Abstract:
A control circuit is configured to control the charge and discharge of a flash unit. The flash unit includes an anode, a cathode, and a trigger electrode. The control circuit includes a charging circuit and a triggering circuit. One terminal of the charging circuit is coupled to a charging terminal and another terminal is coupled to the anode and the cathode. One terminal of the triggering circuit is coupled to a triggering terminal, another terminal is couple to the trigger electrode. The charging circuit includes a first capacitor coupled to the cathode and a second capacitor coupled to the anode. When the charging terminal receives a charging voltage and the triggering terminal receives a high-level voltage, three times charging voltage is formed between the anode and the cathode; then the flash unit generates a flash.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to circuits and, particularly, to a control circuit and a flash system using the same. 
     2. Description of Related Art 
     A flash system typically includes a flash unit and a control circuit. The flash unit is an electric glow discharge device designed to produce extremely intense, incoherent, momentary bright light. The control circuit is employed to provide a high trigger voltage to the flash unit to generate the flash. The intensity of the flash can be increased by increasing the trigger voltage. However, if the trigger voltage is too high, the flash unit may be damaged, which may also be very dangerous to users. 
     What is needed, therefore, is a control circuit and a flash system using the same which can overcome the above-described problem. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The FIGURE is a schematic circuit diagram of a flash system in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present control circuit and the flash system using the same will now be described in detail with reference to the drawing. 
     Referring to the FIGURE, one embodiment of a flash system  100  includes a flash unit  10  and a control circuit  20 . The control circuit  20  is used to control the flash unit  10  to charge and discharge. 
     The flash unit  10  includes a flash tube  11  and a charging capacitor C ch . The flash tube  11  is filled with a noble gas, e.g., xenon, and includes an anode  112 , a cathode  114 , and a triggering electrode  116 . The noble gas can be ionized by applying high voltage to the triggering electrode  116 . The anode  112  and the cathode  114  can carry electrical current through the fully ionized noble gas and produce a bright light. 
     The charging capacitor C ch  is configured for charging the flash tube  11 . The charging capacitor C ch  includes a first terminal and a second terminal. The second terminal is grounded. 
     The control circuit  20  includes a charging circuit  21  and a triggering circuit  22 . The charging circuit  21  is coupled to the anode  112  and cathode  114  of the flash tube  11 . The triggering circuit  22  is coupled to the trigger electrode  116 . 
     The charging circuit  21  includes a first diode D 1 , a second diode D 2 , a third diode D 3 , a first capacitor C 1 , a second capacitor C 2 , a first switching element Q 1 , a first resistor R 1 , a second resistor R 2 , a third resistor R 3 , and a fourth resistor R 4 . 
     The first diode D 1  includes an anode and a cathode. The anode is coupled to the first terminal of the charging capacitor C ch . The cathode of the first diode D 1  is coupled to the anode  112  of the flash tube  11 . 
     The first resistor R 1  includes a first terminal and a second terminal. The first terminal is coupled to the anode of the first diode D 1 . 
     The first capacitor C 1  includes a first terminal and a second terminal. The first terminal is coupled to the second terminal of the first resistor R 1 . 
     The second resistor R 2  includes a first terminal and a second terminal. The first terminal is coupled to the second terminal of the C 1 . The second terminal is grounded. 
     The second capacitor C 2  includes a first terminal and a second terminal. The first terminal is coupled to the cathode of the first diode D 1 . 
     The third resistor R 3  includes a first terminal and a second terminal. The first terminal is coupled to the second terminal of the second terminal of the second capacitor C 2 . The second terminal is grounded. 
     The first switching element Q 1  includes a first terminal, a second terminal, and a control terminal. The control terminal is used to control the connection and disconnection between the first terminal and the second terminal. The first terminal is coupled to the anode of the first diode D 1 . The second terminal is coupled to the second terminal of the second capacitor C 2 . In this embodiment, the first switching element Q 1  is a PNP-type crystal triode, wherein the first terminal is the emitter, the second terminal is the collector, and the control terminal is the base. 
     The fourth resistor R 4  includes a first terminal and a second terminal. The first terminal is coupled to the control terminal of the first switching element Q 1 . The second terminal of the fourth resistor R 4  is coupled to the second terminal of the first resistor R 1 . In this embodiment, the fourth resistor R 4  can be omitted. 
     The second diode D 2  includes an anode and a cathode. The anode of the second diode D 2  is coupled to the cathode  114  of the flash tube  11 . The cathode of the second diode D 2  is coupled to the second terminal of the fourth resistor R 4 . 
     The third diode D 3  includes an anode and a cathode. The anode of the second diode D 2  is coupled to a charging terminal S 1 . The cathode of the second diode D 2  is coupled to the anode of the flash diode D 1 . In this embodiment, the second diode D 2  can be omitted. 
     The triggering circuit  22  includes a second switching element Q 2 , a third capacitor C 3 , and a transformer T. 
     The second switching element Q 2  includes a first terminal, a second terminal, and a control terminal. The control terminal is used to control the connection and disconnection between the first terminal and the second terminal. The first terminal is grounded. The second terminal is coupled to the anode of the second diode D 2 . The control terminal is coupled to a trigger terminal S 2 . In this embodiment, the second switching element Q 2  is a p-channel insulated gate bipolar transistor (p-IGBT), wherein the first terminal is the emitter, the second terminal is the collector, and the control terminal is the gate. 
     The third capacitor C 3  includes a first terminal and a second terminal. The first terminal is coupled to the second terminal of the first resistor R 1 . 
     The transformer T includes a primary winding L 1  with N 1  turns and a secondary winding L 2  with N 2  turns. The ratio of turns N 2  in the secondary winding to the turns N 1  in the primary winding L 1  is N 2 /N 1 =20. The primary winding L 1  includes a first terminal and a second terminal; the first terminal is coupled to the second terminal of the third capacitor C 3 , and the second terminal is grounded. The secondary winding L 2  includes a first terminal and a second terminal; the first terminal is coupled to the triggering electrode  116  of the flash tube  11 , and the second terminal is grounded. 
     In operation, usually, when a camera having the flash system  100  is powered on, a charging voltage V 1  is input to the charging terminal S 1 . The third diode D 3  and the charging capacitor C ch  form a loop. The charging capacitor C ch  is charged. Also, the third diode D 3 , the first resistor R 1 , the first capacitor C 1 , and a second resistor R 2  form a loop. The first capacitor C 1  is charged. Furthermore, the third diode D 3 , the first diode D 1 , the second capacitor C 2 , and the third resistor R 3  form a loop. The second capacitor C 2  is charged. After charging, the voltage of the first terminal of the charging capacitor C ch , the first terminal of the first capacitor C 1 , and the first terminal of the second capacitor C 2  is V 1 . 
     When flash is needed, a user can trigger the flash system by, for example, depressing a shutter button (not shown). Then, a high-level voltage greater than the turn-on voltage of the second switching element Q 2  is applied to the trigger terminal S 2 . The first terminal is electrically connected to the second terminal of the second switching element Q 2 . As the first terminal of the second switching element Q 2  is grounded, the voltage of second terminal changes to about 0 volts. The first terminal of the first capacitor C 1  is accordingly pulled down to about 0 volts. As a result, the second terminal changes to −V 1 . The voltage across the second resistor R 4  changes to about 0 volts, the control terminal accordingly changes to about 0 volts. Thus the first terminal is electrically connected to the second terminal of the first switching element Q 1 . The second terminal of the second capacitor C 2  changes to V 1 , and the first terminal changes to 2*V 1 . 
     As the second terminal of the first capacitor C 1  is coupled to the cathode  114  of the flash tube  11 , and the first terminal of the second capacitor C 2  is coupled to the anode  112  of the flash tube  11 . As a result, the voltage drop between the anode  112  and cathode  114  is 2*V 1 −(−V 1 )=3*V 1 . 
     The transformer T and the third capacitor C 3  form a clapp circuit, and the transformer T changes the charging voltage V 1  to the 20*V 1 . The trigger voltage of the triggering electrode  116  changes to 20*V 1 . With the trigger voltage at 20*V 1  applied to the triggering electrode  116  and the voltage drop of 3*V 1  volts across the anode  112  and cathode  114 , the flash tube  11  discharges. The charging capacitor C ch  then charges the flash tube  11 . 
     It will be understood that the above particular embodiments and methods are shown and described by way of illustration only. The principles and the features of the present invention may be employed in various and numerous embodiment thereof without departing from the scope of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.