CN215773652U

CN215773652U - LED lamp and key pin multiplexing circuit

Info

Publication number: CN215773652U
Application number: CN202121903895.1U
Authority: CN
Inventors: 王春华
Original assignee: Nanjing Qinheng Microelectronics Co ltd
Current assignee: Nanjing Qinheng Microelectronics Co ltd
Priority date: 2021-08-14
Filing date: 2021-08-14
Publication date: 2022-02-08
Anticipated expiration: 2031-08-14

Abstract

The utility model discloses an LED lamp and key pin multiplexing circuit, which comprises a chip and a pin multiplexing unit, wherein the pin multiplexing unit comprises a first branch and a second branch which are connected in parallel, the first branch comprises a key and a first current limiting element which are connected in series, and the second branch comprises an LED lamp; the chip comprises a pin driving module, a current detection module, a driving pin and a multiplexing pin, wherein the pin driving module comprises a plurality of driving circuits, and the driving pin and the multiplexing pin are connected with the driving circuits; two ends of the pin multiplexing unit are respectively connected with the driving pin and the multiplexing pin; the current detection module is connected with the driving circuit on the multiplexing pin and used for detecting the current on the first branch. The key detection of the utility model reuses the row pins and the column pins scanned by the LED lamp, does not need additional chip pins, realizes LED display and key detection, reduces the chip cost and reduces the chip volume.

Description

LED lamp and key pin multiplexing circuit

Technical Field

The utility model belongs to the technical field of electronic circuits, and particularly relates to an LED lamp and a key pin multiplexing circuit.

Background

With the increase of physical life, electronic products have not only been functional, but also required more good sensory experiences for users. For example, in the case of current mechanical keyboards, in addition to the basic functions of the keyboard, light effects are also displayed. This requires an additional increase in light efficiency function and drive pin count for conventional keyboard chips.

The driving pins of the matrix lamp generally comprise a row (COM) and a column (SEG), and if the key scanning function is simultaneously supported but the key pressing state cannot influence the display effect of the lamp, the general method is to share the row pins or the column pins of the lamp driving, and then to jointly complete the key detection through another group of independent pins.

Under the existing condition, the chip with fewer pins can reduce the packaging cost and further influence the chip cost. The same packaged chip will have a smaller volume with a smaller pin count, which allows the circuit board area on which the chip is used to be smaller and easier to route.

Disclosure of Invention

The purpose of the utility model is as follows: in order to solve the problem that in the prior art, more pins of a chip are needed for simultaneously realizing LED lamp display driving and key detection, the utility model provides an LED lamp and a key pin multiplexing circuit.

The technical scheme is as follows: a multiplexing circuit of LED lamps and key pins comprises a chip and a pin multiplexing unit, wherein the pin multiplexing unit comprises a first branch and a second branch which are connected in parallel, the first branch comprises keys and a first current limiting element which are connected in series, and the second branch comprises LED lamps; the chip comprises a pin driving module, a current detection module, a driving pin and a multiplexing pin, wherein the pin driving module comprises a plurality of driving circuits, and the driving pin and the multiplexing pin are connected with the driving circuits; two ends of the pin multiplexing unit are respectively connected with the driving pin and the multiplexing pin; the current detection module is connected with the driving circuit on the multiplexing pin and used for detecting the current on the first branch.

Furthermore, the number of the pin multiplexing units is at least four, and different pin multiplexing units are respectively connected with different driving pins or multiplexing pins to form a connection matrix.

Furthermore, the first branch circuit further comprises a diode, the diode is connected with the key and the first current limiting element in series, and the current flow direction of the diode is from the multiplexing pin to the driving pin.

Furthermore, the plurality of pin multiplexing units connected to the same multiplexing pin and different driving pins share one first current limiting element.

Furthermore, the second branch circuit further comprises a PMOS tube and a second current limiting element, the source electrode of the PMOS tube is connected with the power supply, the drain electrode of the PMOS tube is connected with the anode of the LED lamp, the grid electrode of the PMOS tube is connected with the driving pin, and the second current limiting element is connected with the LED lamp in series.

Further, the first current limiting element is a resistor, the resistance value is R2, and the value of R2 is greater than or equal to 1k Ω and less than or equal to 20k Ω.

Further, if the time for completing one round of scanning of all pins of the chip is T and the number of the driving pins is n, dividing T into n scanning sections, wherein only one driving pin is at a low level in each scanning section, and the rest driving pins are pulled up to be at a high level; each scan segment includes a display driving segment and a key detection segment during which the multiplexing pin is pulled up to a high level.

Furthermore, the current detection module comprises a current mirror circuit, a reference current source and a buffer, wherein the output end of the current mirror circuit and the output end of the reference current source are both connected with the input end of the buffer, and the output end of the buffer outputs a key detection signal.

Furthermore, the driving circuit on the multiplexing pin comprises a first driving tube and a second driving tube, the first driving tube is connected with a power supply, and the second driving tube is connected with the ground; the current mirror circuit comprises a switch and a first transistor, wherein two ends of the switch are respectively connected with a grid electrode and a source electrode of a first driving tube, the grid electrode of the first transistor is connected with the grid electrode of the first driving tube, the source electrode of the first transistor is connected with a power supply, and the drain electrode of the first transistor is connected with a buffer.

Furthermore, the driving circuit and the current detection module on the multiplexing pin work in different time periods, and when the switch is turned off, the driving circuit works; when the switch is closed, the current detection module works, and the multiplexing pin is pulled up to the power supply voltage.

Has the advantages that: the utility model provides an LED lamp and a key pin multiplexing circuit, which can support key scanning while driving the LED lamp to display, compared with the prior art, the key state is judged by detecting current during key scanning, the multiplexing pin is pulled up to be power voltage, the voltage is clamped at a high level after the key is pressed, and the LED lamp cannot be turned on by mistake; the multi-key detection and the composite key are supported, different keys cannot be influenced mutually, and missing detection or false detection cannot be realized. The key detection reuses row pins and column pins scanned by the LED lamp, reduces chip pins, can realize LED display and key detection simultaneously, reduces chip cost and chip volume, and ensures that the circuit board has smaller area and is easy to wire.

Drawings

FIG. 1 is a schematic diagram of an LED lamp and key pin multiplexing circuit according to an embodiment;

FIG. 2 is a schematic circuit diagram of an embodiment without diodes;

FIG. 3 is a schematic diagram of a current sensing module;

FIG. 4 is a schematic diagram illustrating connection between a plurality of pin multiplexing units and a chip according to a first embodiment;

FIG. 5 is a waveform diagram of each row pin in a complete scan cycle;

fig. 6 is a schematic diagram illustrating connection between a plurality of pin multiplexing units on the same multiplexing pin and a chip according to a second embodiment.

Detailed Description

The utility model is further explained below with reference to the figures and the specific embodiments.

The first embodiment is as follows:

in this embodiment, taking a mechanical keyboard driving 32 common-sun LED lamps and 16 keys as an example, the number of the pin multiplexing units is 16, and 16 additional individual LED lamps (without multiplexing keys) are added, as shown in fig. 4. Different pin multiplexing units are respectively connected with different driving pins or multiplexing pins to form a matrix structure. In this embodiment, the driving pin is a COM pin and is only used for driving the LED lamp, and the multiplexing pin is an SEG pin and is used for driving the LED lamp and detecting the current on the key branch. As shown in FIG. 4, the LED lamps D10-D17, D20-D27, D30-D37 and D40-D47 are respectively connected in series with 100 ohm current limiting resistors R1 between the drain of the PMOS transistor controlled by COM1-COM4 and SEG1-SEG 8. Keys S10-S17 and S20-S27 are respectively connected with a diode and a 20k ohm current limiting resistor R2 in series between COM1-COM2 and SEG1-SEG 8. The current limiting resistor can be adjusted according to the color and brightness requirements of different lamps. The chips can be connected to the pin multiplexing unit according to the requirement. The chip comprises 12 driving circuits, 8 current detection modules, 4 COM pins and 8 SEG pins, and compared with the prior art, the chip can save 8 pins. Each pin is connected with a driving circuit, and only the SEG pin is connected with a current detection module.

As shown in fig. 1, the LED lamp and key pin multiplexing circuit includes a chip and 16 pin multiplexing units, and a 16 pin non-multiplexing unit, i.e. an individual LED lamp (the part is the same as the prior art and is not described).

The pin multiplexing unit comprises a first branch and a second branch which are connected in parallel, two ends of the pin multiplexing unit are respectively connected with a multiplexing pin and a driving pin, the multiplexing pin is an SEG pin, and the driving pin is a COM pin. Since the whole circuit comprises a plurality of keys, in order to prevent the keys from being influenced by the pressing of other keys, a diode is connected in series on the first branch, so that the multi-key detection and composite key can be supported, as shown in fig. 1, the current flow of the diode D2 is from SEG to COM, and the current flow of the LED lamp is from COM to SEG. In practice, however, in the case of a key depression identified by detecting a current, the diode D2 is an unnecessary element, as shown in fig. 2. The first branch circuit comprises a key, a diode D2 and a current-limiting resistor R2 which are connected in series; the second branch circuit comprises an LED lamp, a PMOS tube and a current-limiting resistor R1, wherein the current-limiting resistor R1 is connected with the LED lamp in series, and the resistance value of R1 is 100 ohms. The source electrode of the PMOS tube is connected with a 5V power supply, the drain electrode of the PMOS tube is connected with the anode of the LED lamp, and the grid electrode of the PMOS tube is connected with the COM pin. The PMOS tube is used for increasing the driving capability, and an NMOS tube can be used, the NMOS tube can be arranged in the chip, but when the NMOS tube is used, the driving polarity in the chip, and the positive and negative poles of other polar devices such as a diode and the like are reversed according to the principle of the utility model, and the technology is feasible.

The current detection module is connected to the pin driving circuit of the SEG pin and used for detecting the current Ikey on the first branch. The current detection module can be implemented in many ways as long as it can detect Ikey. In this embodiment, the current detection module is implemented by using a current mirror circuit, and includes a current mirror circuit and a reference current source I₀And the buffer A is used for collecting the current on the first branch, and the output end of the current mirror circuit and the output end of the reference current sourceThe output ends of the input end and the output end of the output end are connected with the input end of the buffer, and the output end of the buffer outputs a key detection signal.

As shown in fig. 3, the driving circuit on the SEG pin includes a high voltage driving tube Q12 and a low voltage driving tube Q10, the high voltage driving tube Q12 is connected to the power supply, and the low voltage driving tube Q10 is connected to the ground; the current mirror circuit comprises a switch K and a first transistor Q13, wherein two ends of the switch K are respectively connected with a grid electrode and a source electrode of a high-voltage driving tube Q12, a grid electrode of a first transistor Q13 is connected with a grid electrode of a high-voltage driving tube Q12, a source electrode of the first transistor Q13 is connected with a power supply, and a drain electrode of the first transistor Q13 is connected with a buffer A. The high-voltage driving tube Q12 and the first transistor Q13 are both PMOS tubes, and the low-voltage driving tube Q10 is an NMOS tube. The current mirror circuit is designed on the pin driving circuit, and original components are fully utilized.

The pin driving circuit and the current detection module work in a time-sharing mode, and a switch K is used for determining whether a driving tube in the driving circuit is used as driving or current mirror. When the switch K is turned off, the pin driving circuit works to normally select and output the high-low level of the SEG pin, the gates of the Q10 and the Q12 are respectively driven by the pre-driving circuit of the previous stage, and at the moment, the reference current source I₀Can be closed; when the switch K is closed, the high-voltage driving tube is equivalent to an equivalent diode, the current detection module works, all SEG pins are pulled up to a power supply voltage VCC by pull-up current or pull-up resistors, when the key is pressed down, the current mirror circuit collects current flowing through the equivalent diode (namely current Ikey from the SEG pin to the COM pin from the first branch circuit), the collected current on the equivalent diode and a reference current source are input from the buffer after being mirrored, and the buffer outputs a current detection signal. Subtracting the image current from the reference current source, and when the image current is greater than the reference current, obtaining a high level at the output end of the buffer, which represents that a key is pressed down; when the mirror current is less than the reference current, the output of the buffer gets a low level, indicating that no key is pressed. The reference current is a set current value, and when the current value is determined, the mirror current is ensured to be larger than the current value of the internal reference current source when a key on the first branch is pressed by combining the first current limiting element. Other current detection circuits may be used to detect Ikey, and are not limited to this implementationThe current detection method of the example can be any method as long as the same function can be achieved. In addition, the switch K is closed, and during the key detection, when the key is pressed, the voltage difference between the two ends of the Q12 is clamped to about 0.7V-1.3V, so that the voltage of the multiplexing pin SEG is at least VCC-1.3V, and the multiplexing pin is pulled up to a high potential instead of a low potential, so that the LED lamp cannot be lighted, and the LED lamp cannot be lighted by mistake when the key is pressed.

The value of the current limiting resistor R2 in the first branch circuit needs to consider the size of the reference current source and the proportion of the current mirror image, the resistance value cannot be too large, and it needs to be ensured that when the key is pressed, the generated current Ikey mirror image is larger than the reference current source, so that the current pressed by the key can be ensured to be detected. On the other hand, if the resistance is too small, the level of the SEG pin is pulled low when the key is pressed, which may cause the LED lamp to turn on by mistake. Experiments show that the value of the resistor R2 is generally between 1K and 20K, and if the value of the resistor R2 is 20K in the embodiment, the current Ikey generated when the key is pressed is extremely small, and generally ranges from a few uA to hundreds uA.

As shown in fig. 5, a complete scan cycle T is shown, and since there are 4 COM pins, T is divided into 4 scan segments, each scan segment includes two parts, namely display driving and key detection. In the display drive T_LEDMeanwhile, the I/O pin driving module drives one row pin COM1 to output a low level, the other COMx pins to output a high level, and simultaneously drives the SEG1-SEG8 to output a high level or a low level according to the required LED lamp state. In the display driving period, the PMOS tube Q1 is conducted, the LED lamps in the COM1 row are not lighted when the SEG outputs high level, and are lighted when the SEG outputs low level, and whether the button is pressed or not has no influence on the LED branch. Detecting T at key press_KEYDuring the period, the current detection module is started (the switch K is closed), at the moment, the I/O pin driving module drives one row COM1 to output a low level, other COMx outputs a high level or is pulled up to a high level (the pull-up high level is preferably used when the first branch circuit is not provided with the diode D2), SEG1-SEG8 are pulled up to the high level, the SEG pin is pulled up to the power supply voltage VCC when no key is pressed down, and all LED lamps are not lighted in the state; when the key is pressed, a current I is formed_keyWhen the current detection module detects the current, the key is considered to be pressed,otherwise, without a key press, the SEG pin is clamped at least VCC-1.3V, which is insufficient to turn on the LED. T is_KEYAs well as the blanking time for switching between LED rows. Through the two parts, dynamic driving of the LED lamp on the COM1 is completed, and key detection mounted on the COM1 is scanned. Then, the next COMx pin is driven to be at low level, and the driving of a new group of LED lamps and the detection of a key are started.

Example two:

the second embodiment is different from the first embodiment in that the plurality of pin multiplexing units connected to the same multiplexing pin and different driving pins share the first current limiting element R2, so as to further reduce the cost. In addition, the second current limiting element R1 on the second branch can also be shared, as shown in fig. 6.

Claims

1. The LED lamp and key pin multiplexing circuit is characterized by comprising a chip and a pin multiplexing unit, wherein the pin multiplexing unit comprises a first branch and a second branch which are connected in parallel, the first branch comprises a key and a first current limiting element which are connected in series, and the second branch comprises an LED lamp; the chip comprises a pin driving module, a current detection module, a driving pin and a multiplexing pin, wherein the pin driving module comprises a plurality of driving circuits, and the driving pin and the multiplexing pin are connected with the driving circuits; two ends of the pin multiplexing unit are respectively connected with the driving pin and the multiplexing pin; the current detection module is connected with the driving circuit on the multiplexing pin and used for detecting the current on the first branch.

2. The LED lamp and key pin multiplexing circuit of claim 1, wherein the number of the pin multiplexing units is at least four, and different pin multiplexing units are respectively connected to different driving pins or multiplexing pins to form a connection matrix.

3. The LED lamp and key pin multiplexing circuit of claim 1 or 2, wherein the first branch further comprises a diode, the diode is connected in series with the key and the first current limiting element, and a current of the diode flows from the multiplexing pin to the driving pin.

4. The LED lamp and key pin multiplexing circuit of claim 3, wherein a plurality of pin multiplexing units connected to the same multiplexing pin and different driving pins share a first current limiting element.

5. The LED lamp and key pin multiplexing circuit of claim 1 or 2, wherein the second branch further comprises a PMOS tube and a second current limiting element, a source of the PMOS tube is connected to the power supply, a drain of the PMOS tube is connected to the anode of the LED lamp, a gate of the PMOS tube is connected to the driving pin, and the second current limiting element is connected in series with the LED lamp.

6. The LED lamp and key pin multiplexing circuit of claim 1 or 2, wherein the first current limiting element is a resistor with a resistance value of R2, and the value of R2 is 1k Ω or less and 20k Ω or less.

7. The LED lamp and key pin multiplexing circuit of claim 1 or 2, wherein assuming that the time for all the pins of the chip to complete one round of scanning is T and the number of the driving pins is n, dividing T equally into n scanning sections, wherein only one driving pin is at low level and the remaining driving pins are pulled up to high level in each scanning section; each scan segment includes a display driving segment and a key detection segment during which the multiplexing pin is pulled up to a high level.

8. The LED lamp and key pin multiplexing circuit of claim 1 or 2, wherein the current detection module comprises a current mirror circuit, a reference current source and a buffer, an output terminal of the current mirror circuit and an output terminal of the reference current source are both connected to an input terminal of the buffer, and an output terminal of the buffer outputs the key detection signal.

9. The LED lamp and key pin multiplexing circuit of claim 8, wherein the driving circuit on the multiplexing pin comprises a first driving tube and a second driving tube, the first driving tube is connected with a power supply, and the second driving tube is connected with ground; the current mirror circuit comprises a switch and a first transistor, wherein two ends of the switch are respectively connected with a grid electrode and a source electrode of a first driving tube, the grid electrode of the first transistor is connected with the grid electrode of the first driving tube, the source electrode of the first transistor is connected with a power supply, and the drain electrode of the first transistor is connected with a buffer.

10. The LED lamp and key pin multiplexing circuit of claim 9, wherein the driver circuit and the current detection module on the multiplexing pin operate in a time-phased manner, and when the switch is turned off, the driver circuit operates; when the switch is closed, the current detection module works, and the multiplexing pin is pulled up to the power supply voltage.