No-load protection circuit based on current sampling

Abstract

The utility model discloses a no-load protection circuit based on current sampling, and relates to the technical field of electronic circuits. The no-load protection circuit based on current sampling comprises a voltage processing circuit, a comparator A1 and a control circuit, the voltage processing circuit is used for processing input voltage, the non-inverting input end of the comparator A1 is connected with the voltage processing circuit, the comparator A1 is used for comparing the non-inverting input end voltage with the inverting input end voltage and generating different electric signals, and the control circuit is connected with the non-inverting input end voltage. The control circuit is connected with the output end of the comparator A1 and used for receiving the electric signals output by the comparator A1 and generating protection signals, and the protection signals are used for controlling the on-off state of the no-load protection circuit. The no-load protection circuit provided by the utility model is used for realizing reliable no-load protection and preventing the switch MOS tube from being impacted and damaged.

Description

Technical Field

[0001] This utility model relates to the field of electronic circuit technology, and in particular to an unloaded protection circuit based on current sampling. Background Technology

[0002] In the application of electronic ballasts for ultraviolet lamps and other gas discharge lamps, reliable protection is required when the electronic ballast is powered on while the lamp is disconnected or in an open-circuit state. Currently, the traditional solution is to use the internal circuitry of a dedicated chip in the electronic ballast to detect the operating state of the half-bridge switching MOSFETs to determine the load status. However, this method is highly dependent on imported dedicated chips, resulting in high prices and delivery difficulties. Furthermore, using a dedicated chip to detect the half-bridge MOSFET switching state also has drawbacks such as slow response time and significant stress on the switching MOSFETs. Summary of the Invention

[0003] The purpose of this invention is to provide a no-load protection circuit based on current sampling to achieve reliable no-load protection and prevent the switching MOSFET from being damaged by impact.

[0004] To achieve the above objectives, this utility model provides the following technical solution:

[0005] A no-load protection circuit based on current sampling includes:

[0006] A voltage processing circuit, which is used to process the input voltage;

[0007] Comparator A1, the non-inverting input terminal of comparator A1 is connected to the voltage processing circuit, and comparator A1 is used to compare the voltage at the non-inverting input terminal with the voltage at the inverting input terminal and generate different electrical signals;

[0008] A control circuit is connected to the output terminal of the comparator A1. The control circuit is used to receive the electrical signal output by the comparator A1 and generate a protection signal. The protection signal is used to control the opening and closing of the no-load protection circuit.

[0009] Optionally, the no-load protection circuit further includes a current transformer T1 connected to the voltage processing circuit. The secondary winding of the current transformer T1 is connected to the voltage processing circuit and generates a voltage. The current transformer T1 is used to sample the load lamp current.

[0010] Optionally, the voltage processing circuit includes fast diodes D3, D4, D5, and D6 for voltage rectification.

[0011] Optionally, the voltage processing circuit further includes capacitors C8, C7, C6, and C4 connected in sequence, wherein capacitors C8, C7, C6, and C4 are used to filter the rectified voltage.

[0012] Optionally, the voltage processing circuit further includes resistors R11, R12, R9, and R8. Resistor R11 is disposed between capacitor C8 and capacitor C7, resistor R12 is disposed between capacitor C7 and capacitor C6, resistor R9 is disposed between capacitor C6 and capacitor C4, and resistor R8 is connected to capacitor C4. Resistors R11, R12, R9, and R8 are used to limit the filtered voltage.

[0013] Optionally, the voltage input to the non-inverting input of comparator A1 after limiting by resistors R11, R12, R9, and R8 is greater than 2.5V.

[0014] Optionally, the control circuit includes transistor Q2, diode D1, diode D2 and transistor Q1 connected in sequence. The conduction state of transistor Q2, diode D1, diode D2 and transistor Q1 changes with the electrical signal output by comparator A1, and generates a protection signal for controlling the opening and closing of the no-load protection circuit.

[0015] Optionally, the control circuit further includes an electrically connected resistor R1 and a capacitor C1, wherein the resistor R1 and the capacitor C1 are used to control the timing of the protection action.

[0016] Compared with the prior art, the no-load protection circuit based on current sampling provided by this utility model has the following advantages: First, the no-load protection circuit provided by this application has a fast response speed. By adopting a current sampling method to identify the lamp status, compared with the traditional method of using the internal circuit of a dedicated chip to detect the working status of the half-bridge switching MOSFET, it can detect the no-load state more quickly and take timely protective action, thus improving the response speed of the circuit. Second, it has less impact on the switching MOSFET. The fast and accurate detection and protection mechanism reduces the impact on the MOSFET in the half-bridge switching circuit of the electronic ballast, reduces the risk of MOSFET failure and damage due to no-load and other abnormal conditions, thereby improving the overall reliability and stability of the electronic ballast. On the other hand, the no-load protection circuit provided in this application has a simple structure: the entire no-load protection circuit is relatively simple in structure, mainly composed of common electronic components such as current transformers, diodes, resistors, capacitors, comparators, transistors, etc., which are easy to understand and implement; and the parameters are easy to adjust. By adjusting the charging rate of resistor R1 and capacitor C1, the protection action time can be easily adjusted to adapt to different application scenarios and circuit requirements, which has high flexibility and practicality, and is easy to optimize and adjust in actual production and application; in addition, it helps to reduce costs and solve supply problems, does not rely on expensive imported special chips, avoids the high costs caused by using special chips, effectively reduces the production cost of electronic ballasts, does not rely on imported chips, can avoid production delays caused by chip delivery difficulties, and ensures smooth production and timely product supply. Attached Figure Description

[0017] The accompanying drawings, which are provided to further illustrate the present invention and constitute a part of the present invention, illustrate exemplary embodiments of the present invention and are used to explain the present invention, but do not constitute an undue limitation of the present invention.

[0018] Figure 1 This invention provides an unloaded protection circuit based on current sampling, which is an embodiment of the present invention.

[0019] Figure label:

[0020] 1-Voltage processing circuit; 2-Control circuit. Detailed Implementation

[0021] To make the technical problems, technical solutions, and beneficial effects of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified. "Several" means one or more, unless otherwise explicitly specified.

[0023] Please see Figure 1 The no-load protection circuit based on current sampling provided in this embodiment includes a voltage processing circuit 1, a comparator A1, and a control circuit 2. The voltage processing circuit 1 is used to process the input voltage. The non-inverting input terminal of the comparator A1 is connected to the voltage processing circuit 1. The comparator A1 is used to compare the voltage at the non-inverting input terminal with the voltage at the inverting input terminal and generate different electrical signals. The control circuit 2 is connected to the output terminal of the comparator A1. The control circuit 2 is used to receive the electrical signal output by the comparator A1 and generate a protection signal. The protection signal is used to control the opening and closing of the no-load protection circuit.

[0024] In this application, the no-load protection circuit also includes a current transformer T1 connected to the voltage processing circuit 1. The secondary winding of the current transformer T1 is connected to the voltage processing circuit 1 and generates a voltage. The current transformer T1 is used to sample the load lamp current.

[0025] In this application, the voltage processing circuit 1 includes fast diodes D3, D4, D5 and D6 for voltage rectification.

[0026] Furthermore, the voltage processing circuit 1 also includes capacitors C8, C7, C6, and C4 connected in sequence. These capacitors are used to filter the rectified voltage.

[0027] Furthermore, the voltage processing circuit 1 also includes resistors R11, R12, R9, and R8. Resistor R11 is positioned between capacitors C8 and C7, resistor R12 is positioned between capacitors C7 and C6, resistor R9 is positioned between capacitors C6 and C4, and resistor R8 is connected to capacitor C4. Resistors R11, R12, R9, and R8 are used to limit the filtered voltage.

[0028] It should be noted that after the voltage is limited by resistors R12, R9, and R8, the voltage at the non-inverting input of comparator A1 is greater than 2.5V.

[0029] In this application, the control circuit 2 includes transistor Q2, diode D1, diode D2 and transistor Q1 connected in sequence. The conduction state of transistor Q2, diode D1, diode D2 and transistor Q1 changes with the electrical signal output by comparator A1, and generates a protection signal for controlling the opening and closing of the no-load protection circuit.

[0030] Optionally, the control circuit 2 also includes an electrically connected resistor R1 and capacitor C1, which are used to control the timing of the protection action.

[0031] Working Principle: Under normal operating conditions, when the electronic ballast is working properly (i.e., the lamp load is normal), there is voltage on the secondary side of the 1:100 current transformer T1. This voltage is rectified by four fast diodes D3-D6, converting the AC voltage into a pulsating DC voltage. Then, it is filtered by capacitor C8, limited by resistors R11, R12, R9, and R8, and further filtered by capacitors C7, C6, and C4 before being input to the non-inverting input of comparator A1. By properly setting the values ​​of resistors R11, R12, R9, and R8, the voltage at the non-inverting input of comparator A1 is greater than 2.5V (the reference voltage at the inverting input of comparator A1 obtained by voltage division using resistors R7 and R8). Because the voltage at the non-inverting input is greater than the voltage at the inverting input, comparator A1 outputs a high level. This high level turns on transistor Q2. At this time, the cathode of diode D1 is at a low level, diode D1 is not conducting, transistor Q1 is not triggered to conduct, the protection signal output is high, and the main circuit operates normally.

[0032] In no-load condition, when the electronic ballast is powered on but the lamp is disconnected or open-circuited (i.e., no load), the output voltage of the 1:100 current transformer T1 is 0. At this time, the voltage at the non-inverting input of comparator A1 is less than the voltage at the inverting input, causing comparator A1 to output a low level. Transistor Q2 does not conduct due to its low base voltage. The power supply rapidly charges capacitor C1 through resistor R1. When the voltage across capacitor C1 reaches a certain value, diode D1 conducts, which in turn conducts diode D2, triggering transistor Q1 to conduct. After transistor Q1 conducts, the protection signal outputs a low level and remains low (locked in protection mode until power failure). This low-level protection signal can be applied to the SD terminal of any PWM control IC or other ports, thereby controlling the main circuit to quickly shut down, achieving reliable no-load protection.

[0033] Furthermore, by adjusting the charging rate of resistor R1 and capacitor C1, the protection action time can be adjusted to meet different application scenarios and circuit requirements. For example, if a faster protection action is required, the resistance of resistor R1 can be decreased or the capacitance of capacitor C1 can be increased; if a slightly slower protection action is required, the resistance of resistor R1 can be increased or the capacitance of capacitor C1 can be decreased.

[0034] As can be seen from the structure and operation of the current sampling-based no-load protection circuit described above, on the one hand, the no-load protection circuit provided in this application has a fast response speed. By adopting a current sampling method to identify the lamp status, compared with the traditional method of using the internal circuit of a dedicated chip to detect the working status of the half-bridge switching MOSFET, it can detect the no-load state more quickly and take timely protection action, thus improving the circuit's response speed. On the other hand, it has less impact on the switching MOSFET. The fast and accurate detection and protection mechanism reduces the impact on the MOSFET in the half-bridge switching circuit of the electronic ballast, reduces the risk of MOSFET failure and damage due to no-load and other abnormal conditions, thereby improving the overall reliability and stability of the electronic ballast. On the other hand, the no-load protection circuit provided in this application has a simple structure: the entire no-load protection circuit is relatively simple in structure, mainly composed of common electronic components such as current transformers, diodes, resistors, capacitors, comparators, transistors, etc., which are easy to understand and implement; and the parameters are easy to adjust. By adjusting the charging rate of resistor R1 and capacitor C1, the protection action time can be easily adjusted to adapt to different application scenarios and circuit requirements, which has high flexibility and practicality, and is easy to optimize and adjust in actual production and application; in addition, it helps to reduce costs and solve supply problems, does not rely on expensive imported special chips, avoids the high costs caused by using special chips, effectively reduces the production cost of electronic ballasts, does not rely on imported chips, can avoid production delays caused by chip delivery difficulties, and ensures smooth production and timely product supply.

[0035] In the description of the above embodiments, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0036] The above are merely specific embodiments of this utility model, but the protection scope of this utility model is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the protection scope of the claims.

Claims

1. An open-circuit protection circuit based on current sampling, characterized in that, It comprises: a voltage processing circuit for processing input voltage; a comparator A1, whose non-inverting input is connected to the voltage processing circuit, for comparing the voltage at the non-inverting input with the voltage at the inverting input and generating an electrical signal different from the two; a control circuit connected to the output of the comparator A1, for receiving the electrical signal output by the comparator A1 and generating a protection signal for controlling the on-off of the no-load protection circuit.

2. The current-sampling based no-load protection circuit of claim 1, wherein, The no-load protection circuit further comprises a current transformer T1 connected to the voltage processing circuit, whose secondary winding is connected to the voltage processing circuit and generates voltage, for sampling the load lamp current.

3. The current-sampling based no-load protection circuit of claim 2, wherein, The voltage processing circuit comprises fast diodes D3, D4, D5 and D6 for rectifying voltage.

4. The current-sampling based no-load protection circuit of claim 3, wherein, The voltage processing circuit further comprises capacitors C8, C7, C6 and C4 connected in sequence, for filtering the rectified voltage.

5. The current-sampling based no-load protection circuit of claim 4, wherein, The voltage processing circuit further comprises resistors R11, R12, R9 and R8, the resistor R11 is arranged between the capacitor C8 and the capacitor C7, the resistor R12 is arranged between the capacitor C7 and the capacitor C6, the resistor R9 is arranged between the capacitor C6 and the capacitor C4, and the resistor R8 is connected to the capacitor C4, for limiting the amplitude of the filtered voltage.

6. The current-sampling based no-load protection circuit of claim 5, wherein, The voltage input to the non-inverting input of the comparator A1 after the limiting of the resistors R11, R12, R9 and R8 is greater than 2.5V.

7. The current-sampling based no-load protection circuit of claim 5, wherein, The control circuit comprises transistors Q2, diodes D1 and D2 and a transistor Q1 connected in sequence, the on-off state of the transistors Q2, diodes D1 and D2 and the transistor Q1 changes with the electrical signal output by the comparator A1, and generates a protection signal for controlling the on-off of the no-load protection circuit.

8. The current-sampling based no-load protection circuit of claim 7, wherein, The control circuit further comprises a resistor R1 and a capacitor C1 connected in electrical connection, for controlling the time of adjusting protection action.

Images