TECHNICAL FIELD 
     The present utility model relates to illumination electrical circuitry, and more particularly to a single-pole (two-wire system) trailing-edge phase-controlled light-modulating circuit compatible with various loads. 
     BACKGROUND 
     Most of the existing leading-edge light bulb dimming circuitries use triad to control the phase of supply voltage, which always produces large surge current spikes and thus has a poor applicability in capacitive impedance LED lamps, electronic spotlights, electronic ballast controlled fluorescent lamps, electronic energy-saving lamps, etc. 
     Most of the existing trailing-edge light bulb dimmers use two input wires and two output wires (e.g., four-wire systems), which makes the installation more complicated due to additional wires needing to be connected. For example, a main power supply  7  such as an indoor electrical junction box generally provides one live wire and one neutral wire for connecting to lighting loads; therefore, if a three-wire or four-wire system is to be installed, additional wires need to be provided, and the original electrical wiring will need to be changed, which results in increased labor and material costs. 
     Chinese Patent Application No. 00125744.7 discloses a trailing-edge phase-controlled four-wire system light bulb dimmer. Chinese Patent Application No. 201120003889.0 discloses a two-wire system trailing edge dimmer, in which the triggering circuit and the power supply circuit are connected together. The dimming adjustment not only changes the output voltage, it also changes the voltage level of the supply voltage. Therefore, there is a requirement for further improvement. 
     SUMMARY 
     In the present disclosure, a single-pole (two-wire system) trailing-edge dimming circuit is provided, comprising: a bridge rectification circuit, a power supply circuit, a light-modulating control circuit (alternatively referred to herein as a dimming control circuit), a voltage detection circuit, and an ON/OFF switch circuit; wherein, the bridge rectification circuit has one input terminal connected to the live wire and the other input terminal connected to a load, e.g. a light bulb, which is further connected to the neutral wire; the power supply circuit, the voltage detection circuit, and the ON/OFF switch are all connected in parallel between the positive output terminal and the negative output terminal of the bridge rectification circuit; three input terminals of the dimming control circuit are connected to the negative output terminal of the bridge rectification circuit, the output terminal of the power supply circuit, and the output terminal of the voltage detection circuit, respectively; and the output terminal of the dimming control circuit is connected to the input terminal of the ON/OFF switch. 
     In a further embodiment, the dimming control circuit may utilize a CMOS chip such as a dual monostable multivibrator IC 4528. 
     In a further embodiment, the bridge rectification circuit comprises a switch SW 1 , a fuse F 1 , a varistor RV 1  and a bridge rectification diode BD 1 . SW 1  has one end connected to the live wire of the main power supply and the other end connected to one end of the fuse F 1 . The other end of the fuse F 1  is connected to one end of RV 1  and one AC input terminal of BD 1 . The other end of RV 1  and the other AC input terminal of BD 1  are connected together and function as the output terminal of the two-wire system trailing-edge dimming circuit. 
     In a further embodiment, the power supply circuit comprises a diode D 1 , a resistor R 2 , a resistor R 3 , a capacitor C 9 , a Zener diode ZD 2 , a field effect transistor Q 1 , and a capacitor C 4 . D 1  has its positive terminal connected to the positive output terminal of the full-bridge rectification circuit and its negative terminal connected to one end of R 2  and R 3 ; the other end of R 3  is connected to the drain of Q 1 , and the other end of R 2  is connected to the gate of Q 1 . ZD 2  and C 9  are connected in parallel. The positive terminal of ZD 2  and the negative terminal of C 4  are connected together to the negative output terminal of the bridge rectification circuit; the source of Q 1  and the positive terminal of C 4  are connected together and function as a positive output. 
     In a further embodiment, the voltage detection circuit comprises a resistor R 9 , a Zener diode ZD 1 , a resistor R 13 , a capacitor C 6 , and a transistor Q 6 . R 9  has one end connected to the positive output terminal of the full-bridge rectification circuit and the other end connected to the negative end of ZD 1 . the positive end of ZD 1  is connected to one end of R 13 , one end of C 6 , and the base of Q 6 , while the other end of R 13  and the other end of C 6  are connected to the emitter of Q 6 , and all three of them are connected to the negative output terminal of the full-bridge rectification circuit. The collector of Q 6  is connected to the light-modulating control circuit. 
     In a further embodiment, the active switch comprises a field effect transistor Q 4 , a resistor R 1 , a transistor Q 2 , a transistor Q 3 , a resistor R 11  and a resistor R 7 . R 1  has one end connected to the positive output of the power supply circuit and the other end connected to the collector of Q 2 . The emitter of Q 2  is connected to the emitter of Q 3 , one end of R 7 , and the gate of Q 4 . The other end of R 7  is connected to the collector of Q 3  and the source of Q 4 , which together are connected to the negative output terminal of the full-bridge rectification circuit. The drain of Q 4  is connected to the positive output terminal of the full-bridge rectification circuit, while R 11  has one end connected to the base of Q 2  and the base of Q 3  and the other end connected to the light-modulating control circuit. 
     The advantageous effects of the present utility model include: simple installation due to only two wires being required for the light-modulating circuit; a wide application range for both resistive and capacitive load lamps, including capacitive load LED lamps, electronic spotlights, electronic ballast controlled fluorescent lamps, and electronic energy-saving lamps; and independence of the triggering circuit and the power supply circuit, which avoids mutual restrictions among the triggering circuit and the power supply circuit which might affect the adjustment of the maximum conduction phase angle. In addition, a linear voltage power supply has been used to simplify the dimming control circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing the principle of the utility model. 
         FIG. 2  is the principle diagram of one embodiment of the utility model. 
     
    
    
     DETAILED DESCRIPTION 
     The technical solutions of the present utility model will be described in detail through the following embodiments in connection the drawings. 
     As shown in  FIG. 1 , a trailing-edge (two-wire system) phase-controlled light-modulating circuit  10  according to the present invention comprises a full-bridge rectification circuit  1 , a power supply circuit  2 , a light-modulating control circuit  3 , a voltage detection circuit  4 , and an active switch  5 . The full-bridge rectification circuit  1  has one input terminal connected to the live wire (L) and the other input terminal connected to a light-emitting load  6 , which is further connected to the neutral wire (N). The power supply circuit  2 , the voltage detection circuit  4 , and the active switch  5  are all connected in parallel between the positive output terminal and the negative output terminal of the full-bridge rectification circuit  1 . Three input terminals of the light-modulating control circuit  3  are connected to the negative output terminal of the full-bridge rectification circuit  1 , the output terminal of the power supply circuit  2 , and the output terminal of the voltage detection circuit  4 , respectively, and the output terminal of the light-modulating control circuit  3  is connected to the input terminal of the active switch  5 . The light-emitting load  6  in this embodiment can be either resistive or capacitive, or a combination of resistively and capacitively loaded lamps, such as incandescent lamps, capacitive impedance LED lamps, electronic energy-saving lamps, electronic ballast controlled fluorescent lamps, electronic spotlights, etc. 
     The working principle of the present invention is as follows. The main AC electrical supply is converted, by the full-bridge rectification circuit  1 , into the electrical supply of the positive half cycle of a sine wave which is used as the input power supply for the power supply circuit  2 , the voltage detection circuit  4  and the active switch  5 . The power supply circuit  2  provides a stable DC working voltage to the light-modulating control circuit  3  and the active switch  5  in a linear voltage manner. The voltage detection circuit  4  produces a triggering signal for the light-modulating circuit  3  when the voltage of each input half cycle is lower than the preset voltage detection value. Upon receiving the trigger signal from the voltage detection circuit  4 , the light-modulating control circuit  3  generates two delayed signals simultaneously, with one delay signal controlling the conduction phase angle of the active switch  5 , and the other delay signal shielding the trigger signal which is generated by voltage detection circuit  4 , so as to prevent a secondary trigger in one delay period. The active switch  5  controls the ON/OFF action according to the control signal of the light-modulating control circuit  3 , and achieves the control of the electrical conduction phase angle. 
     The specific circuit diagram of the present utility model is shown in  FIG. 2 . The full-bridge rectification circuit  1  is used to convert the input AC power into the positive half cycle of a sine wave to meet the power input requirement by the power supply circuit  2 , the voltage detection circuit  4 , and the active switch  5 . In this embodiment, the full-bridge rectification circuit  1  comprises a switch SW 1 , a fuse F 1 , a varistor RV 1  and a bridge rectification diode BD 1 . The switch SW 1  has one end connected to the live wire (L) of the main power supply and the other end connected to one end of the fuse F 1 . The other end of the fuse F 1  is connected to one end of RV 1  and one AC input terminal of the bridge rectification diode BD 1 , while the other end of RV 1  and the other AC input terminal of the bridge rectification diode BD 1  are connected together and function as the output terminal of the single-pole (two-wire system) trailing-edge light-modulating circuit. The positive and negative terminals of the bridge rectification diode BD 1  function as the positive and negative output terminals of the full-bridge rectification circuit  1 , respectively. After passing through the full-bridge rectification circuit  1 , the AC power is output as the positive half cycle of a sine wave between the positive end and the negative ends of the bridge rectification diode BD 1 . 
     The power supply circuit  2  functions to provide a stable working voltage for the light-modulating control circuit  3  and the active switch  5  in a linear voltage manner. In this embodiment, the power supply circuit  2  comprises a diode D 1 , a resistor R 2 , a resistor R 3 , a capacitor C 9 , a Zener diode ZD 2 , a field effect transistor Q 1 , and a capacitor C 4 . The diode D 1  has its positive terminal connected to the positive output terminal of the full-bridge rectification circuit  1  and its negative terminal connected to one end of the resistors R 2  and R 3 . The other end of the resistor R 3  is connected to the drain of the field effect transistor Q 1 , and the other end of the resistor R 2  is connected to the gate of the field effect transistor Q 1 , the negative terminal of the Zener diode ZD 2 , and one end of the capacitor C 9 . The other end of the capacitor C 9 , the positive terminal of the Zener diode ZD 2 , and the negative terminal of the capacitor C 4  are connected together to the negative output terminal of the full-bridge rectification circuit  1 . The source of the field effect transistor Q 1  and the positive terminal of the capacitor C 4  are connected together and function as a positive output terminal of the power supply circuit. With the Zener diode ZD 2  on the gate of the field effect transistor Q 1 , the voltage across the capacitor C 4  is stabilized at (Vzd 2 −Vgs). Due to the unidirectional conduction characteristics of the diode D 1 , capacitor C 4  is prevented from discharging when the output voltage of the full-bridge rectification circuit  1  is lower than the voltage across the capacitor C 4 , and thus the voltage stability of C 4  is improved. 
     In this embodiment, the light-modulating control circuit  3  comprises a CMOS chip, specifically a retriggerable dual monostable IC 4528 (U 1 ), as the core, and two retriggerable monostable circuits A and B. The monostable circuit A comprises an adjustable resistor VR 1 , an adjustable resistor VR 2 , a resistor R 4 , a resistor R 5 , a resistor R 16 , and a capacitor C 1 , and functions to set the delay time of the conduction phase angle. VR 1  has one end connected to the positive output terminal of the power supply circuit  2  and the other end connected to one end of the parallel connection of VR 2  and R 4 , while the other end of the parallel connection of VR 2  and R 4  is connected to the pin 2 of U 1  via R 5 . R 16  is connected in parallel with the circuit composed of VR 1 , VR 2 , and R 4 . C 1  is connected between pin 1 and pin 2 of U 1 . VR 1  can be modulated to adjust the conduction phase angle, VR 2  and R 4  are used to set the minimum conduction phase angle, R 5  and R 16  are used to set the maximum conduction phase angle, and the positive output end of the monostable circuit A drives the active switch  5 . The other monostable circuit B comprises a resistor R 6  and a capacitor C 2  and functions to set a time for preventing the delay signal from being triggered for a second time, wherein R 6  is connected between pin 14 and pin 16 of U 1 , C 2  is connected between pin 14 and pin 15 of U 1 , and the positive output end of the monostable circuit B is reversed by the transistor Q 5  and then pulls down the level of the trigger input of the trigger A, so as to prevent secondary trigger in one delay period. 
     The voltage detection circuit  4  generates a triggering signal for the light-modulating control circuit  3  when the output voltage of the full-bridge rectification circuit  1  is below a certain voltage value. In this embodiment, the voltage detection circuit  4  comprises a resistor R 9 , a Zener diode ZD 1 , a resistor R 13 , a capacitor C 6 , and a transistor Q 6 . R 9  has one end connected to the positive output terminal of the full-bridge rectification circuit  1  and the other end connected to the negative end of ZD 1 . The positive end of ZD 1  is connected to one end of R 13 , C 6 , and the base of Q 6 . The other end of R 13  and the other end of C 6  are connected to the emitter of Q 6 , and to the negative output terminal of the full-bridge rectification circuit  1 . The collector of Q 6  is connected to the light-modulating control circuit  3 . The output voltage of the full-bridge rectification circuit  1  is divided by R 9 , ZD 1  and R 13 , and when a divided voltage is lower than the conduction voltage of the transistor Q 6 , the transistor Q 6  is cut off and generates a rising-edge trigger signal for the light-modulating control circuit  3 . 
     The active switch  5  utilizes a field effect transistor as a switch and switches ON/OFF in response to the control signal of the light-modulating control circuit  3  to achieve control of the conduction phase angle of the electrical supply to the electrical load. In this embodiment, the active switch  5  comprises a field effect transistor Q 4 , a resistor R 1 , a transistor Q 2 , a transistor Q 3 , a resistor R 11 , and a resistor R 7 . R 1  has one end connected to the positive output terminal of the power supply circuit  2  and the other end connected to the collector of Q 2 . The emitter of Q 2  is connected to the emitter of Q 3 , one end of R 7 , and the gate of Q 4 . The other end of R 7  is connected to the collector of Q 3  and the source of Q 4 , and to the negative output terminal of the full-bridge rectification circuit  1 . The drain of Q 4  is connected to the positive output terminal of the full-bridge rectification circuit  1 . R 11  has one end connected to the base of Q 2  and the base of Q 3 , and the other end connected to the light-modulating control circuit  3 . Q 2  and Q 3  form a driving circuit for Q 4  to activate and accelerate the switching speed of Q 4 . 
     The present invention has been described in above embodiments with respect to the drawings.
A single-pole (two-wire system) phase-controlled trailing-edge light-modulating circuit comprises a full-bridge rectification circuit, a power supply circuit, a light-modulating control circuit, and a voltage detection circuit. The light-modulating control circuit utilizes a CMOS chip and controls a field effect transistor by detecting specific voltage level to perform a trailing-edge phase control action for modulating light output of resistively and/or capacitively loaded light bulbs, e.g. LED light bulbs. The light-modulating control circuit connects to various lighting loads in series. In addition, the triggering circuit and the power supply circuit of are independent to avoid mutual restrictions to each other that might affect the adjustment of the maximum conduction phase angle.