Multi-gear high-precision LED constant-current dimming circuit

Abstract

The utility model relates to the technical field of LED dimming, and provides a multi-gear high-precision LED constant-current dimming circuit, which comprises an LED lamp group, a dimming circuit, a booster circuit and an under-voltage protection circuit, and is characterized in that a plurality of adjusting resistors R2-R5 which are connected in series are arranged to be matched with a single-pole multi-throw dial switch SW1, so that the resistance value of the circuit on the series circuit can be flexibly adjusted, the current of the LED lamp group can be adjusted, and the dimming effect of the LED lamp group can be improved. Therefore, multi-gear high-precision adjustment is realized; a triode and an MOS tube are arranged to form switch control, the weak current control principle of the triode is utilized, a resistor R1 with the resistance value far larger than that of all resistors in a series adjusting module is arranged in a matched mode, when LED circuit dimming is carried out, the R1 with the large resistance value can neglect the influence of voltage drop of the triode Ibe on R3 / R4 / R5 on LED current precision, and meanwhile a loop of an LED lamp set can be thoroughly turned off when SW1 is turned off; a divider resistor is adopted to carry out real-time feedback detection on the output voltage of the booster circuit, and under-voltage self-detection and self-protection are achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of LED dimming, in particular to a multi-position high-precision LED constant current dimming circuit. Background Art

[0002] The existing light-emitting devices mainly include incandescent lamps, fluorescent tubes, LED lamps, etc. The light-emitting diode (LED) was invented in the 1960s. It uses the electrons and holes in semiconductor materials to combine with each other and release energy, so that the energy band (Energy Gat) level changes, and the energy released is displayed by emitting light. LED has the advantages of small size, long life, low driving voltage, low power consumption, fast reaction rate, good shock resistance, etc., and is widely used in signal indication, digital display and other fields. With the continuous advancement of technology, the development of ultra-bright LED has been successful, especially the development of white light LED, which makes it more and more used in the field of lighting. The existing incandescent lamps and fluorescent tubes use alternating current, while LED lamps are powered by direct current. The adjustment of the light brightness is mainly carried out through resistors or potentiometers. This method of adjustment requires manual setting and is not intelligent enough.

[0003] LED dimming has two types: constant voltage dimming and constant current dimming. Since constant voltage dimming has low precision, constant current dimming can only be used for applications with high dimming precision. The common solution for LED lamp dimming is that MCU controls the constant current circuit to achieve dimming. The MCU power supply requires a high-voltage difference LDO or a buck circuit, and the MCU PWM signal requires a dedicated constant current IC, which is relatively expensive.

[0004] The existing LED lamp code control circuit generally uses a code switch + resistor in parallel to control the output current. The greater the output current, the greater the brightness of the LED lamp; however, the resistor parallel method is too simple, such as Figure 1 This dimming circuit cannot completely turn off the LED. When the DIP switch SW1 is turned off, current flows through the be pin of the switch tube Q2, so the LED lamp cannot be completely turned off.

[0005] In actual use of LED lamps, due to unstable power supply voltage, the output LED often flickers, which not only affects the user experience, but also easily leads to current and power instability, resulting in a decrease in LED luminous efficiency or shortening the life of the LED. Summary of the invention

[0006] The utility model provides a multi-position high-precision LED constant current dimming circuit, which solves the technical problems that the existing LED dimming circuit uses parallel resistors to control the output current, cannot completely shut down the LED and lacks undervoltage protection.

[0007] In order to solve the above technical problems, the utility model provides a multi-speed high-precision LED constant current dimming circuit, including an LED lamp group, a dimming circuit, a boost circuit and an undervoltage protection circuit; the input end of the LED lamp group is connected to the boost circuit, and the output end is connected to the dimming circuit; the dimming circuit includes a first switch module and a series adjustment module, and the adjustment module includes a plurality of series-connected adjustment resistors; the detection end of the undervoltage protection circuit is connected to the output end of the boost circuit, and the control end is connected in series between the power input end and the input end of the boost circuit.

[0008] In a further implementation scheme, the adjustment module includes a dip switch SW1, an adjustment resistor R2, an adjustment resistor R3, an adjustment resistor R4 and an adjustment resistor R5, the adjustment resistors R2, R3, R4 and R5 are connected in sequence, and the dip switch SW1 includes a first contact to a fifth contact; a second switch contact is connected between the adjustment resistor R2 and the adjustment resistor R3, a third switch contact is connected between the adjustment resistor R3 and the adjustment resistor R4, a fourth switch contact is connected between the adjustment resistor R4 and the adjustment resistor R5, and a fifth switch contact is connected between the adjustment resistor R5 and the first switch module;

[0009] The first contact of the dip switch SW1 is electrically connected to the second switch contact / the third switch contact / the fourth switch contact / the fifth switch contact.

[0010] In a further embodiment, the first switch module includes a first switch tube Q1, a second switch tube Q2, a resistor R1 and a diode D1; the first end of the first switch tube Q1 is connected to the adjustment module, the second end is connected to the output end of the LED light group, and the control end is connected to the input end of the LED light group through the resistor R1; the first end of the second switch tube Q2 is connected to the control end of the first switch tube Q1, the second end is connected to the adjustment resistor R5, and the control end is connected to the first end of the first switch tube Q1; the positive pole of the diode is grounded, and the negative pole is connected to the input end of the LED light group.

[0011] In a further embodiment, the undervoltage protection circuit includes a feedback module and a second switch module, the detection end of the feedback module is connected to the output end of the boost circuit, and the feedback end is connected to the second switch module; the second switch module is connected in series between the power input end and the input end of the boost circuit;

[0012] The feedback module includes a voltage-dividing resistor R9, a voltage-dividing resistor R14 and a capacitor C10. One end of the voltage-dividing resistor R9 is connected to the output end of the boost circuit, and the other end is connected to the second switch module as a feedback end; the other end of the voltage-dividing resistor R9 is also grounded through the voltage-dividing resistor R14; the voltage-dividing resistor R14 and the capacitor C10 are connected in parallel.

[0013] In a further implementation scheme, the second switch module includes a third switch tube Q3, a fourth switch tube Q4, a resistor R8 and a resistor R12; the first end of the third switch tube Q3 is connected to the input end of the boost circuit, the second end is connected to the power input end, and the control end is connected to the second end of the fourth switch tube Q4 through the resistor R12; the control end of the fourth switch tube Q4 is connected to the feedback end of the feedback module, and the first end is grounded; the two ends of the resistor R8 are respectively connected to the second end and the control end of the third switch tube Q3.

[0014] In a further embodiment, the resistance of resistor R1 is much greater than the resistance of adjusting resistor R2, the resistance of resistor R1 is much greater than the resistance of adjusting resistor R3, the resistance of resistor R1 is much greater than the resistance of adjusting resistor R4, and the resistance of resistor R1 is much greater than the resistance of adjusting resistor R5.

[0015] In a further embodiment, the first switch tube Q1 is a MOS tube, and the second switch tube Q2 is a triode.

[0016] In a further embodiment, the third switch tube Q3 is a MOS tube, and the fourth switch tube Q4 is a MOS tube.

[0017] The beneficial effects of the utility model are as follows:

[0018] (1) A plurality of adjusting resistors R2 to R5 connected in series are provided, and a single-pole multi-throw rotary switch SW1 is used in combination. A second switch contact is connected between the adjusting resistor R2 and the adjusting resistor R3, a third switch contact is connected between the adjusting resistor R3 and the adjusting resistor R4, a fourth switch contact is connected between the adjusting resistor R4 and the adjusting resistor R5, and a fifth switch contact is connected between the adjusting resistor R5 and the first switch module in sequence, thereby flexibly adjusting the circuit resistance value on the series circuit to adjust the current of the LED lamp group, thereby achieving multi-level high-precision adjustment.

[0019] (2) A transistor and a MOS tube are set to form a switch control. The weak current control principle of the transistor is used. The resistor R1 is set to have a resistance value much larger than all the resistors in the series adjustment module (adjustment resistor R2, adjustment resistor R3, adjustment resistor R4, and adjustment resistor R5). When the LED circuit is turned off and on, the large resistance value of R1 can ignore the influence of the voltage drop of the transistor Ibe on R3 / R4 / R5 on the LED current accuracy. At the same time, when SW1 is turned off, the circuit of the LED lamp group can be completely turned off.

[0020] (3) A voltage divider resistor is used to perform real-time feedback detection on the output voltage of the boost circuit. When the voltage is normal, the fourth switch tube Q4 is turned on to lower the gate voltage of the third switch tube Q3, so that the third switch tube Q3 is turned on. When the voltage is undervoltage, the fourth switch tube Q4 is turned off, and the gate voltage of the third switch tube Q3 is increased, so that the third switch tube Q3 is turned off, thereby realizing undervoltage self-detection and self-protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a code pulling control circuit diagram provided by the background technology of the embodiment of the utility model;

[0022] Figure 2 This is a system block diagram of a multi-level high-precision LED constant current dimming circuit provided by an embodiment of the utility model;

[0023] Figure 3 The utility model embodiment provides Figure 1 Partial circuit diagram of

[0024] Figure 4 The utility model embodiment provides Figure 1 Partial circuit diagram of

[0025] Among them: LED lamp group 1, dimming circuit 2, boost circuit 3, undervoltage protection circuit 4. DETAILED DESCRIPTION

[0026] The following is a detailed explanation of the implementation mode of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and cannot be understood as limitations on the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute limitations on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0027] The utility model embodiment provides a multi-level high-precision LED constant current dimming circuit 2, such as Figure 2 to Figure 4 As shown, in this embodiment, it includes an LED lamp group, a dimming circuit 2, a boost circuit 3 and an undervoltage protection circuit 4; the input end of the LED lamp group is connected to the boost circuit 3, and the output end is connected to the dimming circuit 2; the dimming circuit 2 includes a first switch module and a series adjustment module, and the adjustment module includes a plurality of series-connected adjustment resistors; the detection end of the undervoltage protection circuit 4 is connected to the output end of the boost circuit 3, and the control end is connected in series between the power input end and the input end of the boost circuit 3.

[0028] In this embodiment, the LED lamp group includes one or more groups of lamp strings consisting of a plurality of LED lamps connected in series, and the specific number of lamp strings is set according to a preset power.

[0029] In this embodiment, the boost circuit 3 is a circuit module composed of a boost chip U1, which is used to boost the input voltage VIN to the voltage VOUT required by the LED lamp, and this embodiment will not be described in detail.

[0030] In this embodiment, the adjustment module includes a dip switch SW1, an adjustment resistor R2, an adjustment resistor R3, an adjustment resistor R4 and an adjustment resistor R5. The adjustment resistors R2, R3, R4 and R5 are connected in sequence. The dip switch SW1 includes a first contact to a fifth contact. A second switch contact is connected between the adjustment resistor R2 and the adjustment resistor R3, a third switch contact is connected between the adjustment resistor R3 and the adjustment resistor R4, a fourth switch contact is connected between the adjustment resistor R4 and the adjustment resistor R5, and a fifth switch contact is connected between the adjustment resistor R5 and the first switch module.

[0031] The first contact of the DIP switch SW1 is electrically connected to the second switch contact / the third switch contact / the fourth switch contact / the fifth switch contact.

[0032] In this embodiment, the resistance value of the resistor R1 is much greater than the resistance value of the adjusting resistor R2, the resistance value of the resistor R1 is much greater than the resistance value of the adjusting resistor R3, the resistance value of the resistor R1 is much greater than the resistance value of the adjusting resistor R4, and the resistance value of the resistor R1 is much greater than the resistance value of the adjusting resistor R5. Since the resistor R1 is several times (for example, 10^6 times) greater than the adjusting resistors (R2 to R5), the above description uses the resistance value of the resistor R1 being much greater than the resistance value of the adjusting resistors R2 to R5.

[0033] In this embodiment, the first switch module includes a first switch tube Q1, a second switch tube Q2, a resistor R1 and a diode D1; the first end of the first switch tube Q1 is connected to the adjustment module, the second end is connected to the output end of the LED lamp group, and the control end is connected to the input end of the LED lamp group through the resistor R1; the first end of the second switch tube Q2 is connected to the control end of the first switch tube Q1, the second end is connected to the adjustment resistor R5, and the control end is connected to the first end of the first switch tube Q1; the positive pole of the diode is grounded, and the negative pole is connected to the input end of the LED lamp group.

[0034] In this embodiment, the first switch tube Q1 is a MOS tube or a triode, and the second switch tube Q2 is a triode. Preferably, the first switch tube Q1 is an N-channel MOS tube, and the second switch tube Q2 is an NPN-type triode.

[0035] Under certain temperature and current conditions, the Vbe of the transistor (i.e., the second switch tube Q2) remains basically unchanged;

[0036] Using the Vbe of the second switch tube Q2 as the reference voltage, R2 to R5 and the like as constant current setting resistors, and switching the gear of the DIP switch SW1 to control the number of R2 to R5 resistors connected to achieve current control, then;

[0037] The formula for setting the LED drive current is: Iled = Vbe / Rsense + Ibe

[0038] At this time, the first switch tube Q1 is a MOS tube, which is a transconductance amplifier. Compared with the current amplification of the triode (the second switch tube Q2), the driving current can be very small, and the resistor R1 has a large value, so the influence of the input voltage change on the current of the resistor R1 can be ignored; and the current flowing through the resistor R1 almost all flows through the Ic of the second switch tube Q2, so Ic can be considered to be almost unchanged, and Vbe can be considered to be almost unchanged.

[0039] Where Vbe is the be voltage of the second switch tube Q2, Ibe is the be current of the second switch tube Q2, and Ic is the ce current of the second switch tube Q2. If the resistance value of resistor R1 is set to be much larger than R2-R5 (for example, 10^6 times), Ibe and Ic flowing through the second switch tube Q2 will be much smaller than the current flowing through the LED, so Ibe can be ignored;

[0040] Then the LED drive current setting formula is optimized as: Iled = Vbe / Rsense

[0041] therefore:

[0042] (1) When the first switch contact is connected to pin 5 (fifth switch contact)

[0043] Rsense=R2+R3+R4+R5

[0044] (2) When the first switch contact is connected to pin 4 (the fourth switch contact)

[0045] Rsense=R2+R3+R4.

[0046] At this time, the reference voltage is Q2Vbe-Q2Ic*R5. Since the Ic current is very small, the voltage drop on R5 can be ignored, so the reference voltage is approximately equal to Q2 Vbe.

[0047] (3) When the first switch contact is connected to pin 3 (third switch contact)

[0048] Rsense=R2+R3

[0049] At this time, the reference voltage is Q2Vbe-Q2Ic*(R5+R4). Since the Ic current is very small, the voltage drop on R5 / R4 can be ignored, so the reference voltage is approximately equal to Q2 Vbe.

[0050] (4) When the first switch contact is connected to pin 2 (second switch contact)

[0051] Rsense=R2

[0052] At this time, the reference voltage is Q2Vbe-Q2Ic*(R5+R4+R3). Since the Ic current is very small, the voltage drop on R5 / R4 / R3 can be ignored, so the reference voltage is approximately equal to Q2 Vbe.

[0053] In this embodiment, the undervoltage protection circuit 4 includes a feedback module and a second switch module, the detection end of the feedback module is connected to the output end of the boost circuit 3, and the feedback end is connected to the second switch module; the second switch module is connected in series between the power input end and the input end of the boost circuit 3;

[0054] The feedback module includes a voltage-dividing resistor R9, a voltage-dividing resistor R14 and a capacitor C10. One end of the voltage-dividing resistor R9 is connected to the output end of the boost circuit 3, and the other end is connected to the second switch module as the feedback end LVP; the other end of the voltage-dividing resistor R9 is also grounded through the voltage-dividing resistor R14; the voltage-dividing resistor R14 and the capacitor C10 are connected in parallel.

[0055] In this embodiment, the second switch module includes a third switch tube Q3, a fourth switch tube Q4, a resistor R8 and a resistor R12; the first end of the third switch tube Q3 is connected to the input end of the boost circuit 3, the second end is connected to the power input end, and the control end is connected to the second end of the fourth switch tube Q4 through the resistor R12; the control end LVP-EN of the fourth switch tube Q4 is connected to the feedback end LVP of the feedback module through a peripheral circuit (such as MCU) (after the peripheral circuit detects that the feedback end LVP is undervoltage, it outputs a control signal to the control end LVP-EN of the fourth switch tube), and the first end is grounded; the two ends of the resistor R8 are respectively connected to the second end and the control end of the third switch tube Q3.

[0056] In this embodiment, the third switch tube Q3 is a MOS tube or a triode, and the fourth switch tube Q4 is a MOS tube or a triode. Preferably, the third switch tube Q3 is a P-channel MOS tube, and the fourth switch tube Q4 is an N-channel MOS tube.

[0057] The beneficial effects of the embodiments of the present utility model are as follows:

[0058] (1) A plurality of adjusting resistors R2 to R5 are arranged in series, and a single-pole multi-throw rotary switch SW1 is used to connect a second switch contact between the adjusting resistor R2 and the adjusting resistor R3, a third switch contact between the adjusting resistor R3 and the adjusting resistor R4, a fourth switch contact between the adjusting resistor R4 and the adjusting resistor R5, and a fifth switch contact between the adjusting resistor R5 and the first switch module, so as to flexibly adjust the circuit resistance value on the series circuit to adjust the current of the LED lamp group, thereby realizing multi-level high-precision adjustment.

[0059] (2) A transistor and a MOS tube are set to form a switch control. The weak current control principle of the transistor is used. The resistor R1 is set to have a resistance value much larger than all the resistors in the series adjustment module (adjustment resistor R2, adjustment resistor R3, adjustment resistor R4, and adjustment resistor R5). When dimming the LED circuit, the large resistance R1 can ignore the influence of the voltage drop of the transistor Ibe on R3 / R4 / R5 on the LED current accuracy. At the same time, when SW1 is turned off, the circuit of the LED lamp group can be completely turned off.

[0060] (3) A voltage-dividing resistor is used to perform real-time feedback detection on the output voltage of the boost circuit 3. When the voltage is normal, the fourth switch tube Q4 is turned on to lower the gate voltage of the third switch tube Q3, so that the third switch tube Q3 is turned on. When the voltage is undervoltage, the fourth switch tube Q4 is turned off, and the gate voltage of the third switch tube Q3 is increased, so that the third switch tube Q3 is turned off, thereby realizing undervoltage self-detection and self-protection.

[0061] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principle of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A multi-level high-precision LED constant current dimming circuit, characterized in that: It includes an LED lamp group, a dimming circuit, a boost circuit and an undervoltage protection circuit; the input end of the LED lamp group is connected to the boost circuit, and the output end is connected to the dimming circuit; the dimming circuit includes a first switch module and a series adjustment module, and the adjustment module includes a plurality of series-connected adjustment resistors; the detection end of the undervoltage protection circuit is connected to the output end of the boost circuit, and the control end is connected in series between the power input end and the input end of the boost circuit.

2. A multi-level high-precision LED constant current dimming circuit as claimed in claim 1, characterized in that: The regulating module includes a dip switch SW1, an regulating resistor R2, an regulating resistor R3, an regulating resistor R4 and an regulating resistor R5, wherein the regulating resistors R2, R3, R4 and R5 are connected in sequence, and the dip switch SW1 includes a first contact to a fifth contact; a second switch contact is connected between the regulating resistor R2 and the regulating resistor R3, a third switch contact is connected between the regulating resistor R3 and the regulating resistor R4, a fourth switch contact is connected between the regulating resistor R4 and the regulating resistor R5, and a fifth switch contact is connected between the regulating resistor R5 and the first switch module; The first contact of the dip switch SW1 is electrically connected to the second switch contact / the third switch contact / the fourth switch contact / the fifth switch contact.

3. A multi-level high-precision LED constant current dimming circuit as claimed in claim 2, characterized in that: The first switch module includes a first switch tube Q1, a second switch tube Q2, a resistor R1 and a diode D1; the first end of the first switch tube Q1 is connected to the adjustment module, the second end is connected to the output end of the LED light group, and the control end is connected to the input end of the LED light group through the resistor R1; the first end of the second switch tube Q2 is connected to the control end of the first switch tube Q1, the second end is connected to the adjustment resistor R5, and the control end is connected to the first end of the first switch tube Q1; the positive pole of the diode is grounded, and the negative pole is connected to the input end of the LED light group.

4. A multi-level high-precision LED constant current dimming circuit as claimed in claim 1, characterized in that: The undervoltage protection circuit comprises a feedback module and a second switch module, wherein the detection end of the feedback module is connected to the output end of the boost circuit, and the feedback end is connected to the second switch module; the second switch module is connected in series between the power input end and the input end of the boost circuit; The feedback module includes a voltage-dividing resistor R9, a voltage-dividing resistor R14 and a capacitor C10. One end of the voltage-dividing resistor R9 is connected to the output end of the boost circuit, and the other end is connected to the second switch module as a feedback end; the other end of the voltage-dividing resistor R9 is also grounded through the voltage-dividing resistor R14; the voltage-dividing resistor R14 and the capacitor C10 are connected in parallel.

5. A multi-level high-precision LED constant current dimming circuit as claimed in claim 4, characterized in that: The second switch module includes a third switch tube Q3, a fourth switch tube Q4, a resistor R8 and a resistor R12; the first end of the third switch tube Q3 is connected to the input end of the boost circuit, the second end is connected to the power input end, and the control end is connected to the second end of the fourth switch tube Q4 through the resistor R12; the control end of the fourth switch tube Q4 is connected to the feedback end of the feedback module, and the first end is grounded; the two ends of the resistor R8 are respectively connected to the second end and the control end of the third switch tube Q3.

6. A multi-level high-precision LED constant current dimming circuit as claimed in claim 3, characterized in that: The resistance value of the resistor R1 is much larger than the resistance value of the adjusting resistor R2, the resistance value of the resistor R1 is much larger than the resistance value of the adjusting resistor R3, the resistance value of the resistor R1 is much larger than the resistance value of the adjusting resistor R4, and the resistance value of the resistor R1 is much larger than the resistance value of the adjusting resistor R5.

7. A multi-level high-precision LED constant current dimming circuit as claimed in claim 3, characterized in that: The first switch tube Q1 is a MOS tube, and the second switch tube Q2 is a triode.

8. A multi-level high-precision LED constant current dimming circuit as claimed in claim 5, characterized in that: The third switch tube Q3 is a MOS tube, and the fourth switch tube Q4 is a MOS tube.

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