An output voltage sampling circuit and its sampling method

Abstract

One or more embodiments of this specification disclose an output voltage sampling circuit, including: a main topology circuit module of a switching power supply, including a power device switching tube, configured to modulate an input voltage into a voltage required by a load and output it to the load; a voltage sampling module, with a first input terminal electrically connected to the drain of the power device switching tube and a second input terminal electrically connected to the source of the power device switching tube, or a first input terminal electrically connected to the drain of the power device switching tube and a second input terminal electrically connected to the ground wire, configured to collect the oscillation amplitude of the drain voltage of the power device switching tube to obtain an output voltage value after the power device switching tube is turned off and the current of the inductor in the main topology circuit of the switching power supply is discontinuous.

Description

Technical Field

[0001] The embodiments of this specification relate to the field of electronic circuits, and particularly to an output voltage sampling circuit and a sampling method thereof. Background Art

[0002] With the development of electronic circuits, the integration level of electronic circuit-based solutions is getting higher and higher. For example, in LED power supplies, the integration level of LED power supply driving solutions is becoming increasingly high, and there are fewer external devices for the chip. However, the need for sampling the output voltage of LED driving power supplies has always existed. Precise sampling of the output voltage of LED driving power supplies is beneficial to reducing the system cost, and can greatly improve the reliability of the power supply system and reduce the failure rate. Summary of the Invention

[0003] In order to solve the above technical problems, the main purpose of the embodiments of this specification is to provide an output voltage sampling circuit and a sampling method thereof, so as to solve the technical problem in the prior art that the output voltage cannot be sampled better.

[0004] The technical solutions of one or more embodiments of this specification are implemented in the following manner:

[0005] One or more embodiments of this specification provide an output voltage sampling circuit, including:

[0006] A main topology circuit module of a switching power supply, including a power device switching transistor, configured to modulate an input voltage into a voltage required by a load and output it to the load;

[0007] A voltage sampling module, with a first input terminal electrically connected to the drain of the power device switching transistor and a second input terminal electrically connected to the source of the power device switching transistor, or a first input terminal electrically connected to the drain of the power device switching transistor and a second input terminal electrically connected to the ground wire, configured to collect the voltage oscillation amplitude of the drain of the power device switching transistor after the power device switching transistor is turned off and the current in the inductor in the main topology circuit of the switching power supply is discontinuous, so as to obtain an output voltage value output to the load.

[0008] Preferably, the sampling of the oscillation amplitude is determined according to the voltage change slope of the first oscillation half-cycle of the drain voltage of the power device switching transistor; the output voltage value is the voltage difference between the drain voltage of the power device switching transistor at the start of oscillation and the voltage at the quarter oscillation period point, or half of the voltage difference between the drain voltage of the power device switching transistor at the start of oscillation and the oscillation bottom of the first oscillation half-cycle.

[0009] Preferably, the main topology circuit module of the switching power supply further includes a comparator, configured to output an enable signal for controlling the voltage sampling module to perform sampling.

[0010] Preferably, the first input terminal of the comparator is connected to the gate of the power device switch; the second input terminal of the comparator is connected to a fixed voltage reference, and the output terminal of the comparator is connected to the voltage sampling module.

[0011] Preferably, the detection of the rate of change of the oscillating voltage can also be achieved through an externally connected capacitor. One end of the externally connected capacitor is directly or indirectly connected to the drain of the power switch, and the other end of the externally connected capacitor is connected to the first input terminal of the comparator; the second input terminal of the comparator is connected to a fixed voltage reference, and the output terminal of the comparator is connected to the voltage sampling module.

[0012] Preferably, the voltage sampling module includes a resistive voltage division sampling circuit.

[0013] Preferably, the voltage sampling module is used for:

[0014] After the drain voltage starts to oscillate and when the peak value of the rate of change of the drain voltage is detected, the difference between the voltage value when the drain voltage starts to oscillate and the voltage value at the peak of the rate of change of the drain voltage is determined as the output voltage value.

[0015] Preferably, the voltage sampling module is used for:

[0016] After the drain voltage starts to oscillate and when the rate of change of the drain voltage is detected to be zero, half of the difference between the voltage value when the drain voltage starts to oscillate and the voltage value at the point where the rate of change of the drain voltage is zero is determined as the output voltage value.

[0017] A sampling method for an output voltage sampling circuit includes:

[0018] After the power device switch is turned off and the current of the inductor in the main topology circuit module of the switching power supply stops flowing, the oscillation amplitude of the first oscillating half-cycle of the drain voltage of the power device switch is collected, and the output voltage value output to the load is determined according to the oscillation amplitude.

[0019] Preferably, the sampling of the oscillation amplitude is determined according to the change slope of the first oscillation amplitude of the drain voltage of the power device switch; the output voltage value is the voltage difference between the drain voltage of the power device switch at the start of oscillation and the voltage at the one-quarter oscillation period point, or half of the voltage difference between the drain voltage of the power device switch at the start of oscillation and the oscillation bottom of the first oscillating half-cycle.

[0020] Compared with the prior art, the above at least one technical solution adopted by one or more embodiments of this specification can achieve the following beneficial effects:

[0021] The comparator controls the voltage sampling module to collect the voltage between the drain and source of the power device switching tube according to the gate voltage of the power device switching tube. After the power device switching tube is turned off and the current of the inductor in the buck chopper circuit is discontinuous, the first oscillation amplitude of the voltage between the drain and source of the power device switching tube is collected, and the output voltage for supplying power to the load is determined according to the oscillation amplitude. No auxiliary winding and related sampling pins are required, which reduces the cost and is not easily affected by the transformer coupling coefficient; nor is it necessary to add digital filtering, avoiding the phenomenon that the dynamic response speed is very slow and the output voltage is extremely likely to be out of control for a short time or permanently, and improving the reliability. It has a lower cost than the prior art, is more conducive to improving the system integration, sampling accuracy, response speed and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in this specification. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 Schematic diagram of the circuit principle for sampling the output voltage in the prior art provided by an embodiment of this specification;

[0024] Figure 2 Waveform diagram of sampling the output voltage in another prior art provided by an embodiment of this specification;

[0025] Figure 3 Schematic diagram of the circuit principle of an output voltage sampling circuit provided by an embodiment of this specification;

[0026] Figure 4 For an embodiment of this specification, provided Figure 3 The waveform diagram corresponding to DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] To make the objectives, technical solutions and advantages of this application clearer, the following will clearly and completely describe the technical solutions of this application in combination with the specific embodiments and corresponding drawings of this application. Obviously, the described embodiments are only some embodiments of this application, rather than all embodiments. Based on the embodiments of this specification, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of this application.

[0028] Such as Figure 1As shown, it is a schematic diagram of the circuit principle for sampling the output voltage using an auxiliary winding in the prior art. When the MOS transistor Q (which can of course also be other semiconductor devices, such as a bipolar junction transistor BJT, etc.) is turned off, the main winding T2 supplies power to the load (light-emitting diode) through the freewheeling diode D. During the freewheeling stage, the voltage of the auxiliary winding T1 or the main winding T2 is approximately equal to or proportional to the output voltage supplied to the load. After the MOS transistor Q is turned off, sampling the voltage of the auxiliary winding T1 can obtain the output voltage information. Since the resistor Ra and the resistor Rb are connected in series across the auxiliary winding T1 and the resistance values of the resistor Ra and the resistor Rb are known, the voltages across the resistor Ra and the resistor Rb can be known. Thus, the voltage across the auxiliary winding T1 can be known, and further the voltage across the main winding can be obtained. The sum of the voltage across the main winding and the output voltage supplied to the load is the input voltage. Therefore, the output voltage is the input voltage minus the voltage across the main winding.

[0029] However, obtaining the voltage across the main winding indirectly by collecting the voltage across the auxiliary winding in this way and finally obtaining the output voltage requires adding an auxiliary winding and related sampling pins based on the main winding (the most basic inductor in the buck circuit) T2, which has the disadvantages of high cost and being easily affected by the transformer coupling coefficient.

[0030] As Figure 2 shown, another method is to indirectly sample the output voltage through the freewheeling time of the freewheeling diode (the transformer demagnetization time). Figure 2 It is a graph showing the relationship between the freewheeling time of the freewheeling diode and the output voltage.

[0031] The relationship between the diode freewheeling time Toff (the transformer demagnetization time) and the output voltage V o is: V o =L*I pk / T off . From the waveform diagram, it can be seen that T off is the time when the current in the loop composed of the inductor, the freewheeling diode, and the load in the buck circuit changes from having (starting to freewheel) to having none (0) when V ds is at a high level, that is, the T off interval shown in the figure. For a low power factor drive power supply, L*I pk is fixed. L is the inductor and I pk is the peak current. Then T off =k / V o , where k = L*I pk , that is, the T off time is inversely proportional to the output voltage.

[0032] The method of indirectly sampling the output voltage through the freewheeling time of the freewheeling diode (the demagnetization time of the transformer) has the disadvantages of many variables and poor accuracy. The change of inductance and the difference in peak current will both affect the sampling of the output voltage. Moreover, in order to reduce the influence of noise, digital filtering is usually added. For example, it can be considered as the true value only when the condition is met continuously for 2 times or more. Therefore, the dynamic response speed is very slow. For applications with a relatively small output capacitance, it is extremely easy to have the phenomenon of short-term or permanent out-of-control of the output voltage, which has a great impact on the reliability of the system.

[0033] As Figure 3 shown, it is a schematic circuit diagram of an output voltage sampling circuit provided by the technical solution of this application. The output voltage sampling circuit includes: an AC power supply 1, a rectification circuit module 2, a buck chopper circuit module 3, a voltage sampling module 4, and a load. Among them,

[0034] The AC power supply 1 is connected to the input end of the rectification circuit module 2 and is used to provide an AC power supply.

[0035] The rectification circuit module 2 is a rectifier bridge circuit, and its input end is connected to the AC power supply 1. It is used to convert the AC voltage provided by the AC power supply 1 into a DC voltage and then supply power to the load.

[0036] The buck chopper circuit module 3, its input end is electrically connected to the output end of the rectification circuit module 2, and is used to convert the DC voltage output by the rectification circuit module 2 into the voltage required by the load through buck processing and supply power to the load. In this embodiment, the load is a light-emitting diode.

[0037] The buck chopper circuit module 3 includes a first capacitor C1, a second capacitor C2, a freewheeling diode D1, an inductor L, a first parasitic capacitor C3, a second parasitic capacitor C4, a resistor R1, and a comparator A. The first capacitor C1 is connected in parallel with the output end of the rectification circuit module 2. The negative electrode of the freewheeling diode D1 is connected to the positive output of the rectification circuit module 2, and the negative electrode is connected to the drain of the power device switch Q1. One end of the second capacitor C2 is connected to the negative electrode of the freewheeling diode D1, and the other end is connected to the positive electrode of the freewheeling diode D1 through the inductor L. One end of the first parasitic capacitor C3 is connected to the drain of the power device switch Q1, and the other end is connected to the reverse input end of the comparator A. Both ends of the second parasitic capacitor C4 are respectively connected to the gate and source of the power device switch Q1. One end of the resistor R1 is connected to the source of the power device switch Q1, and the other end is connected to the negative output of the rectification circuit module 2.

[0038] Comparator A is used to output an enable signal for controlling the sampling of the voltage sampling module. The inverting input terminal of Comparator A is connected to the drain of the power device switching transistor Q1 through the first parasitic capacitor C3. The non-inverting input terminal of Comparator A is connected to the negative output of the rectifier circuit module 2, and the output terminal of Comparator A is connected to the voltage sampling module 4. Among them, the non-inverting input terminal of Comparator A is connected to a fixed voltage reference, and this fixed voltage reference can be the ground wire.

[0039] The voltage sampling module 4, whose input terminal is connected to the drain and source of the power device switching transistor Q1 in the buck chopper circuit 3, is used to collect the oscillation amplitude of the first oscillation half-cycle of the voltage between the drain and source of the power device switching transistor Q1 after the power device switching transistor Q1 is turned off and the current in the inductor L in the buck chopper circuit 3 is discontinuous, and determine the output voltage for supplying power to the load according to this oscillation amplitude. The oscillation amplitude is determined according to the change slope of the first oscillation amplitude of the voltage between the drain and source of the power device switching transistor Q1. Refer to Figure 4 . In addition, in practical applications, the potential of the drain voltage can also be collected after the drain voltage oscillates, and the output voltage can be determined according to the maximum and minimum values of the collected potential. After the drain voltage oscillates, the maximum value of the collected potential can be regarded as the oscillation peak, and the minimum value of the collected potential can be regarded as the oscillation valley. Half of the difference between the oscillation peak and the oscillation valley is the output voltage output to the load.

[0040] This voltage sampling module can be a resistor voltage division sampling circuit, and of course, it can also be other voltage sampling circuits.

[0041] In another embodiment, it further includes a third parasitic capacitor C gd , and both ends of the third parasitic capacitor C gd are respectively connected to the drain and gate of the power device switching transistor Q1, as shown by the dotted line part in Figure 4 .

[0042] This specification also provides a sampling method for an output voltage sampling circuit, including:

[0043] After the power device switching transistor is turned off and the current in the inductor in the main topology circuit module of the switching power supply continues to flow, collect the oscillation amplitude of the first oscillation half-cycle of the drain voltage of the power device switching transistor, and determine the output voltage value output to the load according to this oscillation amplitude.

[0044] Optionally, the sampling of the oscillation amplitude is determined according to the change slope of the first oscillation amplitude of the drain voltage of the power device switching transistor; the output voltage value is the voltage difference between the drain voltage of the power device switching transistor at the start of oscillation and the voltage at the quarter oscillation period point, or half of the voltage difference between the drain voltage of the power device switching transistor at the start of oscillation and the oscillation valley bottom of the first oscillation half-cycle.

[0045] Reference Figure 4 , the above steps can be specifically explained as follows: After the power device switch Q1 is turned off, the inductor L, the freewheeling diode D1, and the load form a loop. The inductor L supplies power to the load. When the energy of the inductor is released, the current in this loop becomes 0. After the current in the inductor decreases to 0, the parasitic capacitance between the drain and source of the inductor L and the power device switch Q1 enters the LC oscillation state, and the voltage V between the drain and source of the power device switch Q1 ds subsequently generates oscillation fluctuations. The amplitude information of the LC oscillation usually contains the information of the output voltage, and the output voltage value can be obtained therefrom. When the rectifier circuit module 2 supplies power to the buck chopper circuit module 3 and the power device switch Q1 has not been turned on yet, V g is in the low level state, and V ds is in the high level state. Ignoring the voltage division of the sampling resistor, V ds is the input voltage V in minus the load voltage V o . After the power device switch Q1 is turned on, V g is in the high level. At this time, the power device switch Q1 is turned on, and V ds switches to the low level state. At the same time, the rectifier circuit module supplies the rectified DC voltage to the load and provides energy for the inductor L. When the power device switch Q1 is turned off again and V g is in the low level state, the inductor L supplies power to the load through the freewheeling diode D1, and the inductor L releases energy. After a period of time, the energy of the inductor L is released, and the current in the loop composed of the inductor L, the freewheeling diode D1, and the load becomes 0. During this process, V ds is V in . Then, the inductor L and the capacitance between the drain and source of the power device switch Q1 generate LC oscillation. After a certain blanking time, that is, the input voltage or the high-voltage terminal voltage (between the drain and source) of the power device switch Q1, V ds , is detected before the oscillation and is held or stored. The first oscillation amplitude of the voltage between the drain and source of the power device switch Q1 is collected. Since the oscillation is decaying, because the voltage of V ds after the power device switch Q1 is disconnected is Vin, it is necessary to collect the decaying one starting from Vin. The subsequent decay is more and more inaccurate, so the amplitude of the first oscillation half-cycle is the closest to the true value. When the oscillation midpoint (|dv / dt| maximum point) or the oscillation valley (dv / dt = 0) is detected, V ds is sampled, and then a difference process is performed with the held or stored value. Among them, the oscillation midpoint can be the first quarter oscillation period point after the drain voltage starts to oscillate. If the sampling position is the valley this time, after sampling and calculation, V dsThe oscillation is V IN -V O The difference between the peak and the trough is 2*Vo, and the difference divided by 2 is the output voltage Vo. If the sampling position is the midpoint, V ds The oscillation is V IN -V O The V at the midpoint is the center value. ds The difference from the value held or stored is the output voltage Vo. Under ideal conditions, the voltage between the drain and source of the power device switch tube has the same amplitude for the first oscillation, that is, in the first oscillation half cycle, the amplitudes of the positive and negative 1 / 4 cycles are equal. That is, the output voltage Vo is the voltage difference between the drain and source of the power device switch tube Q1 at the beginning of the oscillation and the midpoint of the oscillation, or half of the voltage difference between the drain and source of the power device switch tube Q1 at the beginning of the oscillation and the bottom of the oscillation of the first half cycle of the oscillation.

[0046] Since the power device switch tube Q1 is in the off state, the second parasitic capacitor C4 is discharged. Before the power device switch tube Q1 is closed again, the inductor L and the parasitic capacitor in the power device switch tube Q1 oscillate to generate an oscillating voltage to reversely charge C4. When C4 is charged to the highest level, V ds In V IN -V O The oscillation center, the two correspond, and then C4 discharges, V ds The oscillation with the largest amplitude is generated, that is, the oscillation to the trough of the second 1 / 4 cycle.

[0047] The voltage of the gate (control terminal) of the power device switch tube Q1 can be processed by the comparator A, and the voltage sampling module 4 can be controlled to perform voltage sampling. ds The sampling signal at the bottom or midpoint voltage of the oscillation can be taken from the power switch control terminal, that is, according to V g The voltage of the voltage sampling module 4 is used to control the sampling. It can also be taken from a dv / dt detection circuit, such as the third parasitic capacitor C connected in parallel to the drain and gate of the power device switch tube Q1. gd , according to C gd The voltage change rate dv / dt controls the voltage sampling module 4 to perform voltage sampling.

[0048] In this embodiment, the signal processing module can also be used to calculate the voltage collected by the voltage sampling module to obtain the output voltage V O , then the output voltage V O Afterwards, the comparator B can be used to compare it with the reference voltage Vref for subsequent processing, such as performing overvoltage protection OVP when the output voltage is too high.

[0049] The comparator controls the voltage sampling module to collect the voltage between the drain and source of the power device switching tube according to the gate voltage of the power device switching tube. After the power device switching tube is turned off and the current in the inductor of the buck chopper circuit is discontinuous, the first oscillation amplitude of the voltage between the drain and source of the power device switching tube is collected, and the output voltage for supplying power to the load is determined according to the oscillation amplitude. There is no need for an auxiliary winding and related sampling pins, which reduces costs and is not easily affected by the transformer coupling coefficient; nor is it necessary to add digital filtering, avoiding the phenomenon that the dynamic response speed is very slow and the output voltage is extremely likely to be out of control for a short time or permanently, and improving the reliability. It has lower costs than the prior art, is more conducive to improving the system integration degree, sampling accuracy, response speed and reliability.

[0050] The above are only the preferred specific implementation manners of one or more embodiments of the present invention specification, but the protection scope of one or more embodiments of the present invention specification is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in one or more embodiments of the present invention specification should be covered by the protection scope of one or more embodiments of the present invention specification. Therefore, the protection scope of one or more embodiments of the present invention specification should be subject to the protection scope of the claims.

Claims

1. An output voltage sampling circuit, characterized in that, it includes: A main topology circuit module of a switching power supply, including a power device switching tube, which is used to modulate the input voltage into the voltage required by the load and output it to the load; A voltage sampling module, the first input terminal is electrically connected to the drain of the power device switching tube and the second input terminal is electrically connected to the source of the power device switching tube, or, the first input terminal is electrically connected to the drain of the power device switching tube and the second input terminal is electrically connected to the ground wire, and is used to collect the drain voltage oscillation amplitude of the power device switching tube after the power device switching tube is turned off and the current of the inductor in the main topology circuit of the switching power supply is discontinuous to obtain the output voltage value output to the load; the sampling of the oscillation amplitude is determined according to the voltage change slope of the first oscillation half cycle of the drain voltage of the power device switching tube.

2. The output voltage sampling circuit according to claim 1, characterized in that, The output voltage value is the voltage difference between the drain voltage of the power device switching tube at the start of oscillation and the voltage at the quarter oscillation period point, or half of the voltage difference between the drain voltage of the power device switching tube at the start of oscillation and the oscillation valley bottom of the first oscillation half cycle.

3. The output voltage sampling circuit according to claim 2, characterized in that, The main topology circuit module of the switching power supply further includes a comparator, which is used to output an enable signal for controlling the voltage sampling module to perform sampling.

4. The output voltage sampling circuit according to claim 3, characterized in that, The first input terminal of the comparator is connected to the gate of the power device switching tube; the second input terminal of the comparator is connected to a fixed voltage reference, and the output terminal of the comparator is connected to the voltage sampling module.

5. The output voltage sampling circuit according to claim 2 or 3, characterized in that, The detection of the voltage change rate of the oscillation is also realized by an external shunt capacitor. One end of the external shunt capacitor is directly or indirectly connected to the drain of the power switch tube, and the other end of the external shunt capacitor is connected to the first input terminal of the comparator; the second input terminal of the comparator is connected to a fixed voltage reference, and the output terminal of the comparator is connected to the voltage sampling module.

6. The output voltage sampling circuit according to claim 3, characterized in that, The voltage sampling module includes a resistive voltage division sampling circuit.

7. The output voltage sampling circuit according to claim 2, characterized in that, The voltage sampling module is used for: After the drain voltage starts to oscillate, when the peak value of the drain voltage change rate is detected, the voltage difference between the voltage value at the start of the drain voltage oscillation and the voltage value at the peak of the drain voltage change rate is determined as the output voltage value.

8. The output voltage sampling circuit according to claim 2, characterized in that, The voltage sampling module is used for: After the drain voltage starts to oscillate, when the drain voltage change rate is detected to be zero, half of the voltage difference between the voltage value at the start of the drain voltage oscillation and the voltage value at the point where the drain voltage change rate is zero is determined as the output voltage value.

9. A sampling method for an output voltage sampling circuit according to any one of claims 1 to 8, characterized in that, comprising: After the power device switch is turned off and the current of the inductor in the main topology circuit module of the switching power supply stops flowing, collect the oscillation amplitude of the first oscillation half cycle of the drain voltage of the power device switch, and determine the output voltage value output to the load according to the oscillation amplitude.

10. The sampling method according to claim 9, characterized in that, The sampling of the oscillation amplitude is determined according to the change slope of the first oscillation amplitude of the drain voltage of the power device switch; the output voltage value is the voltage difference between the drain voltage of the power device switch at the start of oscillation and the voltage at the one-quarter oscillation period point, or half of the voltage difference between the drain voltage of the power device switch at the start of oscillation and the oscillation valley bottom of the first oscillation half cycle.

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