Controllable AC-DC circuit and inverter

Abstract

The utility model provides a controllable AC-DC circuit and an inverter, the controllable AC-DC circuit comprises a transformation rectification circuit, a step-down circuit and a control circuit which are electrically connected in sequence, and the control circuit comprises a comparator, a variable resistor, a sixth capacitor, a second resistor, a sixth resistor, a seventh resistor, a second universal diode and a third universal diode. Alternating current is converted into direct current through the voltage transformation rectifying circuit, the direct current is subjected to voltage reduction through the voltage reduction circuit, low voltage is output, the on-off state of the field effect transistor is controlled through the control circuit, in this way, the effective voltage reduction effect is achieved, and the output value of voltage reduction can be confirmed according to the level state of the comparator. Compared with a circuit diagram in the prior art, the controllable AC-DC circuit has the advantages that the controllable AC-DC circuit only needs to be matched with the variable resistor, the comparator and the sixth capacitor to control the on-off state of the field-effect tube in terms of the overall structure, so that the circuit is simple, and controllable voltage output is easy to realize.

Description

Technical Field

[0001] The present disclosure relates to the technical field of inverters, and in particular, to a controllable AC-DC circuit and an inverter. Background Art

[0002] With the development of AC-DC circuits (circuits for converting alternating current to direct current), in general, alternating current needs to be converted to direct current for power consumption. Generally, the conversion can be performed through full-wave (full-bridge) rectification or half-wave (half-bridge) rectification.

[0003] There are many low-voltage DC requirements in daily life, so it is necessary to convert alternating current to direct current. In addition, the electricity used in daily life is 220V alternating current, while electrical appliances or devices need to operate at a lower voltage to function properly. Therefore, when using electrical appliances or devices, it is necessary to convert alternating current to direct current and step down the direct current to match the current electrical appliances or devices. Currently, it is common for products to have built-in AC-DC conversion. Common AC-DC circuits are controlled using different integrated chips, such as Figure 1 and Figure 2 As shown, the circuit structure of this solution is relatively complex and difficult to implement. Utility Model Content

[0004] The purpose of the present disclosure is to overcome the deficiencies in the prior art and provide a controllable AC-DC circuit and an inverter with a simple circuit structure and easy control of voltage output.

[0005] The purpose of the present disclosure is achieved through the following technical solutions:

[0006] A controllable AC-DC circuit includes:

[0007] A step-down rectification circuit for converting alternating current to direct current;

[0008] A step-down circuit for stepping down the direct current and outputting a low voltage, and the step-down circuit is electrically connected to the step-down rectification circuit;

[0009] The control circuit includes a comparator, a variable resistor, a sixth capacitor, a second resistor, a sixth resistor, a seventh resistor, a second general diode, and a third general diode. The control end of the variable resistor is electrically connected to the buck circuit. The first end of the variable resistor is connected to the anode of the second general diode. The cathode of the second general diode is respectively connected to the first end of the sixth resistor and the anode of the third general diode. The cathode of the third general diode is connected to the second end of the variable resistor. The second end of the sixth resistor is respectively connected to the second end of the comparator and the upper half end of the sixth capacitor. The lower half end of the sixth capacitor is grounded. The fifth end of the comparator is connected to a reference voltage. The fourth end of the comparator is connected to a working voltage. The first end of the comparator is connected to the first end of the second resistor. The second end of the second resistor is respectively connected to the control end of the variable resistor and the first end of the seventh resistor. The first end of the seventh resistor is also connected to the third end of the comparator. The second end of the seventh resistor is grounded.

[0010] In one embodiment, the control circuit further includes a first zener diode and a second zener diode. The anode of the first zener diode is connected to the control end of the variable resistor. The cathode of the first zener diode is connected to the cathode of the second zener diode. The anode of the second zener diode is connected to the second end of the seventh resistor.

[0011] In one embodiment, the control circuit further includes an eighth resistor. The second end of the second resistor is connected to the first end of the eighth resistor. The second end of the eighth resistor is connected to the first end of the seventh resistor.

[0012] In one embodiment, at least one of the seventh resistor and the eighth resistor is a variable resistor.

[0013] In one embodiment, the buck circuit includes a field effect transistor, a first general diode, a third resistor, a fifth capacitor, and an inductor. The first end of the field effect transistor is electrically connected to the step-down rectification circuit. The second end of the field effect transistor is respectively connected to the cathode of the first general diode and the first end of the inductor. The control end of the field effect transistor is connected to the first end of the third resistor. The second end of the third resistor is connected to the control end of the variable resistor. The second end of the inductor is connected to a voltage output terminal. The second end of the inductor is also connected to the upper half end of the fifth capacitor. The lower half end of the fifth capacitor is grounded. The anode of the first general diode is connected to the lower half end of the fifth capacitor.

[0014] In one embodiment, the buck circuit further includes a fourth general diode. The anode of the fourth general diode is connected to the control end of the field effect transistor. The cathode of the fourth general diode is connected to the second end of the third resistor.

[0015] In one embodiment, the step-down rectifier circuit includes a step-down coupling and a rectifier. The input end of the step-down coupling is used to connect to an AC power supply. The output end of the step-down coupling is respectively connected to the second end and the third end of the rectifier. The first end of the rectifier is electrically connected to the step-down circuit, and the fourth end of the rectifier is grounded.

[0016] In one embodiment, the step-down rectifier circuit further includes a second capacitor. The upper half of the second capacitor is connected to the first end of the rectifier, and the lower half of the second capacitor is connected to the fourth end of the rectifier.

[0017] In one embodiment, the step-down rectifier circuit further includes a third capacitor. The upper half of the third capacitor is connected to the upper half of the second capacitor, and the lower half of the third capacitor is connected to the lower half of the second capacitor.

[0018] An inverter includes the controllable AC-DC circuit according to any one of the above embodiments.

[0019] Compared with the prior art, the present disclosure includes but is not limited to the following advantages:

[0020] 1. Alternating current is converted into direct current through the step-down rectifier circuit, and the direct current is stepped down and low voltage is output through the step-down circuit. The switching state of the field effect transistor is controlled by the control circuit, so as to effectively step down the voltage. The output value of the step-down can be confirmed according to the level state of the comparator.

[0021] 2. In terms of the overall structure, compared with the circuit diagram of the prior art, for the controllable AC-DC circuit, only the cooperation of the resistor, the comparator and the sixth capacitor needs to be changed to control the switching state of the field effect transistor. Therefore, the circuit is simple and it is relatively easy to achieve controllable voltage output. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present disclosure, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 It is the circuit diagram of the AC-DC circuit in the prior art;

[0024] Figure 2 It is another circuit diagram of the AC-DC circuit in the prior art;

[0025] Figure 3 It is the overall circuit diagram of the controllable AC-DC circuit in one embodiment;

[0026] Figure 4 The Figure 3 circuit diagram of the step-down rectifier circuit in the controllable AC-DC circuit shown;

[0027] Figure 5 The Figure 3 circuit diagram of the buck circuit in the controllable AC-DC circuit shown;

[0028] Figure 6 The Figure 3 circuit diagram of the control circuit in the controllable AC-DC circuit shown.

[0029] Reference numerals: 10, controllable AC-DC circuit; 100, step-down rectifier circuit; 200, buck circuit; 300, control circuit; T1, step-down coupling; DF1, rectifier; L1, inductor; Q1, field effect transistor; U1A, comparator; D1, first general diode; D2, second general diode; D3, third general diode; D4, fourth general diode; DZ1, first zener diode; DZ2, second zener diode; C2, second capacitor; C3, third capacitor; C5, fifth capacitor; C6, sixth capacitor; R1, variable resistor; R2, second resistor; R3, third resistor; R6, sixth resistor; R7, seventh resistor; R8, eighth resistor. Detailed implementation manners

[0030] For ease of understanding of the present disclosure, the present disclosure will be described more comprehensively below with reference to the relevant drawings. Preferred embodiments of the present disclosure are shown in the drawings. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided so that the understanding of the disclosure content of the present disclosure is more thorough and comprehensive.

[0031] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there can also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present disclosure belongs. The terms used in the specification of the present disclosure herein are only for the purpose of describing specific embodiments and are not intended to limit the present disclosure. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0033] To better understand the technical solutions and beneficial effects of the present disclosure, the following further elaborates on the present disclosure in conjunction with specific embodiments:

[0034] Please refer to Figures 3 to 6 , which is a controllable AC-DC circuit 10 according to an embodiment of the present utility model. The controllable AC-DC circuit 10 includes a step-down rectifier circuit 100, a buck circuit 200, and a control circuit 300 that are sequentially electrically connected.

[0035] Among them, the step-down rectifier circuit 100 is used to convert alternating current into direct current. In this embodiment, as Figure 4 shown, the step-down rectifier circuit 100 includes a step-down coupling T1 and a rectifier DF1. The input end of the step-down coupling T1 is used to connect to an AC power supply. The output end of the step-down coupling T1 is respectively connected to the second end and the third end of the rectifier DF1. The first end of the rectifier DF1 is electrically connected to the buck circuit 200, and the fourth end of the rectifier DF1 is grounded. It can be understood that the step-down rectifier circuit 100 adopts full-bridge rectification to convert alternating current into direct current, and the output DC voltage is 1.41 times the input rectified voltage. Further, the model of the rectifier DF1 is 1B4B42. Of course, in other embodiments, the step-down rectifier circuit 100 can also adopt half-bridge rectification.

[0036] The buck circuit 200 is used to step down the direct current and output a low voltage. The buck circuit 200 is electrically connected to the step-down rectifier circuit 100. In this embodiment, as Figure 5 shown, the buck circuit 200 includes a field effect transistor Q1, a first general diode D1, a third resistor R3, a fifth capacitor C5, and an inductor L1. The first end of the field effect transistor Q1 is electrically connected to the step-down rectifier circuit 100. Specifically, the first end of the field effect transistor Q1 is connected to the first end of the rectifier DF1. The second end of the field effect transistor Q1 is respectively connected to the cathode of the first general diode D1 and the first end of the inductor L1. The control end of the field effect transistor Q1 is connected to the first end of the third resistor R3. The second end of the third resistor R3 is electrically connected to the control circuit 300. The second end of the inductor L1 is connected to the voltage output end. The second end of the inductor L1 is also connected to the upper half end of the fifth capacitor C5. The lower half end of the fifth capacitor C5 is grounded. The anode of the first general diode D1 is connected to the lower half end of the fifth capacitor C5. It can be understood that the field effect transistor Q1, the first general diode D1, the third resistor R3, the fifth capacitor C5, and the inductor L1 form an asynchronous buck bucking method to step down the voltage, so as to provide a normal low voltage for the load.

[0037] As Figure 6As shown, in one embodiment, the control circuit 300 includes a comparator U1A, a variable resistor R1, a sixth capacitor C6, a second resistor R2, a sixth resistor R6, a seventh resistor R7, a second general diode D2, and a third general diode D3. The control terminal of the variable resistor R1 is electrically connected to the buck circuit 200. Specifically, the control terminal of the variable resistor R1 is connected to the second terminal of the third resistor R3. The first terminal of the variable resistor R1 is connected to the anode of the second general diode D2. The cathode of the second general diode D2 is respectively connected to the first terminal of the sixth resistor R6 and the anode of the third general diode D3. The cathode of the third general diode D3 is connected to the second terminal of the variable resistor R1. The second terminal of the sixth resistor R6 is respectively connected to the second terminal of the comparator U1A and the upper half terminal of the sixth capacitor C6. The lower half terminal of the sixth capacitor C6 is grounded. The fifth terminal of the comparator U1A is connected to a reference voltage. The fourth terminal of the comparator U1A is connected to a working voltage. The first terminal of the comparator U1A is connected to the first terminal of the second resistor R2. The second terminal of the second resistor R2 is respectively connected to the control terminal of the variable resistor R1 and the first terminal of the seventh resistor R7. The first terminal of the seventh resistor R7 is also connected to the third terminal of the comparator U1A. The second terminal of the seventh resistor R7 is grounded.

[0038] In this embodiment, the comparator U1A is a hysteresis comparator with inverting input, which can eliminate the self-excited oscillation caused by circuit parasitic coupling and has good feedback performance. Further, the model of the comparator U1A is LF347BN. Its first terminal is the voltage output terminal, the second terminal is the negative voltage input terminal, the third terminal is the positive voltage input terminal. By comparing the voltage values at the first terminal and the second terminal of the comparator U1A, a positive voltage or a negative voltage can be output at the first terminal. The fourth terminal is the power consumption terminal, and the fifth terminal is the power supply terminal.

[0039] In this embodiment, the field effect transistor Q1 is an N-type MOS transistor. Its first terminal is the drain, the second terminal is the source, and the control terminal is the gate. Further, the model of the field effect transistor Q1 is 2N6659.

[0040] For the above controllable AC-DC circuit 10, the alternating current is converted into direct current by the step-down rectification circuit 100, and the direct current is stepped down and a low voltage is output through the buck circuit 200. The switching state of the field effect transistor Q1 is controlled by the control circuit 300, so as to effectively step down the voltage. The output value of the voltage reduction can be confirmed according to the level state of the comparator U1A. In addition, in terms of the overall structure of the controllable AC-DC circuit 10, compared with the circuit diagram of the prior art, the controllable AC-DC circuit 10 only needs the cooperation of the variable resistor R1, the comparator U1A, and the sixth capacitor C6 to control the switching state of the field effect transistor Q1. Therefore, the circuit is simple and it is relatively easy to achieve controllable voltage output.

[0041] It can be understood that, as Figure 5As shown, when current passes through the field-effect transistor Q1, the switching state of the field-effect transistor Q1 is controlled by the control circuit 300. When the field-effect transistor Q1 is turned on, voltage outputs voltage through the field-effect transistor Q1 and the inductor L1. At this time, the inductor L1 stores electrical energy, the fifth capacitor C5 is charged, the current of the first general diode D1 is cut off, and the current and the output voltage rise slowly; when the voltage reaches the preset value, the field-effect transistor Q1 is turned off, the inductor L1 releases electrical energy to generate an induced current, the fifth capacitor C5 discharges, and the current flows through the first general diode D1 to form a loop, and the induced current and the output voltage decrease slowly. At this time, one cycle is completed, and the next cycle is carried out. The control circuit 300 turns on the field-effect transistor Q1 and repeats the corresponding actions when it is turned on. Then the control circuit 300 turns off the field-effect transistor Q1 and also repeats the corresponding actions, thus completing one cycle and repeating this cycle action.

[0042] Further, as Figure 5 and Figure 6 shown, the switching state of the field-effect transistor Q1 can be controlled by the control circuit 300. Specifically, the switching state of the field-effect transistor Q1 is determined by the pulse width modulation (PWM) wave state generated by the comparator U1A. In this embodiment, the conduction or non-conduction of the field-effect transistor Q1 can be controlled by the cooperation of the variable resistor R1, the sixth capacitor C6, and the comparator U1A. Further, the sixth capacitor C6, the sixth resistor R6, and the variable resistor R1 form a capacitor-resistor circuit (RC circuit). The RC circuit serves as both a delay link and a feedback network, and realizes the automatic conversion of the output state through RC charging and discharging. Of course, the upper limit voltage value and the lower limit voltage value of the comparator U1A can be set, so that the comparator U1A compares the upper limit voltage or the lower limit voltage at the third end according to the voltage at the second end (at this time, the voltage is within the upper and lower limit voltage values), and outputs a positive voltage or a negative voltage at the first end.

[0043] When the first end of the comparator U1A outputs a positive voltage, current can charge the sixth capacitor C6 positively through the variable resistor R1, the second general diode D2, and the sixth resistor R6 until the voltage at the second end of the comparator U1A is higher than the upper limit voltage value, and then the first end of the comparator U1A changes to output a negative voltage; when the first end of the comparator U1A outputs a negative voltage, current can charge the sixth capacitor C6 negatively through the variable resistor R1, the second general diode D3, and the sixth resistor R6 until the voltage at the second end of the comparator U1A is higher than the lower limit voltage value, and then the first end of the comparator U1A changes to output a positive voltage. The charging state of the sixth capacitor C6 will be repeated. According to its charging state, the voltage state at the second end of the comparator U1A is confirmed, and then the voltage state at its third end is compared to output the corresponding level, thereby generating a pulse width modulation wave. According to the pulse width modulation wave, the conduction duty cycle is determined to control the switching state of the field-effect transistor Q1.

[0044] In this embodiment, asFigure 6 As shown, the control circuit 300 further includes a first voltage stabilizing diode DZ1 and a second voltage stabilizing diode DZ2. The anode of the first voltage stabilizing diode DZ1 is connected to the control terminal of the variable resistor R1, the cathode of the first voltage stabilizing diode DZ1 is connected to the cathode of the second voltage stabilizing diode DZ2, and the anode of the second voltage stabilizing diode DZ2 is connected to the second end of the seventh resistor R7.

[0045] In this embodiment, as Figure 6 shown, the control circuit 300 further includes an eighth resistor R8. The second end of the second resistor R2 is connected to the first end of the eighth resistor R8, and the second end of the eighth resistor R8 is connected to the first end of the seventh resistor R7.

[0046] Combined with Figure 5 and Figure 6 shown, according to the unidirectional conductivity of the diode, the on and off times of the control field effect transistor Q1 can guide the current to flow through different paths, so that the forward and reverse charging time constants of the capacitor are different. Then, through the forward and reverse charging time constants of the sixth capacitor C6, and according to the three-element method of the first-order RC circuit, the period time of the high and low levels is calculated, and then the conduction duty cycle is confirmed. Ideally, the longer the conduction duty cycle, the closer the output voltage is to the input voltage.

[0047] For example, U0 represents the output voltage after passing through the comparator U1A and the second resistor R2, and Uz represents the total breakdown voltage value of the first voltage stabilizing diode DZ1 and the second voltage stabilizing diode DZ2. When U0 = +Uz, the comparator U1A outputs a positive voltage, and the current flows from the first end of the variable resistor R1 through the second general diode D2 and the sixth resistor D6 to charge the sixth capacitor C6 positively. The forward charging time constant is τ1≈(Rw1 + R6)*C6, where Rw1 is the resistance value between the control pointer of the variable resistor R1 and the first end of Rw1 which is the variable resistor R1; when U0 = -Uz, the comparator U1A outputs a negative voltage, and the current flows from the sixth resistor R6 through the third general diode D3 and the second end of the variable resistor R1 to charge the sixth capacitor C6 negatively. The reverse charging time constant is τ2≈(Rw2 + R6)*C6, where Rw2 is the resistance value between the control pointer of the variable resistor R1 and the second end of Rw1 which is the variable resistor R1. Using the three-element method of the first-order RC circuit, it can be obtained that: the high-level duration T1 of each cycle is approximately T1≈τ1*ln(1 + 2*R7 / R8); the low-level duration T2 is approximately T2≈τ2*ln(1 + 2*R7 / R8); then a cycle time can be formed by one high level and one low level, the cycle time is T = T1 + T2, and the conduction duty cycle is T1 / T = (Rw1 + R6) / (Rw + 2*R6), where Rw is the sum of the first end and the second end of the variable resistor R1, that is, the resistance value of the variable resistor R1 itself, and Rw = Rw1 + Rw2.

[0048] Further, the control pointer of the variable resistor R1 can be toggled to change the resistance values of Rw1 and Rw2, thereby adjusting the forward charging time constant τ1 and the reverse charging time constant τ2 of the sixth capacitor C6. Then, according to the cycle duration, the conduction duty cycle of the pulse width modulation wave is adjusted so that the conduction duty cycle is within a suitable range, which is conducive to the normal conduction and shutdown of the field effect transistor Q1.

[0049] Furthermore, the sixth resistor R6 is a variable resistor. When the sixth resistor R6 is a variable resistor, the resistance value of the sixth resistor R6 is adjusted to adjust the forward charging constant τ1 and the reverse charging constant τ2, thereby adjusting the conduction duty cycle.

[0050] In one embodiment, at least one of the seventh resistor R7 and the eighth resistor R8 is a variable resistor. When one or both of the seventh resistor R7 and the eighth resistor R8 are variable resistors, the resistance value of one or both of the seventh resistor R7 and the eighth resistor R8 can be adjusted to adjust the resistance ratio of the seventh resistor R7 and the eighth resistor R8, thereby adjusting the duration of the high level and the low level, and further adjusting the total period of the high and low levels, and further adjusting the frequency of the PWM wave. In this embodiment, the resistance ratio of the seventh resistor R7 to the eighth resistor R8 is about 10:1.

[0051] As Figure 5 shown, in one embodiment, the buck circuit 200 further includes a fourth general diode D4. The anode of the fourth general diode D4 is connected to the control terminal of the field effect transistor Q1, and the cathode of the fourth general diode D4 is connected to the second terminal of the third resistor R3. It can be understood that the fourth general diode D4 is connected in parallel with the third resistor R3 and then connected in series to the control terminal of the field effect transistor Q1, which can accelerate the opening or closing speed of the field effect transistor Q1 to accelerate the overall time of the inductor L1 to store energy and release electrical energy.

[0052] In order to prevent the rectified direct current from having a voltage mutation and damaging circuit components, in one embodiment, the step-down rectification circuit 100 further includes a second capacitor C2. The upper half of the second capacitor C2 is connected to the first terminal of the rectifier DF1, and the lower half of the second capacitor C2 is connected to the fourth terminal of the rectifier DF1. It can be understood that by setting the second capacitor C2, the rectified direct current can be signal-filtered to avoid the interference of redundant signals, ensure the normal operation of the entire circuit, and enable the load to operate normally.

[0053] However, the rectified direct current not only needs to be voltage-stabilized by a capacitor, but also needs to filter high-frequency and low-frequency signals. As Figure 4As shown, in one embodiment, the step-down rectifier circuit 100 further includes a third capacitor C3. The upper end of the third capacitor C3 is connected to the upper end of the second capacitor C2, and the lower end of the third capacitor C3 is connected to the lower end of the second capacitor C2. It can be understood that the second capacitor C2 and the third capacitor C3 are in parallel. After converting the alternating current into direct current through the rectifier DF1, it is necessary to filter and regulate the direct current to avoid interference from redundant signals and large fluctuations in voltage. The second capacitor C2 and the third capacitor C3 jointly filter the direct current. Specifically, by setting the capacitance values of the second capacitor C2 and the third capacitor C3, high-frequency signals or low-frequency signals can be filtered respectively.

[0054] In this embodiment, as Figure 4 shown, the second capacitor C2 is a high-frequency filtering capacitor with a capacitance of 100 nF, which is a small capacitor and can be used to filter high-frequency signals; and,

[0055] the third capacitor C3 is a low-frequency filtering capacitor with a capacitance of 220 μF, which is a large capacitor and can be used to filter low-frequency signals.

[0056] Of course, in other embodiments, the second capacitor C2 can be a low-frequency filtering capacitor, and the third capacitor C3 can be a high-frequency filtering capacitor, which can also jointly filter high-frequency and low-frequency signals of the direct current.

[0057] The present disclosure also provides an inverter, including the controllable AC-DC circuit 10 according to any one of the above embodiments. When the inverter adopts the controllable AC-DC circuit 10, the switching state of the field effect transistor Q1 can be confirmed by the PWM wave generated by the control circuit 300 and according to the conduction duty ratio of the PWM wave, ensuring reliable high-voltage input and low-voltage output, so that the load can operate normally.

[0058] Compared with the prior art, the present disclosure includes but is not limited to the following advantages:

[0059] 1. The alternating current is converted into direct current through the step-down rectifier circuit 100, and the direct current is stepped down and a low voltage is output through the step-down circuit 200. The switching state of the field effect transistor Q1 is controlled by the control circuit 300, so as to effectively step down the voltage. The output value of the step-down can be confirmed according to the level state of the comparator U1A.

[0060] 2. In terms of the overall structure, compared with the circuit diagram of the prior art, for the controllable AC-DC circuit 10, only the cooperation of the resistor R1, the comparator U1A and the sixth capacitor C6 needs to be changed to control the switching state of the field effect transistor Q1. Therefore, the circuit is simple and it is relatively easy to achieve controllable voltage output.

[0061] The above-described embodiments merely represent several implementation manners of the present disclosure. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the disclosed patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present disclosure, several modifications and improvements can still be made, and these all fall within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure patent shall be subject to the appended claims.

Claims

1. A controllable AC-DC circuit, characterized in that, Comprising: A step-down rectification circuit for converting alternating current into direct current; A buck circuit for stepping down the direct current and outputting a low voltage, the buck circuit being electrically connected to the step-down rectification circuit; A control circuit, including a comparator, a variable resistor, a sixth capacitor, a second resistor, a sixth resistor, a seventh resistor, a second general diode, and a third general diode. The control terminal of the variable resistor is electrically connected to the buck circuit. The first terminal of the variable resistor is connected to the anode of the second general diode. The cathode of the second general diode is respectively connected to the first terminal of the sixth resistor and the anode of the third general diode. The cathode of the third general diode is connected to the second terminal of the variable resistor. The second terminal of the sixth resistor is respectively connected to the second terminal of the comparator and the upper half of the sixth capacitor. The lower half of the sixth capacitor is grounded. The fifth terminal of the comparator is connected to a reference voltage. The fourth terminal of the comparator is connected to a working voltage. The first terminal of the comparator is connected to the first terminal of the second resistor. The second terminal of the second resistor is respectively connected to the control terminal of the variable resistor and the first terminal of the seventh resistor. The first terminal of the seventh resistor is also connected to the third terminal of the comparator. The second terminal of the seventh resistor is grounded.

2. The controllable AC-DC circuit according to claim 1, wherein The control circuit further includes a first zener diode and a second zener diode. The anode of the first zener diode is connected to the control terminal of the variable resistor. The cathode of the first zener diode is connected to the cathode of the second zener diode. The anode of the second zener diode is connected to the second terminal of the seventh resistor.

3. The controllable AC-DC circuit according to claim 1, wherein The control circuit further includes an eighth resistor. The second terminal of the second resistor is connected to the first terminal of the eighth resistor. The second terminal of the eighth resistor is connected to the first terminal of the seventh resistor.

4. The controllable AC-DC circuit according to claim 3, wherein, At least one of the seventh resistor and the eighth resistor is a variable resistor.

5. The controllable AC-DC circuit according to claim 1, characterized in that, The buck circuit includes a field effect transistor, a first general diode, a third resistor, a fifth capacitor, and an inductor. The first terminal of the field effect transistor is electrically connected to the step-down rectification circuit. The second terminal of the field effect transistor is respectively connected to the cathode of the first general diode and the first terminal of the inductor. The control terminal of the field effect transistor is connected to the first terminal of the third resistor. The second terminal of the third resistor is connected to the control terminal of the variable resistor. The second terminal of the inductor is connected to a voltage output terminal. The second terminal of the inductor is also connected to the upper half of the fifth capacitor. The lower half of the fifth capacitor is grounded. The anode of the first general diode is connected to the lower half of the fifth capacitor.

6. The controllable AC-DC circuit according to claim 5, characterized in that, The buck circuit further includes a fourth general diode. The anode of the fourth general diode is connected to the control terminal of the field effect transistor. The cathode of the fourth general diode is connected to the second terminal of the third resistor.

7. The controllable AC-DC circuit according to claim 1, wherein The step-down rectification circuit includes a step-down coupling and a rectifier. The input terminal of the step-down coupling is used to connect to an AC power supply. The output terminal of the step-down coupling is respectively connected to the second terminal and the third terminal of the rectifier. The first terminal of the rectifier is electrically connected to the buck circuit. The fourth terminal of the rectifier is grounded.

8. The controllable AC-DC circuit according to claim 7, characterized in that, The step-down rectifying circuit further includes a second capacitor, an upper half of the second capacitor is connected to a first end of the rectifier, and a lower half of the second capacitor is connected to a fourth end of the rectifier.

9. The controllable AC-DC circuit according to claim 8, wherein, The step-down rectifying circuit further includes a third capacitor, an upper half of the third capacitor is connected to the upper half of the second capacitor, and a lower half of the third capacitor is connected to the lower half of the second capacitor.

10. An inverter, characterized in that, It includes the controllable AC-DC circuit according to any one of claims 1-9.

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