Abstract:
A USB charger for electronic cigarettes, comprising a USB interface configured for connecting with a power supply and a load end configured for connecting with a load, wherein, the USB charger for electronic cigarettes further comprises a voltage comparison unit, a benchmark circuit, a sampling circuit, a current detecting element, a state indicating unit, and a low voltage difference linear regulator connected between the USB interface and the load end; the benchmark circuit is connected between an output end of the low voltage difference linear regulator and an input end of the voltage comparison unit; and the state indicating unit is connected with an output end of the voltage comparison unit; the USB charger for electronic cigarettes of the present invention achieves advantages effects of being safer and improving users&#39; experiences.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application claims priorities under 35 U.S.C. §119(a) on Patent Application No. 201320414571.0 filed in P.R. China on Jul. 11, 2013, the entire contents of which are hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of electrical products, and more particularly, relates to a USB charger for electronic cigarettes. 
     BACKGROUND OF THE INVENTION 
     In most current USB chargers for electronic cigarettes, some ones are straight-through type chargers, wherein such a charger is only equivalent to an adapter (i.e., a USB interface switched into an interface matching battery rods of the electronic cigarettes); some ones only comprise comparators and state indicating units (e.g., state indicator lamps) for indicating charging states, and do not include low voltage difference linear regulators for over-temperature, over-current and short-circuit protection; and some ones only adopt low voltage difference linear regulator (LDO) control, but do not include comparators and state indicating units (e.g., state indicator lamps) for indicating charging states. In use, the above three kinds of USB chargers for electronic cigarettes may generate certain hidden dangers and bring bad experience effects to users. 
     SUMMARY OF THE INVENTION 
     The objective of the present invention is to provide an improved USB charger for electronic cigarettes, aiming at the above-mentioned drawbacks that the USB chargers for electronic cigarettes in the prior art may generate certain hidden dangers and bring bad experience effects to users. 
     The technical solutions of the present invention for solving the technical problems are as follows: a USB charger for electronic cigarettes, comprising a USB interface configured for connecting with a power supply and a load end configured for connecting with a load, the USB charger for electronic cigarettes further comprises a voltage comparison unit, a benchmark circuit, a sampling circuit, a current detecting element, a state indicating unit, and a low voltage difference linear regulator connected between the USB interface and the load end; the benchmark circuit is connected between an output end of the low voltage difference linear regulator and an input end of the voltage comparison unit; and the state indicating unit is connected with an output end of the voltage comparison unit; 
     the low voltage difference linear regulator receives power via the USB interface and charges the load, and is further configured to provide over-current protection, short-circuit protection, and over-temperature protection in real time in the charging process; 
     the current detecting element is configured for detecting the charging current, and forms a voltage thereon; 
     the sampling circuit is configured for acquiring a node voltage between the load end and the current detecting element, and generates a comparison voltage at the input end of the comparison unit according to the node voltage; 
     the benchmark circuit is configured to generate a benchmark voltage, and transmits the benchmark voltage to the voltage comparison unit; 
     the voltage comparison unit is configured to compare the comparison voltage with the benchmark voltage, determine a charging state of the USB charger for electronic cigarettes, and control the state indicating unit to indicate the charging state according to the charging state. 
     Advantageously, the state indicating unit comprises a first light emitting diode and a second light emitting diode, the voltage comparison unit comprises a first voltage comparator and a second voltage comparator, the first light emitting diode and the second light emitting diode are respectively connected with an output end of the first voltage comparator and an output end of the second voltage comparator; 
     the sampling circuit generates the comparison voltage at a positive input end of the first voltage comparator and a negative input end of the second voltage comparator respectively, and the benchmark circuit transmits the benchmark voltage to a negative input end of the first voltage comparator and a positive input end of the second voltage comparator respectively. 
     Advantageously, the current detecting element is a detecting resistor. 
     Advantageously, the detecting resistor is connected between a cathode of the load end and ground; the benchmark circuit comprises a first resistor and a second resistor, and the sampling circuit comprises a third resistor; 
     wherein, the first resistor and the second resistor are connected in series and then are connected between a fifth pin of the low voltage difference linear regulator and ground, and the negative input end of the first voltage comparator and the positive input end of the second voltage comparator are connected between the first resistor and the second resistor respectively; one end of the third resistor is connected between the detecting resistor and the cathode of the load end, and the other end of the third resistor is connected with the positive input end of the first voltage comparator and the negative input end of the second voltage comparator respectively; 
     a cathode of the first light emitting diode is connected with the output end of the first voltage comparator, an anode of the first light emitting diode is connected with an anode of the load end, a cathode of the second light emitting diode is connected with the output end of the second voltage comparator, and an anode of the second light emitting diode is connected with the anode of the load end. 
     Advantageously, the USB charger for electronic cigarettes further comprises a first filter capacitor, one end of the first filter capacitor is connected between the voltage comparison unit and the third resistor, and the other end of the first filter capacitor is connected with the ground. 
     Advantageously, the detecting resistor is connected between the fifth pin of the low voltage difference linear regulator and the anode of the load end; the benchmark circuit comprises a first resistor and a second resistor, and the sampling circuit comprises a fourth resistor, a fifth resistor and a regulating resistor; 
     the first resistor and the second resistor are connected in series and then are connected between the fifth pin of the low voltage difference linear regulator and the ground, the negative input end of the first voltage comparator and the positive input end of the second voltage comparator are respectively connected between the first resistor and the second resistor; the fourth resistor, the fifth resistor and the regulating resistor are connected in series, and then one end of the regulating resistor is connected with the ground, and one end of the fourth resistor is connected between the detecting resistor and the anode of the load end; an anode of the first voltage comparator and a cathode of the second comparator are connected between the fourth resistor and the fifth resistor respectively; 
     the anode of the first light emitting diode is connected with the output end of the first voltage comparator, the cathode of the first light emitting diode is connected with the ground, the anode of the second light emitting diode is connected with the output end of the second voltage comparator, and the cathode of the light emitting diode is connected with the ground. 
     Advantageously, the USB charger for electronic cigarettes further comprises a first pull-up resistor and a second pull-up resistor, the first pull-up resistor is connected between the output end of the first voltage comparator and the fifth pin of the low voltage linear voltage regulator, and the second pull-up resistor is connected between the output end of the second voltage comparator and the fifth pin of the low voltage linear voltage regulator. 
     Advantageously, the fifth pin of the low voltage difference linear regulator is connected with the ground via a sixth resistor and a seventh resistor connected in series, and the fourth pin of the low voltage difference linear regulator is connected between the sixth resistor and the seventh resistor. 
     Advantageously, the USB charger for electronic cigarettes further comprises a second filter capacitor, one end of the second filter capacitor is connected with the fifth pin of the low voltage difference linear regulator, and the other end of the second filter capacitor is connected with the ground. 
     Advantageously, the USB charger for electronic cigarettes comprises a third filter capacitors, one end of the third filter capacitor is connected with the first pin) of the low voltage difference linear regulator, the other end of the third filtering capacitor and is connected with the ground. 
     Advantageously, a first protective resistor is connected between the first light emitting diode and the output end the first voltage comparator; and a second protective resistor is connected between the second light emitting diode and the output end of the second voltage comparator. 
     Advantageously, an over-temperature protection unit, a short-circuit protection unit, and an over-current protection unit are mounted inside the low voltage difference linear regulator; the over-temperature protection unit, the short-circuit protection unit, and the over-current protection unit are connected in series, and then are disposed in an internal circuit connected between the first pin and the fifth pin; when the charging current is more than a preset charging current value of the over-current protection, the over-current protection unit cuts off, and the fifth pin stops outputting a charging voltage; when an internal temperature in the low voltage difference linear regulator exceeds a preset temperature value, the over-temperature protection unit cuts off, and the fifth pin stops outputting the charging voltage; and when the load end is short-circuited, the short-circuit protection unit detects that the charging current instantaneously increases and cuts off, and the fifth pin stops outputting the charging voltage. 
     When implementing the present invention, the following advantageous effects can be achieved: the present invention provides a USB charger for electronic cigarettes, which comprises both a charging state indicating unit for indication a charging state and a low voltage difference linear regulator, has all the functions of charging state indication, over-temperature protection, over-current protection, and short-circuit protection, and achieves advantages effects of being safer and improving users&#39; experiences. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be further described with reference to the accompanying drawings and embodiments in the following, in the accompanying drawings: 
         FIG. 1  is a principle block diagram of an USB charger for electronic cigarettes of the present invention; 
         FIG. 2  is a circuit diagram of an USB charger for electronic cigarettes of one embodiment of the present invention; 
         FIG. 3  is a circuit diagram of an USB charger for electronic cigarettes of another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a USB charger for electronic cigarettes, which comprises a USB interface  101 , a low voltage difference linear regulator (LDO)  102 , a current detecting element  103 , a load end  104 , a benchmark circuit  105 , a sampling circuit  106 , a voltage comparison unit  107 , and a state indicating unit  108 . 
     The USB interface  101 , the low voltage difference linear regulator  102 , the current detecting element  103 , and the load end  104  are electrically connected in series. The benchmark circuit  105  is connected between a voltage output end of the low voltage difference linear regulator  102  and an input end of the voltage comparison unit  107 . One end of the sampling circuit  106  is connected with the input end of the voltage comparison unit  107 , and the other end of the sampling circuit  106  is connected between the current detecting element  103  and the load end  104 . The state indicating unit  108  is connected with the output end of the voltage comparison unit  107 . 
     The low voltage difference linear regulator  102  gets power supply, over-current protection, short-circuit protection, and over-temperature protection via the USB interface  101 . The current detecting element  103  is configured for detecting the charging current and forming a voltage thereon, correspondingly. The sampling circuit  106  is configured for sampling a node voltage between the load end  104  and the current detecting element  103 , and generates a voltage at the input end of the voltage comparison unit  107  according to the node voltage. The benchmark circuit  105  is configured to generate a benchmark voltage, and transmits the benchmark voltage to the voltage comparison unit  107 . The voltage comparison unit  107  is configured to compare the comparison voltage with the benchmark voltage, determine a charging state of the USB charger for electronic cigarettes according to the comparison result, and control the state indicating unit  108  to light according to the charging state. A voltage of the load end  104  can be judged according to the charging state, and then a voltage of the current detecting element  103  can be calculated. The charging current at this time can be obtained by dividing a voltage value of the current detecting unit  103  by a resistance value of the current detecting unit  103 . 
     A signal flow of this embodiment is described as follows: the low voltage difference linear regulator  102  gets power supply via the USB interface  101 , and the voltage output end of the low voltage difference linear regulator  102  outputs a voltage V. The benchmark circuit  105  obtains a constant voltage from the voltage output end, the constant voltage is adjusted by the benchmark circuit  105 , and a benchmark voltage V 0  is generated and output to the input end of the voltage comparing unit  107 . At the same time, when charging current flows through the current detecting element  103 , a partial voltage V 1  is generated at the current detecting element  103 . The sampling circuit  106  is connected between the load end  104  and the current detecting element  103  to sample a node voltage V 2  here, and generates a comparison voltage Vp at the input end of the voltage comparing unit  107  according to the node voltage V 2 . The voltage comparison unit  107  compares V 0  with Vp to judge a charging state, and drives the state indicating unit  108  connected with the voltage comparison unit  107  to light, thereby indicating the charging state. 
     Referring to  FIG. 2 , in this embodiment, the current detecting element  103  is connected between an anode of the load end  104  and the voltage output end of the low voltage difference linear regulator  102 . The voltage output end of the low voltage difference linear regulator  102  is a fifth pin Out. A chip U 1  of the low voltage difference linear regulator  102  is in a type of AP2127K-ADJ. The current detecting element  103  is a detecting resistor R 11 . The benchmark circuit  105  comprises a first resistor R 1  and a second resistor R 2 . The sampling circuit  106  comprises a fourth resistor R 4 , a fifth resistor R 5 , and an adjusting resistor Rx. The voltage comparison unit  107  is a dual voltage comparator U 2 , which comprises a first voltage comparator and a voltage second comparator. Two filter capacitors, which are a second filtering capacitor C 2  and a third filtering capacitor C 3  respectively, are provided. Two protective resistors, which are a first protective resistor R 14  and a second protective resistor R 15  respectively, are provided. Two pull-up resistors, which are a first pull-up resistor R 12  and a second pull-up resistor R 13 , are provided. The state indicating unit  108  includes a first light emitting diode D 1  and a second light emitting diode D 2 . The first light emitting diode D 1  sends out green light, and the second light emitting diode D 2  sends out red light. 
     Circuit connection relations of this embodiment are described as follows: a first pin Vin and a third pin shutdown of the low voltage difference linear regulator  102  get a 5V voltage via the USB interface  101 ; a second pin GND is grounded; the fifth pin Out acts as the voltage output end, and the fifth pin Out is connected with the ground via a sixth resistor R 6  and a seventh R 7  connected in series; and a fourth pin Adj is connected between the sixth resistor R 6  and the seventh resistor R 7 . One end of the second filter capacitor C 2  is connected to the fifth pin Out, and the other end of the second filter capacitor C 2  is grounded. One end of the third filter capacitor C 3  is connected with the first pin Vin, and the other end of the third filter capacitor C 3  is grounded. The first resistor R 1  and the second resistor R 2  are connected in series, one end of the first resistor R 1  is connected with the fifth pin Out, and one end of the second resistor R 2  is grounded. Both a negative input end of the first voltage comparator and a positive input end of the second voltage comparator are connected between the first resistor R 1  and the second resistor R 2 . The detection resistor R 11  is connected between the fifth pin Out and the anode of the load end  104 . The fourth resistor R 4 , the fifth resistor R 5 , and the adjusting resistor Rx are connected in series, one end of the adjusting resistor Rx is grounded, and one end of the fourth resistor R 4  is connected between the detection resistor R 11  and the anode of the load end  104 . Both a positive input end of the first voltage comparator and a negative input end of the second voltage comparator are connected between the fourth resistors R 4  and the fifth resistor R 5 . An anode of the first light emitting diode D 1  is connected with the output end of the first voltage comparator, and a cathode of the first light emitting diode D 1  is grounded. An anode of second light-emitting oxide D 2  is connected with the output end of the second voltage comparator, and a cathode of the second light emitting diode D 2  is grounded. One end of the first pull-up resistor R 12  is connected with the fifth pin Out, and the other end of the first pull-up resistor R 12  is connected with the output end of the first voltage comparator. One end of the second pull-up resistor R 13  is connected with the fifth pin Out, and the other end of the second pull-up resistor R 13  is connected to the output end of the second voltage comparator. The first protective resistor R 14  is connected between the output end of the first voltage comparator and the first light-emitting diode D 1 . The second protective resistor R 15  is connected between the output end of second voltage comparator and the second light-emitting diode D 2 . 
     The sampling circuit  106  samples the node voltage V 2  between the current detecting element  103  and the load end  104 , and generates a comparison voltage Vp at the voltage comparison unit  107 . If Vp is more than the value of V 0 , it is illustrated the charging process is finished. Thus, the first voltage comparator outputs an high electrical level, and the second voltage comparator outputs an low electrical level. At this time, the first light-emitting diode D 1  lights, and the second light emitting diode D 2  does not light. If Vp is less than the value of V 0 , it is illustrated the charging process is continuing. Thus, the first voltage comparator outputs the low electrical level, and the second comparator outputs the high electrical level. At this time, the first light-emitting diode D 1  does not light, and the second light emitting diode D 2  lights. 
     In this embodiment, the first light-emitting diode D 1  and the second light emitting diode D 1  are driven by the high electrical level respectively. Therefore, in order to ensure the output voltages of the first voltage comparator and the second comparator to be high enough to make the first light-emitting diode D 1  and the second light emitting diode D 2  light, the first pull-up resistor R 12  and the second pull-up resistor R 13  are configured. 
     Referring to  FIG. 3 , in this embodiment, the current detecting element  103  is connected between a cathode of the load end  104  and the ground. A chip of the low voltage difference linear regulator  102  is in a type of AP2127K-ADJ. The current detecting element  103  is a detecting resistor R 11 . The benchmark circuit  105  comprises a first resistor R 1  and a second resistor R 2 . The sampling circuit  106  comprises a third resistor R 3 . The voltage comparison unit  107  is a dual voltage comparator, which comprises a first voltage comparator and a second voltage comparator. Three filter capacitors, which are a first filtering capacitor C 1 , a second filtering capacitor C 2  and a third filtering capacitor C 3  respectively, are provided. Two protective resistors, which are a first protective resistor R 14  and a second protective resistor R 15  respectively, are provided. The state indicating unit  108  comprises a first light emitting diode D 1  and a second light emitting diode D 2 . The first light emitting diode D 1  sends out green light, and the second light emitting diode D 2  sends out red light. 
     Circuit connections of this embodiment are described as follows: a first pin Vin and a third pin shutdown of the low voltage difference linear regulator  102  get a 5V voltage via the USB interface  101 ; a second pin GND is grounded; a fifth pin Out acts as the voltage output end, and the fifth pin Out is connected with the ground via a sixth resistor R 6  and a seventh R 7  connected in series; and a fourth pin Adj is connected between the sixth resistors R 6  and the R 7  seventh resistor. One end of the second filter capacitor C 2  is connected to the fifth pin Out, and the other end of the second filter capacitor C 2  is grounded. One end of the third filter capacitor C 3  is connected with the first pin Vin, and the other end of the third filter capacitor C 3  is grounded. The first resistor R 1  and the second resistor R 2  are connected in series, and one end of the second resistor R 2  is ground. Both a negative input end of the first voltage comparator and a positive input end of the second voltage comparator are connected between the first resistor R 1  and the second resistor R 2 . One end of a third resistor R 3  is connected between the detection resistor R 11  and a cathode of the load end  104 , and the other end of the third resistor R 3  is connected with a positive input end of the first voltage comparator and a negative input end of the second voltage comparator respectively. One end of the first filter capacitor C 1  is grounded, and the other end of the first filter capacitor C 1  is connected between the positive input end of the first voltage comparator and the third resistor R 3 . A cathode of the first light emitting diode D 1  is connected with the output end of the first voltage comparator, and an anode of the first light emitting diode D 1  is connected with the anode of the load end. A cathode of second light-emitting diode D 2  is connected with the output end of the second voltage comparator, and an anode of the second light emitting diode D 2  is connected with the anode of the load end. The first protective resistor R 14  is connected between the first light-emitting diode D 1  and the output end of the first voltage comparator. The second protective resistor R 15  is connected with the second light-emitting diode D 2  and the output end of second voltage comparator. 
     When an electronic cigarette charged by the USB charger for electronic cigarettes is not fully charged, a voltage of the load end  104  is Va, and a voltage of the voltage detecting element  103  is Vc. When the electronic cigarette is fully charged, the voltage of the load end  104  is Vb, and the voltage of the current detecting element  103  is Vd; wherein, Va&lt;Vb. The sampling circuit  106  generates a real-time voltage Vp at the output end of the voltage comparison unit  107 . In this embodiment, Vp, the node voltage V 2 , and the voltage on the current detecting element  103  are equal to each other. When the electronic cigarette is fully charged, Vp=Vc=V−Vb; and when the electronic cigarette is not fully charged, the voltage on the current detecting element  103  is Vp=Vd=V−Va. The benchmark voltage is V 0 =V*R 2 /(R 1 +R 2 ). At this time, because Va&lt;Vb, so Vd&gt;Vc. A value between Vc and Vd is selected and used as the benchmark voltage V 0 . When Vp&gt;V 0 , the charging process is finished. The first voltage comparator outputs the high electrical level, and the second voltage comparator outputs low electrical level. Thus, the first light-emitting diode D 1  does not light, and the second light emitting diode D 2  lights. When Vp&lt;V 0 , the charging process is not finished. The first voltage comparator outputs the low electrical level, and the second comparator outputs the high electrical level. Thus, the first light-emitting diode D 1  lights, and the second light emitting diode D 2  does not light. 
     The low voltage difference linear regulator  102  of the aforementioned two embodiments is described in detail as follows. The low voltage difference linear regulator  102  has over-current protection, short-circuit protection, and over-temperature protection function. An over-temperature protection unit, a short-circuit protection unit, and a over-current protection unit are mounted inside the low voltage difference linear regulator. The over-temperature protection unit, the short-circuit protection unit, and the over-current protection unit are connected in series, and then are connected with the internal circuit between the first pin and the fifth pin. When the charging current is more than preset charging current, the over-current protection unit cuts down, and the fifth pin stops outputting voltage. When an internal temperature of the low voltage difference linear regulator exceeds a preset value, the over-temperature protection unit cuts down, and the fifth pin stops outputting electrical levels. When the load end is short-circuited, the short-circuit protection unit detects that the charging current instantaneously increases and cuts off, and the fifth pin stops outputting the charging voltage. 
     Understandably, the ordinary technicians in the field can make improvements and modifications according to the above description, all these improvements and modifications belong to the protection of the present invention.