Dimming circuit

Abstract

The utility model relates to the technical field of power electronics, and provides a dimming circuit in order to realize PWM (Pulse Width Modulation) dimming of a secondary side to a primary side LED (Light Emitting Diode) driving power supply by adopting a simple and reliable circuit, which comprises a step-down voltage stabilizing circuit and an isolation type PWM control signal transmission circuit, and the isolated PWM control signal transmission circuit synchronizes the PWM square wave modulation signal to the primary side of the power panel through an optocoupler, and further converts the first DC voltage into a DIM dimming control voltage synchronized with the PWM signal, and the DIM dimming control voltage is used for being connected to a dimming control pin of an LED driving chip to realize dimming control. The circuit is simple, easy to use, low in cost, high in reliability, wide in applicable VBUS voltage range and high in universality.

Description

Technical Field

[0001] The utility model relates to the technical field of power electronics, in particular to a dimming circuit. Background Art

[0002] For bathroom heater power supply applications, it is required to be able to disconnect the AC input of the LED driver power supply with a single switch when turning off the light to prevent users from electric shock. Existing technologies mainly use the following two methods: 1. Using the VCC voltage of the primary-side power supply chip to convert the high-level reference voltage of the PWM dimming signal; 2. Using a non-isolated high-voltage buck power supply to provide the high-level reference voltage of the PWM dimming signal.

[0003] Technique 1 requires the use of the VCC voltage of the primary-side power supply chip. This requires that the LED driver power supply be connected to the power ground line that provides the VCC voltage. If the VCC voltage provided by the standby power supply is used for power supply, the non-isolated LED driver power supply cannot effectively disconnect from the power grid even in lights-out mode, posing a safety hazard. If the VCC voltage of the LED driver power supply or the pre-stage PFC power supply is used for power supply, the chip selection must include a VCC pin and the transformer must have a VCC winding, which limits the selection and increases the cost. Technique 2 uses a non-isolated high-voltage buck power supply for power supply, which is inherently costly and takes up more PCB space. Utility Model Content

[0004] In order to implement PWM dimming of a primary-side LED driver power supply by a secondary side using a simple and reliable circuit, the present application provides a dimming circuit.

[0005] The technical solution adopted by the present invention to solve the above problems is:

[0006] A dimming circuit includes: a step-down voltage stabilizing circuit and an isolated PWM control signal transmission circuit.

[0007] The step-down voltage stabilizing circuit includes a first resistor group, a voltage stabilizing tube, a first capacitor and an optocoupler controlled terminal.

[0008] After the voltage regulator tube is connected in parallel with the first capacitor, the positive electrode is grounded, and the negative electrode is connected to one end of the first resistor group and the controlled end of the optocoupler respectively. The other end of the first resistor group is connected to the primary side high voltage bus, and the controlled end of the optocoupler outputs the dimming voltage DIM.

[0009] The isolated PWM control signal transmission circuit includes a control terminal group, a switch tube, a fourth resistor and a fifth resistor. The control terminal group includes a third resistor group and an optocoupler control terminal.

[0010] One end of the fifth resistor is connected to the control board, and the other end is respectively connected to one end of the fourth resistor and the gate of the switching tube. The other end of the fourth resistor and the source of the switching tube are grounded, and the drain of the switching tube is connected to the low-voltage DC output end of the secondary side of the power supply through the control end group.

[0011] Furthermore, the first resistor group includes at least one resistor. When the first resistor group includes multiple resistors, the resistors are connected in series, in parallel, or in a combination of series and parallel.

[0012] Furthermore, the step-down voltage stabilizing circuit further includes a second resistor, and the controlled end of the optocoupler is connected to the first capacitor via the second resistor, or the controlled end of the optocoupler is connected to the second resistor to output the dimming voltage DIM.

[0013] Furthermore, the drain of the switching tube is connected to the low-voltage DC output end of the secondary side of the power supply through the optocoupler control end and the third resistor group in sequence; or the drain of the switching tube is connected to the low-voltage DC output end of the secondary side of the power supply through the third resistor group and the optocoupler control end in sequence.

[0014] Furthermore, the third resistor group includes at least one resistor. When the third resistor group includes multiple resistors, the resistors are connected in series, in parallel, or in a combination of series and parallel.

[0015] Furthermore, the isolated PWM control signal transmission circuit further includes a second capacitor connected in parallel with the fourth resistor.

[0016] Compared with the prior art, the present invention has the following beneficial effects: the circuit is simple and easy to use, the cost is low, the reliability is high, the applicable VBUS voltage range is wide, and the versatility is strong. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the dimming circuit structure. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] like Figure 1 As shown, a dimming circuit includes: a step-down voltage regulator circuit and an isolated PWM control signal transmission circuit. The step-down voltage regulator circuit is used to provide a first DC voltage. The isolated PWM control signal transmission circuit synchronizes the PWM square wave modulation signal to the primary side of the power board through an optocoupler, and further converts the first DC voltage into a DIM dimming control voltage synchronized with the PWM signal, which is used to be connected to the dimming control pin of the LED driver chip to realize dimming control.

[0020] Specifically, the step-down voltage stabilizing circuit includes a first resistor group, a voltage stabilizing tube ZD1, a first capacitor C1 and an optocoupler controlled terminal N1-B.

[0021] After the Zener diode ZD1 is connected in parallel with the first capacitor C1, the positive electrode is connected to GND-P (primary side reference ground), and the negative electrode is connected to one end of the first resistor group and the optocoupler controlled end N1-B respectively. The other end of the first resistor group is connected to the primary side high-voltage bus voltage VBUS, and the optocoupler controlled end outputs the dimming voltage DIM.

[0022] The first resistor group can consist of one or more resistors connected in series, in parallel, or in a combination of series and parallel, depending on the VBUS voltage range in the actual application and the voltage and power rating of the selected resistors. In this embodiment, three resistors, R1, R2, and R3, are connected in series. Depending on the actual application needs, resistor R4 can be placed before or after the controlled terminal of the optocoupler, or it can be omitted.

[0023] The first capacitor C1 is connected in parallel with the Zener diode ZD1 to maintain the stability of the voltage at the negative electrode of the Zener diode relative to GND-P. The required stable low-voltage DC voltage is obtained from the negative electrode of the Zener diode. The typical value of this DC voltage is equivalent to the nominal voltage specification of the Zener diode. This voltage is used as the high-level reference voltage of the PWM dimming signal.

[0024] The isolated PWM control signal transmission circuit includes a control terminal group, a switch tube Q1, a fourth resistor R6 and a fifth resistor R7. The control terminal group includes a third resistor group and an optocoupler control terminal N1-A.

[0025] One end of the fifth resistor R7 is connected to the control board, and the other end is respectively connected to one end of the fourth resistor R6 and the gate of the switch tube Q1. The other end of the fourth resistor and the source of the switch tube are connected to GND-S (secondary side reference ground). The drain of the switch tube Q1 is connected to the low-voltage DC output voltage VDC on the secondary side of the power supply through the control terminal group.

[0026] Depending on the power rating of the resistors selected in the actual application, the third resistor group can consist of a single resistor, or multiple resistors connected in series, in parallel, or in a combination of series and parallel. The third resistor group can be placed in front of or behind the optocoupler. In this embodiment, the third resistor group uses a single resistor, R5, placed in front of the optocoupler.

[0027] In addition, in this embodiment, a capacitor C2 is provided to filter out interference signals. Whether C2 is installed can be determined based on actual conditions.

[0028] When the PWM dimming signal from the control board is high, the optocoupler control terminal is on, the optocoupler controlled terminal is on, and the dimming voltage DIM is high. When the PWM dimming signal from the control board is low, the optocoupler control terminal is off, the optocoupler controlled terminal is off, and the dimming voltage DIM is low. The dimming voltage DIM can be directly connected to the dimming pin of the LED driver chip, thus implementing PWM dimming control of the primary-side LED driver power supply by the secondary-side control board. The high level of the DIM dimming voltage is close to the first DC voltage, and the low level is close to 0V.

Claims

1. A dimming circuit, characterized in that: include: Buck-type voltage regulator circuit and isolated PWM control signal transmission circuit, The step-down voltage stabilizing circuit includes a first resistor group, a voltage stabilizing tube, a first capacitor and an optocoupler controlled terminal. After the voltage regulator tube is connected in parallel with the first capacitor, the positive electrode is grounded, and the negative electrode is connected to one end of the first resistor group and the controlled end of the optocoupler respectively. The other end of the first resistor group is connected to the primary side high voltage bus, and the controlled end of the optocoupler outputs the dimming voltage DIM. The isolated PWM control signal transmission circuit includes a control terminal group, a switch tube, a fourth resistor and a fifth resistor. The control terminal group includes a third resistor group and an optocoupler control terminal. One end of the fifth resistor is connected to the control board, and the other end is respectively connected to one end of the fourth resistor and the gate of the switching tube. The other end of the fourth resistor and the source of the switching tube are grounded, and the drain of the switching tube is connected to the low-voltage DC output end of the secondary side of the power supply through the control end group.

2. A dimming circuit according to claim 1, characterized in that: The first resistor group includes at least one resistor. When the first resistor group includes multiple resistors, the resistors are connected in series, in parallel, or in a combination of series and parallel.

3. The dimming circuit according to claim 1, wherein: The step-down voltage stabilizing circuit further includes a second resistor, and the controlled end of the optocoupler is connected to the first capacitor via the second resistor, or the controlled end of the optocoupler is connected to the second resistor to output the dimming voltage DIM.

4. The dimming circuit according to claim 1, wherein: The drain of the switch tube is connected to the low-voltage DC output terminal of the secondary side of the power supply through the optocoupler control terminal and the third resistor group in sequence; or the drain of the switch tube is connected to the low-voltage DC output terminal of the secondary side of the power supply through the third resistor group and the optocoupler control terminal in sequence.

5. A dimming circuit according to claim 4, characterized in that: The third resistor group includes at least one resistor. When the third resistor group includes multiple resistors, the resistors are connected in series, in parallel, or in a combination of series and parallel.

6. A dimming circuit according to any one of claims 1 to 5, characterized in that: The isolated PWM control signal transmission circuit further includes a second capacitor connected in parallel with the fourth resistor.

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