Abstract:
A universal input voltage device is presented which may receive a wide range of regulated and unregulated input voltages, both DC and a wide range of variable frequency AC, and output a desired regulated current at a desired voltage independent of the fluctuation of input voltage and frequency. The circuit includes a preconditioning input circuit, a Buck converter circuit with over voltage protection, flyback and boost circuits, and a shutdown circuit configured to drive a predetermined electrical or electronic device.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 11/874,705, filed Oct. 18, 2007 now U.S. Pat. No. 7,486,030, entitled UNIVERSAL INPUT VOLTAGE DEVICE. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a power supply and, more particularly, a power supply adapted to receive a wide range of regulated and unregulated input voltages, both DC and a wide range of variable frequency AC, independent of fluctuation in voltage and frequency, and output a desired current/voltage to drive any electrical device such as a gas discharge lamp or LED lighting device. 
     BACKGROUND OF THE INVENTION 
     Conventionally, input power requirements for gas discharge lamp lighting devices, such as hot cathode and cold cathode lamps, have been restricted to a specific power source. These gas discharge lighting systems are dependent on power sources of 110 volts or 220 volts AC at frequencies of 50 or 60 Hz, or DC voltages of 12 volts or 24 volts, for example and the same can be said for an LED lighting device. While these power sources are readily available in urban locations most of the time, at times of adverse weather, the consistency of commercial power sources may be compromised. In rural areas, the quality and consistency of local power sources may be variable, independent of adverse weather. Additionally, in adverse environments such as automotive, avionic and military applications, the quality and consistency of the output from electrical and power generation equipment may be unusable as an input power source for electrical and electronic devices in general, and specifically gas discharge lamp lighting devices. 
     Additionally, wind-driven generators and solar cells are not optimized for efficiency because the output from these generators is regulated to provide a usable output power. Regulation is accomplished by governing the rotational speed and thus frequency of the generator, or by using the DC output of a solar cell indirectly through an inverter or to charge a battery. 
     SUMMARY OF THE INVENTION 
     The present invention provides a circuit for driving electrical and electronic devices such as gas discharge lighting devices and LED lighting devices from unregulated input power source ranging from less than 12 volts to 180 volts or more, AC or DC, pulsed DC or halfwave, fullwave rectified and variable frequency AC. The circuit generally includes a Buck converter coupled to a synchronous rectifier/crowbar circuit coupled to a single-ended inverter to provide a high voltage to start discharge and a lower sustaining voltage after start up required by gas discharge lighting devices not restricted to a particular input power source. This circuit automatically adjusts varying input voltages to the necessary output voltage to start and sustain a gas discharge lighting device. 
     The present invention eliminates the conventional steady state voltage requirements of the load i.e. lighting system and allows the electric generation source to operate in a dynamic or static state to achieve optimal power source efficiency. Source inputs may be unregulated electrical power from any centralized, locally distributed or storage source including unloaded permanent magnet generators and alternators. If an unregulated electrical power source is local to where the electricity is used, local transmission of the unregulated electrical power may minimize the resistive line losses during transmission eliminating the conventional conversion processes and the associated loss before transmission. 
     The present invention is well suited for lighting applications that may receive power from a diversified range of energy sources. The present invention is not limited by packaging and may drive linear lengths of lamps as in standard neon tubes, cold cathode fluorescent lamps, compact fluorescent lamp, as well as LED lighting systems. The present invention is also well suited as a universal lighting system driver with applications ranging from transportation systems, to fixed grid tied lighting. And the new applications that will lend themselves to a nonspecific power source lighting system. 
     The present invention may be used to drive a discharge lamp lighting device in which the lamp requires a high voltage to start discharge and a lower sustaining voltage after start up. A current feedback loop for lamp regulation and a lamp open detection circuit may also be included. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram of the circuit of the present invention. 
         FIG. 2A  is a partial view of a detailed schematic of the circuit of the present invention. 
         FIG. 2B  is a continuation of the detailed schematic of  FIG. 2A . 
         FIG. 3  is a DC offset triangular waveform. 
         FIG. 4  is a pulse width waveform showing DC level for normal operation and for an over-voltage condition. 
         FIG. 5  is an alternative circuit with optional diode and capacitor. 
         FIG. 6A  is a waveform output from an astable multivibrator. 
         FIG. 6B  is the waveform of  FIG. 6A  with a DC offset. 
         FIG. 7  is a waveform showing initial ionization, sustaining voltage, and open lamp detect levels. 
     
    
    
     DETAILED DESCRIPTION 
     Referring initially to  FIG. 1 , a functional block circuit diagram of a universal output voltage device is generally indicated by reference numeral  10 . Circuit  10  includes an input  12  to a preconditioning input circuit  14 . An output on line  24  provides initial power to start clock  58  which provides a reference voltage to pulse wave modulator  26 . At the same time, an output on line  25  provides initial power to a switching transistor  41  of Buck converter circuit  40 . An over-voltage circuit  43  in combination with a fuse  56  protects the circuit  10  from over-voltage conditions that may damage the system. An output from the Buck converter circuit  40  powers a boost circuit  73  initially bypassing the shutdown circuit  89  to allow the flyback circuit  81  to provide the power necessary for the initial ionization of the lamp  83 . Once the circuit is running, the shutdown circuit  89  monitors the output of the flyback circuit  81  for an overvoltage condition providing feedback to the comparator  66 . 
     Referring to  FIGS. 2A and 2B , the universal input voltage device is shown in more detail. Universal input voltage device  10  includes input  12  coupled to preconditioning input circuit  14 . Preconditioning input circuit  14  includes a noise filter inductor  16  coupled to a rectifier  18 , filter  20  and prelinear voltage regulator  22 . Preconditioning input circuit  14  provides the initial input conditioning and drive circuit for the universal input voltage device  10 . 
     Preconditioning input circuit  14  is coupled via line  24  a 5-volt power supply  27  for clock  58  and to a single-ended switch mode isolated circuit  26  for high side gate driver circuit  28  of Buck converter  40 . The preconditioning input circuit  14  is also coupled to a Buck converter circuit  40  on line  25  to drive a switching transistor  41 . Line  25  can be unfiltered with filter  20  removed and the ripple at line  25  can be 100 percent. Buck converter circuit  40  may achieve up to a 100% duty cycle and significantly improves the performance of the circuit when the input supply at  12  is lower than the desired voltage output of the Buck converter on line  42 . The output on line  42  drives 5 and 12-volt power supplies  29 , which provide power to the rest of the circuit, as well as the boost circuit  73 . 
     To achieve a 100% duty cycle, a DC offset triangle waveform ( FIG. 3 ) is generated by integrating the output clock cycles on line  30  from the QNot output  106  of the astable multi-vibrator  58  through integrator circuit  32  and comparator  34 . The comparator  34  compares the reference output feedback or compensation pole  36  generated from a voltage feedback from output  42  of Buck converter  40  to the DC offset triangle waveform output of integrator circuit  32  and generates a pulse width output on line  38  referenced to the triangle waveform ( FIG. 3 ) during normal regulations. A DC offset below the triangle waveform generates a 100% pulse width when the input supply at  12  is lower than the desired output at  42 . Additional performance improvements are achieved with this circuit when the input supply is a battery. In addition to compensation pole  36  a second compensation pole  52  is included to stabilize operation of the circuit and provide a relatively high immunity to noise on input  12 . 
     The circuit  10  includes a high voltage protection circuit in the event of component failures resulting in a voltage higher than the desired voltage at output  42  using a combination synchronous rectifier/crowbar combination  43 . The DC output  42  during normal operation is the reference voltage input to comparator  44  on line  45  which is compared to a pulse on line  38 . The pulse width amplitude  38  is set higher by clamp zener diode  54  than the reference provided by output  42  during normal operation (See  FIG. 4 ). Comparator  44  drives synchronous switching transistor  48  closed when the main switching transistor  41  is closed and vice versa to prevent cross conduction of the synchronous switching transistor  48  and the main switching transistor  41  during normal operations. Turn on dead time for the synchronous switch is provided by the DC time consisting of resistor  46  and the gate capacitance of synchronous switching transistor  48  relative to the fast turn on time constant of high side gate driver  28  and the main switching transistor  41 . The turn on dead on time for the main switching transistor  41  is provided by the relative slow turn on time constant of high side gate driver  28  to the fast turn off of the synchronous switching transistor  48  by the direct connection to the open collector of comparator  44 . 
     During normal operation, comparator  44  and synchronous switching transistor  48  act as a synchronous rectifier as well as an output  42  over voltage sensor and a crowbar circuit  43 . When the output at  42  is greater than the desired output voltage referenced to the pulse width amplitude on line  38  set by the clamp zener  54 , comparator  44  detects a fault condition and turns on the synchronous switching transistor  48 . The main switching transistor  41  and synchronous switching transistor  48  are on simultaneously effectively grounding the source and open fuse link  56  which disconnects output  42 . Open fuse link  56  also isolates the single ended switch mode source  26  from over voltage protecting the high side gate driver  28  and associated controller circuitry. 
     The resistor  46  is sourced from the output  42  and aids in the power up sequence and provides drive to the synchronous switching transistor  48  and open fuse link  56 . If more driving time is needed, an optional diode and capacitor  110  ( FIG. 5 ) may be added to isolate the resistor  46  from the discharge rate of the output  52  and filter capacitor  58  to give the fuse link  56  additional time to blow when necessary. 
     The next stage includes clock  58  such as a CMOS  4047 . The DC common pin output on line  60  is a waveform ( FIG. 6A ) which is coupled to capacitor  62  to provide a DC offset waveform on line  64  ( FIG. 6B ) and ramp for CMOS comparator pulse width modulator  66 . Comparator pulse width modulator  66  is current buffered by a high current gate driver  68 . The high current gate driver  68  is capacitively coupled and ground referenced  70  to switching transistor  72 . Capacitor coupled and ground reference  70  ensures that the switching transistor  72  remains in an off state as a fault protection in the event of a drive circuitry failure. 
     A primary transformer  74  is connected to and sourced from output  42 . Primary transformer  74  is also coupled to switching transistor  72  in a ground-applied configuration. Primary transformer  74  is configured in a flyback topology and its output is rectified by diode  76 . Diode  76  is connected to capacitor  78  that has a value chosen to lightly filter the output on line  79  (See  FIG. 7 ). The output on line  79  provides a relatively high voltage to the primary coil of current/voltage transformer  82  to initiate ionization of a discharge lamp  83  and to self adjust to a relative lower sustaining voltage after lamp excitation (See  FIG. 7 ), which increases efficiency. The DC level of the output waveform shifts with the lamp load which provides a way to monitor relative lamp output voltage due to lamp aging and open lamp circuit condition. 
     The output on line  79  is also connected to a voltage divider filter network  86  which provides a DC level relative to the lamp voltage on line  87 . A comparator  100  compares the relative lamp voltage from the voltage divider filter network  86  to a reference voltage  98  on line  99 . If the relative lamp voltage is higher than desired, indicating aging lamps or a lamp open circuit condition (i.e., the lamp has burned out), comparator  100  output  101  goes high. Output  101  is coupled to diode  102  which is in turn coupled to the non-inverting input of comparator  100  thus forming a latched condition. 
     The output  101  of comparator  100  is also coupled to a diode  104  which is coupled to the high current gate driver  68  inverting stage input at  112 . An output on line  101  effectively shuts down the lamp output upon a fault detection. A start up time delay circuit  96  disables output  101  of comparator  100  for a fixed amount of time to allow ionization of gas discharge lamp during normal operation and provide proper power up sequence to avoid inadvertent activation of the fault condition circuitry. 
     A sense resistor  84  senses the primary current of current/voltage transformers  82 . The sensed signal value is proportionally related to lamp current. Sense resistor  84  is connected on line  85  to a filter pole  94 . The output  95  of filter pole  94  is related to the output lamp current and is compared by comparator  90  to the current adjust voltage  92  on line  93 . Current adjust voltage  92  may be replaced by an externally supplied voltage from an external lamp dimming controller. Comparator  90  output  91  is connected to a filter network  88  and a comparator  66  on line  89 . Comparator  66  is a pulse width modulator. Connection to comparator  66  completes the current feedback loop and control of the gas discharge lamp current discussed above. 
     Initially, when power is applied to the circuit  10 , the power is conditioned by preconditioning input circuit  14 . The output on line  24  starts clock  58  which drives the single ended switch mode source  26  on line  30  to start the Buck converter circuit  40 . The output of the Buck converter circuit  40  on line  42  drives the power supplies to the rest of the circuit and activates the boost circuit  73 . The lamp  83  or other electric device is driven by the circuit.