Abstract:
Methods and apparatus for open lamp detection in electronic circuits are disclosed. An example apparatus to perform open circuit detection associated with an electrical component included in a device disclosed herein comprises a sampling circuit to attempt to pull a sampling current through the electrical component during initialization of the device, a comparator to compare a result produced by the sampling circuit to a reference value, and a timing circuit to cause the sampling circuit to attempt to pull the sampling current through the electrical component and to cause an output of the comparator to be stored after the comparator has compared the result produced by the sampling circuit to the reference value.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    This disclosure relates generally to electronic circuits and, more particularly, to methods and apparatus for open lamp detection in electronic circuits. 
       BACKGROUND 
       [0002]    In modern portable consumer devices, such as cellular phones and notebook computers, it is becoming increasingly popular to use white light emitting diodes (WLEDs) to implement device displays. For example, WLEDs may be used to implement a backlight of a display such that the brightness of the backlight is controlled by varying the amount of current through the WLEDs. However, as more current is allowed to flow through the WLEDs to increase the backlight&#39;s brightness, a corresponding increase in forward voltage is needed to keep the WLEDs turned on. 
         [0003]    In many portable devices, a charge pump circuit is used to boost the forward voltage applied to the WLEDs as the battery powering the portable device discharges. For example, voltages at the cathodes of the WLEDs implementing a display&#39;s backlight may be detected and compared to a reference level to determine whether sufficient forward voltage is being applied to the WLEDs. If the detected cathode voltages are not greater than the reference level, the charge pump circuit is activated to boost the voltage applied to the anodes of the WLEDs. However, if one or more WLEDs are in an open lamp condition corresponding to, for example, a missing, disconnected or damaged WLED, the detected cathode voltage(s) for such open lamp WLED(s) may drop below the reference level even when the battery voltage is sufficient to drive the cathode voltages of the other WLEDs higher than the reference level. Such open lamp WLED(s) can, therefore, cause the charge pump to be activated prematurely, thereby reducing the battery life and/or the useful operating time for the portable device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a block diagram of a first example open lamp detection circuit to detect an open lamp condition associated with a light emitting diode included in a first example device. 
           [0005]      FIG. 2  is a block diagram of a second example open lamp detection circuit to detect open lamp conditions associated with multiple light emitting diodes included in a second example device. 
           [0006]      FIG. 3  is a block diagram of a charge pump enable circuit implemented using the second example open lamp detection circuit of  FIG. 2 . 
           [0007]      FIG. 4  is a flowchart representative of a single open lamp detection process that may be implemented by the first example open lamp detection circuit of  FIG. 1   
           [0008]      FIG. 5  is a flowchart representative of a multiple open lamp detection process that may be implemented by the second example open lamp detection circuit of  FIG. 2 . 
           [0009]      FIG. 6  is a flowchart representative of a charge pump enable process that may be implemented by the example charge pump enable circuit of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    A block diagram of a first example device  100  including a first example open lamp detection circuit  105  is shown in  FIG. 1 . The first example open lamp detection circuit  105  is configured according to the methods and/or apparatus described herein to detect an open lamp condition associated with a light emitting diode (LED)  110  included in the first example device  100 . An open lamp condition associated with the example LED  110  may correspond to, for example, the LED  110  being missing from the device or inoperative, a connection to at least one of the cathode  115  or anode  120  of the LED  110  being broken, etc. The example LED  110  may be implemented by, for example, a white LED (WLED) as discussed above. 
         [0011]    The example open lamp detection circuit  105  includes a lamp input  125  configured to be coupled with the cathode  115  of the example LED  110 . In the illustrated example, the open lamp detection circuit  105  operates during an initialization phase occurring before normal operation of the first example device  100  to determine whether the LED  110  coupled to the lamp input  125  is associated with an open lamp condition. The initialization phase is defined by an initialization signal  130  output by a timing circuit  135  included in the example open lamp detection circuit  105 . The example timing circuit  135  is further configured to receive a clock signal  140  and an enable signal  145 . In an example implementation, the clock signal  140  is derived from a local oscillator or other clock source included in or coupled to the first example device  100 . For example, the clock signal  140  may correspond to or be derived from a system clock driving other circuitry included in the device  100 . The enable signal  145  of the illustrated example may correspond to a startup signal generated when the first example device  100  is powered on, reset, etc. 
         [0012]    An inset  150  included in  FIG. 1  illustrates an example initialization signal  130  output by the example timing circuit  135  in response to an example input clock signal  140  and an example input enable signal  145 . In the example illustrated in the inset  150 , the enable signal  145  is asserted by a source external to the open lamp detection circuit  105  at some time after the clock signal  140  becomes active. Then, at a first predetermined time after assertion of the enable signal  145  (e.g., such as after a certain number of clock pulses have occurred), the example timing circuit  135  asserts the initialization signal  130  to indicate the start of the initialization phase. Then, at a later, second predetermined time, the example timing circuit  135  de-asserts the initialization signal  130  to indicate the end of the initialization phase. As noted above, it is during the initialization phase (i.e., when the initialization signal  130  is a logic HIGH) that the open lamp testing is performed. 
         [0013]    To determine whether the LED  110  coupled to the lamp input  125  is associated with an open lamp condition, the example open lamp detection circuit  105  includes a sampling circuit implemented by a sampling transistor  155  to enable the operation of the LED  110  to be examined during the initialization phase defined by the initialization signal  130 . The sampling transistor  155  may be implemented by a field effect transistor (FET) or any other appropriate switching device. In the illustrated example, the initialization signal  130  drives the gate input of the sampling transistor  155 , causing the sampling transistor  155  to be enabled at the start of the initialization phase. Enabling the sampling transistor  155  causes the lamp input  125  and, thus, the cathode  115  of the LED  110  to be pulled toward a ground potential as shown. Because the anode  120  is coupled to the source voltage  160  (labeled as VOUT  160  in  FIG. 1 ), a small sampling current will flow through the LED  110  when the sampling transistor  155  is enabled. This, in turn, causes a voltage differential between the source and drain of the sampling transistor  155 , which further causes a positive voltage to be present at the cathode  115  and, thus, the lamp input  125 , assuming that the LED  110  is operating properly. However, if the LED  110  is associated with an open lamp condition, no sampling current will flow through the LED  110 . With no current able to flow through the LED  110 , enabling the sampling transistor  155  during the initialization phase would cause the lamp input  125  to have a voltage of substantially zero volts corresponding to the ground potential because, with no current flow, the voltage differential between the source and drain of the sampling transistor  155  is zero. 
         [0014]    To determine whether the voltage at the cathode  115  and, thus, the lamp input  125 , corresponds to the LED  110  being in a proper operating condition or an open lamp condition, the example open lamp detection circuit  105  further includes a comparator  165 . The comparator  165  may be implemented by, for example, a differential amplifier or any other comparison circuit/device. The comparator  165  of the illustrated example is configured to compare the voltage at the lamp input  125  (and, thus, the cathode  115  of the LED  110 ) to a reference voltage  170 . The reference voltage  170  may be fixed or programmable, and is selected to be less than the expected voltage at the cathode  115  of the LED  110  (or, equivalently, the expected voltage differential between the source and drain of the sampling transistor  155 ) when the sampling transistor  155  is pulling the sampling current through a properly operating LED  110  (i.e., when the LED  110  is not associated with an open lamp condition). In an example implementation, the reference voltage  170  may be set to approximately 50 mV when the source voltage  160  (i.e., VOUT  160 ) corresponds to, for example, 3.5 V. In such an example implementation, the cathode  115  of the LED  110  (and, thus, the lamp input  125 ) would have a voltage greater than 50 mV when the sampling transistor  155  is enabled and the LED  110  is operating properly. However, if the LED  110  is associated with an open lamp condition, the cathode  115  of the LED  110  (and, thus, the lamp input  125 ) would have a voltage of approximately zero volts (corresponding to a zero voltage differential between the source and drain of the sampling transistor  155 ), which is less than the 50 mV reference voltage  170 . 
         [0015]    The open lamp detection circuit  105  of the illustrated example further includes a latching circuit implemented by a flip flop  175  to latch an output of the comparator  165  corresponding to the comparison of the voltage at the cathode  115  of the LED  110  (and, thus, the lamp input  125 ) to the reference voltage  170  during the initialization phase defined by the initialization signal  130 . The flip flop  175  may be implemented by, for example, a D flip-flop (as shown), or by any other appropriate flip flop, storage element/device, etc. In the illustrate example, the data input of the flip flop  175  is coupled to the output of the comparator  165 , and the clock input of flip flop  175  is coupled to the initialization signal  130  through an inverter  180 . Because an inverted form of the initialization signal  130  is applied to the clock input of the flip flop  175 , the data input of the flip flop  175  coupled to the output of comparator  165  will not be latched until the end of the initialization phase defined by the initialization signal  130 . Waiting until the end of the initialization phase to latch (or, equivalently, to store) the output of the comparator  165  provides sufficient time for the voltage at the cathode  115  of the LED  110  (and, thus, the lamp input  125 ) to settle after the switching transistor  155  has been enabled. 
         [0016]    After the output of the comparator  165  has been latched by the flip flop  175 , the inverting output of the flip flop  175  provides a lamp open signal  185  and the non-inverting output of the flip flop  175  provides a lamp not open signal  190 . In the illustrated example, if the LED  110  is operating properly, the voltage at the cathode  115  of the LED  110  (and, thus, the lamp input  125 ) will be greater than the reference voltage  170 , causing a logic HIGH to be output by the comparator  165 . This logic HIGH output will be latched by the flip flop  175 , resulting in the lamp open signal  185  being a logic LOW and the lamp not open signal  190  being a logic HIGH. This output arrangement indicates that the LED  110  is not associated with an open lamp condition and, therefore, is operating properly. Conversely, if the LED  110  is associated with an open lamp condition, the voltage at the cathode  115  of the LED  110  (and, thus, the lamp input  125 ) will be less than the reference voltage  170 , causing a logic LOW to be output by the comparator  165 . This logic LOW output will be latched by the flip flop  175 , resulting in the lamp open signal  185  being a logic HIGH and the lamp not open signal  190  being a logic LOW. This output arrangement indicates that the LED  110  is associated with an open lamp condition and, therefore, is not operating properly. 
         [0017]    After the initialization phase defined by the initialization signal  130  is complete, the sampling transistor  155  will be disabled and, thus, will not affect the normal operation of the LED  110  and any associated LED control/monitoring circuitry coupled thereto (e.g., as indicated by the directional arrow in  FIG. 1 ). However, the lamp open signal  185  and the lamp not open signal  190  will remain latched and, thus, may be used during later operation of the first example device  100  to indicate whether the LED  110  is associated with an open circuit condition. For example, the lamp open signal  185  may be used as an input to a charge pump enable circuit (not shown) to indicate whether a monitored voltage associated with the LED  110  should be allowed to determine whether a charge pump used to drive the source voltage  160  (i.e., VOUT  160 ) should be enabled. In such an example, the lamp open signal  185  being set to a logic HIGH may indicate to the charge pump enable circuit that the LED  110  corresponding to the lamp open signal  185  is associated with an open lamp condition and, thus, a monitored voltage associated with the LED  110  should not be allowed to enable the charge pump. Conversely, the lamp open signal  185  being set to a logic LOW may indicate to the charge pump enable circuit that the LED  110  corresponding to the lamp open signal  185  is not associated with an open lamp condition (e.g., is operating properly) and, thus, a monitored voltage associated with the LED  110  should be allowed to enable the charge pump. An example charge pump enable circuit employing an open lamp detection circuit (e.g., such as the open lamp detection circuit  105 ) is shown in  FIG. 3  and discussed in greater detail below. 
         [0018]    A block diagram of a second example device  200  including a second example open lamp detection circuit  205  is shown in  FIG. 2 . The second example open lamp detection circuit  205  is configured according to the methods and/or apparatus described herein to detect open lamp conditions associated with the LEDs  210 A and  210 B included in the second example device  200 . The example LEDs  210 A and/or  210 B include respective cathodes  215 A/ 215 B, and anodes  220 A/ 220 B, and may be implemented by, for example, WLED(s) as discussed above. The second example open lamp detection circuit  205  of  FIG. 2  includes some elements in common with the first example open lamp detection circuit  105  of  FIG. 1 . As such, like elements in  FIGS. 1 and 2  are labeled with the same reference numerals. For brevity, the detailed descriptions of these like elements are provided above in connection with the discussion of  FIG. 1  and, therefore, are not repeated in the discussion of  FIG. 2 . 
         [0019]    Turning to  FIG. 2 , the second example open lamp detection circuit  205  includes a lamp input  225 A configured to be coupled with the cathode  215 A of the example LED  210 A, and a lamp input  225 B configured to be coupled with the cathode  215 B of the example LED  210 B. In the illustrated example, the open lamp detection circuit  205  operates during an initialization phase occurring before normal operation of the second example device  200  to determine whether either or both of the LEDs  210 A and  210 B coupled to the respective lamp inputs  225 A and  225 B are associated with open lamp condition(s). The initialization phase is defined by the initialization signal  130  output by a timing circuit  235  included in the example open lamp detection circuit  205 . Similar to the example timing circuit  135  of  FIG. 1 , the example timing circuit  235  is configured to input the clock signal  140  and the enable signal  145  for generating the initialization signal  130  as described above in connection with  FIG. 1 . Additionally, the example timing circuit  235  generates a first channel enable signal  245 A and a second channel enable signal  245 B discussed in greater detail below. 
         [0020]    An inset  250  included in  FIG. 2  illustrates the example initialization signal  130  output by the example timing circuit  235  in response to the example input clock signal  140  and the example input enable signal  145 . The initialization signal  130  and the initialization phase it defines is discussed above in connection with the inset  150  of  FIG. 1 . Additionally, the inset  250  also illustrates the example first and second channel enable signals  245 A- 245 B output by the example timing circuit  235 . In the example illustrated in the inset  250 , at a first predetermined time after assertion of the initialization signal  130 , the example timing circuit  235  asserts the first channel enable signal  245 A to indicate the start of a first window of time during which the operating status of the first LED  210 A may be examined. Then, at a later, second predetermined time, the example timing circuit  235  de-asserts the first channel enable signal  245 A to indicate the end of this first window of time. Additionally, the example timing circuit  235  asserts the second channel enable signal  245 B to indicate the start of a second window of time during which the operating status of the second LED  210 B may be examined. Then, at a later, third predetermined time, the example timing circuit  235  de-asserts the second channel enable signal  245 B to indicate the end of this second window of time. As discussed in greater detail below, the first and second channel enable signals  245 A- 245 B allow the single comparator  165  to be re-used for examining the operational status of both the first and second LEDs  210 A- 210 B in a substantially sequential manner. 
         [0021]    To determine whether the first LED  210 A coupled to the first lamp input  225 A is associated with an open lamp condition, the example open lamp detection circuit  205  includes a first sampling circuit implemented by a sampling transistor  255 A to enable the operation of the LED  210 A to be examined during the first window of time defined by the first channel enable signal  245 A. The sampling transistor  255 A may be implemented by a field effect transistor (FET) or any other appropriate switching device. In the illustrated example, the initialization signal  130  drives the gate input of the sampling transistor  255 A, causing the sampling transistor  255 A to be enabled at the start of the initialization phase. Enabling the sampling transistor  255 A causes the first lamp input  225 A and, thus, the cathode  215 A of the first LED  210 A to be pulled toward a ground potential as shown. Because the anode  220 A is coupled to the source voltage  160  (labeled as VOUT  160  in  FIG. 2 ), a small sampling current will flow through the first LED  210 A when the sampling transistor  255 A is enabled. This, in turn, causes a positive voltage to be present at the cathode  215 A and, thus, the first lamp input  225 A (e.g., due to a voltage differential between the source and drain of the sampling transistor  255 A), assuming that the first LED  210 A is operating properly. However, if the first LED  210 A is associated with an open lamp condition, no sampling current will flow through the LED  210 A. With no current able to flow through the LED  210 A, enabling the sampling transistor  255 A during the initialization phase would cause the lamp input  225 A to have a voltage of substantially zero volts corresponding to the ground potential (e.g., due to a substantially zero voltage differential between the source and drain of the sampling transistor  255 A). 
         [0022]    Similarly, to determine whether the second LED  210 B coupled to the second lamp input  225 B is associated with an open lamp condition, the example open lamp detection circuit  205  includes a second sampling circuit implemented by a sampling transistor  255 B to enable the operation of the LED  210 B to be examined during the second window of time defined by the second channel enable signal  245 B. The sampling transistor  255 B may be implemented by a field effect transistor (FET) or any other appropriate switching device. In the illustrated example, the initialization signal  130  drives the gate input of the sampling transistor  255 B, causing the sampling transistor  255 B to be enabled at the start of the initialization phase. Enabling the sampling transistor  255 B causes the second lamp input  225 B and, thus, the cathode  215 B of the second LED  210 B to be pulled toward a ground potential as shown. Because the anode  220 B is coupled to the source voltage  160  (labeled as VOUT  160  in  FIG. 2 ), a small sampling current will flow through the second LED  210 B when the sampling transistor  255 B is enabled. This, in turn, causes a positive voltage to be present at the cathode  215 B and, thus, the second lamp input  225 B (e.g., due to a voltage differential between the source and drain of the sampling transistor  255 B), assuming that the second LED  210 V is operating properly. However, if the second LED  210 B is associated with an open lamp condition, no sampling current will flow through the LED  210 B. With no current able to flow through the transistor  210 B, enabling the sampling transistor  255 B during the initialization phase would cause the lamp input  225 B to have a voltage of substantially zero volts corresponding to the ground potential (e.g., due to a substantially zero voltage differential between the source and drain of the sampling transistor  255 B). 
         [0023]    To determine whether either or both of the voltages at the cathodes  215 A and  215 B and, thus, the respective lamp inputs  225 A and  225 B, correspond to either or both of the LEDs  210 A and  210 B being in a proper operating condition or an open lamp condition, the example open lamp detection circuit  205  further includes the single comparator  165  described above in connection with  FIG. 1 . The comparator  165  of the illustrated example is configured to sequentially compare the voltages at the lamp inputs  225 A and  225 B (and, thus, the cathode  215 A of the LED  210 A and the cathode  215 B of the LED  210 B, respectively) to a reference voltage  170 . As discussed above in connection with  FIG. 1 , the reference voltage  170  may be fixed or programmable, and is selected to be less than the expected voltages at the cathodes  215 A and  215 B when the sampling currents are pulled through the properly operating LEDs  210 A and  210 B (i.e., when the LEDs  210 A and  210 B are not associated with an open lamp condition). 
         [0024]    To enable the comparator  165  to sequentially compare the voltages at the lamp inputs  225 A and  225 B (and, thus, the cathode  215 A of the LED  210 A and the cathode  215 B of the LED  210 B, respectively) to the reference voltage  170 , the example open lamp detection circuit  205  further includes transmission gates  265 A and  265 B. In the illustrated example, the first channel enable signal  245 A drives a control input of the first transmission gate  265 A. The first transmission gate  265 A, therefore, couples the lamp input  225 A (and, thus, the cathode  215 A of the LED  210 A) to the comparator  165  during the first window of time defined by the first channel enable signal  245 A. During this first window of time, the comparator  165  is able to compare the voltage at the lamp input  225 A (and, thus, the cathode  215 A of the LED  210 A) to the reference voltage  170 . Similarly, the second channel enable signal  245 B drives a control input of the second transmission gate  265 B. The second transmission gate  265 B, therefore, couples the lamp input  225 B (and, thus, the cathode  215 B of the LED  210 B) to the comparator  165  during the second window of time defined by the second channel enable signal  245 A. During this second window of time occurring after the first window of time, the comparator  165  is able to compare the voltage at the lamp input  225 B (and, thus, the cathode  215 B of the LED  210 B) to the reference voltage  170   
         [0025]    The open lamp detection circuit  205  of the illustrated example further includes a latching circuit implemented by flip flops  275 A and  275 B. The flip flop  275 A is configured to latch an output of the comparator  165  corresponding to the comparison of the voltage at the cathode  215 A of the LED  210 A (and, thus, the lamp input  225 A) to the reference voltage  170  during the first window of time defined by the first channel enable signal  245 A. The flip flop  275 B is configured to latch an output of the comparator  165  corresponding to the comparison of the voltage at the cathode  215 B of the LED  210 B (and, thus, the lamp input  225 B) to the reference voltage  170  during the second window of time defined by the second channel enable signal  245 B. The flip flops  275 A and/or  275 B may be implemented by, for example, a D flip-flop (as shown), or by any other appropriate flip flop, storage element/device, etc. 
         [0026]    In the illustrated example, the data input of the flip flop  275 A is coupled to the output of the comparator  165  through an AND gate  278 A whose other input is driven by the first channel enable signal  245 A. The clock input of example flip flop  275 A is also coupled to the first channel enable signal  245 A, but through an inverter  280 A. The AND gate  278 A and the inverter  280 A cause the flip flop  275 A to latch the output of the comparator  165  at the end of the first window of time defined by the first channel enable signal  245 A. This arrangement provides sufficient time for the voltage at the cathode  215 A of the LED  210 A (and, thus, the lamp input  225 A) to settle after the switching transistor  255 A has been enabled, thereby allowing for an accurate comparison with the reference voltage  170 . 
         [0027]    Similarly, in the illustrated example, the data input of the flip flop  275 B is coupled to the output of the comparator  165  through an AND gate  278 B whose other input is driven by the second channel enable signal  245 B. The clock input of example flip flop  275 B is also coupled to the second channel enable signal  245 B, but through an inverter  280 B. The AND gate  278 B and the inverter  280 B cause the flip flop  275 B to latch the output of the comparator  165  at the end of the second window of time defined by the second channel enable signal  245 B. This arrangement provides sufficient time for the voltage at the cathode  215 B of the LED  210 B (and, thus, the lamp input  225 B) to settle after the switching transistor  255 B has been enabled, thereby allowing for an accurate comparison with the reference voltage  170 . 
         [0028]    After the output of the comparator  165  has been latched by the flip flop  275 A, the inverting output of the flip flop  275 A provides a lamp open signal  285 A and the non-inverting output of the flip flop  275 A provides a lamp not open signal  290 A. In the illustrated example, if the LED  210 A is operating properly, the voltage at the cathode  215 A of the LED  210 A (and, thus, the lamp input  225 A) will be greater than the reference voltage  170 , causing a logic HIGH to be output by the comparator  165  during the first window of time defined by the first channel enable signal  245 A. This logic HIGH output will be latched by the flip flop  275 A, resulting in the lamp open signal  285 A being a logic LOW and the lamp not open signal  290 A being a logic HIGH. This output arrangement indicates that the LED  210 A is not associated with an open lamp condition and, therefore, is operating properly. Conversely, if the LED  210 A is associated with an open lamp condition, the voltage at the cathode  215 A of the LED  210 A (and, thus, the lamp input  225 A) will be less than the reference voltage  170 , causing a logic LOW to be output by the comparator  165  during the first window of time defined by the first channel enable signal  245 A. This logic LOW output will be latched by the flip flop  275 A, resulting in the lamp open signal  285 A being a logic HIGH and the lamp not open signal  290 A being a logic LOW. This output arrangement indicates that the LED  210 A is associated with an open lamp condition and, therefore, is not operating properly. 
         [0029]    Similarly, after the output of the comparator  165  has been latched by the flip flop  275 B, the inverting output of the flip flop  275 B provides a lamp open signal  285 B and the non-inverting output of the flip flop  275 B provides a lamp not open signal  290 B. In the illustrated example, if the LED  210 B is operating properly, the voltage at the cathode  215 B of the LED  210 B (and, thus, the lamp input  225 B) will be greater than the reference voltage  170 , causing a logic HIGH to be output by the comparator  165  during the second window of time defined by the second channel enable signal  245 B. This logic HIGH output will be latched by the flip flop  275 B, resulting in the lamp open signal  285 B being a logic LOW and the lamp not open signal  290 B being a logic HIGH. This output arrangement indicates that the LED  210 B is not associated with an open lamp condition and, therefore, is operating properly. Conversely, if the LED  210 B is associated with an open lamp condition, the voltage at the cathode  215 B of the LED  210 B (and, thus, the lamp input  225 B) will be less than the reference voltage  170 , causing a logic LOW to be output by the comparator  165  during the second window of time defined by the second channel enable signal  245 B. This logic LOW output will be latched by the flip flop  275 B, resulting in the lamp open signal  285 B being a logic HIGH and the lamp not open signal  290 B being a logic LOW. This output arrangement indicates that the LED  210 B is associated with an open lamp condition and, therefore, is not operating properly. 
         [0030]    After the initialization phase defined by the initialization signal  130  is complete, the sampling transistors  255 A and  255 B will be disabled and, thus, will not affect the normal operation of the LEDs  210 A and  210 B and any associated LED control/monitoring circuitry coupled thereto (e.g., as indicated by the directional arrows in  FIG. 2 ). However, the lamp open signals  285 A- 285 B and the lamp not open signals  290 A- 290 B will remain latched and, thus, may be used during later operation of the second example device  200  to indicate whether either or both of the LEDs  210 A and  210 B are associated with an open circuit condition. An example application employing the latched lamp not open signals  290 A- 290 B to indicate whether either or both of the LEDs  210 A and  210 B are associated with an open circuit condition is shown in  FIG. 3  and discussed in greater detail below. 
         [0031]    In the illustrated example of  FIG. 2 , the open lamp detection circuit  205  is configured to detect open lamp conditions associated with the two LEDs  210 A and  210 B included in the second example device  200 . However, the example open lamp detection circuit  205 , and/or any other open lamp detection circuit implemented according to the methods and/or apparatus described herein, could be readily adapted to detect open lamp conditions associated with any number of LEDs included in any type of device. Furthermore, the example open lamp detection circuit  205 , the example open lamp detection circuit  105  of  FIG. 1 , and/or any other open lamp detection circuit implemented according to the methods and/or apparatus described herein, could be readily adapted to detect open circuit condition(s) associated with any number and/or type(s) of device component(s), including but not limited to the example LEDs described above. 
         [0032]    For example, using the second example device  200  as a reference, one (or both) of the LEDs  210 A and  210 B could be replaced with any type of electrical component having, for example, two connection nodes. In such an example, one of the component nodes could be coupled to the source voltage  160  and the other of the component nodes could be coupled to a detection input of the example open lamp detection circuit  205  (e.g., such as the lamp input  225 A or the lamp input  225 B). In such an example configuration, the open lamp detection circuit  205  could detect an open circuit condition associated with the electrical component by comparing the voltage at the detection input of the open lamp detection circuit  205  to the reference voltage  170  in the manner described above. The voltage at the detection input of the open lamp detection circuit  205  will correspond to the voltage at the electrical component node which is coupled to the detection input of the open lamp detection circuit  205 . More generally, in this example, the voltage at the detection input of the open lamp detection circuit  205  would be related to the voltage drop between the two connection nodes of the electrical component. The example open lamp detection circuit  205  could be configured to detect an open circuit based on this differential voltage between electrical component nodes (as measured via the detection input of the open lamp detection circuit  205 ) through comparison with an appropriately set reference voltage  170 . 
         [0033]    In the examples of  FIGS. 1 and 2 , open lamp detection is illustrated as being based on detecting a voltage at a cathode (e.g., such as the cathodes  115 ,  215 A and/or  215 B) of a monitored LED (e.g., such as the LEDs  110 ,  210 A and/or  210 B, respectively). However, in other example implementations, open lamp detection according to the methods and apparatus described herein may be based on any appropriate voltage associated with monitored LED. For example, in one implementation, a voltage corresponding to the cathode of the monitored LED but detected via, for example, a resistive element coupled to the cathode could be used for open lamp detection. In another example implementation, a voltage at the anode of the monitored LED or a voltage corresponding to the anode but detected via, for example, a resistive element coupled to the anode could be used for open lamp detection. In yet another example implementation, a voltage detected at another location in the device but still associated with the monitored LED could be used for open lamp detection. 
         [0034]    A block diagram of a third example device  300  including the second example open lamp detection circuit  205  of  FIG. 2  to implement an example charge pump enable circuit  305  is shown in  FIG. 3 . The third example device  300  of  FIG. 3  includes many elements in common with the second example device  200  of  FIG. 2 . As such, like elements in  FIGS. 2 and 3  are labeled with the same reference numerals. For brevity, the detailed descriptions of these like elements are provided above in connection with the discussions of  FIGS. 1 and 2  and, therefore, are not repeated in the discussion of  FIG. 3 . 
         [0035]    Turning to  FIG. 3 , the example device  300  includes the LEDs  210 A and  210 B described above in connection with  FIG. 2 . The example device  300  also includes the example charge pump enable circuit  305  to determine whether to enable a charge pump, inductive voltage converter and/or any other voltage boosting circuit/device (not shown) to boost the source voltage  160  (i.e., VOUT  160 ) driving the LEDs  210 A and  210 B. Furthermore, the charge pump enable circuit  305  of the illustrated example includes the example open lamp detection circuit  205  to prevent the charge pump from being enabled in response to either or both of the LEDs  210 A and  210 B being in an open lamp condition, as discussed in greater detail below. 
         [0036]    In the particular example of  FIG. 3 , and as in the example of  FIG. 2 , the cathode  215 A of the LED  210 A and the cathode  215 B of the LED  210 B are coupled to the respective lamp inputs  225 A and  225 B of the example open lamp detection circuit  205 . Additionally, the cathode  215 A of the LED  210 A is coupled to a voltage monitor  3   10 A and the cathode  215 B of the LED  210 B is coupled to a voltage monitor  310 B. The voltage monitor  310 A is configured to measure the voltage at the cathode  215 A of the LED  210 A and to assert an output signal when the measured voltage falls below a level indicating that the charge pump should be enabled. Similarly, the voltage monitor  310 B is configured to measure the voltage at the cathode  215 B of the LED  210 B and to assert an output signal when the measured voltage falls below a level indicating that the charge pump should be enabled. Either or both of the voltage monitors  310 A and  310 B could be implemented by, for example, a comparator configured to compare an input voltage (e.g., the voltage at the cathode  215 A and/or the cathode  215 B) to a predetermined and/or programmable level at which the charge pump should be enabled to boost the source voltage  160  (i.e., VOUT  160 ). 
         [0037]    However, the voltage at the cathode  215 A and/or the voltage at the cathode  215 B could also drop below this charge pump enable level if their respective LEDs  210 A and  210 B are associated with an open lamp condition. To prevent an open lamp condition associated with the LED  210 A from enabling the charge pump, the output of the voltage monitor  310 A is gated by an AND gate  315 A whose other input is coupled to the lamp not open signal  290 A of the example open lamp detection circuit  205 . Thus, the output of the AND gate  315 A will be asserted only both the voltage at the cathode  215 A is below the charge pump enable threshold and the LED  210 A is not in an open lamp condition. Similarly, to prevent an open lamp condition associated with the LED  210 B from enabling the charge pump, the output of the voltage monitor  310 B is gated by an AND gate  315 B whose other input is coupled to the lamp not open signal  290 B of the example open lamp detection circuit  205 . Thus, the output of the AND gate  315 B will be asserted only when both the voltage at the cathode  215 B is below the charge pump enable threshold and the LED  210 B is not in an open lamp condition. 
         [0038]    To generate a charge pump enable signal  320 , the example charge pump enable circuit  305  further includes an OR gate  325  to combine the outputs of the AND gates  315 A and  315 B. Such an arrangement allows a drop in voltage at either or both of the cathode  215 A of the LED  210 A and the cathode  215 B of the LED  210 B to cause the charge pump enable signal  320  to be asserted. However, the charge pump enable signal  320  will not be asserted if such a detected drop in voltage is due solely to either or both of the LEDs  210 A and  210 B being associated with an open lamp condition. 
         [0039]    Flowcharts representative of example processes that may be implemented by all, or at least portions of, the first example device  100 , the first example open lamp detection circuit  105 , the second example device  200 , the second example open lamp detection circuit  205 , the third example device  300  and/or the example charge pump enable circuit  305  are shown in  FIGS. 4-6 . Additionally or alternatively, any, all or portions thereof of the first example device  100 , the first example open lamp detection circuit  105 , the second example device  200 , the second example open lamp detection circuit  205 , the third example device  300  and/or the example charge pump enable circuit  305 , and/or the example processes represented by the flowcharts of  FIGS. 4-5  and/or  6  could be implemented by any combination of software, firmware, hardware devices and/or combinational logic, other circuitry, etc., such as the hardware circuitry and transistors, etc., shown in  FIGS. 1-3 . Also, some or all of the processes represented by the flowcharts of  FIGS. 4-6  may be implemented manually. Further, although the example processes are described with reference to the flowcharts illustrated in  FIGS. 4-6 , many other techniques for implementing the example methods and apparatus described herein may alternatively be used. For example, with reference to the flowcharts illustrated in  FIGS. 4-6 , the order of execution of the blocks may be changed, and/or some of the blocks described may be changed, eliminated, combined and/or subdivided into multiple blocks. 
         [0040]    An example single open lamp detection process  400  that may be performed by the first example open lamp detection circuit  105  of  FIG. 1  is illustrated in  FIG. 4 . The example single open lamp detection process  400  may be performed, for example, automatically upon activation of the first example device  100  of  FIG. 1 , upon reset of the example device  100 , etc. Referring also to  FIG. 1 , execution of the example single open lamp detection process  400  of  FIG. 4  begins at block  410  at which example open lamp detection circuit  105  detects an enable signal, such as the enable signal  145 . Control then proceeds to block  420  at which the example open lamp detection circuit  105  enables a sampling transistor to pull a sampling current through an LED (e.g., such as the LED  110 ) to test whether the LED is associated with an open lamp condition. For example, at block  420  the timing circuit  135  may assert the initialization signal  130  after detection of the enable signal  145  at block  410 . The asserted initialization signal  130  then causes the transistor  155  to turn ON and begin pulling a sampling current through the LED  110  being examined by the single open lamp detection process  400 . 
         [0041]    Next, control proceeds to block  430  at which the example open lamp detection circuit  105  compares a voltage at the cathode of the LED under test (e.g., such as the LED  110 ) to a reference voltage to determine whether the voltage induced by the sampling current initiated at block  420  is indicative of an open lamp condition. For example, at block  430  the comparator  165  included in the example open lamp detection circuit  105  may be used to compare the voltage at the cathode  115  of the LED  110  to the reference voltage  170 . Additionally, at block  430  the comparison may be performed after a sufficient time has elapsed to allow the cathode voltage of the LED under test to settle. For example, at block  430  the output of the comparator  165  may be latched by the flip flop  175  at the end of the initialization phase defined by the initialization signal  130  to provide sufficient time for the voltage at the cathode  115  of the LED  110  to settle. Control then proceeds to block  440 . 
         [0042]    At block  440 , the example open lamp detection circuit  105  determines whether the cathode voltage of the LED under test is greater than the reference voltage. For example, at block  440  the comparator  165  included in the open lamp detection circuit  105  may output a logic HIGH when the voltage at the cathode  115  of the LED  110  is greater than the reference voltage  170  and a logic LOW when the voltage at the cathode  115  of the LED  110  is less than the reference voltage  170 . If the cathode voltage of the LED under test is greater than the reference voltage (block  440 ), control proceeds to block  450  at which the example open lamp detection circuit  105  sets an open lamp indicator to indicate that the LED is not associated with an open circuit condition or, equivalently, an open lamp condition. However, if the cathode voltage of the LED under test is not greater than the reference voltage (block  440 ), control proceeds to block  460  at which the example open lamp detection circuit  105  sets an open lamp indicator to indicate that the LED is associated with an open circuit condition or, equivalently, an open lamp condition. 
         [0043]    For example, at block  450  the logic HIGH output by the comparator  165  in response to the voltage at the cathode  115  of the LED  110  being greater than the reference voltage  170  may be latched by the flip flop  175 . The logic HIGH latched by the flip flop  175  results in the lamp open signal  185  being a logic LOW and the lamp not open signal  190  being a logic HIGH, thus indicating that the LED  110  is not associated with an open lamp condition. Conversely, at block  460  the logic LOW output by the comparator  165  in response to the voltage at the cathode  115  of the LED  110  being not greater than the reference voltage  170  may be latched by the flip flop  175 . The logic LOW latched by the flip flop  175  results in the lamp open signal  185  being a logic HIGH and the lamp not open signal  190  being a logic LOW, thus indicating that the LED  110  is associated with an open lamp condition. 
         [0044]    After the open lamp indicator is set at either block  450  or block  460 , control proceeds to block  470 . At block  470 , the example open lamp detection circuit  105  outputs the open lamp indicator as set at either block  450  or block  460 . For example, at block  470  the example open lamp detection circuit  105  may output the latched lamp open signal  185  and lamp not open signal  190 . These latched output signals may be used during later operation of the example device  100  to indicate whether the LED  110  is associated with an open circuit condition. The example process  400  then ends. 
         [0045]    An example multiple open lamp detection process  500  that may be performed by the second example open lamp detection circuit  205  of  FIG. 2  is illustrated in  FIG. 5 . The multiple open lamp detection process  500  may be performed, for example, automatically upon activation of the second example device  200  of  FIG. 2 , upon reset of the example device  200 , etc. Referring also to  FIG. 2 , execution of the example multiple open lamp detection process  500  of  FIG. 5  begins at block  510  at which example open lamp detection circuit  205  detects an enable signal, such as the enable signal  145 . Control then proceeds to block  520  at which the example open lamp detection circuit  205  enables sampling transistors to pull sampling currents through multiple LEDs (e.g., such as the LEDs  210 A- 210 B) to test whether any or all of the LEDs are associated with open lamp conditions. For example, at block  520  the timing circuit  235  may assert the initialization signal  130  after detection of the enable signal  145  at block  510 . The asserted initialization signal  130  then causes the transistors  255 A- 255 B to turn ON and begin pulling sampling currents through the respective LEDs  210 A- 210 B being examined by the multiple open lamp detection process  500 . 
         [0046]    Control next proceeds to block  525  at which the example open lamp detection circuit  205  samples the cathode voltage of the next one of the multiple LEDs to allow the sampled voltage to be tested against a reference voltage to determine whether the particular LED is associated with an open lamp condition. For example, at block  525  the timing circuit  235  may generate one of the channel enable signals  245 A- 245 B to cause the corresponding transmission gate  265 A- 265 B to pass the voltage at the cathode  215 A- 215 B corresponding to the particular LED  210 A- 210 B to be examined during the current sampling window of time. 
         [0047]    Next, control proceeds to block  530  at which the example open lamp detection circuit  205  compares the voltage at the cathode of the LED (e.g., such as one of the LEDs  210 A- 210 B) sampled at block  525  to a reference voltage to determine whether the voltage induced by the sampling current initiated at block  520  is indicative of an open lamp condition. For example, at block  530  the comparator  165  included in the example open lamp detection circuit  205  may be used to compare the reference voltage  170  to the voltage at the cathode  215 A- 215 B of the respective LED  210 A- 210 B whose transmission gate  265 A- 265 B is active during the current sampling window of time defined by currently asserted channel enable signal  245 A- 245 B. Additionally, at block  530  the comparison may be performed after a sufficient time has elapsed to allow the cathode voltage of the LED under test to settle. For example, at block  530  the output of the comparator  165  may be latched by the appropriate flip flop  275 A- 275 B at the end of the current sampling window of time defined by the active channel enable signal  245 A- 245 B to provide sufficient time for the cathode voltage of the LED under test to settle. Control then proceeds to block  540 . 
         [0048]    At block  540 , the example open lamp detection circuit  205  determines whether the cathode voltage of the LED under test is greater than the reference voltage. For example, at block  540  the comparator  165  included in the open lamp detection circuit  205  may output a logic HIGH when the voltage at the cathode  215 A- 215 B of the respective LED  210 A- 210 B being passed by the transmission gates  265 A- 265 B during the current sampling window of time is greater than the reference voltage  170 , and a logic LOW when the cathode voltage being passed by the transmission gates  265 A- 265 B during the current sampling window of time is less than the reference voltage  170 . If the cathode voltage of the LED under test is greater than the reference voltage (block  540 ), control proceeds to block  550  at which the example open lamp detection circuit  205  sets an open lamp indicator to indicate that the current LED under test is not associated with an open circuit condition or, equivalently, an open lamp condition. However, if the cathode voltage of the LED under test is not greater than the reference voltage (block  540 ), control proceeds to block  560  at which the example open lamp detection circuit  205  sets an open lamp indicator to indicate that the LED under test is associated with an open circuit condition or, equivalently, an open lamp condition. 
         [0049]    For example, at block  550  the logic HIGH output by the comparator  165  (i.e., because the cathode voltage being passed by the transmission gates  265 A- 265 B during the current sampling window of time is greater than the reference voltage  170 ) may be latched by the appropriate flip flop  275 A- 275 B. The logic HIGH latched by the appropriate flip flop  275 A- 275 B results in this flip-flop&#39;s respective lamp open signal  285 A- 285 B being a logic LOW and this flip-flop&#39;s respective lamp not open signal  290 A- 290 B being a logic HIGH, thus indicating that the corresponding LED  210 A- 210 B under test is not associated with an open lamp condition. Conversely, at block  560  the logic LOW output by the comparator  165  (i.e., because the cathode voltage being passed by the transmission gates  265 A- 265 B during the current sampling window of time) is not greater than the reference voltage  170  may be latched by the appropriate flip flop  275 A- 275 B. The logic LOW latched by the appropriate flip flop  275 A- 275 B results in this flip-flop&#39;s respective lamp open signal  285 A- 285 B being a logic HIGH and this flip-flop&#39;s respective lamp not open signal  290 A- 290 B being a logic LOW, thus indicating that the corresponding LED  210 A- 210 B under test is associated with an open lamp condition. 
         [0050]    After the open lamp indicator is set at either block  550  or block  560 , control proceeds to block  565 . At block  565 , the example open lamp detection circuit  205  determines whether all of the multiple LEDs have been examined by the multiple open lamp detection process  500 . If all of the multiple LEDs have not been examined (block  565 ), control returns to block  525  and blocks subsequent thereto at which the example open lamp detection circuit  205  samples the cathode voltage of the next one of the multiple LEDs to allow the sampled voltage to be tested against a reference voltage to determine whether the particular LED is associated with an open lamp condition. However, if all of the multiple LEDs have been examined (block  565 ), control proceeds to block  570  at which the example open lamp detection circuit  205  outputs the open lamp indicators for all of the multiple LEDs as set at either block  550  or block  560  during various iterations of the example multiple open lamp detection process  500 . For example, at block  570  the example open lamp detection circuit  205  may output the latched lamp open signals  285 A- 285 B and lamp not open signals  290 A- 290 B. These latched output signals may be used during later operation of the example device  200  to indicate whether any or all of the LEDs  210 A- 210 B are associated with an open circuit condition. The example process  500  then ends. 
         [0051]    An example charge pump enable process  600  that may be performed by the example charge pump enable circuit  305  of  FIG. 3  is illustrated in  FIG. 6 . The example charge pump enable process  600  may be performed, for example, automatically upon activation of the third example device  300  of  FIG. 3 , upon reset of the example device  300 , upon/after completion of the initialization phase defined by, for example, the initialization signal  130 , upon/after latching of, for example, the lamp open signals  285 A- 285 B and/or the lamp not open signals  290 A- 290 B, etc. Referring also to  FIG. 3 , execution of the example charge pump enable process  600  of  FIG. 6  begins at block  610  at which the example charge pump enable circuit  305  obtains open lamp indicators corresponding to those LEDs being monitored to determine whether the charge pump driving the LEDs should be enabled. For example, at block  610  the example charge pump enable circuit  305  may obtain the lamp not open signals  290 A- 290 B latched at the end of an initialization phase and corresponding, respectively, to the monitored LEDs  210 A- 210 B. 
         [0052]    Next, control proceeds to block  620  at which the example charge pump enable circuit  305  monitors voltages associated with the LEDs to determine whether the charge pump should be enabled to boost the forward voltage driving the LEDs. For example, at block  620  the voltage monitors  310 A- 310 B may monitor, respectively, the voltages at the cathodes  215 A- 215 B of the LEDs  210 A- 210 B. Control then proceeds to block  630  at which the example charge pump enable circuit  305  gets the next monitored voltage to be tested for determining whether to enable the charge pump. Then at block  640  the example charge pump enable circuit  305  determines whether the monitored voltage obtained at block  630  is less than a charge pump enable level. As discussed above, the charge pump enable level is a predetermined and/or programmable voltage level below which the charge pump should be enabled to boost the forward voltage driving the LEDs. In an example implementation, each of the voltage monitors  310 A- 310 B compares its respective monitored voltage to the charge pump enable level and asserts an output if the monitored voltage falls below the charge pump enable level. 
         [0053]    Returning to block  640 , if the monitored voltage is less than the charge pump enable level, control proceeds to block  650  at which the example charge pump enable circuit  305  determines whether the open lamp indicator for the LED corresponding to this monitored voltage indicates that the LED is associated with an open lamp condition or, equivalently, an open circuit condition. For example, at block  650  the example charge pump enable circuit  305  may determine whether the lamp not open signal  290 A- 290 B for this LED is a logic HIGH indicating that the LED is not associated with an open lamp (e.g., circuit) condition, or a logic LOW indicating that the LED is associated with an open lamp (e.g., circuit) condition. If the open lamp indicator for this LED does indicate an open lamp (e.g., circuit) condition (block  650 ), control proceeds to block  660  at which the example charge pump enable circuit  305  disregards this LED&#39;s monitored voltage and, thus, does not assert a charge pump enable signal in response to this monitored voltage being less than the charge pump enable level. However, if the open lamp indicator for this LED does not indicate an open lamp (e.g., circuit) condition (block  650 ), control proceeds to block  670  at which the example charge pump enable circuit  305  asserts the charge pump enable signal in response to this monitored voltage being less than the charge pump enable level. 
         [0054]    In an example implementation, the process at block  660  and  670  may be implemented by the AND gates  315 A- 315 B and the OR gate  325  included in the example charge pump enable circuit  305 . For example, the AND gates  315 A- 315 B can be used to qualify the output of each voltage monitor  310 A- 310 B using the appropriate lamp not open signal  290 A- 290 B corresponding to the LED monitored by the voltage monitor  310 A- 310 B. If a particular lamp not open signal  290 A- 290 B is a logic LOW (e.g., corresponding to the open lamp condition or, equivalently, the open circuit condition), the AND gates  315 A- 315 B will block the output of the corresponding voltage monitor  310 A- 310 B from being applied to the OR gate  325 . However, if a particular lamp not open signal  290 A- 290 B is a logic HIGH (e.g., corresponding to a closed lamp condition or, equivalently, a closed circuit condition), the AND gates  315 A- 315 B will pass the output of the corresponding voltage monitor  310 A- 310 B to the OR gate  325  which, in turn, will be allowed to assert the charge pump enable signal  320 . 
         [0055]    Returning to  FIG. 6 , after the monitored voltage is disregarded (block  660 ) or allowed to assert the charge pump enable signal (block  670 ), or if the monitored voltage was not less than the charge pump enable level (block  640 ), control proceeds to block  680 . At block  680 , the example charge pump enable circuit  305  determines whether all monitored LED voltages have been processed. If all monitored voltages have not been processed (block  680 ), control returns to block  630  and blocks subsequent thereto at which the example charge pump enable circuit  305  gets the next monitored voltage to be tested for determining whether to enable the charge pump. If, however, all monitored voltages have been processed (block  680 ), control proceeds to block  690  at which the example charge pump enable circuit  305  determines whether the charge pump enable signal has been asserted (e.g., through at least one iteration through block  670 ). If the charge pump enable signal has not been asserted (block  690 ), control returns to block  620  and blocks subsequent thereto at which the example charge pump enable circuit  305  continues to monitors the LED voltage(s) to determine whether the charge pump should be enabled. However, if the charge pump enable signal has been asserted (block  690 ), the example process  600  ends. 
         [0056]    The examples disclosed herein have typically assumed certain voltage polarities for the operational characteristics of the devices, components, circuit elements, etc., used to implement the example methods and apparatus disclosed herein. In these examples, certain positive voltages and/or voltages exceeding a threshold may cause a particular device, component, circuit element, etc., to exhibit one characteristic (e.g., such as turning ON), whereas certain non-positive (e.g., zero and/or negative) voltages and/or voltages not exceeding a threshold may cause the device, component, circuit element, etc., to exhibit a different characteristic (e.g., such as turning OFF). However, it is readily apparent that the methods and apparatus described herein can be used in example implementations based on different, or opposite, polarity definitions. As such, the example methods and apparatus described herein can be readily adapted to ensure that appropriate control/activation voltages are present to provide open lamp detection in many different electronic circuit configurations. 
         [0057]    Finally, although certain example methods, apparatus and articles of manufacture have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.