INVENTION TITLE
TEMPERATURE CONTROLLED LED ARRAY
DESCRIPTION [Para 1] Background of the invention [Para 2] Held of the Invention
[Para 31 The present Invention generally relates to Light Emitting Diode (LED) arrays, and more specifically to a method and apparatus for Increasing reliability of operation of the LED arrays in lamps operating ar. higher temperatures. The invention also relates to the use of such lamps as brake/tail . lamps.of an automobile.
[Para 4] Related Art
[Para S] A light emitting diode (LED) commonly contains a semiconductor
p-n junction, and produces light with an intensity directly proportional to an
electric current flowing through it in the forward direction. Many of such LEDs
are often formed as an array, commonly to generate light of a desired level of
intensity.
[Para 6] LED arrays may In turn be packaged as lamps along with other components such as driver circuits and casings. One such appllcatJon is the use of LED array based lamps as brake and tail lamps In automobiles, in general, the brake light generates light of one intensity in response to brake being
applied, and a tail lamp generates light of another intensity especially during night.
[Para 7] One problem with LED array based lamps Is that the LED arrays may be susceptible to failures at high operating temperatures (i.e., in the general surroundings of the light or automobile). The source of such failures Is often that the operating temperature may cause an Increase in the temperature of P-N junctions in the LEDs, thereby further Increasing the temperature In the immediate vlsclnity of the LED arrays, which could destroy/burn the LED material {including the p-N junction, casing, or wire-bonding of the PN junction to connecting leads).
[Para 8} What is therefore needed Is a method and apparatus for Increasing the reliability of operation of the LED arrays in lamps operating at higher temperatures.
[Para 9) Brief Description of the Drawings [Para 10) The present invention will be described with reference to the accompanying drawings, which are described below briefly. [Para 11] Figure (Fig.) 1 is a block diagram illustrating the details of a portion of a lamp according to an aspect of the present invention. [Para 12] Figure 2 Is a circuit-level diagram illustrating the manner in which temperature compensation is provided according to an aspect of the present invention.
[Para 13] Figure 3 Is a table containing the values of forward current through
an LED array for various values of ambient/operating temperature In one
embodiment.
[Para 14] Figure 4 is a circuit diagram of LED driver'block. HO and
associated LED array illustrating the manner in which.different intensity levels
of an LED array are provided in an embodiment .of the present invention.
[Para 1 5] In the drawings, like reference numbers generally indicate identical.
functionally similar, and/or structurally similar elements. The drawing in which
an element first appears is indicated by the leftmost dlgit(s) in the
corresponding reference number.
[Para 16] Detailed Description [Para 17] l. Overview
[Para 18) A lamp provided according to an aspect of the present invention contains a transistor passing a current of a magnitude determined by a voltage at a control terminal, and an LED array generating light with an intensity proportionate to the magnitude of the current. A driver block then controls the voltage level at the control terminal such that the current magnitude is reduced when the operating temperature rises. As a result, the heat generated by the LED array reduces when the operating temperature rises, thereby avoiding problems such as damage to the LEDs or other components of the lamp,
[Para 13] Such a lamp Is adapted for use as brakeytail lamp of an automobile according to another aspect of the present invention.
[Para 20] Several aspects of the invention are described below with reference to examples for Illustration, It should be understood that numerous specific details, relationships,, and methods are set forth to provide, a full understanding of the invention. One skilled in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details, or with other methods, etc. In other instances, welLknown structures or operations are not shown in detail to. avoid obscuring the Invention.
[Para 21J 2, Lamp
[Para 22] Figure 1 is a block diagram illustrating the details of a portion of a lamp according to aii aspect of the present Invention. The diagram is shown containing LED array 130, transistor 140, resistor (Re)150 and LED driver block 110. Each element is described In further detail below.
[Para 23] For ease of description, Figure 1 Is shown containing only one LED array and associated transistor 140 and resistor 150. Automotive lighting applications typically use multiple LED arrays (similar to LED array 130) and associated transistors and resistors. LED driver block 110 may then provide the signals described below to each of such LED arrays.
[Para 24] LED array 130 may contain one or more LEDs connected in series and powered by voltage on path 113. The Intensity of light emitted by LED array 130 would be proportionate to the current passing through the array (and
seen on path 134). With respect to implementation as a tail lamp in an automobile described below, the currents are controlled to generate a higher light intensity when a brake Is applied (as indicated by path 10!) and a lower-intensity when the lamp is to operate as a tail lamp (as indicated by path 103).
[Para 25] Transistor 140 Is shown as a $JT (bipolar Junction transistor) containing base terminal (connected to path 114), emitter terminal (connected to path 145) and collector terminal (connected to path 134). Transistor 140 Is in an ON state when the vpltage on path 114 exceeds a pre-determined threshold, and is in an OFF state otherwise.
[Para 26J The magnitude of the current flowing through transistor 140 (and thus LEO array 130) is also set by the voltage level on path 114, and the resistance offered by resistor ] 50. Resistor 1 50 is used to set a required value of base current (on path 145), and consequently LEO current (on path 134). Assuming the resistance is fixed, by increasing the voltage on path 114, the current also can be increased.
[Para 27] LEO driver block 110 controls the voltage level on path 114 to turn on/off the light, and also to obtain a desired light intensity from LED array 130. The voltage level on path 114 is controlled such that the voltage level is lowered at higher operating temperatures. As a consequence, LED current on path 134 reduces correspondingly, thereby reducing the junction temperature of the LEDs in LED array 130.
[Para 28] With respect to use In automotive applications, when path .101 Indicates that brake is appli.ed, a. high voltage is applied on path' 114 and a low voltage (but sufficiently high to turn transistor 140 on) is applied on path 114 when the lamp needs to operate merely as a tail light as indicated by path .103. Even when applying the high voltage corresponding to brake light, the voltage level on path 114 (and thus the current on path,!34) is reduced, potentially proportionate to operating temperatures.
[Para 29] The description Is continued with respect to the manner In which such compensation for temperature can be'attained according to an aspect of the present invention. The description is then continued with a .circuit level Implementation of LED driver block 110 in one embodiment.-
. [Para 30] 3. Temperature Compensation [Para 31] Figure 2 is a circuit-level diagram illustrating the manner In which temperature compensation is provided according to an aspect of the present invention. The diagram is shown containing resistors (R1)26S and (R3)270, and diodes(OI) 280 and (D2)281 within LED driver block 110. Some of the components of Figure 1 are also repeated and used in the analysis below. The components in LED driver block 110 operate to reduce the voltage on path 114 in response to an increase in operating temperature, thereby reducing the current in the LED array 130 of Figure 1, as described below.
[Para 32] Resistors R1, R2 and diodes Dl and D2 form a voltage* divider network which receives a voltage (which may be derived from voltage Indicating a "brake operatlon"on path. 101 indicating* as described below-with respect to Figure 3) on path 290. and provides a desired level of voltage on path 114, as described below.
[Para 33] Diodes Dl and D2 operate to provide temperature compensation to LED current on path 134. This may be appreciated by observing from Figure 2 that the voltage provided on path .114 Is equal to the sum of voltage drops across resistor R3, diode Dl and diode 02. Each of voltage drops across diodes Dl and D2 is inversely proportional to operating'.temperature of the circuit of Figure 2. Thus, as temperature varies, the voltage drops across diodes Dl and D2 changes inversely (or by negative correlation) by a corresponding value, thereby changing the voltage provided on path 114.
[Para 34] For example, an Increase In operating temperature may cause junaion temperatures"of LEDs in LED array 130 to increase. However, such an increase in operating temperature.causes a corresponding (and potentially proportional) decrease in voltage drops across diodes Dl and D2, thereby decreasing the voltage provided on path 114. Consequently, LED current on path 134 decreases correspondingly, the power dissipation in LED array 130 reduces and the junction temperature of LEDs in LED array 1 30 is maintained to lie within acceptable limits.
[Para 35] The operation of the circuit of Figure 2 is described In further detail below with respect to an example design specification for illustration.
[Para 36] 4. Illustration with an Example Design Specification .
[Para 37]- For illustration it is assumed that a lamp is to be designed with the
following design specification:
[Para 38] 1. Operating temperature range for the circuit of Figure 2 to be -
40degrees celcius(C) to +85C
[Para 39] 2. Maximum operating junction temperature (Tj) for each of LEDs
200, 210, 220 and 230-230 to be 125 degrees C.
[Para40] Circuit functioning is described below to show that, required
temperature compensation is provided to meet the example specification
above, ft Is assumed that LEDs 200, 210. 220 and 230 are used In a brake lamp
of an automobile, and that a current of 65milliAmperes through LEDs 200-230
is required for a corresponding level of light intensity. The following are also
assumed: Rated Maximum forward current for each of LEDs 200-
230 - 70mllIIAmperes (mA).
[Para 41] Operating forward current through each of LEDs 200-230 = 65mA.
[Para 42] Forward voltage drop at 65mA accross each of LEDs 200-230 =?
2.1Volts(V)
[Para 43] Minimum voltage on path 113 =. 10.5 V
[Para 44] Constant voltages of appropriate required value are available on
paths 101 and T03.
[Para 45] The computations below are shown with respect to LED 200 for illustration. (Assuming LEOs 200-230 have identical characteristics, the computations below would apply also to LEDs 210-230).
[Para 46J operating forward current (emitter current le on path 134) = 65mA ... Equation l
[Para 47] Forward voltage drop (Vf) across LED 20d = 2.10V ...
Equation 2
[Para 48] From equations 1 and 2:
[Para 491 Power dissipation (Pd)= Vf x
IE Equation 3
IParaSO] « 2.1 x 0.065
TParaSl] -0.136W
[Para 52] Thermal resistance(Rj) of casing (not shown) of
[Para S3] LED 200 = 325 degrees C/W Equation 4
[Para 54] From equations 3 and 4:
[Para 55] Increase In Junction temperature (AT)of LED 200 - Pd x RJ
Equation 5
[Para 56] =0.136x325
[Para 57] « 44.2 degrees C
[Para 58]Therefore for the maximum ambient operating temperature (Ta) of 85 C, TJ Is given by:
Tj . = .. Ta+ AT « 129.2 degrees C
Equation 6
[Para 59J It may be seen from equation 6 that the Junction temperature Tj exceeds the permitted maximum of 125 degreesC...
[Para 60] It is now shown that the operation of diodes 280/281 effectively compensates for an increase In ambient temperature Ta, and maintains the junction temperature Tj of LED 200 within acceptable limits (maximum of 125 degrees C, as per example specification).
[Para 61] Application of brakes would cause a constant voltage Vb to be present on path 101. Path 103 is assumed not to be connected to any voltage,
[Para 62] Therefore, voltage (Vbe) on path 114 is given by
[Para 63] Vbe ~ VD1 + VD2 + (Rl x \a.-. ..Equation 7
[Para 64] wherein:
[Para 65] VD1 is the voltage drop across dlode D1. [Para 66] VD2 is the voltage drop across diode D2. [Para 67] Rl is the relstance of Rl (2 70).
[Para 68] l8 is the current through the series path (275) containing Rl,' DV and D2. .
[Para 69] It has been assumed that a constant voltage is available on path 113. Therefore the value of I* may be assumed to be remain substantially constant across required operating temperature range. Consequently, equation 7 may be written as:
[Para 70] Vbe * VD1 + VD2 + kl Equation 8
[Para 71] wherein kl equals the term (Rl x IB) of equation 7.
[Para 72] As is well known,-the. forward voltage drop (such as VDl and .VD2 of equation 7) across a diode is given by the following equation:
tPara 73] forward voltage drop VD= {nkT/q)ln(lD/ls) Equation 9
[Para 74] wherein:
[Para 75] VD = Diode forward voltage,
[Para 76] n = Diode emission coefficient,
[Para 77] k = Boltzman constant
[Para 78] T= Temperature in degrees
[Para 79] q - Charge of electron
[Para 80] ID = Diode forward current
[Para 81] Is = reverse saturation current of diode
[Para 82] .At low values of forward current the relationship between junction temperature (TJd for diodes Dl and D2) and forward voltage VD (VDl and VD2
In Figure 2) is approximately linear, and hence a change in Junction
t
temperature produces a corresponding change by a factor K. This releatlon is given py:
[Para 83] AVD - ∆Tjd/ K Equation 10a
[Para 84} wherein:
[Para 85] AVD is equal to a change In diode forward voltage
[Para 86) ATjd is equal to a (corresponding)change in junction temperature of the diode
[Para 87] K is a proportionality factor (The units -of K are in "C/mV and the value Is typically in the range of 0.4 to 0.8 C/mV). The equation can be simplified to our application as below
[Para 88] Equation 10a may be written as:
[Para 89] AVD - A77x Kl Equation 10b
[Para 90] wherein: K1 = 1 /K, and is typically In the range of 1.25 to 2.S mV/C
[Para 91] For a maximum operating temperature-of 85 degreeC assumed in this example and an ambient temperature of 25 degrees C, change in diode junction temperature is given by: [Para 92] ∆Tjd - 83 - 2S - 60degC
[Para 93] Assuming a minimum value of 1.25 mV/C for Kl, change in diode forward voltage is given by:
[Para 94J ZWD - 75mV ,--:... Equation 11a .
[Para 95] Thus, for a change In ambient temperature from 25 degrees C to
85 degrees C, the change In forward voltage drop across each of diocfes Dl and
D2 is 75mV; and the total change in voltage drop across the series combination
of diodes Dl and D2 Is given by:
[Para961 AVD1 + AVD = 150mV Equation lib
[Para 97] if path 114 were disconnected from LED driver block 110, voltage
(Vbe) on path 114 is given by:
[Para 98] Vbe (without the LED driver block 110)= (12x0.065)+0.7
[Para 99] = 1-48 Volts
Equation 12
[Para 100] wherein
[Para 101] 12 ohms Is the resistance of Re.
[Para 102] 0.065(65mA earlier assumed operating'forward current) is
die current through Re
[Para 103} 0.7 is the cut-in base-to-emitter voltage of transistor 140.
[Para 104J With LED driver block 110 connected to path 114, Vbe of
equation 12 is reduce by 150mV (equation 11 b) and is given by:
[Para 105] . Vbe(with LED-driver block 110 connected) ~ 1.48-0.15 =
1.33V. Equation 13
[Para 106] Thus, the connection of diodes Dl and D2 has effectively
reduced Vbe from 1.48V to 1.33V at an.operating temperature of 85 degrees C.
[Para 107] Therefore the corresponding value of forward current (le) on
pathi 134.(and 145, neglecting base current of transistor 140) Is given by: .
[Para 108] le -033 -0.7) /12
- . ' " -
[Para 109] = • 52.5mA
Equation 14
[Para 110] wherein:
[Para 111] 1.33 Is the value of Vbe computed In equation 13.
[Para 112] 0.7 Is the cut-in base-to-emitter voltage of transistor 140
[Para 113] 12 ohms is the resistance of Re.
[Para 114] The corresponding value of change In junction temperature
of LED 200 Is therefore given by:
[Para 115] ATj « Pd X Rj .
[Para 116] =0.052.5x2.1x325
[Para 117] - 35.5degC ;..„: Equation 15
[Para 118] wherein:
[Para 119] Pd is the power disspated and is equal to 0.052Amperes
(52mA computed in equation 14) multiplied by 2,1V (forward voltage drop
across LED 200), and
[Para 120] Rj Is given in equation 4.
. [Para 121] Thus, from equatio 15, Junction temperature Tj of LED 200 is
given by:
[Para 1221 Tj~Ta+.ATJ
[Para 123] =85 + 35.35
[Para 124] = 120.5 degrees C , .'....; Equation 16,- •■ ■ •
[Para 125] It may be seen from equation T6 that the junction
temperature TJ of LED 200 is less than the maximum value Of 125 degrees C permitted by the design specification..
[Para 126] Thus, it has been shown diat the variation In forward voltage
drop across diodes D1 and D2 has effectively compensated for temperature and helped maintain junction temperature of LED 200 within acceptable limits. Junction temperatures of LEDs 210-230 will similarly be maintained with In the acceptable limit by the operation of diodes D1 and D2 of LED driver block 110.
[Para 127] Figure 3 Is a table containing the values of forward current
through LED array 130 for various values of ambient temperature. Column 1 lists ambient temperatures for which the corresponding forward currents are listed in column 2. It may be verified that the corresponding junction temperatures for the various values of forward current listed in column 2 lie within the acceptable limit required in this example.
(Para 128] • It may also be desirable to have control on the intensity level
of LEDs in LED array. 130. For example", in an automobile, "brake" indication generally requires higher intensity (han a "tail" light intensity. The LED driver blocic 110 of Figures 1 and 2 could incorporate features to facilitate intensity control of LEDs (for brake indication and tail light operation), while providing the temperature-compensation feature described above. Accordingly the description is continued to illustrate such a feature according to another aspect of the present invention.
[Para 129] 5. LED Intensity control to provide brake and tail indications
[Para 130] Figure 4 is a circuit-level diagram of LED driver block 110
and associated LED array illustrating the manner in which different Intensity levels of an LED array are provided in an embodiment of the present invention. The diagram is shown.containing LED array 130, transistor 140, resistor (Re) 150 and LED driver block 110..
[Para 131] LED array 130 is shoWn containing LEDs 200, 210, 220 and
230, and LED driver block 110 is shown containing resistors. 450, and (D5)-440, resistors zener diodes (Zt) 481 and (Z2) 482; and transistor 460. The remaining components of Figure 1 are repeated for ease of description.
[Para 132] Resistors R1, R2 and diodes D1 and D2 form.a voltage
divider network which receives a voltage on path 290, and provide a desired
level of voltage .on path 114 to obtain a corresponding desired level of intensity from LED array 130, as noted above/ Resistors R5 and R4 are current-limiting resistors. Diode D5 is used, to prevent damage to zener diode 22 in the event the voltage between brake (101) and ground (105) is negatlve.Diodes Dl and D2 operate to provide temperature compensation to LED current on path 134 as described above, and the description is not.repeated here for the sake pf conciseness.
[Para 133] Voltages indicating a "brake" operation and a "tail lamp ON"
operation are provided externally on paths 101 and 103 respectively, and generally are provided by a same source. Diode D3 blocks a voltage provided on path 101 from appearing on path 103. Similarly, diode D4 blocks a voltage provided on path 103 from appearing on path 101. Thus diodes D3 and D4 provide protection to voltage sources providing corresponding "brake" and "tail lamp ON* voltages on paths 101 and 103 respectively. Voltage on path 112 for supplying current to LED array 130 is equal to the greater of the voltages on paths 101 and 103 minus diode drop due to D4 or D3. In the example embodiment of Figure 4, voltages on path 101 and 103 are equal, and chosen to be 14 V.
[Para 134] Zener diode Z\ has a breakdown voltage of 5J Volts (V).
Thus, when voltage on path 103 is greater than 5.W plus diode drop (typically 0.7V)due to. D3; the operation of 21 causes a voltage of 5.1 V to be present on path 290. Similarly, zener diode 22 has a breakdown voltage of 5.1 Volts (v).
Thus, when voltage on path 101 is greater than 5.1V plus diode drop (typically
0;7V)due to DS, the operation of Z2 causes a voltage of 5.1 V to be present on
path 291. . .
[Para 135] Transistor 460 is shown as a 5JT (bipolar Junction transistor)
containing base (control) terminal (connected to path 291), emitter terminal (connected to path 292) and collector terminal (connected to path 290), The emitter terminal and the collector terminal form a pair of terminals between which a current path would be present. Transistor 460 Is in an ON state when" the voltage on path 101 exceeds 5.1V plus diode drop (typically 0,7V)due to DS, and is in an OFF state otherwise.
{Para 136] The operation of the circuit of Figure 4 is now described to
illustrate obtaining one (high) intensity level of LED array 130 corresponding to when brake Is applied (i.e a corresponding voltage is present on path 101), and a second (low) intensity level of LED array 130 corresponding to when only tail lamp functioning is required (i.e a corresponding-voltage Is present on path 103, and no voltage Is present on path 101).
[Para 137] Tail light ON operation:
[Para 138] Transistor 460 is in the OFF condition, as there would be no
voltage on path 101 .When a required value of voltage (to indicate tali light ON condition) is present on path 103 (Tail), zener diode Z1 operates in the breakdown region, and 5.1 V is present on path 290.
[Para 1391 Rl, R3, Dl and D2 form a voltage divider-network. Therefore
for a voltage of S.iy on path 290, the value of voltage on path 114 is given by:
[Para 140J Vbe = [(SJ - 0.78) x (33/33033)] +0.78 volte
Equation 17
[Para 141] wherein:
[Para 142) • Vbe is the voltage on path 114.
[Paral43J 5.1V is the voltage on path 290.
[Para 144] 33 is the value of resistance of resistor R3,
[Para 145] 33000 is the value of resistance of resistor Rl.
[Para 146] 0.78V is the sum of diode drops (assumed to be 0.39V) due
to each of 01 and D2.
[Para 147] from equation 17, Vbe (for tali light ON) Is approximately
equal to 1.3V.
[Para 148] Therefore, the value of emitter current (path 145) and
consequently LED.current (path 134) is given by:
[Para 149] LED current - (0.78-0.7)/12 (approximately)
[Para ISO] = 6.66mA
..Equation 18.
[Para 151] Thus an intensity corresponding to 6.66mA is provided by
LED array 130.
[Para 152] Brake light operation:
[Para 1531 A required value of voltageflndicating brake operation) is
applied on path 101. Hence, zener diode Z2 operates in the breakdown region,
and 5.1 V Is present on path 291,thereby turning transistor 460 ON. Thus,
resitor R2 is connected to path 290. This effectively casuses resistors Rl and R2
to be connected hi parallel. Since value of RZ (assumed in this example )680
ohm is much smaller than the value of Rl (33000 ohms), the effective parallel
relstance of Rl and R2 may be approximated by a value of R2, l.e 680 ohms,
and the'effect of resitor Rl may be removed from the calculations given below,
[Para 1541 R2 , R3P Dl and D2 form a voltage divider network. Therefore
for a voltage of 5. IV on path 291, the value.of voltage on path 114.1s given by:
[Para 155] Vbe = [(5:1 - 1.3) x (33/713)1 +1.3 volts
Equation 19
[Para 156] wherein:
[Para 157] Vbe is the voltage on path 114.
[Para 158] 5.1 V is the voltage on path 290.
[Para 159] 33 ohms Is the value of resistance of resistor R3.
[Para 160] 713 ohms Is the sum of resistances R2 (680 ohms> and R3(33
ohms).
[Para 161] 13V is the sum of voltage drops (assumed to be 0.39V due
to each of Dl and D2) plus 0.52V drop due to the base-emitter junction of BJT
460.
{Para 162] From equation 19, Vbe {for brake light operation) is
approximately equal to 1.48V

[Para 163] Therefore,. the value of emitter current (path 145) and
consequently LED turrent (path 134) is given By:
[Para 164] LED current « (l .48-0.7)/12 (approximately)
[Para 165] -65mA Equation 20.
[Para 166] Thus, a greater light intensity corresponding to 65mA is
provided by LED array 130.
[Para 167] It has thus been shown that the LED driver block enables LED-
array 130 to provide two intensity levels, a lower level for a tail light operation, and a higher intensity for a brake operation.
[Para 168] 6. Conclusion
[Para 169] While various embodiments of the present invention have
been described above, it should be understood that they have been presented by way of example only, and hot limitation. Thus, the breadth and scope of the present invention should not be limited by any of the-above described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

What Is claimed Is: [Claim 1] 1. A lamp comprising:
a transistor (140) having a control terminal (114), said transistor passing a current of a magnitude determined by a voltage at said control terminal (114);
a LED array (130) coupled to said transistor (140), and generating light with an intensity, proportionate to said magnitude Qf said current; and
a driver block (110) coupled to said control terminal and generating said voltage with a first level when an operating temperature of said lamp equals a first value, and a with a second level when said operating temperature of said lamp equals a second value, wherein said first value is not equal to said second value and said first level is not equal to said second level.
[Claim 2] 2. The lamp of claim 1, wherein said first value is more than said second value, and said first level causes said magnitude to be lesser compared to the. magnitude caused by said second level, whereby LEDs in said LED array (130) pass less current with an Increase In operating temperature.
[Claim 3] 3. The lamp of claim 2, wherein- said LED array (130) is coupled to said transistor (140) such that the same magnitude of current passes through both of said transistor (140) and said LED array (130).
[Claim 41 4. The lamp of claim 2, wherein said driver block (110) comprises: . at least one component (280, 281) having a cross-voltage-which has a ' negative correlation with said operating temperature,
wherein said voltage is derived across said component (280, 281),
[Claim 5] 5. the lamp of claim 4, wherein said at least one component (280, 281) comprises a diode.
[Claim 6] 6. The lamp of claim 4, wherein said lamp is used in an automohile, wherein said driver block receives a first signal indicating that a brake Is being applied and a' second signal indicating that a tail light is to be present, said driver block (110) receives a first signal (101) Indicating that a brake Is being applied and a second signal (103) indicating that a tall light is to be present, said driver block (110) receiving said first signal (101) and said second signal (103) and generating said voltage with a third voltage level when said first signal (101) indicates that said brake is applied and with a fourth voltage level when said second, signal (103) indicates that said tail light Is to be present.
(Claim 7] 7. The lamp of claim 6, wherein said driver block (110) comprises: a first resistor (270), a second resistor (265) and a third resistor (266); a first transistor (460) having a control terminal (291) and a pair of
terminals (290, 292) having a current channel in between;
a first constant voltage reference (481) and a second constant voltage
reference (482),
. . wherein said second resistor (26 5) and a combination of said first ■ transistor (460) and said third resistor (266) are connected in parallel between a first node and a* second, node, wherein each of said first signal (101) and said second signaf 003) (s coupled to said first node,
wherein a terminal of said first constant voltage reference (481) is coupled to said first node, another terminal of said first constant voltage reference being coupled to a constant voltage level,.
wherein a terminal of said second constant voltage reference (482) Is coupled to said control terminal (291) of said first transistor (460) and said first signal (101)., another terminal of said second constant Voltage reference (482) being coupled to a constant voltage level,
wherein one of said pair of terminals (290) of said first transistor (460) is - coupled to said first node, and the other one of said pair of terminals (292) of said first transistor (460) Is coupled to said third resistor (266),
wherein said first resistor (270) is coupled between said second node and said at least one component (280, 281).
[Claim 8] 8. The lamp of claim 7, wherein said at least one component (280, 281) comprises a diode, and said first constant voltage reference (481) comprises a zener diode.