Abstract:
A fault detection circuit connects to and determines the occurrence of failure in an inverter circuit. The inverter circuit comprises three outputs to connect three groups of lamps respectively, and the fault detection circuit comprises a magnetic unit and a signal detection unit. The magnetic unit comprises first, second and third flux generating windings electrically connected to the three outputs of the inverter circuit, and a flux detection winding. If no fault occurs on the outputs of the inverter circuit, total flux generated by the flux generating windings is cancelled out. As long as any fault occurs on the outputs of the inverter circuit, flux generated by the flux generating windings cannot be canceled out, and the flux detection winding is electromagnetically coupled accordingly and driven by the generated flux to output a coupling signal, based on which the signal detection unit generates an alert signal accordingly.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to detection circuits, and especially to a fault detection circuit. 
     2. Description of Related Art 
     Referring to  FIG. 8  and  FIG. 9 , a commonly used fault detection circuit  1  is connected to an inverter circuit  2  with a plurality of outputs, to detect whether one or more of the outputs of the inverter circuit  2  are faulty. The outputs of the inverter circuit  2  are divided into two groups. The inverter circuit  2  drives a light source module  22 , and comprises a transformer unit  21  and a protection unit  23 . The fault detection circuit  1  comprises a magnetic unit  11  and a signal detection unit  12 . 
     The magnetic unit  11 , connected to the inverter circuit  2 , determines whether one or more of the outputs of the inverter circuit  2  are faulty, and comprises a first magnetic winding  111 , a second magnetic winding  112  and a third magnetic winding  113 . 
     The first magnetic winding  111  is connected to one group output of the inverter circuit  2 , and the second magnetic winding  112  is connected to another group output of the inverter circuit  2 . In addition, wrapping directions of the first magnetic winding  111  and the second wrapping winding  112  are opposite. Thus, when one or more of the outputs of the inverter circuit  2  are faulty, total flux generated by the first and second magnetic windings  111 ,  112  cannot be canceled out. Accordingly, the third magnetic winding  113  generates a detection signal. The signal detection unit  12  generates an abnormal signal according to the detection signal, and outputs the abnormal signal to the protection unit  23 . The protection unit  23  protects the inverter circuit  2 . 
     However, when the number of abnormal lamps of the light source module  22  corresponding to the two groups of output of the inverter circuit  2  are the same, flux generated by the first and second magnetic windings  111 ,  112  is the same and can also be canceled out. In this instance, the third magnetic winding  113  detects no flux and does not generate the abnormal signal, thus, the abnormal of the inverter circuit  2  is not detected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a first embodiment of a fault detection circuit of the present disclosure, showing connections between the fault detection circuit and a transformer unit, a power source, a current balancing circuit and a light source module; 
         FIG. 2  is a detailed circuit diagram of one embodiment of the fault detection circuit of  FIG. 1 ; 
         FIG. 3  is another block diagram of one embodiment of the fault detection circuit of  FIG. 1 ; 
         FIG. 4  is another detailed circuit diagram of one embodiment of the fault detection circuit of  FIG. 1 ; 
         FIG. 5  is a block diagram of a second embodiment of a fault detection circuit of the present disclosure, showing connections between the fault detection circuit and a transformer unit, a power source, a current balancing circuit and a light source module; 
         FIG. 6  is a detailed circuit diagram of one embodiment of the fault detection circuit of  FIG. 5 ; 
         FIG. 7  is another block diagram of one embodiment of the fault detection circuit of  FIG. 5 ; 
         FIG. 8  is a block diagram of a commonly used fault detection circuit, showing connections between the fault detection circuit and an inverter circuit; and 
         FIG. 9  is a detailed circuit diagram of the fault detection circuit of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     Similar components in embodiments of the present disclosure described have the same labels. 
       FIG. 1  is a schematic diagram of a first embodiment of a fault detection circuit  3  of the present disclosure, and  FIG. 2  a detailed circuit diagram of one embodiment of the fault detection circuit  3  of  FIG. 1 . The fault detection circuit  3  is connected to an inverter circuit  4  with a plurality of outputs, to detect whether any of the plurality of outputs of the inverter circuit  4  are faulty. In one embodiment, the outputs of the inverter circuit  4  are divided into three groups (described in detail below) to drive a light source module  43  respectively. The fault detection circuit  3  comprises a magnetic unit  31  and a signal detection unit  32 . In one embodiment, the signal detection unit  32  can be a commonly used protection circuit, to protect the inverter circuit  4 . 
     In one embodiment, the inverter circuit  4  receives electrical signals output from a power source  5  and then converts the electrical signals to alternating current (AC) signals to drive three light source modules  43 , which comprises a transformer unit  41  and a current balancing circuit  42 . In one embodiment, the transformer circuit  41  comprises a primary winding and three secondary windings. The three secondary windings are corresponding to the three outputs of the inverter circuit  4 . Each of the secondary windings of the transformer circuit  41  has a high voltage terminal (HV 1  or HV 2  or HV 3 ) and a low voltage terminal (LV 1  or LV 2  or LV 3 ) respectively. The high voltage terminals HV 1 , HV 2 , HV 3  are jointly connected to the current balancing current circuit  42 , and the low voltage terminals LV 1 , LV 2 , LV 3  are jointly connected to the fault detection circuit  3 . Voltage phases of the high voltage terminals HV 1 , HV 2  are the same, different in voltage phase from the high voltage terminal HV 3 . The current balancing circuit  42  balances current flowing through the light source modules  43 . In one embodiment, each light source module  43  comprises one or more lamps. The number of the light source module  43  can be three or more, which is not limited. 
     The magnetic unit  31  comprises a first magnetic winding  311 , a second magnetic winding  312 , a third magnetic winding  313 , and a magnetic detection winding  314 . The first, second and third magnetic windings  311 ,  312 ,  313  are connected to the low voltage terminals LV 1 , LV 2 , LV 3 , respectively. One end of each magnetic winding is defined as an input, and the other end thereof is defined as an output. Inputs of the first, second, and third magnetic windings  311 ,  312 ,  313  are connected to the low voltage terminals LV 1 , LV 2 , LV 3  respectively, and the outputs thereof are connected to ground. 
     Alternatively, voltage phases of the high voltage terminals HV 1 , HV 2 , HV 3  or low voltage terminals LV 1 , LV 2 , LV 3  can be the same. In this instance, wrapping direction, and input and output direction of the first, second, and third magnetic windings  311 ,  312 ,  313  of the fault detection circuit  3  need to be arranged to cancel out total flux generated by the fault detection circuit  3 , when the high voltage terminals HV 1 , HV 2 , HV 3  and the low voltage terminals LV 1 , LV 2 , LV 3  are normal. 
     When the outputs of the inverter circuit  4  are normal, the total flux generated by the first, second, and third magnetic windings  311 ,  312 ,  313  can be cancelled out. Thus, a formula N 1 *I 1 +N 2 *I 2 =N 3 *I 3  can be expressed, wherein N 1 , N 2 , and N 3  are turn numbers of the first, second, and third magnetic windings  311 ,  312 ,  313 , and I 1 , I 2 , I 3  are total current flowing through the first, second, and third magnetic windings  311 ,  312 ,  313 . Because the current flowing through each lamp is substantially the same, the formula can be changed to N 1 *L 1 +N 2 *L 2 =N 3 *L 3 , wherein L 1 , L 2 , L 3  are the number of lamps corresponding to the first, second, and third magnetic windings  311 ,  312 ,  313 . In detail, the turn number of the first magnetic winding  311  multiplies the number of lamps corresponding to the first magnetic winding  311 , which is defined as a first flux. The turn number of the second magnetic winding  312  multiplies by the number of lamps corresponding to the second magnetic winding  312 , which is defined as a second flux. The turn number of the third magnetic winding  313  multiplies by the number of lamps corresponding to the third magnetic winding  313 , which is defined as a third flux. In one embodiment, the first flux added to the second flux is equal to the third flux. When one or more of the outputs of the inverter circuit  4  are faulty, the total flux generated by the first, second, and third magnetic windings  311 ,  312 ,  313  cannot be canceled out. Thus, the formula is not satisfied. 
     For example, if the turn numbers of the first, second, and third magnetic winding  311  are 11, 5, 6 respectively, and the numbers of the lamp corresponding to the first, second, and third magnetic winding  311 ,  312 ,  313  are 1, 5, 6 respectively, a formula 11*1+5*5=6*6 is formed. However, when a lamp corresponding to the first magnetic winding  311  and third magnetic winding  313  are faulty, a formula 11*0+5*5≠6*5 can be applied. Thus, the total flux generated by the first, second, and third magnetic windings  311 ,  312 ,  313  cannot be canceled out. 
     When one or more of the outputs of the inverter circuit  4  are faulty, the magnetic detection winding  314  senses the total flux generated by the first, second, and third magnetic windings  311 ,  312 ,  313 , and generates a detection signal. The signal detecting unit  32  accordingly generates an abnormal signal according to the detection signal. 
     Only total flux generated by the first, second, and third magnetic windings  311 ,  312 ,  313  is lower than a predetermined threshold, signal detection unit  32  generates no abnormal signal and the flux can be canceled out. If the total flux generated by the first, second, and third magnetic windings  311 ,  312 ,  313  exceeds the predetermined threshold, the magnetic detection winding  314  also generates the detection signal accordingly, and then the signal detection unit  32  generates the abnormal signal according to the detection signal. In the other words, although the outputs of the inverter circuit  4  are normal, the total flux generated by the first, second, and third magnetic windings  311 ,  312 ,  313  also cannot be canceled out. 
     Referring to  FIG. 3 , the transformer unit  41  comprises two individual transformers  411  having the same effectiveness. 
     In one embodiment, voltage phase of the high voltage terminal HV 1  is the same as that of the high voltage terminal HV 2 , which is different from that of the high voltage terminal HV 3 . Similarly, voltage phase of the low voltage terminal LV 1  is the same as that of the low voltage terminal LV 2 , which is different from that of the low voltage terminal LV 3 . Alternatively, voltage phases of the high voltage terminals HV 1 , HV 2  can be the same as that of the high voltage terminal HV 3 , and voltage phases of the low voltage terminal LV 1 , LV 2  can be the same as that of the low voltage terminal LV 3 , only needing to change polarities of the first, second, and third magnetic windings  311 ,  312 ,  313 , but not limited thereto. 
       FIG. 4  is another detailed circuit diagram of one embodiment of the fault detection circuit  3 , differing from the fault detection circuit  3  of  FIG. 2  only in that the magnetic unit  31  of  FIG. 4  comprises a fourth magnetic winding  315 . 
     Similarly, each of the magnetic windings  311 ,  312 ,  313 ,  314  has an input and an output. The inputs of the first, second magnetic winding  311 ,  312  are connected to the low voltage terminals LV 1 , LV 2  respectively, and the outputs thereof are connected to the input of the fourth magnetic winding  315 . The input of the third magnetic winding  313  is connected to the low voltage terminal LV 3 , and the outputs of the third magnetic winding  313  and the fourth magnetic winding  315  are connected to ground. 
     Therefore, when the outputs of the inverter circuit  4  are normal, the total flux generated by the magnetic windings  311 ,  312 ,  313 ,  314  can be canceled out. In one embodiment, the turn number of the first magnetic winding  311  multiplied by the number of lamps corresponding to the first magnetic winding  311 , equals the turn number of the second magnetic winding  312  multiplied by the number of lamps corresponding to the second magnetic winding  312 . Similarly, the turn number of the third magnetic winding  313  multiplied by the number of lamps corresponding to the third magnetic winding  313 , equals the turn number of the fourth magnetic winding  315  multiplied by the number of lamps corresponding to the fourth magnetic winding  315 . Thus, two formulae can be applied. When one or more outputs of the inverter circuit  4  are faulty, the total flux generated by the magnetic windings  311 ,  312 ,  313 ,  315  cannot be canceled. In this instance, at least one of the formulae is not satisfied. 
     For example, if the turn numbers of the first, second, third, and fourth magnetic windings  311 ,  312 ,  313 ,  315  are 5, 5, 2, 2 respectively, and the numbers of the lamps corresponding to the first, second, and third and fourth magnetic windings  311 ,  312 ,  313 ,  315  are 3, 3, 6, 6 respectively, the two formulae: 5*3=5*3 and 2*6=2*6 can be applied. Thus, the outputs of the inverter circuit  4  are normal. However, when one lamp corresponding to both of the first magnetic winding  311  and the third magnetic winding  313  are faulty, the formulae become 5*2≠5*3 and 2*5=2*5. Therefore, one of the formulae is not satisfied, and flux generated by the first, second, and third and fourth magnetic windings  311 ,  312 ,  313 ,  315  cannot be canceled. 
     When one or more of the outputs of the inverter circuit  4  are faulty, the magnetic detection winding  314  senses the flux generated by the first, second, third, and fourth magnetic windings  311 ,  312 ,  313 ,  315 , and generates a detection signal. The signal detecting unit  32  generates an abnormal signal according to the detection signal, accordingly 
       FIG. 5  is a schematic diagram of a second embodiment of a fault detection circuit  3  of the present disclosure, and  FIG. 6  a detailed circuit diagram of one embodiment of the fault detection circuit  3 . The fault detection circuit  3  is connected to an inverter circuit  4  with a plurality of outputs, detecting whether one or more of the plurality of outputs of the inverter circuit  4  are faulty. In one embodiment, the outputs of the inverter circuit  4  are divided into two groups. The fault detection circuit  3  comprises a first magnetic winding  33 , a second magnetic winding  34 , a first magnetic sensing winding  35 , a third magnetic winding  36 , a fourth magnetic winding  37 , a second magnetic sensing winding  38  and a signal detection unit  32 . In one embodiment, the signal detection unit  32  can be a commonly used protection circuit, to protect inverter circuit  4 . 
     In one embodiment, the inverter circuit  4  receives electrical signals output from a power source  5  and then converts the electrical signals to AC signals to drive a light source module  43 , which comprises a transformer unit  41  and a current balancing circuit  42 . In one embodiment, the transformer unit  41  comprises a primary winding and two secondary windings. The two secondary windings are corresponding to the two outputs groups of the inverter circuit  4 . Each of the secondary windings of the transformer circuit  41  has a high voltage terminal (HV 1  or HV 2 ) and a voltage terminal (LV 1  or LV 2 ) respectively. The low voltage terminals LV 1  and LV 2  are connected to ground. In one embodiment, the two high voltage terminals HV 1 , HV 2  are divided into four high voltage terminals HV 1 , HV 1 ′, HV 2 , HV 2 ′, connected to a lamp respectively. The current balancing circuit  42  balances current flowing through the light source module  43 . In one embodiment, the light source module  43  comprises at least four lamps or more. 
     When the outputs of the inverter circuit  4  are normal, the total flux generated by the first, second, third, and fourth magnetic windings  33 ,  34 ,  36 ,  37  can be canceled out. In one embodiment, the turn number of the first magnetic winding  33  multiplied by the number of lamps corresponding to the first magnetic winding  33 , equals the turn number of the second magnetic winding  34  multiplied by the number of lamps corresponding to the second magnetic winding  34 . Similarly, the turn number of the third magnetic winding  36  multiplied by the number of lamps corresponding to the third magnetic winding  36 , equals the turn number of the fourth magnetic winding  37  multiplied by the number of lamps corresponding to the fourth magnetic winding  37 . Thus, two formulae can be applied. When one or more of the outputs of the inverter circuit  4  are faulty, the total flux generated by the magnetic windings  33 ,  34 ,  36 ,  37  cannot be canceled. In this instance, at least one of the formulae is not satisfied. 
     For example, if the turn numbers of the first, second, and third and fourth magnetic windings  33 ,  34 ,  36 ,  37  are respectively 5, 5, 5, 5, and the numbers of the lamps corresponding to the first, second, third, and fourth magnetic windings  33 ,  34 ,  36 ,  37  are 3, 3, 3, 3 respectively, the two formulae: 5*3=5*3 and 5*3=5*3 can be applied. Thus, the outputs of the inverter circuit  4  are not faulty. However, when one lamp corresponding to both of the first magnetic winding  33  and the third magnetic winding  36  are faulty, the formulae become 5*2≠5*3 and 5*2≠5*3. Therefore, both the formulae are not satisfied, and flux generated by the first, second, and third and fourth magnetic windings  33 ,  34 ,  36 ,  37  cannot be canceled out. 
     When one or more of the outputs of the inverter circuit  4  are faulty, the magnetic detection windings  35 ,  38  detect the flux generated by the first, second, third, and fourth magnetic windings  33 ,  34 ,  36 ,  37 , and generates a detection signal respectively. The signal detecting unit  32  generates an abnormal signal according to the detection signals accordingly. 
     Referring to  FIG. 7 , the transformer unit  41  comprises two individual transformers  411  having the same effectiveness. 
     When the number of abnormal lamps in the light source module  43  corresponding to the high voltage terminals is equal to that corresponding to the low voltage terminals, one or more formulae are applied to determine if one or more of the outputs of the inverter circuit  4  are faulty. Thus, the same number of abnormal lamps corresponding to the high voltage terminals and the low voltage terminals can be detected. 
     Although the features and elements of the present disclosure are described in various inventive embodiment in particular combinations, each feature or element can be configured alone or in various within the principles of the present disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.