TWI538372B - Buck DC converter and its fast response circuit - Google Patents

Description

Buck DC converter and its fast response circuit

The present invention relates to a step-down DC converter and a fast response circuit thereof, and more particularly to a step-down DC converter capable of providing a fast transient response capability of a step-down DC converter and a fast response circuit thereof.

With the development of the electronics industry, various electronic devices have been continuously developed due to the development trend and human needs under the advancement of electronic technology, such as handheld electronic devices with different functional orientations, notebook computers, and desktops. Computer, etc.

Since electronic products need to operate stably with sufficient power, the power supply circuit of each load in the electronic product is quite important. The power supply circuit supplies the appropriate voltage and current according to the power demand of the load. When the load is changed between light load (low power consumption) and heavy load (high power consumption), the power supply circuit must be able to respond quickly. Switching.

In the conventional power supply circuit, the power supply between the light load and the heavy load is switched by a step-down DC converter. The conventional step-down DC converter simply uses a feedback voltage and passes through an error amplifier. Afterwards, a compensation voltage is obtained, and a duty cycle of the step-down DC converter is adjusted by comparing the compensation voltage with a ramping signal to control the output voltage of the step-down DC converter. . However, since the output of the error amplifier is externally connected with a resistor and a capacitor and grounded as a frequency compensation, and the potential of the compensation voltage is discharged from the output of the error amplifier by the capacitor, the original is located When the compensation voltage with a high potential is transferred to the low-potential compensation voltage of the light-load supply state, the capacitor is discharged It takes time to cause the conventional architecture to quickly adjust the compensation voltage that was originally at a high potential to a low potential (waiting for the capacitor to be discharged), which in turn leads to a duty cycle that should be quickly switched to light load. There is a duty ratio for the duty cycle of the heavy load for a period of time. This condition causes the step-down DC converter under heavy load to still supply an excessive output voltage at the initial stage of switching to a light load state (also known as "output peak voltage". That is, the conventional step-down DC converter is difficult to achieve fast switching when the load is heavy to light load, and the loop response of the entire step-down DC converter is slow, so that the output peak voltage of the heavy load to the light load cannot be Effectively reduced.

Therefore, how to speed up the adjustment speed of the compensation voltage and make the loop reaction speed become faster, thereby effectively reducing the output peak voltage when the heavy load is transferred to the light load is a problem to be solved by the present invention.

In order to solve the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a fast response circuit of a step-down DC converter, which can quickly adjust the compensation voltage and the discharge of the acceleration capacitor (shortening the discharge time), thereby accelerating the compensation voltage. The adjustment speed and the loop reaction speed are faster, and the output peak voltage at the time of heavy load to light load is effectively reduced.

To achieve the above and other objects, the present invention provides a fast response circuit for a step-down DC converter, which generates an adjustment error voltage according to a comparison between a feedback voltage and a reference voltage at an output end of the step-down DC converter. The power stage of the step-down DC converter performs the duty ratio adjustment of the duty cycle. The fast response circuit includes: a compensation unit that receives the voltage of the comparison result for storage; and a detection unit coupled to the compensation unit And receiving the comparison result, generating a switching voltage according to the voltage of the comparison result and the voltage stored by the compensation unit; and a switching unit, wherein the input end receives the potential of the comparison result and is coupled to the step-down DC converter An input end of the power stage, the output end of the switch unit is grounded, and the control end of the switch unit is coupled to the detecting unit to respond to the switch The voltage is turned on and the path between the ground and the ground when the load is transferred from the heavy load to the light load, so that the potential of the received voltage of the power stage input terminal of the step-down DC converter is pulled down.

In one embodiment of the present invention, the compensation unit includes a resistor unit and a capacitor unit, and one end of the resistor unit receives the voltage of the comparison result and is coupled to the first end of the detecting unit. The other end is coupled to the second end of the detecting unit and one end of the capacitor unit, and the other end of the capacitor unit is grounded.

In an embodiment of the invention, the detecting unit is a comparator, and the positive phase input terminal of the comparator receives the voltage stored by the compensation unit, and the inverting input terminal of the comparator receives the comparison result. The voltage is generated to turn on the switching voltage of the switching unit in response to the condition that the voltage stored by the compensation unit is higher than the voltage of the comparison result when the heavy load is transferred to the light load.

To achieve the above and other objects, the present invention further provides a step-down DC converter including a power stage, a filter circuit, a first voltage dividing circuit, an error amplifier, and a detecting and fast charging and discharging circuit. The power stage receives an input voltage and adjusts the input voltage based on an internal duty cycle thereof; the filter circuit receives the adjusted input voltage, converts the input voltage into an inductor current, and the inductor current Filtering to generate the output voltage; the first voltage dividing circuit receives and divides the output voltage to generate a feedback voltage; the error amplifier receives a reference voltage and the feedback voltage, and based on the reference voltage and The voltage difference of the feedback voltage generates an error voltage; the fast response circuit is coupled between the power stage and the error amplifier. The fast response circuit includes a compensation unit, a detection unit and a third switch. The frequency compensation unit is a voltage division energy storage circuit and is configured to receive the error voltage to generate a voltage division and store the potential thereof. The detecting unit generates a switching voltage according to the error voltage and a voltage stored by the compensation unit; and the third open relationship receives the switching voltage, and is turned on or off in response to the switching voltage to selectively Error power Pressing the ground generates and outputs a corresponding adjustment error voltage to the power level, wherein the power level adjusts a duty ratio of the duty cycle.

In an embodiment of the invention, when the third switch is turned on, the potential of the error voltage begins to drop due to grounding.

In an embodiment of the invention, the third switch (the switching unit) is an N-type metal oxide semiconductor field effect transistor (NMOS).

In an embodiment of the invention, the power stage includes a logic unit to receive the adjustment error voltage, the logic unit can be a flip-flop, and the reset end of the flip-flop receives the adjustment error voltage, the positive and negative The set terminal of the device receives a clock signal, and the output of the flip-flop outputs a duty cycle for the power level to adjust the input voltage.

In an embodiment of the present invention, the input end of the switch unit receives the error voltage and is coupled to the reset end of the flip-flop, the output end of the switch unit is grounded, and the control end of the switch unit is coupled to the The detecting unit turns on the switching unit when the heavy load is turned to light load in response to the switching voltage, so that the potential of the error voltage is pulled down to become the adjusted error voltage input to the power stage.

Thereby, the buck DC converter of the present invention accelerates the adjustment speed of the compensation voltage and makes the loop reaction by the power stage, the filter circuit, the first voltage dividing circuit, the error amplifier and the fast response circuit. The speed is faster, which effectively reduces the output peak voltage when the load is heavy to light load.

100‧‧‧Buck DC Converter

110‧‧‧Power level

111‧‧‧gate driver

112‧‧‧Logical unit

120‧‧‧Filter circuit

130‧‧‧First voltage divider circuit

140‧‧‧Error amplifier

150‧‧‧Response fast circuit

151‧‧‧Compensation unit

152‧‧‧Detection unit

C‧‧‧ capacitor

C1‧‧‧ first end

C2‧‧‧ second end

Clk‧‧‧ clock signal

I _L ‧‧‧Inductor current

L‧‧‧Inductance

L1‧‧‧ first end

L2‧‧‧ second end

R‧‧‧resistance

R1‧‧‧ first end

R2‧‧‧ second end

R _A ‧‧‧resistance

R _B ‧‧‧resistance

R _L ‧‧‧Load resistor

S1‧‧‧ first switch

S2‧‧‧ second switch

S3‧‧‧ third switch

V _AE ‧‧‧Adjust error voltage

V _D ‧‧‧ partial pressure

V _E ‧‧‧ error voltage

V _FB ‧‧‧Responsive voltage

V _IN ‧‧‧ input voltage

V _OUT ‧‧‧ output voltage

V _REF ‧‧‧reference voltage

V _S ‧‧‧Switching voltage

FIG. 1 is a circuit diagram of a step-down DC converter according to an embodiment of the present invention.

In order to fully understand the objects, features and advantages of the present invention, the present invention will be described in detail by the following specific embodiments and the accompanying drawings. Please refer to FIG. 1, which is a circuit diagram of a step-down DC converter according to an embodiment of the present invention. The step-down DC converter 100 includes a power stage 110, a filter circuit 120, a first voltage dividing circuit 130, an error amplifier 140, and a fast response circuit 150.

The power stage 110 receives a system input voltage V _IN, and a duty cycle based on its inside (duty cycle) is adjusted to output the input voltage V _IN after the adjustment.

In detail, the power stage 110 includes a first switch S ₁ , a second switch S ₂ , a gate driver 111 , and a logic unit 112 . The first switch S ₁ is coupled to the input voltage V _IN , and when the first switch S ₁ is turned on, outputs the input voltage V _IN to the filter circuit 120, and generates an inductor in the filter circuit 120. Current I _L ; the second switch S ₂ is grounded, and when the second switch S ₂ is turned on, the filter circuit 120 is grounded; the gate driver 111 receives a duty cycle to control the The first switch S ₁ and the second switch S ₂ are turned on or off; and the logic unit 112 determines a duty ratio of the duty cycle based on an adjustment error voltage V _AE and a clock signal Clk, and The duty cycle is output to the gate driver 111.

In this embodiment, the first switch S ₁ may be a P-type metal oxide semiconductor field effect transistor (PMOS), and the second switch S ₂ may be an N-type metal oxide semiconductor field effect transistor (NMOS). The logic unit 112 can be a flip-flop, and the reset terminal (R) of the flip-flop receives the adjustment error voltage V _AE , and the set terminal (S) of the flip-flop receives the clock signal Clk, The output terminal (Q) of the flip-flop outputs the duty cycle to the gate driver 111. The form of the first switch S ₁ , the second switch S _{2 ,} and the logic unit 112 are not limited thereto, and any electronic component that can achieve the same function does not deviate from the scope of the present invention.

The filter circuit 120 can be a low pass filter circuit for transmitting and storing energy and filtering out AC noise waves. The filter circuit 120 includes an inductor L, a capacitor C, and a resistor R. The inductor L has a first end L1 and a second end L2. The first end L1 of the inductor L receives the input voltage V _IN and converts the input voltage V _IN into an inductor current I _L , and the The second end L2 of the inductor L outputs an output voltage V _OUT . The capacitor C has a first end C1 and a second end C2. The first end C1 of the capacitor C is coupled to the inductor L. The second end L2 has a first end R1 and a second end R2. The first end R1 of the resistor R is coupled to the second end C2 of the capacitor C, and the second end of the resistor R R2 is grounded. The form of the filter circuit 120 is not limited thereto. Any electronic component that can achieve the same function belongs to the scope of protection of the present invention.

The first voltage dividing circuit 130 receives and divides the output voltage V _OUT to generate a feedback voltage V _FB , and the first voltage dividing circuit 130 is connected by two resistors (R _A , R _B ) connected in series. composition. The form of the first voltage dividing circuit 130 is not limited thereto, and all electronic components that can achieve the same function are within the scope of the present invention.

The error amplifier 140 receives a reference voltage V _REF and the feedback voltage V _FB , and generates an error voltage V _E based on the voltage difference between the reference voltage V _REF and the feedback voltage V _FB .

In detail, the error amplifier 140 has an inverting terminal (-), a non-inverting terminal (+) and an output terminal, and the inverting terminal of the error amplifier 140 receives the feedback voltage V _FB , the error amplifier The non-inverting terminal of 140 receives the reference voltage V _REF and is based on the voltage difference between the reference voltage V _REF and the feedback voltage V _FB such that the output of the error amplifier outputs the error voltage V _E . The form of the error amplifier 140 is not limited thereto, and all electronic components that can achieve the same function are within the scope of the present invention.

The present invention generates an adjustment error voltage V _AE for the step-down DC conversion by comparing the feedback voltage V _FB of the output terminal of the step-down DC converter 100 with a reference voltage V _REF by the fast response circuit 150. The power stage 110 of the device 100 adjusts the duty ratio of the duty cycle. The fast response circuit 150 is coupled between line 140 and the power level of the error amplifier 110, and the fast response circuit 150 includes a compensation unit 151, a detecting unit 152, and a third switch (switch unit) S _3.

The compensation unit 151 is a voltage division energy storage circuit, which is composed of a resistor R and a capacitor C connected in series, and is used for receiving the error voltage V _E to generate a voltage divider V _D and storing the capacitor therein. C.

The detecting unit 152 detects the error voltage V _E and the divided voltage V _D stored by the capacitor C, and generates a switching voltage V _S . More specifically, the detecting unit 152 generates a switching voltage V _S according to the comparison result of the feedback voltage V _FB and the reference voltage V _REF and the divided voltage V _D . The compensation unit 151 can also be referred to as a compensation unit for frequency compensation.

The output of the third switch S ₃ is coupled to the ground. The input end of the third switch S ₃ is coupled to the output end of the error amplifier 140 and the input end of the power stage 110 (for example, the foregoing positive and negative The reset terminal of the device is configured to control the error voltage V _{E to} input the potential of the power stage 110. The third switch S ₃ receives the switching voltage V _S and determines whether to turn on or off according to the magnitude of the switching voltage V _S , that is, when the switching voltage V _{S is} greater than the threshold voltage of the third switch S ₃ , The switching voltage V _{S is} turned on, otherwise it is turned off, thereby adjusting the error voltage V _E to generate and output a corresponding adjustment error voltage V _AE to the power stage 110 to adjust the duty ratio of the duty cycle. In detail, when the third switch S _{3 is} turned on, the potential stored in the capacitor C of the compensation unit 151 is rapidly discharged due to the third switch S ₃ that conducts the ground path, so that the error voltage V _E The potential can be quickly responded to decrease; when the third switch S _{3 is} turned off, the error voltage V _E is not affected by the grounding point and can be input to the input end of the power stage 110 (for example, the foregoing flip-flop can be Reset end). In this embodiment, the third switch S ₃ is an N-type metal oxide semiconductor field effect transistor (NMOS), but the form is not limited thereto, and any electronic component capable of achieving the same function belongs to the present invention. The scope.

When the buck DC converter 100 is operated, when the buck DC converter 100 is in a heavy load state, the feedback voltage V _FB , the error is made due to the large output voltage V _OUT required for the heavy load. voltage V _E and a duty cycle of the responsibility of the larger; when the down DC converter 100 to the light load state, due to the smaller required light load the output voltage V _OUT, so that the feedback voltage V _FB, The error voltage V _E and the responsibility of the duty cycle are relatively small.

Further, when the step-down DC converter is in dynamic load conversion, wherein the dynamic load conversion can be converted from heavy load to light load or light load to heavy load, where the buck DC converter 100 is described by taking heavy-duty to light-loading as an example: during the process of transferring heavy load to light load, the duty ratio V _OUT and the duty ratio of the duty cycle are changed from large to small, and the feedback voltage V _FB is first lowered. The error voltage V _{E is} lowered (because the difference from the reference voltage V _REF becomes smaller), and the error voltage V _E is discharged by the compensation unit 151 at this time, that is, the detecting unit 152 of the present invention is caused by The divided voltage V _{D of the} non-inverting input terminal (previously stored at the potential of the capacitor C) is higher than the error voltage V _E of the inverting input terminal, and the switching voltage V _S of the high potential is output, the third switch S ₃ The path of being turned on and grounded, the potential of the error voltage V _E is immediately pulled down quickly, so that the duty ratio of the duty cycle at the light load can be quickly determined, and the adjustment input to the power stage 110 is quickly adjusted. error voltage V _AE and through this architecture of the present invention Loop so that the reaction rate becomes faster, effectively reducing the overloading of the peak output voltage at light load transfer.

In summary, the step-down DC converter of the present invention has a circuit configuration between the power stage, the filter circuit, the first voltage dividing circuit, the error amplifier, and the fast response circuit. The compensation unit, the detecting unit and the switching unit of the fast response circuit are used to effectively reduce the output peak voltage when the heavy load is transferred to the light load.

The invention has been described above in terms of the preferred embodiments, and it should be understood by those skilled in the art that the present invention is not intended to limit the scope of the invention. It should be noted that variations and permutations equivalent to those of the embodiments are intended to be included within the scope of the present invention. Therefore, the scope of protection of the present invention is defined by the scope of the patent application.

100‧‧‧Buck DC Converter

110‧‧‧Power level

111‧‧‧gate driver

112‧‧‧Logical unit

120‧‧‧Filter circuit

130‧‧‧First voltage divider circuit

140‧‧‧Error amplifier

150‧‧‧Response fast circuit

151‧‧‧Compensation unit

152‧‧‧Detection unit

C‧‧‧ capacitor

C1‧‧‧ first end

C2‧‧‧ second end

Clk‧‧‧ clock signal

I _L ‧‧‧Inductor current

L‧‧‧Inductance

L1‧‧‧ first end

L2‧‧‧ second end

R‧‧‧resistance

R1‧‧‧ first end

R2‧‧‧ second end

R _A ‧‧‧resistance

R _B ‧‧‧resistance

R _L ‧‧‧Load resistor

S ₁ ‧‧‧first switch

S ₂ ‧‧‧second switch

S ₃ ‧‧‧third switch

V _AE ‧‧‧Adjust error voltage

V _D ‧‧‧ partial pressure

V _E ‧‧‧ error voltage

V _FB ‧‧‧Responsive voltage

V _IN ‧‧‧ input voltage

V _OUT ‧‧‧ output voltage

V _REF ‧‧‧reference voltage

V _S ‧‧‧Switching voltage

Claims (9)

A fast response circuit of a step-down DC converter generates an adjusted error voltage for a power level of the step-down DC converter according to a comparison between a feedback voltage of the output of the step-down DC converter and a reference voltage a logic unit performs a duty ratio adjustment of the duty cycle, the fast response circuit includes: a compensation unit that receives the voltage of the comparison result for storage; and a detection unit coupled to the compensation unit and receives the comparison result, Generating a switching voltage according to the voltage of the comparison result and the voltage stored by the compensation unit; and a switching unit whose input end receives the potential of the comparison result and is coupled to the logic unit of the power level of the step-down DC converter The output end of the switch unit is grounded, and the control end of the switch unit is coupled to the detection unit to turn on the path between the ground and the ground under the comparison result received during the heavy load to light load in response to the switch voltage. The potential of the receiving voltage of the logic unit of the power stage of the step-down DC converter is pulled down to adjust the duty ratio of the duty cycle, wherein The compensation unit includes a resistor unit and a capacitor unit. One end of the resistor unit receives the voltage of the comparison result and is coupled to the first end of the detecting unit. The other end of the resistor unit is coupled to the detecting unit. The second end and one end of the capacitor unit are grounded at the other end of the capacitor unit. The fast response circuit of claim 1, wherein the detecting unit is a comparator, the positive phase input terminal of the comparator receives the voltage stored by the compensation unit, and the inverting input terminal of the comparator receives The voltage of the comparison result in response to heavy load to light load The condition that the voltage stored by the compensation unit is higher than the voltage of the comparison result produces a switching voltage that turns on the switching unit. The fast response circuit of claim 1 or 2, wherein the switching unit is an N-type metal oxide semiconductor field effect transistor. A step-down DC converter includes: a power stage that receives an input voltage, the power stage includes a first switch, a second switch, a logic unit, and a gate driver, the first switch, the second The switch and the logic unit are connected through the gate driver, the first open relationship is coupled to the input voltage, the second open relationship is grounded, the logic unit generates a duty cycle, and the gate driver receives the responsibility a cycle to control the opening or closing of the first switch and the second switch to adjust the input voltage; a filter circuit coupled to the first switch and the second switch of the power stage, when the first switch is turned on The filter circuit receives the adjusted input voltage, converts the input voltage into an inductor current, and filters the inductor current to generate an output voltage. When the second switch is turned on, the filter circuit is grounded; a first voltage dividing circuit coupled to the filter circuit to receive and divide the output voltage to generate a feedback voltage; an error amplifier coupled to the first voltage dividing circuit for receiving a reference voltage and the feedback voltage, and an error voltage is generated based on the voltage difference between the reference voltage and the feedback voltage; and a fast response circuit coupled between the power stage and the error amplifier, the fast The response circuit contains: A compensation unit is a voltage division energy storage circuit, and is configured to receive the error voltage to generate a voltage division and store the potential thereof; a detection unit generates a voltage according to the error voltage and the voltage stored by the compensation unit a switching voltage; and a switching unit that receives the switching voltage and turns on or off in response to the switching voltage to selectively ground the error voltage to generate and output a corresponding adjusted error voltage to the logic of the power stage a unit for the logic unit of the power stage to adjust a duty ratio of the duty cycle, wherein the compensation unit includes a resistor unit and a capacitor unit, and one end of the resistor unit receives the error voltage and is coupled to the detecting unit The other end of the resistor unit is coupled to the second end of the detecting unit and one end of the capacitor unit, and the other end of the capacitor unit is grounded. The step-down DC converter of claim 4, wherein when the switching unit is turned on, the potential of the error voltage begins to drop due to grounding. The buck DC converter of claim 5, wherein the logic unit is configured to receive the adjustment error voltage. The buck DC converter of claim 6, wherein the logic unit is a flip flop. The step-down DC converter of claim 7, wherein the reset terminal of the flip-flop receives the adjustment error voltage, the set terminal of the flip-flop receives a clock signal, and the output of the flip-flop outputs a responsibility The cycle is used by the power stage to adjust the input voltage. The step-down DC converter of claim 8, wherein the input end of the switch unit receives the error voltage and is coupled to the reset end of the flip-flop, the output end of the switch unit is grounded, and the switch unit is The control terminal is coupled to the detecting unit to turn on the switching unit when the heavy load is turned to light load in response to the switching voltage, so that the potential of the error voltage is pulled down to become the adjusted error voltage input to the power stage.