Abstract:
An automatic power supply converting circuit includes a live input terminal, a neutral input terminal, a relay, a regulator, a voltage divider circuit, an identifying circuit, a switch circuit and a voltage doubling circuit. The live input terminal and the neutral input terminal are configured for receiving a first alternating current (AC) voltage. The regulator is configured for filtering and steadying the first AC voltage and outputting a regulated voltage. The voltage divider circuit is configured for sampling the first AC voltage and outputting a divided voltage. The identifying circuit is configured for comparing a divided voltage with a reference voltage, and outputting a control signal. The switch circuit is configured for controlling the relay to be conductive or not. The voltage doubling circuit is capable of being controlled by the relay and outputting a doubled voltage.

Description:
BACKGROUND 
   1. Field of the Invention 
   The present invention relates to an automatic converting circuit of a power supply. 
   2. Description of Related Art 
   There are different types of AC power supplies, such as 110V and 220V. Some power circuits of computers integrate a voltage doubling circuit therein to satisfy different power supplies. For example, when the AC power supply is 110V, the users select the voltage doubling circuit through a manual switch, then the voltage doubling circuit converts the AC power supply 110V in 220V, and the load circuit receives the 220V voltage. However, there is a risk of error because the manual switch depends on the users. 
   What is needed is to provide an automatic power supply converting circuit which can automatically convert 110V to 220V. 
   SUMMARY 
   An exemplary automatic power supply converting circuit is configured for converting a first AC voltage to a second AC voltage to a load circuit. The converting circuit includes a live input terminal, a neutral input terminal, a relay, a regulator, a voltage divider circuit, an identifying circuit, a switch circuit and a voltage doubling circuit. The live input terminal and the neutral input terminal are configured for receiving the first AC voltage. The regulator is configured for filtering and steadying the first AC voltage and outputting a regulated voltage. The voltage divider circuit is configured for sampling the first AC voltage and outputting a divided voltage. The identifying circuit which includes a comparator is configured for receiving the divided voltage, comparing the divided voltage with a reference voltage, and then outputting a control signal according to the comparison result. The switch circuit is configured for controlling the relay to be conductive or not according to the control signal. The voltage doubling circuit is capable of being controlled by the relay and outputting a doubled voltage. 
   Other advantages and novel features of the present invention will become more apparent from the following detailed description of an embodiment when taken in conjunction with the accompanying drawing, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     A circuit diagram represents an automatic power supply converting circuit which is connected to a load circuit in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Referring to the circuit diagram, an automatic power supply converting circuit in accordance with an embodiment of the present invention is configured for automatically supplying a 220V voltage to a load circuit of a computer when an AC power supply is 110V. The converting circuit includes a live input terminal L, a neutral input terminal N, a relay J 1 , a regulator  10 , a voltage divider circuit  20 , an identifying circuit  30 , a switch circuit  40 , and a voltage doubling circuit  50 . 
   The regulator  10  includes two resistors R 1  and R 2 , two diodes D 1  and D 2 , and two capacitors C 1  and C 2 . The resistor R 1  and the capacitor C 2  are connected in parallel between the input terminal L and an anode of the diode D 1 . The resistor R 2  and the capacitor C 2  are connected in series between a cathode of the diode D 1  and the input terminal N. An anode of the diode D 2  is connected to the input terminal N. A cathode of the diode D 2  is connected to a node A between the capacitor C 2  and the resistor R 2 . The regulator  10  regulates the 110V AC power supply and filters noise. The node A acts as an output terminal of the regulator  10  to output a regulated voltage. In this embodiment, the resistances of the resistors R 1 , R 2  are respectively 1 MΩ and 22Ω, and the capacitances of the capacitors C 1 , C 2  are respectively 1 μF and 470 μF. 
   The voltage divider circuit  20  includes a diode D 3 , two resistors R 3  and R 4 , a capacitor C 3 , and a variable resistor RP 1 . The variable resistor RP 1  includes two opposites, terminals  1 ,  2  and a sliding terminal  3 . An anode of the diode D 3  is connected to the input terminal L. A cathode of the diode D 3  is connected to the terminal  1  of the variable resistor RP 1  via the resistor R 3 . The terminal  2  of the variable resistor RP 1  is connected to the input terminal N via the resistor R 4 . The sliding terminal  3  of the variable resistor RP 1  is connected to the input terminal N via the capacitor C 3 . The sliding terminal  3  acts as an output terminal of the voltage divider circuit  20  to output a divided voltage. In this embodiment, the resistances of the resistors R 3 , R 4  are respectively 330KΩ and 10KΩ, the maximum resistance of the variable resistor RP 1  is 47KΩ, and the capacitance of the capacitor C 3  is 47 μF. 
   The identifying circuit  30  includes a resistor R 5 , two capacitors C 4  and C 5 , a diode D 4 , and a comparator IC 1 . The resistor R 5  is connected between a non-inverting input terminal VB and a positive power supply terminal Vcc of the comparator IC 1 . A positive power supply terminal Vcc of the comparator IC 1  is connected to a node A of the regulator  10 . A inverting input terminal VA of the comparator IC 1  is connected to the sliding terminal  3  of the variable resistor RP 1 . The capacitor C 4  is connected between the non-inverting input terminal VB and the inverting input terminal VA. The capacitor C 5  is connected between the non-inverting input terminal VB and the input terminal N. A cathode of the diode D 4  is connected to the non-inverting input terminal VB. An anode of the diode D 4  is connected to the input terminal N. The input terminal N is connected to a negative power supply terminal Vss of the comparator IC 1 . The node between the resistor R 5  and the diode D 4  outputs a reference voltage from the regulator  10  to the non-inverting input terminal VB of the comparator IC 1 . In this embodiment, the resistance of the resistor R 5  is 2.2KΩ, and the capacitances of the capacitors C 4 , C 5  are respectively 47 nF and 0.1 μF. 
   The relay J 1  includes a coil K 1  and a switch S 1 . The switch circuit  40  includes two resistors R 6  and R 7 , a transistor Q 1 , and a diode D 5 . The resistor R 7  is connected between an input terminal N and an output terminal Vo of the comparator IC 1 . An output terminal Vo of the comparator IC 1  is connected to a first terminal (base) of the transistor Q 1  via the resistor R 6 . A second terminal (emitter) of the transistor Q 1  is connected to the input terminal N. A third terminal (collector) of the transistor Q 1  is connected to an anode of the diode D 5 . A cathode of the diode D 5  is connected to the node A. The coil K 1  is connected between the node A and the third terminal of the transistor Q 1 . In this embodiment, the resistances of the resistors R 6 , R 7  are respectively 10KΩ and 22KΩ. 
   The voltage doubling circuit  50  includes a bridge rectifier  52 , two capacitors C 01  and C 02 , and two resistors R 0  and R 02 . The bridge rectifier  52  includes four diodes D 01 , D 02 , D 03  and D 04 . A positive input terminal VA of the bridge rectifier  52  is connected to the input terminal L. A positive output terminal VO 1  of the bridge rectifier  52  is connected to a negative output terminal VO 2  of the bridge rectifier  52  via the capacitors C 0  and C 02  in series and also via the resistors R 0  and R 02  connected in series. The node between the capacitors C 01  and C 02  is connected to the node between the resistors R 01  and R 02 . The switch S 1  is a single-pole double-throw switch, and includes a first contact  1 , a second contact  2  and a common terminal  3 . A negative input terminal VB of bridge rectifier  52  is connected to the second contact  2  of switch S 1 . The first contact  1  of switch S 1  is connected to the node between the capacitors C 0  and C 02 . The common terminal  3  of switch S 1  is connected to the input terminal N. A load circuit  60  is connected between the positive output terminal VO 1  and the negative output terminal VO 2  of the bridge rectifier  52 . 
   In working, the AC power supply is input via the input terminal L and the input terminal N, and filtered and steadied by the regulator  10 . The node A outputs the regulated voltage to the identifying circuit  30  and the switch circuit  40 . The voltage divider circuit  20  samples the input voltage, and then outputs the divided voltage to the VA of the comparator IC 1  of the identifying circuit  30 . 
   The non-inverting input terminal VB of the comparator IC 1  is provided with the reference voltage by the node between the resistor R 5  and the diode D 4 , the comparator IC 1  compares the divided voltage with the reference voltage, and then outputs a control signal to the transistor Q 1  of the switch circuit  40 . The transistor Q 1  is turned on or off according to the control signal, thereby controlling the coil K 1  to be conductive or not. Thereinto, when the divided voltage is less than the reference voltage, the comparator IC 1  outputs a high voltage control signal; when the divided voltage is greater than the reference voltage, the comparator IC 1  outputs a low voltage control signal. In this embodiment, the reference voltage is 6V. 
   When the comparator IC 1  outputs the low voltage control signal, the transistor Q 1  is turned off, the coil K 1  is conductive, the common terminal  3  of the switch S 1  is connected to the second contact  2  of the switch S 1 , and the voltage doubling circuit  50  outputs the input voltage from the input terminal L and the input terminal N. When the comparator IC 1  outputs a high voltage control signal, the transistor Q 1  is turned on, the coil K 1  is not conductive, and the common terminal  3  of the switch S 1  is connected to the first contact  1  of the switch S 1 , and the voltage doubling circuit  50  works in a voltage doubling mode to outputs a voltage that is double to the input voltage from the input terminal L and the input terminal N. 
   For example, a load circuit  60  requires 220V. Before using the converting circuit, the variable resistor RP 1  is adjusted as follows. 110V AC power is supplied between the input terminal L and the input terminal N, and sliding the sliding terminal  3  of the variable resistor RP 1  through manual to change the valuable resistance of the variable resistor RP 1  to make the divided voltage of the voltage divider circuit  20  be 4-5V. In other embodiments, the variable resistor RP 1  can be deleted, then make the voltage at the node between the resistors R 3  and R 4  be 4-5V via changing the resistances of the resistors R 3  and R 4 . After adjusting the resistance, the automatic power supply converting circuit is put into use. When the AC power supply is 110V, the divided voltage is less than the reference voltage, and then the comparator IC 1  outputs a high voltage control signal. The transistor Q 1  is turned on, and the common terminal  3  of the switch S 1  is connected to the first contact  1  of the switch S 1 . The voltage doubling circuit  50  works in the voltage doubling mode and provides the load circuit  60  with 220V. 
   When the AC power supply is 220V, the divided voltage is greater than the reference voltage, and the comparator IC 1  outputs a low voltage control signal. The transistor Q 1  is turned off, and the common terminal  3  of the switch S 1  is connected to the second contact  2  of the switch S 1 . The voltage doubling circuit  50  provides the 220V to the load circuit  60  directly. 
   The capacitor C 3  can absorb the instant pulse at the instant of connecting to or disconnecting from the AC power supply. The resistor C 4  can remove the instant pulse between the converting input terminal VA and the non-inverting input terminal VB, thereby preventing the comparator IC 1  misjudging. The diode D 5  protects the coil K 1  of the relay J 1  via absorbing the reverse high voltage of the coil K 1 . 
   It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.