Patent Publication Number: US-2010118460-A1

Title: DC drive

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The invention relates to a direct current (DC) drive, and more particularly to use a rectifier to enable an input voltage of a voltage input terminal not only drives an external electronic device but also provides a desired DC for DC drive. 
     (2) Description of the Prior Art 
     Conventionally, if positive and negative circuits have to be simultaneously used, two different voltage source paths are needed. In addition, the two different voltage source paths are not used effectively and directly to internal circuit. 
     For example, when a DC motor is controlled to rotate clockwise or counterclockwise, two symmetrical circuits are often used to control the motor. However, the internal circuit for controlling the DC motor often needs the power source so that the manufacturing cost is increased and the stability thereof is influenced. More particularly, after the integrated circuit is manufactured, the decrease of the extra voltage source inputs has become the most important consideration for enhancing the stability and decreasing the cost. 
     In view of these, a DC drive is needed to solve the conventional drawbacks. 
     SUMMARY OF THE INVENTION 
     The invention provides a DC drive for respectively providing desired voltages for the DC drive according to different input voltages. 
     The invention further provides a protecting device for DC drive to control a latch unit to latch a voltage output unit according to a comparison control signal generated via a comparing unit. 
     In one embodiment, a DC drive is provided. The DC drive includes a voltage input unit, a comparing unit, a latch unit and a voltage output unit. The voltage input unit for providing a DC voltage has at least one input terminal and at least one output terminal. The comparing unit receives the DC voltage and generates a comparison control signal according to a comparison result obtained by comparing a voltage of a positive voltage terminal with a voltage of a negative voltage terminal. The latch unit is connected to the comparing unit and the voltage input unit. The voltage output unit is connected to the latch unit and receives the DC voltage from the voltage input unit. The latch unit selectively provides the DC voltage to the voltage output unit according to the comparison control signal. 
     In another embodiment, a protecting device for DC drive applied to an electronic device is provided. The DC drive protecting device includes a voltage input unit, a comparing unit, a latch unit, a voltage output unit and a protecting circuit. The voltage input unit for providing a DC voltage has at least one input terminal and at least one output terminal. The comparing unit receives the DC voltage and generates a comparison control signal according to a comparison result obtained by comparing a voltage of a positive voltage terminal with a voltage of a negative voltage terminal. The latch unit is connected to the comparing unit and the voltage input unit. The voltage output unit is connected to the latch unit and receives the DC voltage from the voltage input unit. The protecting circuit is coupled to the voltage output unit and the electronic device to prevent a reverse voltage. The latch unit selectively provides the DC voltage to the voltage output unit according to the comparison control signal. 
     Further aspects, objects, and desirable features of the invention will be better understood from the detailed description and drawings that follow in which various embodiments of the disclosed invention are illustrated by way of examples. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a DC drive of the invention. 
         FIG. 2   a  shows a structure of a rectifier unit of  FIG. 1 . 
         FIG. 2   b  shows another structure of the rectifier unit of  FIG. 2   a.    
         FIG. 2   c  shows still another structure of the rectifier unit of  FIG. 1 . 
         FIG. 3  is a schematic circuit diagram showing the DC drive of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention discloses a DC drive, wherein a rectifier is used at a voltage input unit so that the DC drive uses the same input voltage, and a latch unit is used to latch a voltage output unit. In order to describe the invention in detail, illustrations will be made with reference to  FIGS. 1 to 3 . 
       FIG. 1  is a block diagram showing a DC drive of the invention. In this embodiment, a DC drive  100  is provided. The DC drive  100  includes a voltage input unit  102 , a comparing unit  104 , a latch unit  106  and a voltage output unit  108 . The voltage input unit  102  has at least one output terminal for providing a DC voltage Vin. The comparing unit  104  receives the DC voltage Vin, and generates a comparison control signal CCS (to be described herein below) according to a comparison result obtained by comparing a voltage of a positive voltage terminal with a voltage of a negative voltage terminal. The latch unit  106  is connected to the comparing unit  104  and the voltage input unit  102 . The voltage output unit  108  is connected to the latch unit  106 , and receives the DC voltage Vin from the voltage input unit  102 . The latch unit  106  selectively provides the DC voltage Vin to the voltage output unit  108  according to the comparison control signal CCS. 
     In addition, the DC drive  100  further includes a protecting circuit  110 , coupled to the voltage output unit  108 , for preventing a reverse voltage. For example, the DC drive  100  generates a reverse discharge voltage after the voltage output unit  108  output, the reverse voltage has a discharge path through the protecting circuit  110 , and doesn&#39;t feed back to the DC drive  100  so that the protection effect can be achieved. 
     Perfectly,  FIG. 2   a  shows a structure of a rectifier unit of  FIG. 1 . As shown in  FIG. 2   a,  the voltage input unit  102  includes a rectifier unit composed of at least one diode. In this embodiment, the diodes  1022 ,  1024  are constituted of the rectifier unit. When the DC voltage Vin is at the high level H, the diode  1022  turns on and provides the high level H to the n terminal of the diode  1022 . On the contrary, when the DC voltage Vin is at the low level L, the diode  1024  turns on and provides the low level L to the p terminal of the diode  1024 . More particularly, the diodes  1022 ,  1024  are connected to the comparing unit  104  of  FIG. 1  to provide the driving voltage required by the comparing unit  104 . Thus, the DC voltage Vin can be directly provided to the DC drive  100 . In addition, a voltage Vout at the output terminal of the voltage input unit  102  is equal to the voltage Vin at the input terminal of the voltage input unit  102 . 
       FIG. 2   b  shows another structure of the rectifier unit of  FIG. 2   a.  In this embodiment, as shown in  FIG. 2   b,  the voltage input unit  102  has two voltage input terminals Vin 1  and Vin 2 , which simultaneously or respectively input a high level voltage or a low level voltage. As shown in the drawing, when the input voltages at the voltage input terminals Vin 1  and Vin 2  are the high level voltages, the output voltage at the VH terminal is the high level voltage. That is, the diodes  1022   a,    1022   b  allow the high level voltage to pass through and reach the VH terminal. When the input voltages of the voltage input terminals Vin 1  and Vin 2  are the low level voltages, the input voltages cannot reach the VH terminal through the diodes  1022   a  and  1022   b.  On the contrary, the following drawing shows the state wherein the diodes  1024   a,    1024   b  allow the low level voltages to pass through. That is, when the input voltages at the voltage input terminals Vin 1  and/or Vin 2  are the low level voltages, the input voltages reach the VL terminal through the diodes  1024   a,    1024   b.    
       FIG. 2   c  shows still another structure of the rectifier unit of  FIG. 1 . In another embodiment, as shown in  FIG. 2   c,  the voltage input unit  102  may further be a bridge rectifier unit having at least one bridge voltage input unit and at least one bridge voltage output unit. In this embodiment, the bridge rectifier unit is composed of four diodes  1026 ,  1028 ,  1030 , and  1032 . The DC voltages Vin 1  and Vin 2  with different levels are inputted. The DC voltage Vin 1  turns on the diode  1028  so that the high level VH is provided within the period t 1 , and the diode  1032  is in the off state. On the contrary, The DC voltage Vin 2  turns on the diode  1030  so that the low level VL is provided within the period t 2 , and the diode  1026  is in the off state. That is, in the same time, the bridge rectifier unit of the invention can be utilized to turn on the diodes  1028  and  1030  within the period t 1 , or to turn on the diodes  1026 ,  1032  within the period t 2 . Meanwhile, the driving voltage required by the comparing unit  104  is provided. For example, the comparing unit  104  may be an operational amplifier (OPA), which may be driven by the driving voltage (the high level VH and the low level VL) provided by the voltage input unit  102 . In addition, the voltages Vout 1 , Vout 2  at the output terminals of the voltage input unit  102  are equal to the voltages Vin 1 , Vin 2  at the input terminals. 
       FIG. 3  is a schematic circuit diagram showing the DC drive of the invention. In this embodiment, a DC drive protecting device  200  applied to an electronic device  202 , such as a DC motor, is provided. The protecting device for DC drive  200  includes a voltage input unit  204 , symmetrical comparing units  206   a,    206   b,  symmetrical latch units  208   a,    208   b,  voltage output terminals  210   a,    210   b  and a protecting circuit  212 . The voltage input unit  204  has voltage input terminals  204   a,    204   b  and is for providing the DC voltages Vin 1 , Vin 2 , for example, having different levels voltages. The comparing units  206   a,    206   b  respectively receive the DC voltages Vin 1 , Vin 2 , and generate comparison control signals CCSa and CCSb according to a comparison result obtained by comparing the voltage of a positive voltage terminal  2062   a  (or  2062   b ) with the voltage of a negative voltage terminal  2064   a  (or  2064   b ). For example, the comparing units  206   a,    206   b  are composed of operational amplifiers (OPAs), are driven by the voltages VH and VL provided from the outside, and have a positive and a negative voltage input terminals and an output terminal. The latch unit  208   a  (or  208   b ) is connected to the comparing units  206   a,    206   b  and the voltage input unit  204 . The voltage input unit  204  is connected to the latch unit  208   a  (or  208   b ), and receives the DC voltages Vin 1  and Vin 2  from the voltage input unit  204 . The protecting circuit  212  is coupled to the voltage output terminals  210   a,    210   b  and the electronic device  202  to prevent the reverse voltage. The latch units  208   a  and  208   b  selectively provide the DC voltages Vin 1  and Vin 2  to the voltage output terminals  210   a  and  210   b  according to the comparison control signals CCSa and CCSb. 
     The operations of the voltage input unit  204 , the symmetrical comparing units  206   a  and  206   b,  the symmetrical latch units  208   a,    208   b,  the voltage output terminals  210   a,    210   b  and the protecting circuit  212  are the same as those of the above-mentioned embodiment. In addition, the comparing units  206   a,    206   b  further respectively include a reference voltage generating units  2066   a,    2066   b,  which are respectively connected to the positive voltage terminal  2062   a  (or  2062   b ) and the negative voltage terminal  2064   a  (or  2064   b ) of the comparing units  206   a  and  206   b.  The reference voltage generating units  2066   a  and  2066   b  are connected to the resistors R 1   a  (or R 1   b ) and R 2   a  (or R 2   b ), and provide as a divided voltage to the positive voltage terminal  2062   a  (or  2062   b ) to form a reference voltage circuit. More particularly, the latch units  208   a  and  208   b  control the voltage outputs through the comparing units  206   a  and  206   b  when the current I exceeds a predetermined current. In this embodiment, for example, the latch unit is composed of a bipolar junction transistor (BJT) Q 1  (or Q 2 ) and/or a metal-oxide-semiconductor field-effect transistor (MOSFET) MOS 1  (or MOS 2 ). When the comparison result shows that the voltage of the negative voltage terminal  2064   a  (or  2064   b ) is higher than that of the positive voltage terminal  2062   a  (or  2062   b ), the MOSFET MOS 1  (or MOS 2 ) reaches a saturation mode. At this time, the voltage Vds between the drain and the source of the MOSFET MOS 1  (or MOS 2 ) is increased so that a biasing voltage is formed after the voltage Vds is fed back to the base of the transistor Q 1  (or Q 2 ) through the resistor R 3 . Thus, the transistor Q 1  (or Q 2 ) is turned on to turn off the MOSFET MOS 1  (or MOS 2 ) so that the object of latching can be achieved. 
     Furthermore, the voltage input unit  204  has the voltage input terminals  204   a,    204   b  connected to the rectification circuit  2042 , and provides the voltage required by the DC drive protecting device according to the levels of the DC voltages Vin 1 , Vin 2 , respectively. For example, the rectification circuit  2042  may be composed of at least one diode. The rectification circuit provides the DC voltages Vin 1 , Vin 2  of the voltage input unit  204  to the comparing units  206   a,    206   b  or provides one of the DC voltages Vin 1 , Vin 2  of the voltage input unit  204  to the comparing units  206   a,    206   b  (not shown in the drawing). 
     New characteristics and advantages of the invention covered by this document have been set forth in the foregoing description. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention. Changes in methods, shapes, structures or devices may be made in details without exceeding the scope of the invention by those who are skilled in the art. The scope of the invention is, of course, defined in the language in which the appended claims are expressed.