Abstract:
An electrical isolation circuit that sets a voltage level for programming a product is contained in a stand-alone module. The electrical circuit includes a first input terminal connected to a first optocoupler, which provides a first level of isolation, a transformer, which provides a second level of isolation, and a second optocoupler, which provides a third level of isolation. The circuit outputs a signal to a level setting circuit prior to outputting the signal. An advantage of the module is it interfaces with a plurality of programming boxes, so new modules do not have to be created.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to electronic module interfaces and, more particularly to electrical isolation circuits.  
           [0002]    Electrical isolation circuits including level setting provide isolation between high voltage power and low voltage power lines. Such isolation circuits also isolate electrical circuits during hi-pot testing. In addition, isolation circuits set the correct voltage level for input pins programming a product, e.g., an electrically commutated motor.  
           [0003]    Electrical isolation is an important consideration if the components of a system use different power sources, have noisy signals, or operate at different ground potentials. Isolation is needed to prevent the effects of ground currents. Therefore, isolation circuitry is necessary to ensure the correct noise-free, voltage level is applied to the input pins when a product is being programmed. If an incorrect or noisy voltage level is applied to the input pins of a product during programming, the product can be damaged or the resulting programming will be invalid.  
           [0004]    It is desirable to use a stand-alone electrical isolation circuit that will interface between a product and a programming box. It is also desirable to have the electrical isolation circuitry contain an optically coupled isolator. Finally, it is desirable to have the isolation circuit work in series with existing, known programming boxes to create the correct voltage level or reduce noise during programming.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    In an exemplary embodiment of the invention an electrical isolation circuit that sets a voltage level for programming a product is contained in a stand-alone module. The module contains input and output connectors to electrically couple the module to the product being programmed and interface to a programming box. An advantage of the module is that it interfaces with a plurality of programming boxes, so new modules do not have to be created for each specific programming box.  
           [0006]    The electrical circuit includes, in one embodiment, a first input terminal connected to a first optocoupler, which provides a first level of isolation. The electrical circuit also includes an oscillator circuit electrically connected to a D-flip-flop to generate a square wave. The square wave feeds a transformer that provides a second level of isolation. The square wave is inverted by the transformer and then rectified by a full-wave bridge rectifier. The full-wave bridge rectifier outputs a DC voltage to a voltage regulator that powers the electrical circuit. A third level of isolation is provided by a second optocoupler, which outputs a signal to a level setting circuit prior to outputting the signal to an output terminal.  
           [0007]    As a result, a cost-effective and reliable electrical circuit including optically coupled isolators and a transformer to isolate between high voltage power and low voltage programming signal lines is provided. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a schematic illustration of an exemplary embodiment of the invention; and  
         [0009]    [0009]FIG. 2 is a diagram of an isolation module connected between two electrical circuits. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0010]    [0010]FIG. 1 is a schematic illustration of an exemplary embodiment of electrical circuit  10 . Electrical circuit  10  includes a receive circuit  12 , a transmit circuit  14 , a filter circuit  16 , an oscillator circuit  18  and a power supply circuit.  
         [0011]    Receive circuit  12  includes an input terminal data-in  19  electrically connected in series to a resistor  20 , which is connected to a base of transistor  21 . The emitter of transistor  21  is connected to Vcc and a collector is connected to an optocoupler  22 . Optocoupler  22  includes a light emitting diode (LED)  23  and a transistor  24 . Connected to a node  25  is the anode of LED  23 , a capacitor  26  and a resistor  28 . LED  23  is optically connected to a transistor  24 .  
         [0012]    Transistor  24  and a transistor  30  are connected together in a Darlington configuration. A collector of transistor  24  is connected to a collector of transistor  30  at a node  32 . An emitter of transistor  24  is connected to a base of transistor  30  at node  34 . A base of transistor  24  is connected to a resistor  32  that is connected to a node  36 . Node  36  is connected to a node  34  that is connected to a base of transistor  22 . In addition, node  36  is connected to a resistor  38 , which is connected to an emitter of transistor  30  at a node  40 . The output of the Darlington configured transistors is taken at node  40 .  
         [0013]    Transmit circuit  14  includes a terminal input  44  that is connected in series to a resistor  46 , which is connected to a node  48 . Node  48  is connected to a cathode of diode  50  and to an optocoupler  52 . An anode  54  of a diode  50  is tied to a node  56 , which is tied to ground. Optocoupler  52  includes a light emitting diode (LED)  58  and a transistor  60 . A base of transistor  60  is connected to a resistor  62 , which is connected to an emitter of transistor  60  at a node  64 . Node  64  is connected to ground. A collector of transistor  60  is connected to a node  66 , which is tied to a pull-up resistor  68  that is connected to Vcc power. Node  66  is connected to a base of transistor  70 . An emitter of transistor  70  is connected to ground and a collector is connected to a pull-up resistor  72  at a node  74 . Pull-up resistor  72  is connected to Vcc power. Node  74  is connected to a base of transistor  76 . An emitter of transistor  76  is connected to ground and a collector is connected to a pull-up resistor  78  at a node  80 . Pull-up resistor  78  is connected to Vcc power, and a node  80  is connected to an output terminal data-out  82 .  
         [0014]    Filter network  16  includes a terminal  86 . A signal is input at terminal  86  and terminal  86  is connected to a diode  88  that is connected to a node  90 . Node  90  is connected to a capacitor  92  and to a node  94 . Node  94  is connected to a cathode of a zener diode  96  whose anode is connected to ground, and node  94  is connected to a capacitor  98 .  
         [0015]    An oscillator  18  includes a resistor  102  connected to an inverter  104  and to a node  106 . Inverter  104  is connected to a node  110 . A resistor  108  is connected in between node  106  and node  110 . Node  106  is connected to a capacitor  112 , which is further connected to a node  114 . An inverter  116  is connected to node  110  and node  114 . Node  114  is connected to a D-flip-flop  118  at a clock terminal  120 . D-flip-flop&#39;s  118  has a set terminal  122  and a reset terminal  124 , which are both connected to ground. D-flip-flop&#39;s  118  has an input terminal  126  that is connected to a node  128 , which is connected to D-flip-flop&#39;s inverted output terminal, Output-Q/ 130 . D-flip-flop&#39;s  118  has a non-inverted output terminal, Output-Q  132 , that is connected to a node  134 .  
         [0016]    Node  128  is connected to an inverter  136  and to an inverter  138 . The outputs of inverters  136  and  138  are connected together at a node  140 . Node  134  is connected to an inverter  142  and an inverter  144 . The outputs of inverters  142  and  144  are connected together at a node  146 . Node  146  is connected to a primary winding  148  of a transformer  150 . Node  140  is connected to primary winding  148  of transformer  150 . A secondary winding  152  of transformer  150  is connected to a node  154  and a node  156 . Node  154  and node  156  are connected to a full-wave bridge rectifier  158 . Full-wave bridge rectifier  158  includes a plurality of diodes  160 ,  162 ,  164  and  166 . Node  154  is connected to an anode of diode  160  and a cathode of diode  162 . Node  156  is connected to a cathode of diode  164  and an anode of diode  166 . An anode of diode  162  and an anode of diode  164  are connected at a node  168 , which is connected to ground. A cathode of diode  160  and a cathode of diode  166  are connected to a node  170 .  
         [0017]    The output of full-wave bridge rectifier  158  is taken at node  170 . Node  170  is connected to a node  172 . Node  172  is connected to a capacitor  174  and a voltage regulator  176 . Voltage regulator  176  is connected to a node  178 . Node  178  is connected to a capacitor  180 , Vcc power, and a resistor  182 . Resistor  182  is connected to a LED  184 .  
         [0018]    The function of receive circuit  12  and transmit circuit  14  is to provide an interface between two electrical circuits (not shown) operating at different voltages. Module  10  is connected to first electrical circuit, e.g., an electric motor (not shown), and to a second electrical circuit, e.g., a programming box (not shown). In one embodiment, the electric motor is to be programmed by the programming box. Receive circuit  12  receives a signal from the electric motor having a first voltage level, and receive circuit  12  adjusts this voltage prior to transmitting the signal to the programming box. The programming box then sends a signal having a second voltage level to module  10 . Transmit circuit  14  accepts the voltage signal from the programming box and adjusts the voltage level to an operating voltage of the electric motor prior to transmitting it the electric motor. Therefore, the two electrical circuits are able to communicate even though they operate at different operating voltages.  
         [0019]    Receive circuit  12  accepts signals from the electric motor at data-in  19  terminal. The electric motor sends a voltage signal having a first voltage level, which receive circuit  12  adjusts prior to providing the signal to the programming box. The input voltage signal is input to data-in  19  and the voltage is reduced by resistor  20 . The reduced voltage is input to the base of pnp transistor  21 , which is activated. When transistor  21  is activated, a current is transmitted to optocoupler  22 . Optocoupler  22  includes light emitting diode (LED)  23  and transistor  24 . In one embodiment, Optocoupler  22  is activated when the voltage across LED  23  is at least 1.2 volts and the forward current through LED  23  is at least 10 uA. When LED  23  is activated, an optical signal is transmitted to transistor  24 . The optical signal generates a current in the base of transistor  24 , which biases transistor  24  so it is turned on. When transistor  24  is on, current flows from the collector. In one embodiment, if the forward current through LED  23  is 20 mA, the resulting collector current produced in transistor  24  will be 1 mA when the voltage across the collector-to-emitter is 0.1 volts. Optocoupler  22  serves to isolate the input voltage at input terminal  19  from the remainder of circuit  10 . Because transistor  24  is only activated by photons emitted by LED  23 , optocoupler  22  isolates the signal at data-in  19 . Optocoupler  22  has a fixed output voltage, based on the input voltage to LED  23 . This output voltage is amplified by the darlington configuration of transistors  24  and  30 . The amplified voltage is output from pin J1-B at node  40  to the programming box.  
         [0020]    The programming box transmits a voltage signal at a second voltage level to transmit circuit  14 . Transmit circuit  14  operates by accepting the signal from the programming box input at terminal  44  and adjusting the voltage prior to transmission to the electric motor. After accepting the signal at terminal  44 , resistor  46  reduces the input voltage and diode  50  serves to maintain the voltage at node  48  at a particular level. If the voltage at node  48  exceeds the breakdown voltage of diode  50 , diode  50  will short to ground to protect optocoupler  52 . In one embodiment, diode  50  is a voltage reference. In an alternative embodiment, the voltage reference is at least a zener diode and a resistor divider network. Optocoupler  52  includes LED  58  and transistor  60 . In one embodiment, Optocoupler  52  is activated when the voltage across LED  58  is at least 1.2 volts and the forward current through LED  58  is at least 10 uA. In an over current condition, LED  58  in optocoupler  52  will short-circuit causing input signal to be grounded. LED  58  will be activated when the voltage at node  48  exceeds its forward voltage potential. When LED  58  is activated, an optical signal is transmitted to transistor  60 . The optical signal generates a current in the base of transistor  60 , which biases transistor  60  so it is turned on. When transistor  60  is on, current flows from the collector. Because transistor  60  is only activated by photons emitted by LED  58 , optocoupler  52  isolates the signal on terminal  44  from output terminal  82 . In one embodiment, if the forward current through LED  58  is 20 mA, the resulting collector current produced in transistor  60  will be 1 mA when the voltage across the collector-to-emitter is 0.1 volts.  
         [0021]    The output of the signal from transistor  60  is taken from its collector at node  66 . In one embodiment, the signal at node  66  is inverted with respect to the signal input to transistor  60 . Connected to node  66  is resistor  68 , which serves to pull-up the voltage at node  66  to a value approximately at Vcc when transistor  60  is turned off. When transistor  60  is activated, the voltage at node decreases. Resistor  68  also serves to determine a threshold operating voltage at the input to optocoupler  52  and to set the response time of transistor  60 .  
         [0022]    The output signal at node  66  is input to the base of transistor  70 . Transistor  70  is connected to transistor  76  in a cascaded amplifier configuration. Both transistor  70  and transistor  76  are operating as amplifiers. By connecting transistor  70  and transistor  76  together the total gain is the product of the two transistors. The cascaded amplifier configuration is a level setting circuit. The output of transistor  76  is the amplified voltage at data-out terminal  82  that is supplied to the electric motor.  
         [0023]    Oscillator  18 , configured as a hex inverter oscillator, is a clock generator. Inverters  104  and  116 , resistors  102  and  108 , and capacitor  112  are used to generate an oscillating square wave of a fixed frequency. The square wave has two components: a low voltage and a high voltage both of equal time duration. The low voltage part of the square wave is created when capacitor  112  charges through resistor  108 . The high voltage part of the square wave is created when capacitor  112  discharges through resistor  102 . The oscillating square wave of fixed frequency is input to the clock input terminal  120  of D-flip-flop  118 .  
         [0024]    D-flip-flop  118  includes an input terminal  126 , a clock terminal  120 , a first output-Q  132  and a second output-Q/ 130 . Output-Q  132  and Output-Q/ 130  are complements of one another. Output-Q  132  and Output-Q/ 130  only change during a positive transition of the clock pulse input to clock terminal  120 . Output-Q  132  will change to the value at input terminal  126  on a positive transition of a clock pulse. Once changed, Output-Q  132  will remain constant until another clock pulse is provided. The output of D-flip-flop  118  is a square wave.  
         [0025]    Output-Q  132  is connected to inverters  142  and  144 . Inverter  142  and inverter  144  are connected in parallel between node  134  and node  146 . By connecting inverters  142  and  144  in parallel, more current is able to flow to ground, e.g., sourced to ground, when Output-Q  132  transitions from a high to a low voltage. In addition, by connecting inverters  142  and  144  in parallel, additional current is available to drive transformer  150 . The output from D-flip-flop  118  output-Q  132  and output-Q/ 130  is a square wave. The output from output-Q  132  is opposite to the output from output-Q/ 130 , e.g., when output-Q  132  output is a high voltage level, the output of output-Q/ 130  terminal is a low voltage level. The square wave is input to inverters  142  and  144  at node  134 , and the inverse square wave is input to inverters  138  and  136  at node  128 . The output signal from inverters  142  and  144  is “inverted” at node  146  compared to the input signal at node  134 . The output signals from inverters  142  and  144  at node  146  are input to a primary winding  148  of transformer  150 .  
         [0026]    Similarly, Output-Q/ 130  is connected to inverters  136  and  138  at node  128 . Inverter  136  and inverter  138  are connected in parallel between node  128  and node  140 . By connecting inverters  136  and  138  in parallel, more current is able to flow to ground, e.g., sourced to ground, when the output of inverters  136  and  138  transitions from a high to a low voltage. In addition, by connecting inverters  136  and  138  in parallel, additional current is available to drive transformer  150 . The output from D-flip-flop  118  output-Q/ 130  and output-Q  132  is a square wave. The output from output-Q/ 130  terminal is opposite to the output from output-Q  132  terminal, e.g., when output-Q/ 130  terminal output is a high voltage level, the output of output-Q  132  is a low voltage level. The square wave is input to inverters  136  and  138  at node  128 . The output signal from inverters  136  and  138  “inverted” at node  140  compared to the input signal at node  128 . The output signal from inverters  136  and  138  at node  140  are input to primary winding  148  of transformer  150 .  
         [0027]    Transformer  150  includes a primary winding  148  and a secondary winding  152 . Both primary winding  148  and secondary winding  152  have the same number of turns; therefore, transformer is a 1:1 transformer. In one embodiment, transformer is not a step-up or a step-down transformer. Primary windings  148  are in the opposite direction of secondary windings  152  causing the polarity of the voltage at the terminals of secondary winding  152  to be opposite the polarity of the voltage at the terminals of the primary winding  148 . Transformer  150  serves to isolate the voltage generated by oscillator  100  and the rectified DC voltage to voltage regulator  176 .  
         [0028]    The secondary winding  152  of transformer  150  is connected to a full-wave bridge rectifier  158 . Full-wave bridge rectifier  158  converts the square wave to a DC voltage. The DC voltage is input to a voltage regulator  176 . Capacitors  174  and capacitor  180  connected to voltage regulator  176  serve to reduce fluctuations in the DC voltage.  
         [0029]    Full-wave bridge rectifier  158 , capacitors  174  and  180 , and voltage regulator  176  together regulate a dc voltage and are used as a power supply for module  10 .  
         [0030]    [0030]FIG. 2 is diagram is a diagram of an isolation module  10  connected between two electrical circuits (not shown). Cables  200 , from a first electrical circuit, and cable  202 , from a second electrical circuit, attach to input connector  204  and output connector  206  to electrically couple with module  10 . Printed circuit board (PCB)  208  provides the electrical isolation between the two electrical circuits. Grommets  210  and  212  are used to reinforce connectors  204  and  206  to case  214 . In one embodiment, case  214  is fabricated from plastic.  
         [0031]    The first electrical circuit connected to cable  200  operates at a different voltage compared to the second electrical circuit connected to cable  202 . Module  10  optocouplers  18  and  52  (shown in FIG. 1) electrically isolate the first electrical circuit from the second electrical circuit, and module  10  provides an interface through which the two electrical circuits can communicate. In one embodiment, the first electrical circuit is a programming box. Module  10  is configured to enable a plurality of existing programming boxes to be connected to the second electrical circuit without modification.  
         [0032]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.