Fast starting circuit and driving chip for common cathode LED display screen
By designing a fast-start circuit and a detection control module, the problem of long turn-on time for common-cathode LED display switches was solved, achieving fast startup and improving display effect and power stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHENGDU LIPPXIN MICROELECTRONIC CO LTD
- Filing Date
- 2023-11-06
- Publication Date
- 2026-06-02
Smart Images
Figure CN117437876B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of integrated circuit technology, and in particular to a fast start-up circuit and driver chip for a common-cathode LED display. Background Technology
[0002] Figure 1 This is a common common-anode constant current source driver chip, comprising: a reference current generation circuit, a bias generation circuit, and N constant current source output channels. The reference current generation circuit generates a reference current I0. PM0 and PM1 form a current mirror, outputting a current I1 proportional to the reference current I0. NM_C0 and NM1 also form a current mirror. If the switching transistor NM_C1 of the constant current output channel is turned on, that constant current output channel will output an output current IOUT proportional to I1, thus lighting the LED.
[0003] However, the NM_C1 is relatively large and has large parasitic capacitance. If only the amplifier AMP_C is used to drive it, the NM_C1 will turn on slowly and for a long time, thus affecting the display effect.
[0004] Similarly, for common cathode LED displays, such as Figure 2 As shown, the switching transistor PM_C1 in the constant current output channel has the same problem. Due to its large parasitic capacitance, PM_C1 requires a large current to turn on, which will result in a long turn-on time for PM_C1 and affect the display effect.
[0005] Therefore, how to quickly open the constant current output channel of the constant current driver chip adapted to the common cathode display has become an urgent problem to be solved. Summary of the Invention
[0006] Therefore, it is necessary to provide a fast start-up circuit and driver chip for a common-cathode LED display to address the above-mentioned technical problems, thereby solving the problem that the long discharge time of parasitic capacitance in the prior art leads to a long turn-on time of the switching transistor.
[0007] In a first aspect, this application provides a fast start-up circuit for a common-cathode LED display screen, comprising:
[0008] The fast start module is used to discharge the control terminal of the switching transistor of the constant current output channel when the channel start signal is valid, and to stop discharging after receiving the stop signal.
[0009] The detection control module is used to output a stop signal when the detected current is greater than a preset threshold; where the detected current represents the control terminal potential of the switching transistor.
[0010] Furthermore, the fast start module includes: a switching unit and a first current unit;
[0011] The switching unit closes when the channel open signal is valid and before a stop signal is received;
[0012] The first current unit is used to discharge the control terminal of the switching transistor after the switching unit is closed.
[0013] Furthermore, the detection control module includes: a logic unit, a detection unit, and a control unit;
[0014] The logic unit is used to control the switching unit to open or close based on the channel open signal and the detection terminal signal;
[0015] The detection unit is used to convert the control terminal voltage of the switching transistor into a detection current, and output a detection terminal signal that represents the magnitude of the detection current and the preset threshold through the detection terminal;
[0016] The control unit is used to reset the detection terminal signal to a low level when the channel open signal is invalid.
[0017] Furthermore, the detection unit includes: a second current unit and a first transistor;
[0018] The output terminal of the second current unit is grounded, and the input terminal is connected to the second terminal of the first transistor. The connection point serves as the detection terminal to output the detection terminal signal.
[0019] The control terminal of the first transistor is connected to the control terminal of the switching transistor, and the first terminal of the first transistor is connected to the power supply voltage.
[0020] or,
[0021] The detection unit includes: a second current unit, a first transistor, and a second transistor;
[0022] The output terminal of the second current unit is grounded, and the input terminal is connected to the second terminal of the first transistor. The connection point serves as the detection terminal to output the detection terminal signal.
[0023] The control terminal of the first transistor is connected to the control terminal of the switching transistor.
[0024] When the channel enable signal is valid, the second transistor connects the first terminal of the first transistor to the power supply voltage.
[0025] Furthermore, the control unit includes a third transistor;
[0026] The third transistor has its first terminal connected to the detection terminal and its second terminal grounded. The control terminal receives the inverse signal of the channel enable signal so as to reset the potential of the detection terminal to a low level when the channel enable signal is invalid.
[0027] Furthermore, the first current unit is also used to control the potential of the control terminal of the switching transistor before the fast start module receives the stop signal, so as to avoid the potential of the control terminal of the switching transistor exceeding the limit.
[0028] Furthermore, the first current unit includes: a fourth transistor, a fifth transistor, a sixth transistor, and a reference current generating circuit;
[0029] The fourth and fifth transistors form a current mirror;
[0030] The reference current generating circuit, the fifth transistor, and the sixth transistor are connected in series between the power supply voltage and ground.
[0031] The first terminal of the fourth transistor is electrically connected to the control terminal of the switching transistor, and the second terminal is electrically connected to the switching unit.
[0032] The control terminal of the sixth transistor is shorted to the first terminal, and the second terminal of the sixth transistor is connected to a high level.
[0033] The reference current generating circuit is used to generate the current in the input branch of the current mirror.
[0034] Furthermore, the switching unit includes a seventh transistor;
[0035] The seventh transistor, controlled by the output signal of the logic unit, controls whether the first current unit discharges the control terminal of the switching transistor.
[0036] Furthermore, the switching unit includes a seventh transistor and an eighth transistor connected in series;
[0037] The seventh transistor is controlled by the second output signal of the logic unit to be turned on after the detection terminal signal is reset and before the detection current is greater than a preset threshold.
[0038] The eighth transistor is controlled by the first output signal of the logic unit to conduct when the channel enable signal is valid.
[0039] Furthermore, the logic unit includes: NOT gate and NOR gate;
[0040] The input of the NOT gate receives the channel enable signal, and its output is connected to the first input of the NOR gate.
[0041] The second input of the NOR gate receives the detection signal, and the output is connected to the control terminal of the seventh transistor.
[0042] Furthermore, the logic unit includes a first inverter;
[0043] The logic unit directly outputs the channel open signal as the first output signal, and inverts the detection signal through the first inverter to output the second output signal.
[0044] Secondly, this application also provides a driver chip for a common-cathode LED display screen, comprising: a constant current source driver circuit for outputting a constant current through a constant current output channel; and a fast start-up circuit for the common-cathode LED display screen as described in the first aspect, wherein the output terminal of the fast start-up circuit is electrically connected to the control terminal of the switching transistor of the constant current output channel of the constant current source driver circuit.
[0045] The advantages of this application are:
[0046] This application sets up a fast start-up circuit to quickly discharge the parasitic capacitor in the early stage of the channel turn-on signal, thereby quickly lowering the gate potential of the switch PM_C1 of the constant current source output channel and turning on PM_C1. Without increasing power consumption, it speeds up the turn-on of PM_C1 and improves the display effect. Attached Figure Description
[0047] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0049] Figure 1 A schematic diagram of a constant current drive chip for a common anode LED display screen provided for related technologies;
[0050] Figure 2 A schematic diagram of a constant current drive chip for a common cathode LED display provided for related technologies;
[0051] Figure 3 This is a schematic diagram of a fast start circuit in one embodiment of this application;
[0052] Figure 4 This is a schematic diagram of a fast-start circuit module in one embodiment of this application;
[0053] Figure 5 This is a schematic diagram of a fast startup module in one embodiment of this application;
[0054] Figure 6 This is a schematic diagram of the detection control module in one embodiment of this application;
[0055] Figure 7 This is a circuit diagram of the detection unit in one embodiment of this application;
[0056] Figure 8 This is a circuit diagram of the detection unit in another embodiment of this application;
[0057] Figure 9 This is a circuit diagram of the control unit in one embodiment of this application;
[0058] Figure 10 This is a framework diagram of a logic unit in one embodiment of this application;
[0059] Figure 11 This is a circuit diagram of a logic unit in one embodiment of this application;
[0060] Figure 12 This is a framework diagram of a logic unit in another embodiment of this application;
[0061] Figure 13 This is a circuit diagram of a logic unit in another embodiment of this application;
[0062] Figure 14 This is a circuit diagram of the first current unit in one embodiment of this application;
[0063] Figure 15 This is a schematic diagram of a driver chip for a common-cathode LED display screen provided in one embodiment of this application. Detailed Implementation
[0064] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.
[0065] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.
[0066] When using the terms “including,” “having,” and “comprising” as described herein, another component may be added unless explicitly qualifying terms such as “only,” “consisting of,” etc. are used. Unless otherwise stated, singular terms may include plural forms and should not be construed as having a quantity of one.
[0067] It should be understood that although the terms “first,” “second,” etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, without departing from the scope of this application, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.
[0068] In this application, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a direct connection or an indirect connection through an intermediate medium, or they can refer to the internal connection of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.
[0069] Please see Figure 3-4 In some embodiments, this application provides a fast start-up circuit 100 for a common-cathode LED display screen, comprising:
[0070] The fast start module 101 is used to discharge the control terminal of the switching transistor of the constant current output channel 200 when the channel start signal is valid, and to stop discharging after receiving the stop signal.
[0071] The detection control module 102 is used to output a stop signal when the detection current (Id) is greater than a preset threshold (Iref); wherein the aforementioned detection current (Id) represents the control terminal potential (VGate magnitude) of the switching transistor.
[0072] Preferably, the channel activation signal is a PWM (Pulse Width Modulation) signal, also known as a pulse width adjustment signal. Specifically, when PWM is high, it indicates that the switch of the constant current output channel needs to be closed to activate the constant current output channel and output a constant current to light up the LED. The width of the high PWM level indicates the LED's illumination time.
[0073] When the channel enable signal is valid (e.g., PWM is high), it indicates that a constant current needs to be output to light up the LED. In this application, the control terminal of the switching transistor is only controlled by the first current I1 during the initial stage of the channel enable signal being valid (e.g., ...). Figure 3 The PM_C1 gate discharges, accelerating the pull-down of the VGate potential. This acceleration phase occurs after the channel enable signal is valid and before the stop signal is received. The stop signal is output after the current (detection current) representing the VGate potential exceeds a preset threshold (the actual VGate potential is less than a preset value).
[0074] Compared to using a comparator (which results in a large chip area, slow system response, and large hysteresis) to directly compare the VGate potential with a preset voltage, this application determines when to stop using the fast start-up circuit to discharge the gate of the switching transistor by comparing the current. The advantage is that it greatly saves chip area and improves response speed.
[0075] In one implementation, such as Figure 5 The fast start module 101 includes: a switching unit 1012 and a first current unit 1011;
[0076] The switching unit 1012 is closed when the channel enable signal (e.g., PWM signal) is valid and before a stop signal is received;
[0077] The first current unit 1011 is used to discharge the control terminal of the switching transistor (through the first current I1) after the switching unit 1012 is closed.
[0078] The switching unit 1012 switches on and off in response to the channel open and stop signals. It closes initially when the channel open signal is valid, ensuring that the fast start module 101 can pull down the control terminal potential VGate of the switching transistor through the first current unit 1011 during the initial valid state of the channel open signal, thereby accelerating the opening of the constant current output channel. After the detection control module 102 detects that the detection current exceeds a preset threshold, it sends a stop signal to the switching unit 1012 of the fast start module 101, disconnecting the switching unit 1012 and stopping the discharge of the control terminal of the switching transistor using the first current unit 1011. It should be noted that for a period of time afterward, the channel open signal remains high, but the fast start circuit no longer pulls down the control terminal of the switching transistor.
[0079] In one implementation, such as Figure 6 The detection control module 102 includes: a logic unit 1021, a detection unit 1022, and a control unit 1023;
[0080] The logic unit 1021 is used to control the switching unit 1012 to turn on or off (by outputting the SW signal) according to the channel enable signal (e.g., PWM) and the detection terminal signal (V1);
[0081] The detection unit 1022 is used to convert the control terminal voltage (VGate) of the switching transistor into a detection current (Id), and output a detection terminal signal (V1) that represents the magnitude of the detection current (Id) and a preset threshold (Iref) through the detection terminal.
[0082] The control unit 1023 is used to reset the detection terminal signal (V1) to a low level when the channel open signal is invalid.
[0083] When the channel open signal is valid and the detection terminal signal V1 is invalid (e.g., low), the output signal of the logic unit 1021 will control the switch unit 1012 to close; when the detection terminal signal V1 becomes valid (e.g., high), that is, after the detection current is greater than the preset threshold, the output signal of the logic unit 1021 (i.e., the output stop signal) will control the switch unit 1012 to open.
[0084] As mentioned above, this application compares the detection current (Id) with a preset threshold (Iref), which is essentially comparing the relationship between VGate and a preset voltage. To achieve this comparison, the detection unit 1022 first converts VGate into a detection current (Id) that can characterize its magnitude, and then compares the detection current (Id) with the preset threshold (Iref).
[0085] In this application, the detection unit 1022 can operate after the channel open signal is valid (i.e., perform the aforementioned voltage and current conversion and comparison). An enable unit can be provided to enable the aforementioned detection unit 1022 to start operating and perform the aforementioned voltage and current conversion and comparison when the channel open signal is valid.
[0086] In one implementation, such as Figure 7 The detection unit 1022 includes: a second current unit Iref and a first transistor PM1;
[0087] The output terminal of the second current unit Iref is grounded to GND, and its input terminal is connected to the second terminal of the first transistor PM1. The connection point serves as the detection terminal to output the detection terminal signal (V1).
[0088] The control terminal of the first transistor PM1 is connected to the control terminal of the switching transistor (potential is VGate), and the first terminal of the first transistor PM1 is connected to a high level (e.g., power supply voltage VDD).
[0089] When the channel open signal is valid, VGate will be gradually pulled low. During the process of VGate decreasing, PM1 will gradually open, the current Id flowing through PM1 will gradually increase, and the detection terminal voltage V1 will change. When Id is greater than Iref (which can be considered as VGate decreasing to a preset voltage), V1 will become high. After the logic unit 1021 receives this high level, it will output a stop signal to stop pulling down the control terminal voltage VGate of the switching transistor.
[0090] In another embodiment, such as Figure 8 The detection unit 1022 includes the aforementioned enabling unit, and the detection unit 1022 includes: a second current unit Iref, a first transistor PM1, and a second transistor PM2;
[0091] The output terminal of the second current unit Iref is grounded, and its input terminal is connected to the second terminal of the first transistor PM1. The connection point serves as the detection terminal to output the detection terminal signal V1.
[0092] The control terminal of the first transistor PM1 is connected to the control terminal (potential VGate) of the switching transistor;
[0093] When the channel enable signal is valid, the second transistor PM2 connects the first terminal of the first transistor PM1 to the power supply voltage VDD. At this time, the second transistor PM2 is between the power supply voltage VDD and the first transistor PM1.
[0094] However, in practice, the second transistor PM2 can also be positioned between the first transistor PM1 and the second current unit Iref. That is, the second transistor PM2 can be positioned between the first transistor PM1 and the second current unit Iref. Figure 8 The positions of the first transistor PM1 and the second transistor PM2 are interchanged.
[0095] In this embodiment, by setting a second transistor PM2 (enable unit), it can be ensured that the detection unit 1022 only compares the detection current with the preset threshold when the channel open signal is valid, which can reduce power consumption. This will be described in detail later in this application.
[0096] In one implementation, such as Figure 9 The control unit 1023 includes a third transistor NM1;
[0097] The third transistor NM1 has its first terminal connected to the detection terminal (V1) and its second terminal grounded to GND. The control terminal receives the inverse signal of the channel enable signal (e.g., PWMN) to reset the detection terminal potential V1 to a low level, such as ground voltage GND, when the channel enable signal is invalid (e.g., PWM=0).
[0098] In the embodiments of this application, when the channel enable signal is invalid, V1 remains at a low level. When the channel enable signal is valid, the first transistor PM1 of the detection unit 1022 gradually begins to conduct, and the present current (Id) gradually increases, thereby causing V1 to change (gradually increase). V1 can characterize the relationship between the detected current (Id) and a preset threshold. When Id exceeds Iref, V1 becomes a high level, at which point fast startup can be stopped, i.e., the fast startup circuit stops pulling down the control terminal potential of the switch transistor.
[0099] In one embodiment, the first current unit 1011 is further configured to control the voltage (VGate) of the switch control terminal before the fast start module 101 receives the stop signal, so as to avoid the voltage of the switch control terminal exceeding the limit.
[0100] It should be noted that "exceeding the limit" can refer to a value that is not lower than a certain value, or that is not too low or too small.
[0101] In this application, the detection control module 102 determines the magnitude of the detection current and the preset threshold (essentially, whether the VGate voltage has reached the preset value) to stop the fast-start circuit from pulling down VGate, which can prevent the VGate voltage from exceeding a certain value to some extent. However, when the fast start is too fast or there are other interferences, the detection control module 102 may not have enough time to react, and the VGate voltage will be pulled very low. Since the switching transistor of the common-cathode LED display is a PMOS, an excessively low VGate voltage will cause the constant current output channel to have an excessively large output current, which will affect the power supply.
[0102] Therefore, before the fast start module 101 receives the stop signal (i.e. before the detection control module 102 normally compares and finds that the detection current exceeds the preset threshold Iref), it is necessary to use certain technical means to keenly capture the changes in VGate voltage, and adaptively control and adjust it to avoid sudden or instantaneous low VGate voltage.
[0103] Based on this, such as Figure 14 A first current unit 1011 of this application includes: a fourth transistor PM4, a fifth transistor PM5, a sixth transistor PM6, and a reference current generating circuit I0;
[0104] The fourth transistor PM4 and the fifth transistor PM5 form a current mirror;
[0105] The reference current generating circuit, the fifth transistor PM5, and the sixth transistor PM6 are connected in series between ground and the power supply voltage.
[0106] The first terminal of the fourth transistor PM4 is electrically connected to the control terminal of the switching transistor, and the second terminal is electrically connected to the switching unit.
[0107] The control terminal and the first terminal of the sixth transistor PM6 are shorted together, and the second terminal is connected to a high-level voltage, such as the power supply voltage VDD.
[0108] The reference current generating circuit is used to generate the current I0 in the input branch of the current mirror.
[0109] The current I0 is the current flowing through PM5, while in this application, the first current unit 1011 can generate a first current I1 (i.e. the current flowing through PM4) that is a mirror image of the current I0.
[0110] VGate is gradually pulled down by I1, meaning the source potential of PM4 will gradually decrease. Since the gate potential of PM4 is VDD-VGS... (PM6) -VGS (PM5) If W is a fixed value, then the source potential (VGate) of PM4 will be at least at W + VTH. (PM4)Nearby, including VTH (PM4) To ensure a minimum turn-on voltage that allows current to flow between the source and drain of PM4, VGate will not be pulled too low. For example... Figure 3 Since the switching transistor PM_C1 of the constant current output channel is a P-type transistor, a low VGate will cause the output current of the constant current output channel to be too large, causing a surge in the power supply. Therefore, the circuit of this embodiment ( Figure 14 This ensures that VGate will not be pulled too low, thus preventing excessive current output from the constant current output channel and avoiding impact on the power supply, which is beneficial to the stability of the power supply.
[0111] In other words, the solution in this embodiment ensures that VGate is pulled down to near the turn-on potential of the constant current output channel's switching transistor PM_C1, thereby guaranteeing rapid startup of the switching transistor. Simultaneously, it prevents VGate from being pulled down too low, which could result in excessive current output through the switching transistor and cause a surge in power supply voltage. Therefore, it ensures both rapid startup and power supply stability.
[0112] In one implementation, such as Figure 10 The switching unit 1012 of this application includes a seventh transistor NM2;
[0113] The seventh transistor NM2 is controlled by the output signal SW of the logic unit 1021 to control whether the first current unit 1011 discharges the control terminal of the switching transistor.
[0114] In this embodiment, when the seventh transistor NM2 is turned on, the VGate potential will be rapidly pulled down through NM2 and I1.
[0115] In one implementation, such as Figure 11 The logic unit 1021 includes: NOT gate and NOR gate;
[0116] The input of the NOT gate receives the channel enable signal, and its output is connected to the first input of the NOR gate.
[0117] The second input of the NOR gate receives the detection signal V1, and the output is connected to the control terminal of the seventh transistor NM2.
[0118] This logic unit 1021 enables control such as when the channel enable signal is valid and the detection signal V1 is invalid (low level). Figure 10 The switch unit shown is closed (seventh transistor NM2 is turned on), and when the channel open signal is invalid or the detection terminal signal V1 flips to high, the control is as follows: Figure 10 The switch unit shown is open (the seventh transistor NM2 is open).
[0119] In one implementation, such as Figure 12The switching unit 1012 of this application includes a seventh transistor NM2 and an eighth transistor NM3 connected in series;
[0120] The seventh transistor NM2 is controlled by the second output signal SW2 of the logic unit 1021 to be turned on after the detection terminal signal V1 is reset and before the detection current is greater than a preset threshold.
[0121] The eighth transistor NM3 is controlled by the first output signal SW1 of the logic unit 1021 to be turned on when the channel enable signal is valid.
[0122] In one implementation, such as Figure 13 The logic unit 1021 includes a first inverter;
[0123] The logic unit 1021 directly outputs the channel enable signal as the first output signal, and inverts the detection terminal signal V1 through the first inverter to output it as the second output signal.
[0124] It should be noted that in this embodiment, when the switching unit 1012 includes two transistors, the logic unit 1021 has two functions: one is to directly output the channel opening signal, which can be simply considered to be achieved through a single wire, but in reality, it can be achieved through other logic circuits; the other is to invert the detection terminal signal V1 and then output it.
[0125] In one implementation, such as Figure 10 , 12 -14. The fast start-up circuit of this application also includes a fast shutdown module. This module is used to pull up (charge) the control terminal potential VGate of the switching transistor to a preset potential, such as VDD, when the channel turn-on signal is invalid. In this way, the switching transistor of the constant current output channel will be turned off, thereby stopping the output of constant current and extinguishing the LED.
[0126] Please continue reading Figure 10 , 12 -14. The fast shutdown module includes a second current unit and a ninth transistor PM3. The ninth transistor PM3 is controlled by a channel turn-on signal. When the channel turn-on signal is invalid, it charges the control terminal of the switching transistor by outputting a second current I2.
[0127] Here, we will supplement the explanation of the function of the enable unit (taking PM2 as an example). When PWM=0, if PM2 does not exist, that is, the source of PM1 is directly connected to VDD, the VGate voltage will gradually increase. In the initial stage, when the VGate voltage is still small, PM1 may still be conducting. In this case, there is current in the branch where PM1 is located, which will result in energy consumption and may also cause errors in the logic unit operation.
[0128] A second aspect of this application provides a driver chip for a common-cathode LED display screen, comprising:
[0129] A constant current source drive circuit 20 is used to output a constant current through a constant current output channel 200; and a fast start circuit 100 for a common cathode LED display as described in the first aspect, the output terminal of which is electrically connected to the control terminal of the switching transistor of the constant current output channel of the constant current source drive circuit.
[0130] Typically, a constant current output channel is configured with a fast-start circuit. A constant current drive circuit includes multiple constant current output channels.
[0131] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0132] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.
Claims
1. A fast start-up circuit for a common-cathode LED display screen, characterized in that, The circuit includes: The fast start module includes a switching unit and a first current unit, which is used to discharge the control terminal of the switching transistor of the constant current output channel when the channel start signal is valid, and to stop the discharge after receiving a stop signal; The detection control module includes a logic unit, a detection unit, and a control unit, used to output the stop signal when the detected current is greater than a preset threshold; wherein the detected current represents the control terminal potential of the switching transistor; The switching unit closes when the channel open signal is valid and before the stop signal is received; The first current unit is used to discharge the control terminal of the switching transistor after the switching unit is closed; The logic unit is used to control the switching unit to open or close based on the channel opening signal and the detection terminal signal. The detection unit is used to convert the control terminal voltage of the switching transistor into the detection current, and output the detection terminal signal representing the magnitude of the detection current and the preset threshold through the detection terminal; The control unit is configured to reset the detection terminal signal to invalid when the channel opening signal is invalid.
2. The fast start-up circuit for a common-cathode LED display screen according to claim 1, characterized in that, The detection unit includes: a second current unit and a first transistor; The output terminal of the second current unit is grounded, and the input terminal is connected to the second terminal of the first transistor. The connection point serves as the detection terminal to output the detection terminal signal. The control terminal of the first transistor is connected to the control terminal of the switching transistor, and the first terminal of the first transistor is connected to the power supply voltage. or, The detection unit includes: a second current unit, a first transistor, and a second transistor; The output terminal of the second current unit is grounded, and the input terminal is connected to the second terminal of the first transistor. The connection point serves as the detection terminal to output the detection terminal signal. The control terminal of the first transistor is connected to the control terminal of the switching transistor; When the channel enable signal is valid, the second transistor connects the first terminal of the first transistor to the power supply voltage.
3. The fast start-up circuit for a common-cathode LED display screen according to claim 2, characterized in that, The control unit includes a third transistor; The third transistor has a first terminal connected to the detection terminal and a second terminal grounded. The control terminal receives the reverse signal of the channel open signal so as to reset the potential of the detection terminal to invalid when the channel open signal is invalid.
4. The fast start-up circuit for a common-cathode LED display screen according to any one of claims 1-3, characterized in that, The first current unit is also used to control the potential of the control terminal of the switching transistor before the fast start module receives the stop signal, so as to avoid the potential of the control terminal of the switching transistor exceeding the limit.
5. The fast start-up circuit for a common-cathode LED display screen according to claim 4, characterized in that, The first current unit includes: a fourth transistor, a fifth transistor, a sixth transistor, and a reference current generating circuit; The fourth and fifth transistors form a current mirror; The reference current generating circuit, the fifth transistor, and the sixth transistor are connected in series between ground and the power supply voltage. The first terminal of the fourth transistor is electrically connected to the control terminal of the switching transistor, and the second terminal is electrically connected to the switching unit. The control terminal and the second terminal of the sixth transistor are shorted together, and the first terminal of the sixth transistor is connected to a high level. The reference current generating circuit is used to generate the current in the input branch of the current mirror.
6. The fast start-up circuit for a common-cathode LED display screen according to any one of claims 1-3, characterized in that, The switching unit includes a seventh transistor; The seventh transistor is controlled by the output signal of the logic unit to control whether the first current unit discharges the control terminal of the switching transistor.
7. The fast start-up circuit for a common-cathode LED display screen according to any one of claims 1-3, characterized in that, The switching unit includes a seventh transistor and an eighth transistor connected in series; The seventh transistor is controlled by the second output signal of the logic unit to turn on after the detection terminal signal is reset and before the detection current is greater than a preset threshold. The eighth transistor is controlled by a first output signal of the logic unit to be turned on when the channel enable signal is valid.
8. The fast start-up circuit for a common-cathode LED display screen according to claim 6, characterized in that, The logic unit includes: NOT gate and NOR gate; The input terminal of the NOT gate receives the channel open signal, and the output terminal is connected to the first input terminal of the NOR gate. The second input terminal of the NOR gate receives the detection terminal signal, and the output terminal is connected to the control terminal of the seventh transistor.
9. The fast start-up circuit for a common-cathode LED display screen according to claim 7, characterized in that, The logic unit includes a first inverter; The logic unit directly outputs the channel open signal as the first output signal, and inverts the detection signal through the first inverter to output the second output signal.
10. A driver chip for a common-cathode LED display screen, the driver chip comprising: A constant current source drive circuit is used to output a constant current through a constant current output channel; Furthermore, the fast start-up circuit of the common cathode LED display screen as described in any one of claims 1-9, wherein the output terminal of the fast start-up circuit is electrically connected to the control terminal of the switching transistor of the constant current output channel of the constant current source drive circuit.