectures or to meet different needs.

For example, please refer to FIG. 1A. FIG. 1A is a schematic diagram of a conventional buck converter 10. The buck converter 10 includes an input terminal 100, a low-pass module 110, a control module 120, a switch module 130, an output terminal 140, and an output module 150. The input terminal 130 is configured to receive a first input voltage signal VIN1. The low-pass module 110 is composed of an inductor 112 and a capacitor 114 for performing low-pass filtering on the first input voltage signal VIN1 to generate a second input voltage signal VIN2. The control module 120 is a pulse width modulation (PWM) controller for generating a control signal VCON to the switch module l30 according to the second input voltage signal VIN2. The switch module 130 includes an upper bridge switch transistor 132, a lower bridge switch transistor 134, an amplifier 136 and an inverting amplifier 138 for controlling the upper bridge switching transistor according to the control signal VCON (and its inverted signal). The conduction state of 132 and the lower bridge switching transistor 134, thereby adjusting the current of a node N1. The output module 150 is coupled to the node N1, and is composed of a capacitor 152 and an inductor 154 for generating an output voltage signal VOUT through the inductor-capacitor effect. Briefly, the control module 120 adjusts the value of the output voltage signal VOUT by adjusting the duty cycle of the upper bridge switching transistor 132 and the lower bridge switching transistor 134.

In order to properly control the opening and closing of the DC converter 10, the control module 120 further compares the second input voltage signal VIN2 with a predetermined switching threshold voltage VTH. Please refer to FIG. 1B. FIG. 1B is a schematic diagram showing changes of the second input voltage signal VIN2 and the input current i _IN through one of the inductors 112 during the shutdown of the buck converter 10. When the DC converter 10 is turned off, the first input voltage signal VIN1 will drop to 0, causing the second input voltage signal VIN2 to gradually decrease. When the second input voltage signal VIN2 is less than the switching threshold voltage VTH, the control module 120 turns off the DC converter 10. However, in this case, since the current i _IN flowing through the sense 112 suddenly decreases, the second input voltage signal VIN2 will instantaneously be higher than the first input voltage signal VIN1 to conform to the continuous nature of the current of the inductor 112. In other words, when the DC converter 10 is turned off, the second input voltage signal VIN2 generates a glitch, and the spurt may cause the second input voltage signal VIN2 to be greater than the switching threshold voltage VTH, causing the DC converter 10 that should be turned off. Return to the power on state. Therefore, the shutdown mode of the DC converter 10 is necessary for improvement.

Accordingly, it is a primary object of the present invention to provide a control device for a DC converter and its associated DC converter.

The invention discloses a control device for a DC converter, comprising a delay comparator for generating a circuit enable reset signal according to one of the DC converter input voltage signals; a controller coupled to the delay a comparator for enabling a reset signal according to the circuit to provide a reference voltage signal; a first comparator coupled to the controller for comparing the reference voltage signal with one of the DC converters for returning a voltage signal To generate a comparison result, an oscillator for generating an oscillating voltage signal, and a second comparator coupled to the first comparator and the oscillator for comparing the comparison result and the oscillating voltage signal To generate a control signal to one of the switching modules of the DC converter.

The present invention further discloses a DC converter including an input terminal for receiving an input voltage signal, an output terminal for outputting an output voltage signal, and a feedback module coupled to the output terminal for The output voltage signal generates a feedback voltage signal; a switch module includes a first end for receiving a control signal; a second end; an upper bridge switch transistor coupled to the input end, the The first end and the second end are configured to control the conduction state of the input end to the second end according to the control signal; and the lower bridge switch transistor is coupled to the first end, the second end, and a second end The ground end is configured to control the conduction state of the second end to the ground end according to one of the control signals; the output module includes an output inductor, and one end of the switch module is coupled to the switch module The second end is coupled to the output end; an output resistor coupled to the output end; and an output capacitor coupled between the output resistor and the ground end; and a control device including a delay comparison Coupled to the input The terminal is configured to generate a circuit enable reset signal according to the input voltage signal; a controller coupled to the delay comparator for enabling a reset signal according to the circuit to provide a reference voltage signal; a first comparison The controller is coupled to the controller and the feedback module for comparing the reference voltage signal with the feedback voltage signal to generate a comparison result; an oscillator for generating an oscillation voltage signal; and a first The first comparator is coupled to the first comparator, the oscillator, and the first end of the switch module for comparing the comparison result and the oscillating voltage signal to generate the control signal to the switch module.

Please refer to FIG. 2, which is a schematic diagram of the DC converter 20 according to an embodiment of the present invention. The DC converter 20 includes a low-pass module 210, an input terminal 200, an output terminal 240, a feedback module 260, a switch module 230, an output module 250, and a control device 22. The structure and operation mode of the low-pass module 210, the switch module 230, and the output module 250 are similar to those of the low-pass module 110, the switch module 130, and the output module 150 in FIG. That is, the low-pass module 210 is composed of an inductor 212 and a capacitor 214 for performing low-pass filtering on the first input voltage signal VIN1 to generate a second input voltage signal VIN2. The switch module 230 includes an upper bridge switch transistor 232, a lower bridge switch transistor 234, an amplifier 236 and an inverting amplifier 238 for controlling the upper bridge switching transistor according to the control signal VCON (and its inverted signal). The conduction state of 232 and the lower bridge switch transistor 234, thereby adjusting the current level of a node N2. The output module 250 is coupled to the node N2, and is composed of a capacitor 252, an inductor 254 and a resistor R1 for generating an output voltage signal VOUT through the inductor-capacitor effect. In addition, the feedback module 260 is composed of resistors R2 and R3 for generating a feedback voltage signal VFB according to the output voltage signal VOUT. The control device 22 is used to generate the control signal VCON, which avoids the problems caused by the glitch during shutdown, as described in detail below.

The control device 22 includes a delay comparator 220, a controller 222, a first comparator 224, an oscillator 226, and a second comparator 228. The delay comparator 220 is configured to generate a circuit enable reset signal VPOR according to the second input voltage signal VIN2. The controller 222 is configured to provide a reference voltage signal VREF according to the circuit enable reset signal VPOR. The first comparator 224 is configured to compare the reference voltage signal VREF with the feedback voltage signal VFB to generate a comparison result VCMP. The oscillator 226 is used to generate an oscillating voltage signal VOSC. The second comparator 228 is configured to compare the comparison result VCMP and the oscillating voltage signal VOSC to generate the control signal VCON to the switch module 229.

Briefly, the present invention instructs the controller 222 to begin lowering the reference voltage signal VREF through the circuit enable reset signal VPOR. The decrease of the reference voltage signal VREF reduces the comparison result VCMP of the first comparator 224, and further reduces the duty cycle of the control signal VCON through the second comparator 228, so that the switching module 230 is over the bridge switching transistor 232. The duty cycle is reduced and the duty cycle of the lower bridge switching transistor 234 is increased, causing the output voltage signal VOUT to decrease. As a result, the output current i _OUT of one of the output terminals 240 and one of the input currents i _{IN of the} input terminal 200 will be lowered to reduce the surge occurring on the second input voltage signal VIN2. In addition, through the feedback module 260, the feedback voltage signal VFB is proportional to the output voltage signal VOUT:

As can be seen from the above equation, when the output voltage signal VOUT drops due to the decrease of the reference voltage signal VREF, the feedback voltage signal VFB also decreases. In other words, the change of the feedback voltage signal VFB follows the reference voltage signal VREF. Please refer to FIG. 3, which is a schematic diagram showing changes of the second input voltage signal VIN2 and the input current i _IN during the shutdown of the DC converter 20. Comparing FIGS. 1B and 3, the present invention reduces the input current i _IN such that the glitch appearing on the second input voltage signal VIN2 is also reduced to prevent the DC converter from erroneously returning to the power-on state.

It should be noted that the delay comparator 220 is configured to compare the second input voltage signal VIN2 with a preset first threshold voltage VTH1 and a second threshold voltage VTH2 to generate a corresponding circuit enable reset signal VPOR. It works as shown in Figure 4. In FIG. 4, when the second input voltage signal VIN2 is raised from the low level to be higher than the first threshold voltage VTH1, the circuit enable reset signal VPOR is switched from a low level V _L to a high level V _H , Indicates that the DC converter 20 is turned on. Conversely, when the second input voltage signal VIN2 is reduced from the high level to less than the second threshold voltage VTH2, the circuit enable reset signal VPOR is switched from the high level V _H to the low level V _L to instruct the controller 222 Start reducing the reference voltage signal VREF.

Please continue to refer to FIG. 5, which is a schematic diagram of the controller 222 in FIG. The controller 222 includes a flexible shutdown circuit 500, a subtractor 502, a bandgap voltage generator 504, a multiplexer 506, and a microcontroller 508. The flexible shutdown circuit 500 is configured to generate a flexible off voltage signal VSS according to the circuit enable reset signal VPOR. The subtracter 502 is configured to subtract a differential voltage VD from the flexible off voltage signal VSS and output a subtraction result VSUB. The bandgap voltage generator 504 is used to generate a bandgap voltage VBG. The multiplexer 506 is configured to generate the reference voltage signal VREF according to the subtraction result VSUB and the bandgap voltage VBG. The microcontroller 508 is configured to select the input signal source of the multiplexer 506 based on the subtraction result VSUB and the bandgap voltage VBG.

Briefly, when the circuit enable reset signal VPOR indicates that the controller 222 begins to lower the reference voltage signal VREF, the flexible shutdown circuit 500 reduces the flexible turn-off voltage signal VSS. Next, the subtractor 502 subtracts the differential voltage VD from the flexible off voltage signal VSS. Finally, the multiplexer 506 outputs the subtraction result VSUB as the reference voltage signal VREF.

Please refer to FIG. 6. FIG. 6 is a schematic diagram of the flexible shutdown circuit 500 in FIG. The flexible shutdown circuit 500 includes a first current source 600, a capacitor 602, a node N3, a first switch 604, a second current source 606, and a second switch 608. When the circuit enable reset signal VPOR is at the high level V _H , the first switch 604 is turned on and the second switch 608 is turned off; meanwhile, the first current source 600 charges the capacitor 602 to increase the flexible turn-off voltage signal VSS on the node N3. . Conversely, when the circuit enable reset signal VPOR is at the low level V _L , the first switch 604 is turned off and the second switch 608 is turned on; at the same time, the capacitor 602 is discharged via the second current source 606 to lower the flexible turn-off voltage signal VSS.

It should be noted here that the input signal source of the multiplexer 506 differs depending on the subtraction result VSUB. In the controller 222, the microcontroller 508 selects different input signal sources of the multiplexer 506 according to the subtraction result VSUB to provide different reference voltage signals VREF. More specifically, when the subtraction result VSUB is greater than the bandgap voltage VBG, the microcontroller 508 selects the bandgap voltage VBG as the input signal source of the multiplexer 506; when the subtraction result VSUB is smaller than the bandgap voltage VBG and greater than a ground voltage VGND When the microcontroller 508 selects the subtraction result VSUB as the input signal source of the multiplexer 506; and when the subtraction result VSUB is less than the ground voltage VGND, the microcontroller 508 selects the ground voltage VGND as the input signal source of the multiplexer 506. For example, please refer to FIG. 7A and FIG. 7B. FIG. 7A and FIG. 7B respectively show the time value of the reference voltage signal VREF, the subtraction result VSUB and the flexible off voltage signal VSS when the DC converter 20 is turned on and off. schematic diagram. It can be seen from FIG. 7A and FIG. 7B that, regardless of whether the DC converter 20 is turned on or off, the slope of the change of the reference voltage signal VREF is related to the magnitude of the subtraction result VSUB and the bandgap voltage VBG and the ground voltage VGND. Different and different. It should be noted that in FIG. 7B, when the subtraction result VSUB is smaller than the bandgap voltage VBG and greater than the ground voltage VGND, the reference voltage signal VREF is the subtraction result VSUB of the flexible off voltage signal VSS minus the difference voltage VD, Therefore, the falling slope of the reference voltage signal VREF is the same as the falling slope of the flexible off voltage signal VSS. The falling slope of the flexible off voltage signal VSS is determined by dividing one of the discharge currents i _DIS drawn by the second current source 606 by the ratio of the capacitance of the capacitor 602.

In the prior art, when the user wants to turn off the DC converter, the glitch generated on the second input voltage signal VIN2 may cause the second input voltage signal VIN2 to be greater than the switching threshold voltage VTH, causing the DC converter to erroneously return to the power-on. status. In contrast, the present invention reduces the output voltage signal VOUT through the control device 22 before the DC converter 20 is turned off to reduce the input current i _IN , thereby reducing the surge generated on the second input voltage signal VIN2. In this way, the present invention can prevent the DC converter 20 from erroneously returning to the power-on state.

In summary, the present invention reduces the output voltage of the DC converter in advance according to the variation of the input voltage of the DC converter before shutdown to reduce the surge effect at the input end of the DC converter to properly turn off the DC converter.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

10, 20. . . DC converter

twenty two. . . Control device

120. . . Control module

100, 200. . . Input

110, 210. . . Low pass module

112, 154, 212, 254. . . inductance

114, 152, 214, 252, 602. . . capacitance

220. . . Delay comparator

224. . . First comparator

228. . . Second comparator

222. . . Controller

226. . . Oscillator

130, 230. . . Switch module

132, 232. . . Upper bridge switch transistor

134, 234. . . Lower bridge switch transistor

136, 236. . . Amplifier

138, 238. . . Inverting amplifier

140, 240. . . Output

150, 250. . . Output module

R1, R2, R3. . . resistance

260. . . Feedback module

500. . . Flexible shutdown circuit

502. . . Subtractor

504. . . Bandgap voltage generator

506. . . Multiplexer

508. . . Microcontroller

600. . . First current source

604. . . First switch

606. . . Second current source

608. . . Second switch

VBG. . . Band gap voltage

VD. . . Differential voltage

VGND. . . Ground voltage

VIN1. . . First input voltage signal

VIN2. . . Second input voltage signal

VOUT. . . Output voltage signal

VCON. . . Control signal

VFB. . . Feedback voltage signal

VCMP. . . Comparing results

VREF. . . Reference voltage signal

VTH1. . . First threshold voltage

VTH2. . . Second threshold voltage

VPOR. . . Circuit enable reset signal

VOSC. . . Oscillating voltage signal

VSUB. . . Subtraction result

VSS. . . Flexible off voltage signal

V _L . . . Low level

V _H . . . High level

i _DIS . . . Discharge current

i _IN . . . Input Current

i _OUT . . . Output current

N1, N2, N3. . . node

Figure 1A is a schematic diagram of a conventional buck converter.

Figure 1B is a schematic diagram showing changes in an input voltage and an input current during a conventional buck converter shutdown process.

FIG. 2 is a schematic diagram of a control device for a DC converter according to an embodiment of the present invention.

FIG. 3 is a schematic diagram showing changes in an input voltage and an input current during a DC converter shutdown process according to an embodiment of the present invention.

4 is a schematic diagram showing an input/output relationship of a delay comparator according to an embodiment of the present invention.

FIG. 5 is a schematic diagram of a controller according to an embodiment of the present invention.

Figure 6 is a schematic diagram of a flexible shutdown circuit in accordance with an embodiment of the present invention.

FIG. 7A is a schematic diagram showing temporal changes of related signals when the DC converter is started according to the embodiment of the present invention.

FIG. 7B is a schematic diagram showing temporal changes of related signals when the DC converter is turned off according to an embodiment of the present invention.

20. . . DC converter

twenty two. . . Control device

200. . . Input

210. . . Low pass module

212, 254. . . inductance

214, 252. . . capacitance

220. . . Delay comparator

224. . . First comparator

228. . . Second comparator

222. . . Controller

226. . . Oscillator

230. . . Switch module

232. . . Upper bridge switch transistor

234. . . Lower bridge switch transistor

236. . . Amplifier

238. . . Inverting amplifier

240. . . Output

250. . . Output module

R1, R2, R3. . . resistance

260. . . Feedback module

VIN1. . . First input voltage signal

VIN2. . . Second input voltage signal

VOUT. . . Output voltage signal

VCON. . . Control signal

VFB. . . Feedback voltage signal

VCMP. . . Comparing results

VREF. . . Reference voltage signal

VTH1. . . First threshold voltage

VTH2. . . Second threshold voltage

VPOR. . . Circuit enable reset signal

VOSC. . . Oscillating voltage signal

i _IN . . . Input Current

i _OUT . . . Output current

N2. . . node

Claims (19)

A control device for a DC converter includes: a delay comparator for generating a circuit enable reset signal according to one of the DC converter input voltage signals; and a controller coupled to the delay comparison The first comparator is coupled to the controller for comparing the reference voltage signal with one of the DC converters to feed back the voltage signal, and the first comparator is coupled to the controller. To generate a comparison result; an oscillator for generating an oscillating voltage signal; and a second comparator coupled to the first comparator and the oscillator for comparing the comparison result and the oscillating voltage signal, Generating a control signal to a switch module of the DC converter; wherein the delay comparator compares the input voltage signal with a first threshold voltage and a second threshold voltage to generate the circuit enable reset signal, The first threshold voltage is greater than the second threshold voltage. The control device of claim 1, wherein the controller comprises: a flexible shutdown circuit coupled to the delay comparator for enabling a reset signal according to the circuit to generate a flexible off voltage signal; a subtractor And coupled to the flexible shutdown circuit for subtracting a differential voltage signal from the flexible off voltage signal and outputting a subtraction result; a bandgap voltage generator for generating a bandgap voltage; a multiplexer coupled The subtractor, the bandgap voltage generator, the first comparison And a ground terminal for generating the reference voltage signal according to the flexible shutdown voltage signal and the bandgap voltage; and a microcontroller coupled to the subtractor, the bandgap voltage generator and the multiplexer And selecting one of the input sources of the multiplexer according to the subtraction result and the bandgap voltage. The control device of claim 2, wherein the flexible shutdown circuit comprises: a first current source for providing a charging current; a capacitor coupled to the subtractor and the ground for receiving the charging a current to provide the flexible shutdown voltage to the subtractor; a node formed between the capacitor and the first current source; a first switch coupled between the first current source and the node for The second current source is coupled to the ground end, and the second current source is coupled to the second current source and the second current source is coupled to the ground state according to the circuit enabling the reset signal. Between the nodes, the reset signal is enabled according to the circuit, and the conduction state of the node to the second current source is controlled. The control device of claim 2, wherein the microcontroller selects the bandgap voltage as the input signal source of the multiplexer when the subtraction result is greater than the bandgap voltage. The control device of claim 2, wherein the microcontroller selects the subtraction result as the input signal source of the multiplexer when the subtraction result is less than the bandgap voltage and greater than a ground voltage. The control device of claim 2, wherein the microcontroller selects the voltage of the ground as the input signal source of the multiplexer when the subtraction result is less than the ground voltage. The control device of claim 2, wherein when the input voltage signal is lower than the first threshold voltage and lower than the second threshold voltage, a falling slope of the reference voltage signal generated by the controller is The falling slope of the flexible off voltage signal is the same. The control device of claim 7, wherein the falling slope of the flexible off voltage signal is determined by a ratio of a discharge current drawn by the second current source divided by a capacitance value of the capacitor. A DC converter includes: an input terminal for receiving an input voltage signal; an output terminal for outputting an output voltage signal; and a feedback module coupled to the output terminal for outputting The voltage signal generates a feedback voltage signal; a switch module includes: a first end for receiving a control signal; a second end; an upper bridge switch transistor coupled to the input end, the first end and the second end for controlling the control signal according to the control signal The first end, the second end, and the ground end are coupled to the first end, the second end, and the ground end, and are configured to control the first signal according to one of the control signals An output module includes: an output inductor, one end of which is coupled to the second end of the switch module, and the other end of which is coupled to the output end; an output resistor, An output capacitor is coupled between the output resistor and the ground; and a control device includes: a delay comparator coupled to the input for receiving the input The voltage signal generates a circuit enable reset signal; a controller coupled to the delay comparator for enabling a reset signal according to the circuit to provide a reference voltage signal; a first comparator coupled to the control And the feedback module for comparing the reference a voltage signal and the feedback voltage signal to generate a comparison result; an oscillator for generating an oscillation voltage signal; and a second comparator coupled to the first comparator, the oscillator, and the switch mode The first end of the group is used to compare the comparison result with the oscillation voltage No. to generate the control signal to the switch module; wherein the delay comparator compares the input voltage signal with a first threshold voltage and a second threshold voltage to generate the circuit enable reset signal, the first The threshold voltage is greater than the second threshold voltage. The DC converter of claim 9, further comprising: an input inductor coupled to the input end, the other end coupled to the delay comparator and the upper bridge switch transistor; and an input capacitor One end is coupled between the input inductor, the delay comparator and the upper bridge switch transistor, and the other end is coupled to a ground end. The DC converter of claim 9, wherein the feedback module comprises: a first resistor, one end of which is coupled to the output end, the other end of which is coupled to the first comparator; and a second resistor One end is coupled to the first resistor and the first comparator, and the other end is coupled to the ground end. The DC converter of claim 9, wherein the switch module further comprises: a non-inverting amplifier coupled between the first end and the upper bridge switch transistor for amplifying the control signal; An inverting amplifier is coupled between the first end and the lower bridge switch transistor for amplifying the control signal and generating the inverted signal of the control signal. The DC converter of claim 9, wherein the controller comprises: a flexible shutdown circuit coupled to the delay comparator for enabling a reset signal according to the circuit to generate a flexible off voltage signal; And coupled to the flexible shutdown circuit for subtracting a differential voltage signal from the flexible off voltage signal and outputting a subtraction result; a bandgap voltage generator for generating a bandgap voltage; a multiplexer coupled Connected to the subtractor, the bandgap voltage generator, the first comparator and a ground terminal for generating the reference voltage signal according to the flexible off voltage signal and the bandgap voltage; and a microcontroller, coupled The subtractor, the bandgap voltage generator and the multiplexer are configured to select one of the input sources of the multiplexer according to the subtraction result and the bandgap voltage. The DC converter of claim 13, wherein the flexible shutdown circuit comprises: a first current source for providing a charging current; a capacitor coupled to the multiplexer and the ground for receiving The charging current is provided to provide the flexible shutdown voltage to the multiplexer; a node is formed between the capacitor and the first current source; a first switch is coupled between the first current source and the node And a second current source coupled to the ground end; and a second switch coupled to the second current, the second current source is coupled to the ground end; and the second current source is coupled to the ground current; Between the source and the node, used to The circuit enables a reset signal to control the conduction state of the node to the second current source. The DC converter of claim 13, wherein the microcontroller selects the bandgap voltage as the input signal source of the multiplexer when the subtraction result is greater than the bandgap voltage. The DC converter of claim 13, wherein the microcontroller selects the subtraction result as the input signal source of the multiplexer when the subtraction result is less than the bandgap voltage and greater than a ground voltage. The DC converter of claim 13, wherein the microcontroller selects the voltage of the ground as the input signal source of the multiplexer when the subtraction result is less than the ground voltage. The DC converter of claim 13, wherein a falling slope of the reference voltage signal generated by the controller is when the input voltage signal is lower than the first threshold voltage and lower than the second threshold voltage The slope of the falling of the flexible off voltage signal is the same. The DC converter of claim 18, wherein the falling slope of the flexible off voltage signal is determined by a ratio of a discharge current drawn by the second current source divided by a capacitance value of the capacitor.