Patent Publication Number: US-7583068-B2

Title: Method for driving voltage-controlled devices or current-controlled devices

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is related to the area of circuits, in particular, related to multifunctional driver controllers that, in one aspect, are capable of controlling both current-controlled device and voltage-controlled devices. 
   2. Description of Related Art 
   WLED (White Light-Emitting Diode) and OLED (Organic Light Emitting Diode) are being widely used for illuminating. It is commonly known that a current going through a WLED controls the brightness of the emitting light from a WLED, however OLED brightness is controlled by the voltage applied across. Thus, WLED controller and OLED controller are quite different from each other. A WLED controller requires a low reference voltage, such as 100-300 mV, while an OLED controller requires a high reference voltage, such as 1.23V. A WLED controlled by an OLED controller would lead to high power consumption while an OLED controlled by a WLED controller would cause considerable problems. 
   The markets and applications for WLED and OLED are huge. There is a need for techniques that could perfectly control both WLED and OLED. 
   SUMMARY OF THE INVENTION 
   This section is for the purpose of summarizing some aspects of the present invention and to briefly introduce some preferred embodiments. Simplifications or omissions in this section as well as in the abstract or the title of this description may be made to avoid obscuring the purpose of this section, the abstract and the title. Such simplifications or omissions are not intended to limit the scope of the present invention. 
   In general, the present invention pertains to multifunctional driver controller capable to drive one or more voltage-controlled devices or current-controlled devices. According to one aspect of the present invention, a multifunctional driver controller comprises a selection unit receiving a control signal, one of a first reference voltage and a second reference voltage, the selection unit selecting either one of the first reference voltage and the second reference voltage per the control signal, and a control circuit receiving a reference voltage from the selection unit and a feedback signal from a load being driven by a controlled analog signal from the control circuit, wherein the controlled analog signal is either a controlled voltage signal or a controlled current signal, the control circuit compares the reference voltage with the feedback signal and adjusts the controlled analog signal in reference to a difference between the reference voltage and the feedback signal until the feedback signal converges to the reference voltage. 
   The present invention may be implemented in a discrete or integrated circuit. According to one embodiment, the present invention is a method for a voltage-controlled device or a current-controlled device, the method comprises receiving a control signal to select one of a first reference voltage and a second reference voltage as a reference voltage; comparing the reference voltage with a feedback signal; adjusting a controlled analog signal in reference to a difference between the reference voltage and the feedback signal until the feedback signal converges to the reference voltage; providing the controlled analog signal appropriate to drive the current-controlled device when the control is set a first state; providing the controlled analog signal appropriate to drive the voltage-controlled device when the control is set a second state, wherein the feedback signal is obtained from a load being driven by the controlled analog signal, the load being either one of the voltage-controlled device or the current-controlled device. 
   One of the objects, features, and advantages of the present invention is to provide a driver controller capable to drive one or more voltage-controlled devices or current-controlled devices. 
   Other objects, features, and advantages of the present invention will become apparent upon examining the following detailed description of an embodiment thereof, taken in conjunction with the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
       FIG. 1  shows a functional block diagram of a multifunctional driver controller according to one embodiment of the present invention; 
       FIG. 2  shows the multifunctional driver controller acting as a LED driver; 
       FIG. 3  shows the multifunctional driver controller acting as a WLED driver; 
       FIG. 4  shows an exemplary circuit diagram of one embodiment of the present invention to drive a number of LEDs; 
       FIG. 5  shows an exemplary circuit diagram of one embodiment of the present invention to drive an OLED; 
       FIG. 6  shows another exemplary circuit diagram of one embodiment of the present invention to drive a number of LEDs; 
       FIG. 7  shows another exemplary circuit diagram of one embodiment of the present invention to drive an OLED; and 
       FIG. 8  is a square wave signal with a certain duty cycle diagram generated from a triangle signal. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The detailed description of the present invention is presented largely in terms of procedures, steps, logic blocks, processing, or other symbolic representations that directly or indirectly resemble the operations of devices or systems contemplated in the present invention. These descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. 
   Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the order of blocks in process flowcharts or diagrams or the use of sequence numbers representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention. 
   The present invention discloses designs of multifunctional driver controllers. According to one aspect of the present invention, one embodiment of the driver controller can be advantageously used to control either an LED (e.g., WLED) or an OLED.  FIG. 1  shows a functional block diagram of the multifunctional driver controller  100  according to one embodiment of the present invention. The multifunctional driver  100  comprises a selection unit  110 , a control circuit  120  and detection unit  130 . 
   The selection unit  110  is coupled to a control signal  105 , a first reference voltage  101  and a second reference voltage  102 . The selection unit  110  selects either the first reference voltage  101  or the second reference voltage  102  per the control signal  105 . In one embodiment the first reference voltage is a low reference voltage and the second reference voltage is a high reference voltage. The selection unit further is coupled to a reset signal (not shown). 
   The control circuit  120  is coupled to the selection unit  110  for receiving the selected reference voltage, and a voltage input and a ground which are not shown. A controlled signal output  103  outputs a controlled analog signal that may be either a controlled voltage signal or a controlled current signal. A feedback signal  104  is provided to the control circuit  120 . In operation, the control circuit  120  compares the selected reference voltage with the feedback signal and adjusts the controlled analog signal in reference to the comparison result until the feedback signal converge to the selected reference voltage. Thus the controlled analog signal is converged to a benchmark counterpart to the selected reference voltage. The control circuit  120  is further coupled to a reset signal (not shown). 
   The detection unit  130  is coupled to the selection unit  110  and the control circuit  120  with reset signals. The detection unit  130  is used to detect if the power has been applied to the controller  100 . When such an event happens and proved to be valid, the detection unit  130  sends reset signals to the selection unit  110  and the controlling circuit  120  respectively. 
   As shown in  FIG. 1 , in one embodiment, the controller  100  is coupled to a boost circuit  140 . The boost circuit  140  is provided between the controller  100  and a device to be driven. The purpose of the boost circuit  140 , the name suggests, is to boost the controlled signal output from the controller  100 . There are many ways to implement the boost circuit  140 , which are known to those skilled in the art. 
   A different reference voltage could drive a different device. In one application, if a low reference voltage is selected by the selection unit  110 , the control circuit  120  could be used to output a controlled current signal, and at the same time, the feedback signal could be a current feedback signal, thus the multifunctional driver controller  100  may be used to control a current-controlled device, such as WLED. For the selected voltage being a low reference voltage, the working voltage for a current-controlled device could be low, thus reducing power consumption. 
   In another application, if a high reference voltage is selected by the selection unit  110 , the control circuit  120  could be used to output a controlled voltage signal, and at the same time, the feedback signal could be a voltage feedback signal, thus the multifunctional driver controller  100  may be used to control a voltage-controlled device, such as OLED. For the selected voltage being a high reference voltage, the controller  100  may well control the OLED and lead small errors. To facilitate the understanding of the present invention, the following description is based on controlling WLED and OLED. Those skilled in the art can appreciate that the present invention may be used to control many other current-controlled devices or voltage-controlled devices. 
   The controller  100  receives an enable signal. In one embodiment, the frequency of the enable signal is far below a clock frequency and far above what the human could recognize, therefore, controlling the enable signal frequency could also control the brightness of WLED or OLED. 
   As it shown in  FIG. 2 , the detection unit  130  and the control circuit  120  are coupled to a voltage source VDD. The controlled signal output  103  of the control circuit  120  is coupled to a boost circuit that includes an NMOS, an inductor L, a diode D and a capacitor C. The controlled signal output  103  is coupled to the gate of the NMOS and inductor L, diode D and capacitor C are coupled between VDD and the ground. The source of NMOS is coupled to the ground and the drop is coupled between the diode D and the capacitor C. A node voltage between inductor L and diode D is used as an output voltage Vout. The output voltage is coupled with one or more WLEDs and a feedback resistor R is coupled between the WLED and the ground. The voltage of feedback resistor R is the feedback signal and this voltage indicates the current flow through the WLED that is the controlled current signal. The first reference voltage of the selection unit  110  is a low reference voltage (e.g., 100 mV). The second reference voltage of selection unit  110  is a high reference voltage (e.g., 1.22V). 
   The selection unit  110  selects a low reference voltage as reference voltage. Comparing the feedback voltage and the low reference voltage, the control circuit  120  adjusts the controlled current signal in reference to the comparison result till the feedback voltage equal to the low reference voltage. Therefore, by adjusting the low reference voltage, it is possible to adjust the current flow through a WLED and then control its brightness. 
     FIG. 3  is a block functional diagram of a multifunctional drive controller acting as an OLED driver. The OLED driver circuit looks similar to that for the WLED, and the differences are noted in the following. An OLED is coupled between Vout and ground and a voltage-division circuit is in parallel coupled to the OLED. The voltage-division circuit comprises two resistors Rvs 1  and Rvs 2  and the middle node voltage is the feedback voltage. 
   When driving OLED, the selection unit  110  selects a high reference voltage. Comparing the feedback voltage and the high reference voltage, the controlled current signal is adjusted in reference with the comparison result till the feedback voltage equal to the high reference voltage, thus adjusting the high reference voltage can control the voltage coupled to OLED and then control its brightness. 
   Several methods could be used to realize the control circuit  120 ,  FIG. 4  to  FIG. 7  shows a detailed control circuit  120  in accordance with one embodiment of the present invention. As shown in  FIG. 4 , the control circuit  120  comprises an error amplifier  127 , an oscillator  121 , a PWM (Pulse Width Modulation) comparator  122 , a logic driving unit  123 , a delay circuit  124  and a power output switch  125 . 
   The oscillator  121  is used to generate a triangle wave signal. The triangle wave signal is coupled to the negative input of the PWM comparator  122 . In addition, the oscillator  121  also provides a clock signal to the selection unit  110  and the delay circuit  120 . 
   The negative input of the error amplifier  127  is coupled to the feedback input of the multifunction driver  100  for receiving the controlled analog feedback signal. The positive input of the error amplifier  127  is a reference voltage input in the multifunction driver  100 . The error amplifier  127  is used to compare the feedback signal and the reference voltage and amplify the difference (error) and subsequently output the error which is referred to as a voltage Vea. 
   The PWM comparator  122  is used to compare the triangle wave signal and the Vea, and output a square wave with a certain duty cycle.  FIG. 8  shows the detailed working principle. When an electric potential of the triangle wave is higher than Vea, the PWM comparator  122  outputs a high, otherwise outputs a low. The square wave is sent to the logic unit  123 . 
   The power output switch  125  includes a pair of PMOS and NMOS and their gates are coupled to the logic driving unit  123 , their sources are coupled to the inductor L, the PMOS drop is coupled to Vdd while the NMOS drop is coupled to the ground. 
   The delay circuit  124  is provided to have accurate times by counting the triangle wave signal so as to provide an accurate delay of the square wave signal and to shut down the logic driving unit  123  during an unstable state at the beginning. It also has a reset to reset the control circuit  110 . The logic driving unit  123  receives the square wave signal from the delay circuit  124  as a switch signal. As it shown in  FIG. 4  to  FIG. 7 , when the square wave signal is high, it opens the NMOS, the node voltage between L and D is pulled to ground and LC releases energy and this is called a shutdown moment. When the square wave is low, it closes the NMOS, VDD charges the LC and this is called open moment. The square wave signal is also called a switch signal. The delay circuit  124  is used to assure that the logic driving unit generates a wrong signal during the unstable period. Therefore, judging Vea could adjust the square wave duty cycle to adjust the shutdown moment. 
   The selection unit  110  can also be realized using different circuits.  FIG. 4  and  FIG. 5  show a first one and  FIG. 6  and  FIG. 7  show a second one. The first embodiment selection unit  110  comprises a flip-flop  111 , a current source  115 , a first control switch  113 , a second control switch  114  and a current source  115 . 
   The first control switch  113  is used to control the first reference voltage provided to the selection unit  110  and the second control switch  114  is used to control the second reference voltage provided to the selection unit  110 . Of cause the two switches  113  and  114  connect one reference voltage to the selection unit  110 . The (D) flip-flop  111  has an input d, a clock input clk, a reset input r, a positive output q and a negative output qb. In one embodiment, the oscillator  121  provides a clock signal to the D flip-flop  111 . The reset input r is the reset of the selection unit  110  and the reset signal is from the detection unit  130 . 
   The flip-flop  111  latches data in d, sends the data to q and reverses the data to qb at the moment of a rising clock edge. The reset signal r is used to reset the D flip-flop. The q signal is used to control the first switch  111  and the qb signal is used to control the second switch  114 . The current source is coupled between d and the ground and d is the control signal of the selection unit  110 . 
   The d and VDD are coupled selectively under a control (e.g., a voltage control pin). When d is connected to VDD, the d is high, the q is high, the first control switch  113  is close and a low reference voltage is chosen, the qb is low, the second control switch  114  is open, the high reference voltage is abandoned. It is used to control a WLED as shown in  FIG. 4 . When the d is disconnected from VDD, the d is low, the q is low, the first control switch  113  is open and the low reference voltage is abandoned; the qb is high, the second control switch  114  is close, the high reference voltage is chosen. It is used to control an OLED as shown in  FIG. 5 . 
   For a logic state being unstable at the beginning, it is required to reset the required logic state. The detection unit  130  is used to reset the D flip-flop and the delay circuit. In one embodiment, the voltage pin to control the connection between d and VDD, and the voltage pin between the detection circuit and VDD could be combined together as a single voltage pin. 
     FIG. 6  and  FIG. 7  show the second embodiment in which the selection unit  110  comprises a D flip-flop  111 , a comparator  112 , a first control switch  113 , a second control switch  114  and a comparator. The first control switch  113 , the second control switch  114  and D flip-flop are the same as in the first embodiment. The differences are that d is not connected to a current source but the output of the comparator  105 . The positive input of the comparator is the input reference voltage and the negative input thereof is the control end of the selection unit  110  which is coupled to the feedback of control circuit  120 . 
   As it shown in  FIG. 7 , when OLED is loaded, the feedback voltage  105  is a voltage-division voltage which is equal to Vout*Rvs 2 /(Rvs 1 +Rvs 2 ), where Rvs 1  and Rvs 2  are the voltage division resistors. The feedback voltage will converge to a high reference voltage eventually. While in  FIG. 6 , when WLED is loaded, the feedback voltage  105  will converge to a low reference voltage in the end. The feedback voltage  105 , when OLED is loaded, could be any voltage as long as there is no error. 
   The feedback voltage  105  in the multifunctional driver as shown in  FIG. 7  is higher than the reference voltage, and the comparator  112  will output a low electric level, and the d in D flip-flop is low, q is low, the first switch is open, la ow reference voltage is abandoned and qb is high, the second switch is closed, and the high reference voltage is chosen. 
   The feedback voltage in the multifunctional driver as shown in  FIG. 6  is lower than the reference voltage, and the comparator outputs a high electric level, and d in D flip-flop is high, q is high, the first switch is closed, a low reference voltage is chosen and qb is low, the second switch is open, and the high reference voltage is abandon. In the embodiments shown in  FIG. 4  to  FIG. 7 , the D flip-flop is used to save a state, any other flip-flops, such as RS flip-flop, could be used to achieve the same goal. 
   The present invention introduces two different reference voltages so that different voltages will satisfy different designs. The present invention has been described in sufficient details with a certain degree of particularity. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope of the invention as claimed. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description of embodiments.