LED constant-voltage output chopping dimming circuit

Abstract

An LED constant-voltage output chopping dimming circuit comprises a direct-current voltage input positive end, a direct-current voltage input negative end, a voltage-limiting Schottky diode, a dimming control end, a dimming MOS tube, an output positive end and an output negative end, the direct-current voltage input positive end is connected with the voltage-limiting Schottky diode and the output positive end, the direct-current voltage input negative end is connected with an S pin of the dimming MOS tube, and the output positive end is connected with the output negative end. The dimming control end is connected with a G pin of the dimming MOS tube, and a pin of the voltage limiting Schottky diode is connected with a D pin of the dimming MOS tube and the output negative end. Compared with the prior art, in order to solve the problem that the instantaneous voltage of the constant-voltage output chopping dimming circuit is increased during working, stable voltage output is maintained by adding the voltage-limiting Schottky diode.

Description

Technical Field

[0001] The utility model relates to a circuit, in particular to an LED constant voltage output chopping dimming circuit. Background Art

[0002] The working principle of the LED constant voltage output chopper dimming circuit is as follows: At full power output, the output power is equal to the square of the input voltage divided by the equivalent resistance of the LED light strip. At this time, the PWM level is high for the entire time period, and the dimming MOS tube is fully turned on. If you want to reduce the output power to 30%, just set the PWM level to a high level within the 30% time period. In order to prevent the human eye from noticing frequent flickering, the high and low switching frequency of PWM is usually set at 1kHz or higher. At the same time, in order to reduce the loss of the dimming MOS tube, we need to use a dimming MOS tube with a lower withstand voltage, whose Vds is slightly higher than the input voltage Uo. For example, if the output Uo of the driver is 24V, a dimming MOS tube with a Vds of 30V should be selected. Although it seems completely fine from the circuit diagram, the dimming MOS tube is often damaged in actual use and testing. After analyzing the cause, it was found that when the LED constant voltage output chopper dimming circuit needs to be connected to the LED light strip with a slightly longer wire, the inductance of this wire will increase to the extent of participating in the circuit. This may cause the moment when the MOS tube is turned off. Since the LED light line needs to maintain the current unchanged, the length of the wire required by the use environment may cause the instantaneous voltage on the dimming MOS tube Vds to be as high as about 80V. Therefore, the selected MOS tube must be able to withstand such a high voltage, otherwise it may be damaged. The conduction loss of the MOS tube with high internal voltage is large (the conduction loss of the MOS tube with the same current specification is proportional to its withstand voltage), which is not advisable. In addition, because the inductance is generated by the connecting wire of the LED light strip, it is affected by its length and placement. It is difficult to determine how high the instantaneous voltage on the dimming MOS tube Vds will rise.

[0003] To solve the above problems, we made a series of improvements. Utility Model Content

[0004] The purpose of the utility model is to provide an LED constant voltage output chopper dimming circuit to overcome the above-mentioned shortcomings and deficiencies in the prior art.

[0005] An LED constant voltage output chopper dimming circuit comprises: a DC voltage input positive terminal, a DC voltage input negative terminal, a voltage limiting Schottky diode, a dimming control terminal, a dimming MOS tube, an output positive terminal and an output negative terminal, wherein the DC voltage input positive terminal is connected with the voltage limiting Schottky diode and the output positive terminal, the DC voltage input negative terminal is connected with the S pin of the dimming MOS tube, the dimming control terminal is connected with the G pin of the dimming MOS tube, the pin of the voltage limiting Schottky diode is connected with the D pin of the dimming MOS tube and the output negative terminal, the DC voltage input positive terminal is connected with the positive terminal of the LED constant voltage output part through a wire, the DC voltage input negative terminal is connected with the negative terminal of the LED constant voltage output part through a wire, the output positive terminal is connected with the positive pole of an LED light strip through a wire, and the output negative terminal is connected with the negative pole of the LED light strip through a wire.

[0006] Beneficial effects of the utility model:

[0007] Compared with the traditional technology, the utility model aims to solve the problem that the instantaneous voltage of the constant voltage output chopper dimming circuit becomes high during operation, and maintains a stable voltage output by adding a voltage-limiting Schottky diode. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a structural schematic diagram of the utility model.

[0009] Reference numerals:

[0010] A DC voltage input positive terminal 100 , a DC voltage input negative terminal 200 , a voltage-limiting Schottky diode 300 , a dimming control terminal 400 and a dimming MOS tube 500 .

[0011] Output positive terminal 600 , output negative terminal 700 , LED constant voltage output part 800 and LED light strip 900 . DETAILED DESCRIPTION

[0012] The following is a further description of the present invention in conjunction with specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0013] Example 1

[0014] Figure 1 It is a structural schematic diagram of the utility model.

[0015] like Figure 1As shown, an LED constant voltage output chopper dimming circuit includes: a DC voltage input positive terminal 100, a DC voltage input negative terminal 200, a voltage limiting Schottky diode 300, a dimming control terminal 400, a dimming MOS tube 500, an output positive terminal 600 and an output negative terminal 700, the DC voltage input positive terminal 100 is connected to the voltage limiting Schottky diode 300 and the output positive terminal 600, the DC voltage input negative terminal 200 is connected to the S pin of the dimming MOS tube 500, and the dimming control terminal 400 is connected to the dimming MO The G pin of the S tube 500 is connected, the pin of the voltage-limiting Schottky diode 300 is connected to the D pin of the dimming MOS tube 500 and the output negative terminal 700, the DC voltage input positive terminal 100 is connected to the positive terminal of the LED constant voltage output part 800 through a wire, the DC voltage input negative terminal 200 is connected to the negative terminal of the LED constant voltage output part 800 through a wire, the output positive terminal 600 is connected to the positive electrode of the LED light strip 900 through a wire, and the output negative terminal 700 is connected to the negative electrode of the LED light strip 900 through a wire.

[0016] The innovative point of the utility model is that Figure 1 A voltage limiting Schottky diode 300 is added to the position in the middle. In this way, when the dimming MOS tube 500 is turned off, the equivalent inductance of the LED lamp line can flow back to the LED constant voltage output part 800 and the LED light strip 900 through the voltage limiting Schottky diode 300, so that the voltage on the dimming MOS tube 500Vds is clamped at Uo+0.7V. If Uo=24V, the voltage of the dimming MOS tube 500Vds is 25V. The dimming MOS tube 500 can safely use a 30V tube with low conduction loss. Although the LED constant voltage output chopper dimming circuit does not contain an inductor device, the fast dimming control terminal 400 switching signal plus the output wire greater than 0.7 meters still makes the output wire generate an inductance sufficient to significantly increase the voltage on the dimming MOS tube 500Vds. This is also a problem that is generally ignored in the industry. People often think that only current dimming circuits have inductance, but according to the above theory, the actual constant voltage output chopper dimming circuit will also have inductance under certain circumstances. Therefore, it is necessary to add an absorption path like the main circuit of the forward-flyback circuit with a transformer. In the present utility model, we choose to add a diode. The reason why the present utility model chooses the voltage-limiting Schottky diode 300 to suppress the voltage among the types of diodes is that its effect is better than other diodes. The purpose of the present utility model is to reduce the switching loss of the dimming MOS tube 500, so it needs to have the performance of fast opening and fast closing, but the faster the speed, the faster the peak current will pass. Therefore, in selecting a diode, we choose a voltage-limiting Schottky diode 300, which is much better than ordinary diodes in suppressing transient voltage, and is therefore particularly suitable for the problem to be solved by the present invention.

[0017] Compared with the traditional technology, the utility model aims to solve the problem that the instantaneous voltage of the constant voltage output chopper dimming circuit becomes high during operation, and maintains a stable voltage output by adding a voltage-limiting Schottky diode.

[0018] The specific implementation modes of the present invention are described above, but the present invention is not limited thereto. The present invention can also have various changes without departing from the purpose of the present invention.

Claims

1. An LED constant voltage output chopper dimming circuit, characterized in that: include: A DC voltage input positive terminal (100), a DC voltage input negative terminal (200), a voltage-limiting Schottky diode (300), a dimming control terminal (400), a dimming MOS tube (500), an output positive terminal (600), and an output negative terminal (700), wherein the DC voltage input positive terminal (100) is connected to the voltage-limiting Schottky diode (300) and the output positive terminal (600), the DC voltage input negative terminal (200) is connected to the S pin of the dimming MOS tube (500), and the dimming control terminal (400) is connected to the G pin of the dimming MOS tube (500). The pin of the voltage-limiting Schottky diode (300) is connected to the D pin of the dimming MOS tube (500) and the output negative terminal (700), the DC voltage input positive terminal (100) is connected to the positive terminal of the LED constant voltage output part (800) through a wire, the DC voltage input negative terminal (200) is connected to the negative terminal of the LED constant voltage output part (800) through a wire, the output positive terminal (600) is connected to the positive electrode of the LED light strip (900) through a wire, and the output negative terminal (700) is connected to the negative electrode of the LED light strip (900) through a wire.

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