High-stability LED blanking circuit

Abstract

This invention relates to the field of LED driving technology, specifically a high-stability LED blanking circuit. Its key feature is the inclusion of a first level shifting circuit and a second level shifting circuit. The input terminal of both the first and second level shifting circuits is connected to a reference voltage VREF. When the lower blanking enable switch is closed, the first level shifting circuit clamps the voltage at one end of the LED corresponding to the ground terminal of the LED driving circuit, thereby ensuring that the voltage drop across the LED is lower than its on-state voltage drop. Similarly, when the upper blanking enable switch is closed, the second level shifting circuit clamps the voltage at one end of the LED corresponding to the VDD terminal of the LED driving circuit, again ensuring that the voltage drop across the LED is lower than its on-state voltage drop. This blanking circuit does not shorten the LED's lifespan and provides stable blanking functionality.

Description

Technical Field

[0001] This invention relates to the field of LED driving technology, specifically a high-stability LED blanking circuit. Background Technology

[0002] LED display drivers have been widely used in various fields, including white goods, small appliances, smart homes, and outdoor display lights.

[0003] Common array-type LED display driver circuits such as Figure 1 The three types are shown. The first type is as follows: Figure 1 The left side shows a switch with constant current at the upper port and scanning at the lower port; the second type is as follows... Figure 1 The middle one shows a constant current switch at the lower port and a scanning switch at the upper port; the third type is as follows... Figure 1 As shown on the right, this includes both upper-port scanning and lower-port scanning types, generally referred to as a constant-voltage array LED driver structure. Due to parasitic capacitance and inductance, array LED display driver circuits accumulate charge when the corresponding display is off. A single unidirectional control signal can enable this charge (in a very small amount), causing a weak current to flow through the LEDs, resulting in a slight illumination of LEDs that shouldn't be lit. To avoid this phenomenon, blanking is required in the array LED display driver circuit. There are two common blanking methods: one is simpler, directly connecting the LED to an inverted potential when off. For example, if the value is high when active, connect it to ground when off; if it's low when active, connect it to the power supply. The other method is to set a reference potential and connect the port to that potential when off. Alternatively, one end can be blanked while the other remains untreated.

[0004] Currently, taking an array-type LED display driver circuit with constant current output (high-level enable) and scanning port (low-level enable) as an example, two blanking structures are shown below: Figure 2 As shown. Figure 2 The circuit on the left operates as follows: at the upper port A, when display data control is valid, the upper blanking enable is off; when display data control is invalid, the upper blanking enable is closed, pulling upper port A low. At the lower port B, when scan control is valid, the lower blanking enable is off; when scan control is invalid, the lower blanking enable is closed, pulling lower port B high. This structure is very simple and practical. However, when both ends of the LED are in blanking mode, a severe negative voltage exists. Taking 5V as an example, when both ends of the LED are in blanking mode, there will be a negative voltage of -5V. If the LED is subjected to a negative voltage exceeding -2V for a long time, its lifespan will be drastically shortened. Therefore, this blanking structure will shorten the lifespan of the LED. Figure 2The circuit on the right operates as follows: when the display data control or scan control signal is invalid, the upper blanking enable or lower blanking enable closes, connecting port A or B to the upper blanking reference voltage or the lower blanking reference voltage. The disadvantage of this structure is that because multiple ports share a single reference voltage, the opening or closing of multiple switches or several switches can cause an impact on the reference voltage, leading to abnormal blanking function. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a highly stable LED blanking circuit that does not shorten the lifespan of the LED and has a stable blanking function.

[0006] To solve the above problems, the following technical solutions are provided:

[0007] The high-stability LED blanking circuit of this invention is characterized by including a first level shifting circuit and a second level shifting circuit. The output of the first level shifting circuit is connected to one end of the LED corresponding to the ground terminal of the LED driver circuit via a lower blanking enable switch, and the input of the first level shifting circuit is connected to a reference voltage VREF. The output of the second level shifting circuit is connected to one end of the LED corresponding to the VDD terminal of the LED driver circuit via an upper blanking enable switch, and the input of the second level shifting circuit is connected to the reference voltage VREF. The first level shifting circuit is used to clamp the voltage at one end of the LED corresponding to the ground terminal of the LED driver circuit when the lower blanking enable switch is closed, thereby ensuring that the voltage drop across the LED is lower than its forward voltage drop. The second level shifting circuit is used to clamp the voltage at one end of the LED corresponding to the VDD terminal of the LED driver circuit when the upper blanking enable switch is closed, thereby ensuring that the voltage drop across the LED is lower than its forward voltage drop.

[0008] The first level shifting circuit shifts the reference voltage VREF upward by a value of A1; the second level shifting circuit shifts the reference voltage VREF downward by a value of A2.

[0009] The value of A1 + A2 ≤ 2V.

[0010] The charging terminal of the first level shift circuit is connected to a current source I1, and the discharging terminal of the first level shift circuit is connected to a current source I2. The current source I1 is used to charge the output terminal of the first level shift circuit, and the current source I2 is used to discharge the current of the first level shift circuit, ensuring that the voltage at the output terminal of the first level shift circuit is not fed back to the input terminal.

[0011] The charging terminal of the second level shift circuit is connected to a current source I3, and the discharging terminal of the first level shift circuit is connected to a current source I4. Current source I4 is used to discharge the output terminal of the second level shift circuit, and current source I3 is used to charge the second level shift circuit, ensuring that the output voltage of the second level shift circuit is not fed back to the input terminal.

[0012] The above approach has the following advantages:

[0013] Because the output of the first level shift circuit of the high-stability LED blanking circuit of this invention is connected to the LED end corresponding to the ground terminal of the LED driver circuit through the lower blanking enable switch, and the input of the first level shift circuit is connected to the reference voltage VREF, and the output of the second level shift circuit is connected to the LED end corresponding to the VDD terminal of the LED driver circuit through the upper blanking enable switch, and the input of the second level shift circuit is connected to the reference voltage VREF, the first level shift circuit is used to clamp the voltage of the LED end corresponding to the ground terminal of the LED driver circuit when the lower blanking enable switch is closed, thereby ensuring that the voltage drop across the LED is lower than its on-state voltage drop. The second level shift circuit is used to clamp the voltage of the LED end corresponding to the VDD terminal of the LED driver circuit when the upper blanking enable switch is closed, thereby ensuring that the voltage drop across the LED is lower than its on-state voltage drop. This circuit, by utilizing the first level shift circuit, the second level shift circuit, and the reference voltage VREF, can ensure that the LED is not under a negative voltage of -2V, thus not affecting the lifespan of the LED. Moreover, under the action of the level shifting circuit, the two ends of the LED are isolated from the reference voltage VREF, so that the reference voltage VREF will not be affected by the changes of other port switches, thus ensuring the stability of blanking. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of an array-type LED display driver circuit;

[0015] Figure 2 This is a circuit diagram of the blanking structure in the background technology;

[0016] Figure 3 This is a schematic diagram of the high-stability LED blanking circuit of the present invention;

[0017] Figure 4 This is a schematic diagram of the first level displacement circuit;

[0018] Figure 5 This is a schematic diagram of the second level displacement circuit. Detailed Implementation

[0019] The following is in conjunction with the appendix Figure 3-5 The present invention will be further described in detail with reference to the embodiments.

[0020] The high-stability LED blanking circuit of the present invention includes a first level shifting circuit and a second level shifting circuit. The output terminal of the first level shifting circuit is connected to one end of the LED corresponding to the ground terminal of the LED driver circuit through a lower blanking enable switch, and the input terminal of the first level shifting circuit is connected to a reference voltage VREF. The output terminal of the second level shifting circuit is connected to one end of the LED corresponding to the VDD terminal of the LED driver circuit through an upper blanking enable switch, and the input terminal of the second level shifting circuit is connected to the reference voltage VREF.

[0021] The first level shift circuit is used to clamp the voltage at one end of the LED corresponding to the ground terminal of the LED driver circuit when the lower blanking enable switch is closed, thereby ensuring that the voltage drop across the LED is lower than its on-state voltage drop. The first level shift circuit shifts the reference voltage VREF upward by a value of A1.

[0022] like Figure 4 As shown, the charging terminal of the first level shifting circuit is connected to a current source I1, and the discharging terminal of the first level shifting circuit is connected to a current source I2. Current source I1 is used to charge the output terminal of the first level shifting circuit, and current source I2 is used to discharge the current of the first level shifting circuit, ensuring that the output voltage of the first level shifting circuit is not fed back to the input terminal.

[0023] Current source I1 is the current source that sustains the operation of the level shifting circuit, and its current is generally small. Current source I2 is the discharge current source; in steady state, the current is equal to that of current source I1, but it has a large current fluctuation margin.

[0024] The upper shift circuit takes an input reference voltage VREF and an upper shift voltage ΔA1. In steady state, the output voltage is VREF + ΔA1. When the output voltage is lower than VREF + ΔA1, current source I2 decreases, and current source I1 charges the output terminal. When the output voltage is higher than VREF + ΔA1, current source I2 increases, discharging the current. The output voltage is not fed back to the input port; it is regulated by the current source I2.

[0025] The first level shift circuit is used for lower blanking. Since the LED terminal corresponding to the ground terminal of the LED driver circuit is turned off, this port enters a high-impedance state. However, it contains stored charges such as parasitic capacitance and inductance. Furthermore, the LED terminal corresponding to the ground terminal of the LED driver circuit is at a low level when operating. Therefore, under normal circumstances, the upper shift circuit charges the port using current source I1, gradually raising the voltage to VREF+ΔA1 and maintaining it. However, if a momentary upward overshoot occurs at the port, current source I2 is needed to discharge the voltage, reducing it to VREF+ΔA1.

[0026] The second level shift circuit is used to clamp the voltage at one end of the LED corresponding to the VDD terminal of the LED driver circuit when the upper blanking enable switch is closed, thereby ensuring that the voltage drop across the LED is lower than its on-state voltage drop. The second level shift circuit shifts the reference voltage VREF downward by a value of A2.

[0027] like Figure 5 As shown, the charging terminal of the second level shift circuit is connected to current source I3, and the discharging terminal of the first level shift circuit is connected to current source I4. Current source I4 is used to discharge the output terminal of the second level shift circuit, and current source I3 is used to charge the second level shift circuit, ensuring that the output voltage of the second level shift circuit is not fed back to the input terminal.

[0028] Current source I4 is the current source that sustains the operation of the level shifting circuit, and its current is generally small. Current source I3 is the discharge current source; in steady state, the current is equal to that of current source I4, but there is a large current fluctuation margin.

[0029] The second level shift circuit takes an input reference voltage VREF and shifts the voltage down by ΔA2. In steady state, the output voltage is VREF - ΔA2. When the output voltage is higher than VREF - ΔA2, current source I1 discharges at the output terminal, and the current injected by current source I2 decreases. When the output voltage is lower than VREF - ΔA2, current source I2 increases, charging the input port and raising its voltage. The output voltage is not fed back to the input port; it is regulated by the current source I2.

[0030] The second level shift circuit is used for upper blanking. Since the LED terminal corresponding to the VDD terminal of the LED driver circuit is turned off, it enters a high-impedance state. However, it contains stored charges such as parasitic capacitance and inductance. Furthermore, the LED terminal corresponding to the VDD terminal of the LED driver circuit is at a high level during operation. Therefore, under normal circumstances, the second level shift circuit discharges the port using current source I4, gradually reducing the voltage to VREF-ΔA2 and maintaining it. However, if a momentary downward overshoot occurs at the port, it needs to be charged by current source I3 to raise the voltage to Vref-ΔA2.

[0031] In this embodiment, considering the suppression of negative pressure and the pressure difference that may be caused after clamping, it is necessary to ensure that A1+A2≤2V.

[0032] The following is a detailed description of the invention using an LED driver circuit with constant current output (high-level enable) at the upper port and scanning port (low-level enable) at the lower port as an example.

[0033] like Figure 3As shown, the low-level enabled LED driver circuit includes a power supply VDD, an LED constant current driver 1, and a scan control switch 3. The power supply VDD is connected to the LED constant current driver 1 to provide power. The LED constant current driver 1 converts the increased electrical energy from the power supply VDD into the driving voltage and current of the LED and outputs a constant current. The output port of the LED constant current driver 1 is the LED end corresponding to the VDD terminal of the LED driver circuit, i.e., terminal A. One end of the scan control switch 3 is the LED end corresponding to the ground terminal of the LED driver circuit, i.e., terminal B. The other end of the scan control switch 3 is grounded. In use, the LED is connected between terminals A and B. The LED constant current driver 1 is used for display data control (high-level enabled), and the scan control switch 3 is used for scan control (low-level enabled).

[0034] like Figure 3 As shown, the high-stability LED blanking circuit of this embodiment includes a first level shifting circuit 4 and a second level shifting circuit 5. The output terminal of the first level shifting circuit 4 is terminal C, and the input terminal of the first level shifting circuit 4 is connected to the reference voltage VREF. The output terminal of the second level shifting circuit 5 is terminal D, and the input terminal of the second level shifting circuit 5 is connected to the reference voltage VREF. Terminal B is connected to terminal C through a lower blanking enable switch 6, and terminal A is connected to terminal D through an upper blanking enable switch 2. The first level shifting circuit 4 shifts the reference voltage VREF upward by a value of A1. The second level shifting circuit 5 shifts the reference voltage VREF downward by a value of A2.

[0035] After the lower blanking enable switch 6 is closed, the voltage at point C will be clamped near VREF+A1, which is equal to VREF+A1.

[0036] After the upper blanking enable switch 2 is closed, the voltage at point D will be clamped near VREF-A2, which is equal to VREF-V2.

[0037] Due to the effect of the level shifting circuit, the voltages at points C and D are physically blocked and will not directly backflow to the reference voltage VFEF terminal. When multiple level shifting circuits share a single reference voltage, the reference voltage will not be affected by the switching changes of other ports.

[0038] When the blanking enable switch 2 is turned on and port B is active, the voltage at point D ensures that the LED cannot be lit normally. For example, in a typical RGB (red, green, blue) LED, the on-state voltage drop of the R (red) LED is the lowest, usually 1.8V. Therefore, Vref-A2 < 1.8V.

[0039] When the blanking enable switch 6 is closed, port A is effective, and the voltage at point C ensures that the LED cannot be lit normally. For example, in a typical RGB (red, green, blue) LED, the on-state voltage drop of the R (red) LED is the lowest, usually 1.8V, so VDD-(Vref+A1)<1.8V.

[0040] When powered by 5V and using LEDs of the above specifications, Vref-A2 can be set to 1.5V and Vref+A1 can be set to 3.5V. In this case, both the lifespan of the LED and the high stability of the blanking function are ensured.

[0041] This invention discharges charge through a level shifting circuit with a current channel. The implementation scheme is simple and reliable, and it does not affect the reference voltage or cause abnormal blanking function. By preset the level shifting potential, the negative voltage range is controlled without affecting the lifespan of the LED.

Claims

1. A high-stability LED blanking circuit, characterized in that, The system includes a first level shift circuit and a second level shift circuit. The output of the first level shift circuit is connected to one end of the LED corresponding to the ground terminal of the LED driver circuit via a lower blanking enable switch, and the input of the first level shift circuit is connected to a reference voltage VREF. The output of the second level shift circuit is connected to one end of the LED corresponding to the VDD terminal of the LED driver circuit via an upper blanking enable switch, and the input of the second level shift circuit is connected to a reference voltage VREF. The first level shift circuit is used to clamp the voltage at one end of the LED corresponding to the ground terminal of the LED driver circuit when the lower blanking enable switch is closed, thereby ensuring that the voltage drop across the LED is lower than its forward voltage drop. The second level shift circuit is used to clamp the voltage at one end of the LED corresponding to the VDD terminal of the LED driver circuit when the upper blanking enable switch is closed, thereby ensuring that the voltage drop across the LED is lower than its forward voltage drop. The first level shifting circuit shifts the reference voltage VREF upward by a value of A1; the second level shifting circuit shifts the reference voltage VREF downward by a value of A2; and A1 + A2 ≤ 2V.

2. The high-stability LED blanking circuit as described in claim 1, characterized in that, The charging terminal of the first level shift circuit is connected to a current source I1, and the discharging terminal of the first level shift circuit is connected to a current source I2. The current source I1 is used to charge the output terminal of the first level shift circuit, and the current source I2 is used to discharge the current of the first level shift circuit, ensuring that the voltage at the output terminal of the first level shift circuit is not fed back to the input terminal.

3. The high-stability LED blanking circuit as described in claim 1, characterized in that, The charging terminal of the second level shift circuit is connected to a current source I3, and the discharging terminal of the first level shift circuit is connected to a current source I4. The current source I4 is used to discharge the output terminal of the second level shift circuit, and the current source I3 is used to charge the second level shift circuit, ensuring that the output voltage of the second level shift circuit is not fed back to the input terminal.

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