WO2008099979A2

WO2008099979A2 - Apparatus for driving led display panel

Info

Publication number: WO2008099979A2
Application number: PCT/KR2007/000819
Authority: WO
Inventors: Chi-Ho Song; Sergiy Nedilko
Original assignee: Xmpdisplay Co., Ltd.
Priority date: 2007-02-15
Filing date: 2007-02-15
Publication date: 2008-08-21
Also published as: WO2008099979A3; KR20100005023A

Abstract

The invention relates to an apparatus for driving LED panels. All the LEDs (HLR1...HLRn, HLG1...HLGn, HLB1...HLBn) are divided into three separate groups (with red /R/, green /G/ and blue /B/ color respectively) where LEDs (HLR1...HLRn, HLG1...HLGn, HLB1... HLBn) are serially connected within each group. Each group is driven by a special set of two current regulators, a current limiter (CLR, CLG, CLB) and a dynamic current regulator (CRR, CRG, CRB). All the groups are supplied from a common high- voltage DC power supply, and the mentioned individual sets of current regulators are serially coupled with the groups. Thus, the current can be set for each R, G, B group separately and independently while in operation. This makes it easy to adjust brightness, color temperature and gamma correction. During the turn-off period, current from the LEDs (HLR1...HLRn, HLG1...HLGn, HLB1... HLBn) is shunted away by MOSFET parallel n-channel switches (QR1...QRn, QG1...QGn, QB1...QBn). This allows the total current to the group to be maintained constant, and the total current consumption of the LED display panel does not exceed the third current consumption of a conventional LED panel.

Description

[DESCRIPTION] [Invention Title] LED's Driving Apparatus in Display Panel

[Technical Field]

The present invention relates to an LED's driving apparatus. This apparatus for driving LEDs is serially connected within each R, G and/or B group using a special set of two current regulators; current limiter at high side (that means it is connected to anodic end of a group) and dynamically adjustable current regulator at low side (that means it is connected to cathode end of a group). There are also flying shunting MOSFET switches in each group. The invention solves the problem of high total consumable current to an LED display panel in conventional designs that require high-current (and therefore expensive) power supplies.

[Background Art]

A LED display panel is a display device for restoring image data input as an electrical signal with a plurality of LEDs arranged in an array of RGB pixels to selectively emit light. Each RGB pixel contains separately or jointly packaged R, G, B LEDs. Conventional LED display panels are largely classified into array type LED display panels and matrix type LED display panels. This is according to the type of arrangement of the LEDs in the display panel. The type of arrangement depends on whether some anodes or cathodes of LEDs are connected together to form the matrix or not. The underlying principle of LED matrices is that each LED can be addressed by specifying its location in terms of rows and columns, whereas every LED of array type LED display panels is driven separately and independently using an individual supplying wire for each LED. However, the driving principles of both array type LED display panels and matrix type LED display panels generally have the same power supply structure. The main (usually one) low-voltage power supply serves both Circuit of module controller and LED driver circuits. Also, conventional LED display panels differ depending on if they have a resistor-based type or a semiconductor-based type of current source/sinks which serve as the current limiters.

FIG. 1 shows one possible typical variant of the internal structure of an LED matrix module which consists of a specified quantity of LED matrix panels. An LED array that is arranged in a matrix, together with common-line and access-line drivers, together with according shift registers, is usually integrated inside an LED matrix display panel, whereas, all other circuits are integrated in a control-circuit board of display module.

Referring to FIG. 1, the module controller manages and processes the video data for the module and has several key functions, which are as follows:

1. Common-line drive control - manages the multiplexing action of the module. It controls which common-line is to be energized and synchronizes with the access-line drive control to ensure that the correct row data is fed into the access-line drivers.

2. Access-line drive control - determines which LED in the currently energized common- line row is to be turned ON. The outputs of access-line driver IC turn the LEDs on or off: a "1 " will turn on the LED and vice-versa.

3. Gray scale control - gray scales are the brightness levels of each LED in a pixel can be controlled to. A typical full-color system can have up to 256 gray scales. That means each LED 's brightness can be tuned from minimum to maximum brightness in 256 steps. If each pixel has three LEDs - red, green and blue - the number of color combinations is 256x256x256 = 16.7 million. Gray scales are achieved by dividing each scan period into 256 time slots (more slots are needed for a larger number of gray levels). Thus, the access-line drivers are latched with data 256 times in a single scan period.

4. Brightness control - brightness control is different from gray scales. Brightness control refers to the control of the display's overall luminance value, not an individual LED. Manipulating the length of the scan period can control the overall luminance or brightness.

5. Cascade control — generates the control signals used to interface other modules.

6. RAM - stores the incoming video data. Usually, a double-buffering method is used because the video data received still needs to be processed. So, while one buffer is used to drive the display, the second buffer contains freshly received data to be operated on. These two processes can happen in parallel.

7. Gamma correction — corrects the non-linear transfer function of the LED display screen. Put another way, the signal transfer between the electrical and optical components of the display system is non-linear. This leads to expansion of the bright region and compression of the dim region. NTSC and PAL video signals are gamma-corrected prior to transmission to eliminate the non-linear effect of the display. Hence, the display must take this into account to obtain a linear signal transfer function.

8. Color-space transformation - is necessary with rich-color tiles because its color space is limited compared to full-color tiles and color televisions. For this reason, rich-color tiles cannot be used for display of full-color video. It can be used in limited color video like cartoons. [Note : pp.1-8 are a quotation of "introduction to Driving LED Matrics by Agilent Technologies, Inc. Application Note 1216, May 7.2001 "J

In a conventional LED driving apparatus, the main (usually one) low-voltage power supply powers both the module controller and LED display panels. At the same time, each LED is driven from the previously mentioned power supply using individual serially coupled current source/sink (resistor in the simplest case) that limits current to the LED at a safe operation value.

[Disclosure]

[Technical Problem]

In a conventional LED driving apparatus, when all driving circuits are connected in parallel to the only power supply, total pulse current consumption of each conventional LED display panel reaches high value when all the LEDs are turned on. Total pulse current consumption of a module that has a few of these panels, is respectively multiplied by the quantity of panels in the module. Total pulse current consumption of a module is relative low when all LEDs are turned off. Therefore, the current swing between states is extremely high. Such circumstances require use of an expensive high-current, low- voltage power supply with excellent voltage stabilization within the whole range of current consumption. It is well known that such power supplies are very expensive although it's low efficiency. To supply high current it is necessary to use thick power conductors. Also high pulse current creates strong ground stresses due to limited conduction of power wires and their considerable inductance. These grounding stresses complicate the work of design engineers. Also, it is not easy to adjust or to regulate the current to the current sources/sinks due to their large quantity. But such control (using regulable current sources/sinks), however, can be very helpful in order to control brightness, color, gamma curve, etc.

[Technical Solution] To solve the previously mentioned problems:

It is the first objective of the present invention to provide an apparatus for driving an LED display panel with serial connection of LEDs in the panel using only one external common high- voltage low-current DC power supply. It is the second objective of the present invention to provide an apparatus for driving an LED display panel using three separate groups (with R, G, B color respectively) where LEDs are serially connected within each LED group, and each group is driven by an individual set of current regulators. One regulator from each mentioned set is dynamically adjustable to set the pulse current to the LEDs precisely, over time, in order to control over brightness, contrast, color and gamma curve easily.

It is a third objective of the present invention to provide an apparatus for driving an LED display panel using flying MOSFET switches. Flying switches shunt current away from the LEDs.

It is the fourth objective of the present invention to provide an apparatus for driving an LED display panel using a charge pumping method for driving the gates of flying MOSFET shunts, executed by using a low- voltage, low-current power supply. It is also used for the supplying of power to the module controller.

To achieve these objectives, an apparatus is provided that has serial connection of LEDs in the panel within the R, G, B group, where current to each group is regulated while in operation by an individual set of two current regulators (a constant current limiter at the high side of the group and a dynamically controllable current regulator at the low side of the group), and where all the groups are supplied from one external common high-voltage, low-current DC power supply. The module controller and circuitry for driving by MOSFET gates are supplied from a low- voltage, low-current power supply. For driving LEDs to get the grey-scale, each LED has an individual shunting MOSFET switch that is connected in parallel to the corresponding LED. Also, there is a special circuitry (VD_dRn diodes together with QdR switch and corresponding wires) using diodes and one MOSFET for the connection of shunting MOSFET drains to GND. This provides the possibility to charge/discharge the gate-source capacities of shunting MOSFET switches when turning the LEDs off/on respectively. Discharge of gate-source capacities is provided by a low- voltage serial-to-parallel converter ICs with high-voltage open drain outputs. Charge to them is provided by corresponding chains of diodes and resistors connected to the positive low- voltage power supply.

The apparatus for driving a LED display panel includes serially connected LEDs in each the R, G, B group and individual current regulators for each group, wherein all the LEDs with the same color belong to the corresponding group, each LED is equipped by one corresponding low- voltage MOSFET in-parallel n-channel switch QRI ...QR₀, QGI • • -Q_Gn5 QBI . ■ -Q_BΠ, which make it possible to turn the corresponding LED off by shunting the current away, all the R, G, B groups are supplied from a common positive high-voltage DC PS (+V_dd), the charging current to QRI • • • QiRn, QGI • • ■ QG_Π, QB i • • • QBΠ gates is provided by a common positive low- voltage DC PS (+Vcc) by using logic level voltages, each switch Q_R1... QR₁₁, Q_GI ■ • • QG_Π, Q_BI • • . Qεn is coupled by a filtering capacitor CR₁...CRΠ, CG_I .. -CG₁₁, CB_I ...Cs_n between gate and source, charging of gate- source capacitance of QRI . .. QR₀, QGI - - QGn, Q_BI - - -QB_Π is provided by the serial chains of high- voltage diodes VDRI ...VDR₁₁, VDQ₁...VDG, VDB₁. • -VDe_n in forward polarity and current- limiting resistors RR₁...RR₁₁, R_GI ...RGΠ, R_BI • • .R_BΠ,, the chains go from +V<χ towards the gates, discharging of gate-source capacitance of QRI ...QR₁₁, QGI .. -Q_GΠ, Q_BI ■ • Q_BΠ is provided by serial to high-voltage parallel converter ICs DR, DG, DB with open drain outputs, low-voltage inputs of DR, DG, DB are driven by an external control circuitry.

The apparatus further includes an AC-DC converter as +V_dd power source to supply R, G, B groups.

The apparatus further includes an AC-DC step-down pulse mode converter, which supplies an control circuitry as +V_CC power source in order to drive the gates of QRI . ..QRΠ, QGI - . -QG_Π, Q_BI • • • Q_BΠ switches by logic level voltages .

The apparatus further includes high-voltage diode circuitry VDdRi- - ■ VD d_Rn+i, VDdGi- - -VDdGnH, VDdBi - --VDdB_n+! and high-voltage MOSFET n-channel switches QdR, QdG, QdB for reducing the drain potentials of Q_RI... Q_R11, Q_GI - . -QG_Π, QBi-.-Qβn switches to GND when addressing the gates of QR₁... QR₁₁, QGI - . -QGΠ, QBI - . -QBH switches.

The apparatus further includes current limiters CLR, CL₀, CL_B that limit the current to Q_dR, Q_dG, Q_dB switches to a preset value in order to prevent overload of the +VDD power source and overcurrent of Q_dR, Q_dG, Qd_B switches when Qd_R, Q_dG, QdB are on. The low ends of the current limiters CL_R, CLQ, CL_B in the apparatus further are connected directly to the high ends (anode) of LED chains of R, G, B groups. The gates of Qd_R, QdG, Qd_B are driven by conventional external control circuitry.

The apparatus further includes high-voltage diode circuitry VD_gRi... VDgR_n, VDgGi...VDgG_n, VDgB i... VDgBn that prevents shift of drain potentials of QR₁.. . QRΠ, QGI • • -QGn, QBI • • -QBn switches below GND when addressing the gates of QR_I . - .QR_Π, QGI - - -Q_GΠ, QBI - - - QBΠ switches and anodes

VD_gGi...VD_gGn, VD_gBi... VDg_Bn are connected to GND, whereas, cathodes are connected to the sources of corresponding QRI . . . QR_Π, Q_GI - . - Q_GΠ, QBI - -QB_Π switches.

The apparatus further includes Zener diodes VD_hR, VD_hG, VD_hB at high side of each R, G, B LED groups and wherein cathodes of VD_hR, VD_hG, VD_hB are connected to +V_DD whereas anodes are connected to the high ends of the constant current limiters CCLR, CCLG, CCL_B and wherein Zener diodes VDhR, VDhG, VD_hB are optional and preventing an overvoltage of Qd_R, Qd_G5 Qd_B switches when Qd_R, QdG₅ QdB are open and wherein such overvoltage can occur if +Vdd exceeds +Vds_maχ of Qd_R switch and wherein if no such overvoltage, some pieces of wires are soldered instead of Zener diodes VDhR, VDhG, VD_11B-

The apparatus further includes Zener diodes VDI_R, VDI_G, VDIB and dynamically adjustable current regulators CR_R, CRQ, CR_B5 connected each other in series at the low side of each R, G, B LED group and wherein cathodes of VDI_R, VDJQ, VDB are connected directly to the low ends of LED chains of R, G, B groups, whereas, anodes are connected to the high ends of the corresponding current regulators CRR, CRG, CRB and wherein current regulators CRR, CRQ, CRB are driven by an external control circuitry.

[Description of Drawings]

The previously mentioned objectives and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:

FIG.l. is a line drawing of the internal structure of a module with conventional LED matrix display panels.

FIG.2. is schematic drawing of the invented LED display panel having three separate groups (with R, G, B color respectively) where LEDs are connected in series within each group.

[Best Mode]

An apparatus for driving an LED display panel will now be described in detail with reference to the accompanying FIG.2. drawing. Such LED display panel has three separate groups of LEDs. LEDs are serially connected within each group.

The reference numerals shown in FIGS 1 and 2 of the present invention as follows:

GND - ground connection (0 Volts)

-Vac - input alternate current voltage (~380 Volts usually)

+Vdd - output high voltage for supplying R, G, B LED groups

+Vcc - output low voltage for supplying digital circuits and drivers (+5 Volts usually)

HL_RI ... HL_RΠ - Red LEDs (n pieces)

CLR - fixed current limiter of R Group Channel during an addressing period

CRR - adjustable current regulator of R Group Channel during an active period

VD_hR - optional Zener diode for preventing an overvoltage of Qd_R switch

VD_1R - Zener diode for preventing a drop of LEDs' potentials below +Vcc during an active period

Q_RI • • • Q_RΠ - MOSFET switches for driving Red LEDs (n pieces) CR₁ ... C_R11 - gate coupling capacitors of corresponding QRI ... QR₁, switches (n pieces) R_RI • • • R_RΠ - pull-up resistors for charging gates Of Q_R1 ... Q_R1, switches (n pieces) VD_RI ... VD_RΠ - diodes for preventing of reverse current through RR₁ ... R_Rn during an active period (n pieces)

Q_dR - MOSFET for switching LEDs' potentials to GND during an addressing period R_dR - gate driving resistor for Qd_R switch VDdRi... VDdR_n+i - gathering diodes for Qd_R switch (n+1 pieces) VD_gRi... VDg_Rn - diodes for preventing a drop of LEDs' potentials below GND during an addressing period n - quantity of Red LEDs in R Group Channel

When the panel is in a bright state for some time (as in case of conventional design with a low- voltage main power supply), the total consumed current of a LED module reaches tens and hundreds Amperes. On the other hand, when the dark state of a screen image is continued, the total consumed current of a LED display panel is quite small. Due to the mentioned reasons, the main power supply of a conventional LED display module must satisfy all of the mutually contradictory conditions. It must have a wide current range, while maintaining precision stabilization of low-voltage throughout the whole range. Also, it must have high efficiency during unavoidable power dissipation in conductors and semiconductors due to high currents. Conventional LED display panel design, represented in FIG.l. has all the mentioned disadvantages. This invention, when used in an LED display panel (with serially connected LEDs), reduces the influence of these extreme conditions.

For this purpose, according to the apparatus of LED display panel shown in FIG.2, all the LEDs which have the same color are connected in series in the panel. Three LED groups exist: R₅ G and B, and each group is the base of the according group channel. Each group has a serial chain made from the LEDs in the same polarity and with the same corresponding color. It is a necessity to set equal current to all the LEDs with the same color. This guaranties equal brightness of all the LEDs inside the group, independent of their different forward voltages when the LEDs are ranked in advance accordingly to luminous intensity for the same current. At the same time, it is possible to set a different current for each group. The current can be regulated over time using specially designed control circuitry, i.e. current regulators with voltage driven input that are controlled using digital-analog converters. This makes it easy to adjust peak brightness, color temperature and gamma curve of a panel.

FIG.2. is a detail of an R group channel. The G and B group channels are typical and not shown for clarity. The following description represents the structure and operation of an R group channel and is typical for both G and B groups.

Operation of the represented panel has two time periods that alternate repeatedly. The first one is an active period when LEDs are turned on. The second one is addressing period when LEDs are turned off (dispowered) and when charging/discharging of the gates of low-voltage MOSFET switches Q_RI ...QR₂₁ is occurring.

R group consists of HL_R1...HL_R0 LEDS connected in series in forward polarity. Anode HLRI is the high end of the group and cathode HL_Rn is the low end of the group. Cathode HL_RI is connected to GND through the chain of dynamically adjustable current regulator CR_R and Zener diode VDi_R . CR_R is dynamically regulable and determines the current to the group for all the active period when LEDs can light, i.e. when Qd_R is switched off. HLR_n cathode and Q R_n source are interconnected. Their potential must be maintained higher than +V _cc for the entire active period (i.e., when Q _dR is switched off). VD_IR maintains this potential higher than +V _cc for any current to the group. Qd_R is switched on for addressing period. Qd_R is driven through R_dR resistor (the last determines switching times of QdR) by an external conventional logic level circuitry. Q_dR connects all HLR₁... HLR₁₁ cathodes, related QRI . .. QR₁, sources and high end of LED chain to GND through VDdR₁... VDdRiv_H diodes. Such connection makes possible charge/discharge of the gates of low- voltage MOSFET switches

using logic level voltages inside GND...+V_CC range during addressing period. Fixed current limiter CLR prevents the overload of Q_dR and +Vdd power source when Qd_R is switched on_? . The value of limiting current for CLR is preset a bit higher than the peak achievable for CRR . In this case there is no current limiting (no voltage drop too respectively) on CLR during active period when CLR works as a near zero Ohm resistor.

Optional Zener diode VD_hR prevents an over voltage of Q_dR switches when Q_dR are open (switched off). Such over- voltage can occur if +V_dd exceeds ÷V_dsmax of Q_dR switch. If no such over- voltage, a piece of wire can be soldered instead of Zener diode VD_hR.

Logic level low- voltage MOSFET switches QRI ...Q_Rn are connected in parallel to corresponding HLR₁...HLR_Π LEDS for shunting the current out from dedicated LEDs during the active period in case when the dedicated LEDs must be turned off. During the active period, drain potentials of Q_RI • • -QR_H are flying together with cathode potentials of HLR₁...HL_Rn LEDs.

Q_RI ■ • ■ Q_RΠ are driven by low- voltage control circuitry using charge pumping method. The chain of current-limiting resistor RR₁...RR₁₁ and diode VDR₁...VD_Rn in forward polarity provides the charging process of each gate-drain capacity CR₁...C_Rn. The anode of the last one is connected to low-voltage DC PS (+V_CC) and the mentioned resistor is connected to the gate. A diode VDR₁...VDR₁₁ breaks the charging current and prevents reverse current to the resistor when the gate's potential is higher than +V_CC. The n-Channel Serial-to-Parallel Converter IC provides a discharge of each gate-drain capacity. IC has Open Drain High- Voltage Outputs connected to each QR₁...Q_RΠ gate and can connect them to GND. IC is driven by an external conventional logic level circuitry. IC requires high-voltage open drain outputs due to high potentials when QR_I - ■ -Q_Rn are "flying" during an active period. IC can be replaced by a set of discrete components (low- voltage latch ICs that are driven by high-voltage MOSFETs in small packages) if it is reasonable due to lower cost and better routability of panel's PCB.

The operation sequence for the invented panel repeats as follows: 1. Active period (lighting). ICs outputs and Q_dR are switched off (open). State of Q_R1... Q_Rn (switched on or off in dependency of their accumulated gate charge) determines what HL_RI ...HL_R11 LEDS are on, CR_R determines their current (i.e., their brightness).

2. End of active period (stop lighting). CR_R is switched off.

3. Start of addressing period. Q_dR is switched on. CR_R starts limiting the current.

4. Addressing period. State of IC ' s outputs Q_R1... Q_RΠ (switched on or open drain) determines what gates of Q_RI ...Q_R0 (i.e., C_RI ...C_RΠ) are discharging/charging respectively.

5. End of addressing period. Q_dR is switched off that causes the end of discharging/charging currents to C_R1... C_Rn.

6. Return to point 1.

[Industrial Applicability]

This new LED driving apparatus reduces power losses, Electro-Magnetic Interference (EMI) and the amount of power required. In the new invention, all the LEDs are divided into three separate groups (with Red, Green, Blue color respectively) where LEDs are serially connected within each group. Each group is driven by a special set of two current regulators (a current limiter and a dynamically current regulator). All the groups are supplied from a common high-voltage DC power supply, using the mentioned individual sets of current regulators that are serially coupled with the groups. Thus, the current can be set for each R, G, B group separately and independently while in operation. This makes it easy to adjust brightness, color temperature and gamma curve. During the turn-off period, current from the LED is shunted away by a MOSFET(Metal-Oxide Semiconductor Field-Effect Transistor) in-parallel n-channel switch. This allows the total current to the group to be maintained constant using current regulators. Also, the total consumable current to this new invented LED display panel doesn't exceed the triple current to each LED of conventional designs.

Claims

[CLAIMS]

[Claim 1]

An apparatus for driving a LED display panel including serially connected LEDs in each the R, G, B group and individual current regulators for each group, wherein all the LEDs with the same color belong to the corresponding group, each LED is equipped by one corresponding low- voltage MOSFET in-parallel n-channel switch QRI-.-Q_RH, QG₁... QG_Π, Q_BI-.-Q_BU, which make it possible to turn the corresponding LED off by shunting the current away, all the R, G, B groups are supplied from a common positive high-voltage DC PS (+V_dd), the charging current to QRI-..QRΠ, QGI-.-QGΠ, QBI.-.QBΠ gates is provided by a common positive low-voltage DC PS (+V_CC) by using logic level voltages, each switch QR₁... Q_R11, QGI -QG_Π, QBI-..QB_Π is coupled by a filtering capacitor CRI-.-CR_Π, CGI-.-CG_Π, C_BI-.-CB_Π between gate and source, charging of gate- source capacitance of QRI...QR_Π, Q_GI-.-Q_GΠ, Q_BI--.Q_BΠ is provided by.the serial chains of high- voltage diodes VD_RI... VD_R11, VDGI...VDG, VDBI... VDB₁₁ in forward polarity and current- limiting resistors R_Ri₁₁₁R_Rn, RG_1^1Rc_n, RBI-.-R_BΠ,, the chains go from +V<χ towards the gates, discharging of gate-source capacitance of QR₁... QR_Π, QGI -QG_Π, QBI -QB_Π is provided by low- voltage serial to high-voltage parallel converter ICs D_R, DG, DB with open drain outputs, low- voltage inputs of D_R, DG, D_B are driven by an external control circuitry.

[Claim 2]

The apparatus according to claim 1, wherein the apparatus further includes an AC-DC converter as +V_dd power source to supply R, G, B groups.

[Claim 3]

The apparatus according to claim 1, wherein the apparatus further includes an AC-DC step-down pulse mode converter, which supplies an control circuitry as +V_CC power source in order to drive the gates of QR₁...QR_Π, QGI-.-QG_Π, QBI-.-QBΠ switches by logic level voltages .

[Claim 4]

The apparatus according to claim 1, wherein the apparatus further includes high- voltage diode circuitry VDdRi... VDdRnH, VD_dG1...VD_dGn+i, VDdBi... WW. and high-voltage MOSFET n- channel switches Q_dR, QdG, Qd_B for reducing the drain potentials of QRI-.-QRH, QGI-.-QGΠ, Q_BI...QB_Π switches to GND when addressing the gates of QRI...QRΠ, QGI. -QGΠ, QBI.-.QBΠ switches. L £

[Claim 5]

The apparatus according to claim 1, wherein the apparatus further includes current limiters CLR, CLG, CLB that limit the current to Q_dR, QdG, Qd_B switches to a preset value in order to prevent overload of the +VDD power source and overcurrent of Q_dR, Q_dG, Q_dB switches when Q_dR, Q_dG, Qd_B are on. The low ends of the current limiters CL_R, CLG, CLB in the apparatus further are connected directly to the high ends (anode) of LED chains of R₅ G, B groups. The gates of Q_dR, QdG; Qd_B are driven by conventional external control circuitry.

[Claim 6]

The apparatus according to claim 1, wherein the apparatus further includes high- voltage diode circuitry

VD_gGi ... VD_gGn, VDgBi- .. VDgB_n that prevents shift of drain potentials of QRI . ..QRΠ, QGI- - -QGH» QBI - . -QB_Π switches below GND when addressing the gates of QRI - QRH, QGI - . - QGΠ, QBI .. -QBΠ switches and anodes of VDgRi... VDgR_n, VD_gG1...VD_gGn, VDgB 1...VDg_Bn are connected to GND, whereas, cathodes are connected to the sources of corresponding QR₁...QR₀, QGI ... Qcn, Q_B i • • QBΠ switches.

[Claim 7]

The apparatus according to claim 1, wherein the apparatus further includes Zener diodes VD_hR, VDhG, VDhB at high side of each R, G, B LED groups and wherein cathodes of VD_hR, VD_nG, VD_hB are connected to +VDD whereas anodes are connected to the high ends of the constant current limiters CCL_R, CCLQ, CCLB and wherein Zener diodes VD_hR, VD_hG, VD_hB are optional and preventing an overvoltage of Qd_R, QdG, QdB switches when QdR, QdG, QdB are open and wherein such overvoltage can occur if +Vdd exceeds +Vd_Smaχ of Qd_R switch and wherein if no such overvoltage, some pieces of wires are soldered instead of Zener diodes VD_hR, VD_hG, VD_hB-

[Claim 8]

The apparatus according to claim 1, wherein the apparatus further includes Zener diodes VDIR, VDi_G, VDi_B and dynamically adjustable current regulators CRR, CRG, CRB, connected each other in series at the low side of each R, G, B LED group and wherein cathodes of VDI_R, VDI_G, VD® are connected directly to the low ends of LED chains of R, G, B groups, whereas, anodes are connected to the high ends of the corresponding current regulators CRR, CRG, CRB and wherein current regulators CRR, CRG, CRB are driven by an external control circuitry.