Abstract:
A power management protection circuit and method provides for a fast, real-time hardware logic control of the power control components of a motor, whereby the over-current condition is an integral of the over-current level and over-current time duration, and provides means for complete turn-off of motor voltage within a few microseconds when a specified energy level has been exceeded or an extended time for the user to take corrective actions if thermal conditions permit. Motor turn-off remains until a snubber diode current has reduced to a safe level even if the stall condition is no longer present. It allows the properties of load-dump current through the snubber diode to drive the protection control logic, and also provides for sensing the temperature of both the snubber diode and the power MOSFET switch. As temperature rises in these power devices, the trolling motor maximum voltage is reduced. Voltage control based on temperature feedback is a hardware function that operates concurrently and independently from the over-current sensing and voltage turn-off.

Description:
FIELD 
     The present application is directed to the field of trolling motors. More specifically, the present application is directed to the field of stalled-motor power-management circuit design in trolling motors. 
     BACKGROUND 
     In general, when a trolling motor is stalled due to prop entanglement or other prop disruptions that slow or stop shaft rotation, then motor surge-currents, excess sustained currents, and over-heating of all main current components can cause partial to total failure of various system components and put the trolling motor at risk for unwanted operations and/or the possibility of fire. 
     When corrective means are applied to an intermittent stalled motor over-current condition, then a secondary response time problem is presented. If the corrective system is too fast then intermittent stalls will create an undesirable intermittent operation, but if the corrective system is too slow then locked rotor stalls can quickly overcome the system with damage. 
     Existing motor protection methods either regulate the current to a maximum value or shuts off the entire system like a circuit breaker which requires a total power up sequence. Methods that regulate stall current to a safe level for the electronics is still not safe for the user since the motor will immediately start turning when the user frees the obstruction from the prop that has the motor in the stall condition. When the prop starts turning immediately then the user is at risk for injury. The method that shuts everything off and requires power-up is safe but a very unnecessary nuisance. 
     The existing motor protection solutions are typically fixed at detecting stalled conditions at 100% voltage, similar to a circuit breaker configuration, wherein a stalled condition that occurs at 50% voltage or 75% voltage or any other percentage of voltage would not be detected properly. As an example, if a motor is operating at 50% of the pulse width modulation (PWM) signal voltage and the motor of the trolling motor is wound up in a weed or other obstruction, a user is only protected if the motor is operating at 100% PWM. In the case of this example, a user may raise the motor up, remove the weeds from the motor, and because the motor was only operating at 50% PWM, there is a good chance that the motor starts up while the user is removing the weeds from the motor, as the obstruction in this case would not trip a circuit fixed at 100% PWM. What is needed then is a proportional reference, and not a fixed reference in such a circuit. 
     SUMMARY 
     The circuit and method of the present application provides for a fast, real-time hardware logic control of the power control components whereby the over-current condition is an integral of the over-current level and over-current time duration. The circuit and method of the present application provides means for complete turn-off of motor voltage within a few microseconds when a specified energy level has been exceeded or an extended time for the user to take corrective actions if thermal conditions permit. Motor turn-off remains until snubber diode current has reduced to a safe level even if the stall condition is no longer present. It allows the properties of load-dump current through the snubber diode to drive the protection control logic, and also provides for sensing the temperature of both the snubber diode and the power MOSFET switch. As temperature rises in these power devices, the trolling motor maximum voltage is reduced. Voltage control based on temperature feedback is a hardware function that operates concurrently and independently from the over-current sensing and voltage turn-off. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are graphical representations illustrating a tolling motor head assembly incorporating an embodiment of the present application; and, 
         FIGS. 2A and 2B  are schematic diagrams illustrating an embodiment of the protection circuits of the present applications. 
         FIG. 3  is a flow chart illustrating a method according to an embodiment of the present application 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1A , a controller head assembly  100  according to an embodiment of the present application is illustrated. Here, the controller head assembly includes a controller head cover  105 , a throttle handle  110  and a motor column  120  leading to the trolling motor unit (not shown).  FIG. 1B  illustrates the controller head assembly  100  with the controller head cover  105  removed. Again, the throttle handle  110  provides the user with a steering, throttle and directional control of the trolling motor, and the column cover  125  protects the junction between the motor column  120  and the controller head assembly  100 . In  FIG. 1B , a controller board  190  is illustrated, and this is preferably where the circuit of the present application is physically located. Of course it will be known to one skilled in the art that several of the connections and components listed and illustrated in the following schematic diagrams will be physically located in other parts of the trolling motor, but the majority of the circuit components will be located on the controller board  190 . It should also be noted that the controller board  190  may be better utilized physically in other spaces of the controller head assembly  100  or in other portions of the trolling motor system generally. 
     The present invention uses the voltage drop in the main power switching device as an indication of current through the main power switching device and therefore through the motor. It should be noted that the main power switching device is a MOSFET or power MOSFET in a preferred embodiment, but it is understood that an insulated gate bi-polar transistor (IGBT) or any other power switching device may be used. For the purpose of discussion, the preferred MOSFET device will be used throughout the specification. Since Pulse Width Modulator (PWM) switching is taking place with the MOSFET, it is not generally considered a current sensor as well. The actual current is also a function of the PWM waveform which varies with duty cycle and distortions from MOSFET rise and fall times. In the present application, the MOSFET drain to source voltage is sampled in synchronization with the PWM gate voltage on the MOSFET and also corrected for rise and fall time that distort the representation. The circuit of the present application also takes advantage of the fact that MOSFET on resistance will increase slightly with increased temperature. Since increased resistance is proportional to temperature, the sensing is more sensitive under conditions that require more sensitivity—that is higher current results in higher temperature which results in higher resistance which results in higher voltage representing the current. 
     Over-current is measured by sensing the voltage drop across the drain-to-source resistance of the power MOSFET switch.  FIGS. 2   a  and  2   b  illustrates this with a very low level voltage sample that is the input  3  to an amplifier U 2 A that increases the amplitude. The open switch voltage of the MOSFET is extremely large compared to the closed switch voltage and would overdrive the amplifier U 2 A but diode D 10  clamps the input to the diode forward voltage drop. Output of the U 2 A amplifier in  FIG. 2   b  is gated with the PWM to synchronize and extract the actual current signal from the more complex signal combination of on, off, and transient switching signals sampled from the MOSFET. A propagation delay circuit of R 30 , R 34 , and C 15  prevent the gating transistor Q 7  from responding to PWM transition errors that would distort the true current. 
     R 33  and C 16  form an integrator to measure the rise in energy represented by the over-current condition. The over-current energy comparator U 2 C initiates a sampling time delay when the energy level reaches a specified level. Once the sampling time is exceeded then the PWM is turned off by the second U 2 C comparator and initiates a standby time delay. During the standby delay, the trolling motor will remain off even if the over-current condition is remedied. The user is required to return the throttle control which determines the PWM control voltage to the motor off level in order to reset the standby mode. If the stalled current condition is remedied then the motor operation will continue normally but if the stalled current condition remains then the standby mode will be re-entered immediately. 
     The integrating circuit R 33 , C 16  provides a sampling time window which allows the prop to strike objects that produce transient over-current condition without starting the standby delay. The standby delay allows the snubber diode D 10  current to diminish due to the motor inductance load-dump to a safe thermal level. 
       FIG. 2  also contains the temperature control circuit of which the present invention includes for total power management. Thermistors located on the power MOSFET and snubber diode are connected with R 43 , R 44 , R 345 , and R 46  in the form of a wheatstone bridge for the comparator LM 339 . Either of the thermistors can unbalance the wheatstone bridge due to excessive heat and once the comparator level is exceeded then the comparator output turns on the PWM suppression switch Q 8  and cuts back the trolling motor voltage within microseconds. This thermal protection operates concurrently and independently with the over-current protection. 
     Restating some of the disclosure above, and providing additional detail,  FIGS. 2A and 2B  illustrate a power management protection circuit  200  of the present application. This power management protection circuit  200  is coupled with a battery at terminals T 1  and T 2 , and provides power management protection to the trolling motor circuit (not shown). The MOSFET Q 1  provides the sample signal when it is conducting, that is when voltage from the drain D of Q 1  is conducting the MOSFET Q 1  is being utilized as a current sensor. This is effectuated in that the drain D voltage comes down to resistor R 28 , and the current associated with this voltage is inputted into the U 2 A amplifier. Preferably, this amplifier U 2 A has a gain of 2.3. However, amplifiers of various gain may be used to increase the signal to noise ratio of the inputted drain voltage. The forward voltage drop of the diode D 10  is approximately and preferably 0.6 volts. Therefore, when sampling the MOSFET voltage, when the MOSFET turns off the voltage going into the amplifier U 2 A can only rise to a 0.6 volt level of the diode D 10  and when the MOSFET turns on, the voltage is approximately 0.1 volts. 
     At the output  1  of the amplifier U 2 A, a voltage divider circuit including resistor R 32 , resistor R 33  and transistor Q 7  having an output of the collector of the transistor Q 7 . This voltage divider behaves very much like a switch such that when the MOSFET is conducting and the voltage into the amplifier U 2 A is 0.1, the voltage out of the voltage divider circuit will be approximately 0.25 volts, and when the MOSFET is turned off and the voltage into the off amp U 2 A goes to 0.6 volts thus saturating the amplifier U 2 A, the transistor Q 7  actually turns off. This voltage divider circuit or switch is then synchronized with resistor R 30  that provides an inverted PWM signal, such that the switch is synchronized with the PWM control voltage of the MOSFET Q 1 . Accordingly, then when Q 1  is turned on, the switch is turned off, and when Q 1  is turned off, the switch is turned on. The switch signal output of Q 7  will then have a peak representing the current translated non-resistive MOSFET Q 1  voltage. Because the switching characteristics of the MOSFET Q 1  are not perfect, a delay circuit including capacitor C 15  and resistor R 34  are implemented to account for the MOSFET Q 1  delay. This delay circuit will delay the control signal so that it simulates the delay that is taking place in the MOSFET Q 1 . After this delay circuit is implemented, a square wave is outputted with a varying duty cycle that varies with the PWM and the peak value. 
     Still referring to  FIGS. 2   a  and  2   b , an integrator circuit including resistor R 33  and capacitor C 16  averages this square wave outputted from the delay circuit above. It is this average wave from the integrator circuit that is compared to a reference voltage to determine whether the circuit  200  trips, and this occurs when the average value wave exceeds the reference voltage. However it should be noted that a time component is also incorporated into this determination and will be discussed further below. The reference voltage is derived from the PWM control voltage over resistor R 36  which adjusts the fixed voltage over resistors R 40  and  41 . Adding these two voltages creates a variable reference that is the highest referenced voltage. The averaged wave must achieve this highest over current before it trips. If the motor is dropped to a lower speed and the PWM decreases, the average voltage to the motor is lower, and thus the PWM control voltage modifying the fixed voltage over R 40  and R 41  is also lower. This lower PWM control voltage then lowers the reference, thus creating a variable reference. 
     When the average wave voltage is higher than the reference voltage, the output of U 2 C connected to the resistor R 37  will go low and begins discharging the capacitor C 5 . This creates a delay, such that it provides an amount of time that the over current condition exists before the circuit  200  will trip. In other words, first the comparison determines whether the average signal is greater than the reference voltage, and then this over current condition must occur for a predetermined amount of time. In a preferred embodiment, this delay should occur for a half of a second, but may be adjusted to a user&#39;s specification. This delay circuit that determines this time includes resistor R 37  and capacitor C 5 . If the over current condition is remedied prior to the discharge of capacitor C 5 , then the circuit will not trip, and normal operating will proceed. If the delay ends and the circuit is still in overload then the operational amplifier U 2 D will trip and the output of this amplifier U 2 D will stop the PWM, thus stopping the transistor Q 7 . This creates a situation where the PWM is on but not modulating the MOSFET Q 1 , and the circuit is still looking for the voltage signal from the MOSFET Q 1 . This creates a latched condition for the MOSFET Q 1  until the PWM voltage is returned to zero. Once this occurs, then the circuit is re-set and once throttle is returned to the circuit, the normal operation will proceed. 
     Lastly, a recovery circuit including resistor R 38  and capacitor C 5  provides a delay time from which the throttle must be turn to the off position before it can be turned back on to effectuate normal throttle and circuit  200  operation. Preferably this recovery time is one second, but can be adjusted by adjusting the values of R 38  and C 5 . 
     A method  300  of power management protection for a trolling is illustrated in the flow chart in  FIG. 3 . In step  305 , a drain voltage of a MOSFET in the above-referenced circuit is amplified, and in step  310  the amplified voltage is divided with a voltage divider such that the output of the voltage switches between an on and off state. As discussed above, the voltage divider of the present method and system acts as a switch in this fashion. In step  315 , the voltage divider synchronized with a PWM signal, and in step  320  a PWM control signal is delayed to account for the MOSFET delay. This synchronizing step  315  ensures that when the MOSFET is turned on, the switch is turned off, and when the MOSFET is turned off, the switch is in an on position. The delaying step  320  transforms the output of the amplifier such that the signal is now a square wave of varying duty cycle that varies with the PWM and the peak value. In step  325 , this outputted signal is then averaged with an integrating circuit, such that the square wave is transformed into an average value signal of the previous square wave. This averaged wave is now compared to a variable reference signal in steps  330  and  335 . Here, if the average signal is greater than the sum of a fixed voltage and the PWM control voltage for a predetermined delay time defined by the discharge of the delay capacitor, then the circuit is latched in a trip state in step  340 . If one of the first two conditions of steps  330  and  335  are not met, then the circuit continues normal operation in step  305 . Referring back to step  340 , if the throttle has been manually set to throttle off for a predetermined recovery time in step  345 , then the circuit is reset to a normal operating position in step  350  and the method reverts back to step  305 . As can be seen with respect to steps  340  and  345 , if the throttle is not set to throttle off for this recovery time, then the circuit remains latched in step  340 . 
     It should also be noted that the resistance of the MOSFET Q 1  increases when the temperature of the MOSFET Q 1  increases, occurring naturally in normal operation. When the circuit  200  operates and the resistance increases, a voltage value is produced that creates a higher current condition that then causes the over current circuit  200  as described above to trip sooner than if such a MOSFET Q 1  were not used for this purpose. This provides an extra safeguard to safe operation of the trolling motor.