Silicon controlled rectifier follow current sampling circuit

Abstract

The invention discloses a silicon controlled rectifier follow current sampling circuit, which comprises a silicon controlled rectifier dimmer Q1, a rectifying circuit, a voltage sampling circuit, a follow current on-off control circuit and a linear constant current circuit, and is characterized in that the output voltage of the silicon controlled rectifier dimmer Q1 is rectified by the rectifying circuit and then is respectively input into the input end of the voltage sampling circuit and the positive end of the linear constant current circuit; the output end of the voltage sampling circuit is electrically connected with the control end of the follow current on-off control circuit, the positive end of the follow current on-off control circuit is electrically connected with the control end of the linear constant current circuit, and the negative end of the linear constant current circuit and the negative end of the follow current on-off control circuit are respectively grounded; when the voltage sampling circuit detects that the conduction angle of the silicon controlled dimmer Q1 is larger than or equal to A, the follow-current on-off control circuit controls the linear constant current circuit not to work, and when the voltage sampling circuit detects the conduction angle of the silicon controlled dimmer Q1, the follow-current on-off control circuit controls the linear constant current circuit not to work. And when A is greater than A, the follow-current on-off control circuit controls the linear constant current circuit to work so as to maintain the conduction of the silicon controlled dimmer Q1.

Description

Technical Field

[0001] The present invention relates to the technical field of LED control, and particularly to a thyristor freewheeling sampling circuit. Background Art

[0002] When we use thyristor dimming, when the thyristor load current is lower than the holding current of the thyristor, the thyristor will turn off, and at this time, the lamp will flash. To solve this problem, we usually add a thyristor freewheeling circuit to ensure that the minimum holding current of the thyristor is not exceeded. However, 1. The thyristor freewheeling circuit adopted in the existing thyristor drive circuit has high power consumption and large heat generation, reducing the overall drive efficiency. Because the existing circuit does not have the function of turning off the freewheeling circuit, when the input voltage is higher, the power consumption of the freewheeling circuit is greater, and the heat generation is also greater; and the existing thyristor freewheeling all adopts a linear constant current circuit. When the conduction angle of the thyristor is larger, the output voltage of the thyristor is also larger, and the power of the linear constant current circuit is also larger, and the heat generation is also greater. 2. The sampling error of the existing circuit is large. Because the conduction of the optocoupler is controlled by controlling the triode through resistor voltage division, there is also a sampling delay phenomenon, and sampling cannot be realized in the range where the voltage division is lower than the control voltage of the triode. This is also the reason why the existing thyristors cannot achieve high-precision consistency. 3. The existing thyristor freewheeling circuit can only adapt to a narrow voltage range and cannot achieve wide-voltage operation. 4. The sampling signal of the existing thyristor freewheeling circuit is greatly affected by the input voltage, resulting in poor dimming compatibility and poor dimming consistency. 5. The existing thyristor freewheeling circuit requires an auxiliary power supply for operation, increasing the cost. Summary of the Invention

[0003] An object of the present invention is to at least solve one of the technical problems existing in the prior art, and to provide a thyristor freewheeling sampling circuit.

[0004] The thyristor freewheeling sampling circuit according to an embodiment of the present invention includes: a thyristor dimmer Q1, a rectifier circuit, a voltage sampling circuit, a freewheeling on-off control circuit, and a linear constant current circuit. The output voltage of the thyristor dimmer Q1 is rectified by the rectifier circuit and then input to the input end of the voltage sampling circuit and the positive end of the linear constant current circuit respectively. The output end of the voltage sampling circuit is electrically connected to the control end of the freewheeling on-off control circuit. The positive end of the freewheeling on-off control circuit is electrically connected to the control end of the linear constant current circuit. The negative end of the linear constant current circuit and the negative end of the freewheeling on-off control circuit are grounded respectively; when the voltage sampling circuit detects that the conduction angle of the thyristor dimmer Q1 ≥ A, the freewheeling on-off control circuit controls the linear constant current circuit not to work, and when the voltage sampling circuit detects that the conduction angle of the thyristor dimmer Q1 < A, the freewheeling on-off control circuit controls the linear constant current circuit to work to maintain the conduction of the thyristor dimmer Q1.

[0005] The thyristor freewheeling sampling circuit according to the embodiments of the present invention has at least the following beneficial effects: The circuit can automatically turn off the linear constant current circuit through the freewheeling on-off control circuit. When the voltage sampling circuit detects that the conduction angle of the thyristor dimmer Q1 ≥ A (when the thyristor load current is not lower than the holding current of the thyristor), the freewheeling on-off control circuit controls the linear constant current circuit not to work. When the voltage sampling circuit detects that the conduction angle of the thyristor dimmer Q1 < A (when the thyristor load current is lower than the holding current of the thyristor), the freewheeling on-off control circuit controls the linear constant current circuit to work to maintain the conduction of the thyristor dimmer Q1. However, the existing circuit does not have the function of turning off the linear constant current circuit. When the input voltage is higher, the power consumption of the linear constant current circuit is greater, and the heat generation is also greater. Therefore, this solution can effectively reduce the heat generation of the linear constant current circuit, reduce power consumption, and improve the reliability of the circuit.

[0006] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The following further describes the specific embodiments of the present invention with reference to the drawings; Figure 1 is the schematic diagram of the thyristor freewheeling sampling circuit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0008] This part will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the drawings. The function of the drawings is to supplement the description in the text part of the specification, enabling people to intuitively and vividly understand each technical feature and the overall technical solution of the present invention. However, it should not be construed as a limitation on the protection scope of the present invention.

[0009] In the description of the present invention, it should be understood that for the orientation description, such as the orientation or positional relationship indicated by up, down, front, back, left, right, etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention.

[0010] In the description of the present invention, the meaning of several is one or more, the meaning of multiple is two or more. Understanding greater than, less than, exceeding, etc. does not include the present number, and understanding above, below, within, etc. includes the present number. If there is a description of first and second, it is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0011] Refer toFigure 1 , a thyristor freewheeling sampling circuit of the present invention includes: a thyristor dimmer Q1, a rectifier circuit 10, a voltage sampling circuit 20, a freewheeling on-off control circuit 30, and a linear constant current circuit 40. The output voltage of the thyristor dimmer Q1 is rectified by the rectifier circuit 10 and then input to the input terminal of the voltage sampling circuit 20 and the positive terminal of the linear constant current circuit 40 respectively. The output terminal of the voltage sampling circuit 20 is electrically connected to the control terminal of the freewheeling on-off control circuit 30. The positive terminal of the freewheeling on-off control circuit 30 is electrically connected to the control terminal of the linear constant current circuit 40. The negative terminal of the linear constant current circuit 40 and the negative terminal of the freewheeling on-off control circuit 30 are grounded respectively; when the voltage sampling circuit 20 detects that the conduction angle of the thyristor dimmer Q1 ≥ A, the freewheeling on-off control circuit 30 controls the linear constant current circuit 40 not to work, and when the voltage sampling circuit 20 detects that the conduction angle of the thyristor dimmer Q1 < A, the freewheeling on-off control circuit 30 controls the linear constant current circuit 40 to work to maintain the conduction of the thyristor dimmer Q1. The value of A is related to the holding current of the thyristor dimmer. Assume that when the conduction angle of the thyristor dimmer is 20%, the corresponding load power just maintains the minimum holding current of the thyristor. At this time, A = 20%. The specific advantages of this circuit are: this circuit can automatically turn off the linear constant current circuit 40 (i.e., the freewheeling circuit) through the freewheeling on-off control circuit 30. When the voltage sampling circuit 20 detects that the conduction angle of the thyristor dimmer Q1 ≥ A (at this time, the thyristor load current is not lower than the holding current of the thyristor), the freewheeling on-off control circuit 30 controls the linear constant current circuit 40 not to work, and when the voltage sampling circuit 20 detects that the conduction angle of the thyristor dimmer Q1 < A (at this time, the thyristor load current is lower than the holding current of the thyristor), the freewheeling on-off control circuit 30 controls the linear constant current circuit 40 to work to maintain the conduction of the thyristor dimmer Q1. However, the existing circuit does not have the function of turning off the freewheeling circuit. When the input voltage is higher, the power consumption of the freewheeling circuit is greater, and the heat generation is also greater. Therefore, this solution can effectively reduce the heat generation of the linear constant current circuit 40, reduce power consumption, and improve the reliability of the circuit.

[0012] In some embodiments, the freewheeling on-off control circuit 30 includes a diode D3 and a switching transistor U3. The positive terminal of the diode D3 is electrically connected to the control terminal of the linear constant-current circuit 40. The negative terminal of the diode D3 is electrically connected to the positive terminal of the switching transistor U3. The negative terminal of the switching transistor U3 is grounded. The linear constant-current circuit 40 includes a switching transistor Q2 (which can be a MOS transistor), a switching transistor Q3 (which can be a bipolar transistor), and a resistor R12. The positive terminal of the switching transistor Q2 is electrically connected to the output terminal of the rectification circuit 10 through a series-connected resistor. The control terminal of the switching transistor Q2 is respectively electrically connected to the positive terminal of the diode D3 and the positive terminal of the switching transistor Q3. The negative terminal of the switching transistor Q2 is respectively electrically connected to the positive terminal of the resistor R12 and the control terminal of the switching transistor Q3. The negative terminals of the resistor R12 and the switching transistor Q3 are respectively grounded. The voltage sampling circuit 20 includes a resistor R6 and a resistor R11. One end of the resistor R6 is electrically connected to the output terminal of the rectification circuit 10. The other end of the resistor R6 and one end of the resistor R11 are respectively electrically connected to the control terminal of the switching transistor U3. The other end of the resistor R11 is grounded. When the conduction angle of the thyristor dimmer Q1 is maximum, the corresponding load power is also maximum. When the conduction angle of the thyristor dimmer Q1 is minimum, the corresponding load power is also minimum. Assuming that when the conduction angle of the thyristor dimmer Q1 is 20%, the corresponding load power just maintains the minimum holding current of the thyristor. Then we set the voltage across the resistor R11 in the voltage detection circuit to be slightly greater than the reference voltage of the switching transistor U3. In this way, when the conduction angle of the thyristor dimmer Q1 is greater than 20%, the voltage across the resistor R11 will be greater than the reference of the switching transistor U3, and the switching transistor U3 starts to conduct. Through the diode D3, the gate voltage of the MOS transistor Q2 is pulled down, and the MOS transistor Q2 turns off. The linear constant-current circuit 40 does not work. At this time, since the load power is greater than the minimum holding current of the thyristor dimmer Q1, the thyristor dimmer Q1 and the load circuit work normally, and the linear constant-current circuit 40 does not work, reducing the loss, decreasing the heat generation, and improving the overall efficiency of the drive. When the conduction angle of the thyristor dimmer Q1 is less than 20%, the output voltage of the thyristor dimmer Q1 decreases, and the voltage division across the voltage division resistor R11 is lower than the reference voltage of the switching transistor U3. The switching transistor U3 turns off, restoring the gate control of the MOS transistor Q2. The linear constant-current circuit 40 is used to maintain the conduction of the thyristor dimmer Q1 to ensure that the thyristor dimmer Q1 works normally at low loads. At the same time, due to the high accuracy of the reference voltage of the switching transistor U3, the compatibility and consistency of dimming can be greatly improved.

[0013] In some embodiments, a voltage clamping circuit 50 is further included. The voltage clamping circuit 50 includes a resistor R5 and a diode D6. One end of the resistor R5 is electrically connected to the output end of the rectification circuit 10. The other end of the resistor R5 is respectively electrically connected to the negative end of the diode D6, the positive end of the freewheeling on-off control circuit 30, and the control end of the linear constant current circuit 40. The positive end of the diode D6 is grounded. The diode D6 is a zener diode, and its zener voltage is generally set to be about 80% less than the gate voltage of the MOS transistor Q2, ensuring that the voltage will not be greater than the gate voltage of the MOS transistor Q2 at any time.

[0014] In some embodiments, a voltage stabilizing circuit 60, a driving circuit 70, and a zero-crossing detection circuit 80 are further included. The input end of the voltage stabilizing circuit 60 is electrically connected to the output end of the rectification circuit 10, and the output end of the voltage stabilizing circuit 60 is electrically connected to the driving circuit 70. The input end of the zero-crossing detection circuit 80 is electrically connected to the input end of the voltage stabilizing circuit 60, and the output end of the zero-crossing detection circuit 80 is electrically connected to the control end of the driving circuit 70. The voltage stabilizing circuit 60 includes a diode D1, a diode D2, and a capacitor C2. The positive end of the diode D1 is electrically connected to the output end of the rectification circuit 10. The negative end of the diode D1 is respectively electrically connected to the negative end of the diode D2, one end of the capacitor C2, and the input end of the driving circuit 70. The positive ends of the diode D2 and the other end of the capacitor C2 are respectively grounded. The zero-crossing detection circuit 80 includes a diode D4, a capacitor C4, and a switching transistor U2. The negative end of the diode D4, one end of the capacitor C4, and the control end of the switching transistor U2 are respectively electrically connected to the input end of the voltage stabilizing circuit 60. The positive end of the switching transistor U2 is electrically connected to the driving circuit 70. The positive end of the diode D4, the other end of the capacitor C4, and the negative end of the switching transistor U2 are respectively grounded. The driving circuit 70 includes an optocoupler U1, a resistor R1, and a resistor R8. One input end of the optocoupler U1 is electrically connected to the output end of the voltage stabilizing circuit 60, and the other input end of the optocoupler U1 is electrically connected to the positive end of the switching transistor U2. The voltage stabilization is generally set to about 5V. Since the power consumption of the optocoupler U1 is very small, a reasonable capacitor C2 can obtain a stable 5V voltage. Whether the conduction angle of the thyristor dimmer is less than 20% or the maximum conduction angle of the thyristor dimmer, theoretically, as long as the output voltage of the thyristor dimmer is greater than 5V, a stable 5V voltage can be obtained on the capacitor C2 to provide power for the operation of the optocoupler U1, without the need for an additional auxiliary power supply. Moreover, this circuit module is independent and does not need to share the ground with the main power circuit, greatly reducing various interferences from the main circuit and improving the sampling and control accuracy.

[0015] And when the pulsating DC voltage is greater than the reference voltage of switch U2, generally the reference voltage of switch U2 is 2.5V, switch U2 conducts, optocoupler U1 conducts, and the secondary of optocoupler U1 outputs a high-level signal. When thyristor dimmer Q1 is in the phase-cutting state, if thyristor dimmer Q1 does not conduct, there is no output voltage. At this time, it is lower than the reference voltage of switch U2, and switch U2 turns off, causing optocoupler U1 to turn off, and the secondary signal output of the optocoupler is pulled low to a low level through resistor R8. Due to the very high accuracy of the reference voltage of switch U2, zero-crossing detection is well achieved. Through the filtering of capacitor C4, the anti-interference ability of the circuit is well improved. This circuit cleverly realizes accurate zero-crossing sampling through switch U2. Existing circuits all control the conduction of the optocoupler by controlling a triode through resistor voltage division, with large sampling errors and sampling delays, and sampling cannot be achieved in the area where the voltage division is lower than the control voltage of the triode. There is a range of dozens of volts in this area, which is also the reason why existing thyristors cannot achieve high-precision consistency.

[0016] That is, by cleverly using the fact that switch U2 has only two states, conduction and cut-off, the conduction angle of the thyristor dimmer is sampled into an accurate digital signal for subsequent control. Even better, when no thyristor dimmer is connected to the circuit input, after rectification, the output is a complete continuous sine half-wave. At this time, by reasonably selecting the value of capacitor C4 to make it greater than the reference voltage of switch U2 throughout the pulsating cycle, then switch U2 is in the conduction state throughout the cycle, optocoupler U1 is also in the conduction state throughout the cycle, the secondary of optocoupler U1 is also in the conduction state throughout the cycle, and the signal output is always at a high level. At this time, the subsequent circuit can control the brightness and color temperature of the LED by reading the time of the high level, which enables the circuit input to be compatible with the PUSH function.

[0017] Even better, when no thyristor dimmer is connected to the circuit input, after rectification, the output is a complete continuous sine half-wave. At this time, the voltage on resistor R11 will be greater than the base voltage of switch U3 in 80% of the time cycle, and switch U3 starts to conduct. Through diode D3, the gate voltage of MOS transistor Q2 is pulled low, and MOS transistor Q2 turns off. Linear constant-current circuit 40 does not work, reducing heat generation. Only in the remaining 20% of the time cycle does linear constant-current circuit 40 work. And at this time, since the voltage in this 20% cycle is in a relatively low range, the power consumption of linear constant-current circuit 40 is very low and the heat generation is small. Therefore, it is well compatible with both thyristor dimmer Q1 and PUSH functions.

[0018] When a PUSH signal is input, the PUSH switch conducts, and a complete half-wave sine signal is output after passing through the rectifier circuit 10. Then, through the zero-crossing detection circuit 80, the optocoupler U1 can be kept conducting throughout the sine cycle, and the output signal is at a high level. The subsequent circuit can realize the PUSH-related functions by detecting the duration of the high level, but the existing circuit cannot achieve this function.

[0019] That is, the circuit structure is simple, effectively reducing the power consumption and heat generation of the circuit, reducing the size of the power components, and improving the efficiency and reliability of the entire system while effectively reducing costs; moreover, this circuit can be compatible with the PUSH function, without the need for an additional PUSH sampling circuit, achieving precise detection, improving the dimming compatibility and consistency. And it realizes independent module operation, which is conducive to making it into a module plug-in and achieving good compatibility with conventional products.

[0020] It is easy for those skilled in the art to understand that, on the premise of no conflict, the above preferred methods can be freely combined and superimposed.

[0021] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made by using the content of the specification and drawings of the present invention under the inventive concept of the present invention, or directly or indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A thyristor freewheeling sampling circuit, characterized in that Comprising: A thyristor dimmer Q1, a rectifier circuit (10), a voltage sampling circuit (20), a freewheeling on-off control circuit (30), and a linear constant current circuit (40). The output voltage of the thyristor dimmer Q1 is rectified by the rectifier circuit (10) and then input to the input terminal of the voltage sampling circuit (20) and the positive terminal of the linear constant current circuit (40) respectively. The output terminal of the voltage sampling circuit (20) is electrically connected to the control terminal of the freewheeling on-off control circuit (30). The positive terminal of the freewheeling on-off control circuit (30) is electrically connected to the control terminal of the linear constant current circuit (40). The negative terminal of the linear constant current circuit (40) and the negative terminal of the freewheeling on-off control circuit (30) are grounded respectively. When the voltage sampling circuit (20) detects that the conduction angle of the thyristor dimmer Q1 ≥ A, the freewheeling on-off control circuit (30) controls the linear constant current circuit (40) not to work. When the voltage sampling circuit (20) detects that the conduction angle of the thyristor dimmer Q1 < A, the freewheeling on-off control circuit (30) controls the linear constant current circuit (40) to work to maintain the conduction of the thyristor dimmer Q1.

2. The thyristor freewheeling sampling circuit according to claim 1, wherein: The freewheeling on-off control circuit (30) includes a diode D3 and a switching tube U3. The positive terminal of the diode D3 is electrically connected to the control terminal of the linear constant current circuit (40). The negative terminal of the diode D3 is electrically connected to the positive terminal of the switching tube U3. The negative terminal of the switching tube U3 is grounded.

3. The thyristor freewheeling sampling circuit according to claim 2, wherein: The linear constant current circuit (40) includes a switching tube Q2, a switching tube Q3, and a resistor R12. The positive terminal of the switching tube Q2 is electrically connected to the output terminal of the rectifier circuit (10) through a series-connected resistor. The control terminal of the switching tube Q2 is electrically connected to the positive terminal of the diode D3 and the positive terminal of the switching tube Q3 respectively. The negative terminal of the switching tube Q2 is electrically connected to the positive terminal of the resistor R12 and the control terminal of the switching tube Q3 respectively. The negative terminal of the resistor R12 and the negative terminal of the switching tube Q3 are grounded respectively.

4. The silicon-controlled rectifier freewheeling sampling circuit according to claim 2, wherein: The voltage sampling circuit (20) includes a resistor R6 and a resistor R11. One end of the resistor R6 is electrically connected to the output terminal of the rectifier circuit (10). The other end of the resistor R6 and one end of the resistor R11 are electrically connected to the control terminal of the switching tube U3 respectively. The other end of the resistor R11 is grounded.

5. The thyristor freewheeling sampling circuit according to claim 1, wherein: It further includes a voltage clamping circuit (50). The voltage clamping circuit (50) includes a resistor R5 and a diode D6. One end of the resistor R5 is electrically connected to the output terminal of the rectifier circuit (10). The other end of the resistor R5 is electrically connected to the negative terminal of the diode D6, the positive terminal of the freewheeling on-off control circuit (30), and the control terminal of the linear constant current circuit (40) respectively. The positive terminal of the diode D6 is grounded.

6. The thyristor freewheeling sampling circuit according to claim 1, characterized in that: It further includes a voltage stabilizing circuit (60) and a driving circuit (70). The input terminal of the voltage stabilizing circuit (60) is electrically connected to the output terminal of the rectifier circuit (10). The output terminal of the voltage stabilizing circuit (60) is electrically connected to the driving circuit (70).

7. The thyristor freewheeling sampling circuit according to claim 6, characterized in that: It further includes a zero-crossing detection circuit (80). The input end of the zero-crossing detection circuit (80) is electrically connected to the input end of the voltage stabilization circuit (60), and the output end of the zero-crossing detection circuit (80) is electrically connected to the control end of the drive circuit (70).

8. The thyristor freewheeling sampling circuit according to claim 7, wherein: The voltage stabilization circuit (60) includes a diode D1, a diode D2, and a capacitor C2. The positive end of the diode D1 is electrically connected to the output end of the rectification circuit (10). The negative end of the diode D1 is respectively electrically connected to the negative end of the diode D2, one end of the capacitor C2, and the input end of the drive circuit (70). The positive end of the diode D2 and the other end of the capacitor C2 are respectively grounded.

9. The thyristor freewheeling sampling circuit according to claim 7, characterized in that: The zero-crossing detection circuit (80) includes a diode D4, a capacitor C4, and a switching tube U2. The negative end of the diode D4, one end of the capacitor C4, and the control end of the switching tube U2 are respectively electrically connected to the input end of the voltage stabilization circuit (60). The positive end of the switching tube U2 is electrically connected to the drive circuit (70). The positive end of the diode D4, the other end of the capacitor C4, and the negative end of the switching tube U2 are respectively grounded.

10. The thyristor freewheeling sampling circuit according to claim 9, characterized in that: The drive circuit (70) includes an optocoupler U1, a resistor R1, and a resistor R8. One input end of the optocoupler U1 is electrically connected to the output end of the voltage stabilization circuit (60), and the other input end of the optocoupler U1 is electrically connected to the positive end of the switching tube U2.

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