U.S. patent application number 15/863273 was filed with the patent office on 2019-07-11 for three speed electronic winch contactor.
This patent application is currently assigned to MotoAlliance. The applicant listed for this patent is JIMMIE DOYLE FELPS, Scott Charles Heupel. Invention is credited to JIMMIE DOYLE FELPS, Scott Charles Heupel.
Application Number | 20190210845 15/863273 |
Document ID | / |
Family ID | 67106481 |
Filed Date | 2019-07-11 |
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United States Patent
Application |
20190210845 |
Kind Code |
A1 |
FELPS; JIMMIE DOYLE ; et
al. |
July 11, 2019 |
THREE SPEED ELECTRONIC WINCH CONTACTOR
Abstract
A winch control system having a solid state winch contactor and
a boost power supply for a vehicle equipped with an electric winch
and especially for off-road vehicles, is disclosed. This invention
automatically provides three winch speeds: a "slow start" ("creep")
speed for "parking" the hook and for "sneaking" up on a load, a
normal speed for normal winch operation and a fast speed for taking
less time to unwind and rewind the winch rope when there is no load
on the winch. Protection features for the winch contactor and/or
the winch include, but are not limited to, electronic winch motor
braking, current limiting, over temperature, undervoltage and
reverse battery. Winch current limiting is adjustable from 100 amps
to 300 amps, chosen for the purpose of accommodating various winch
sizes.
Inventors: |
FELPS; JIMMIE DOYLE;
(Colorado Springs, CO) ; Heupel; Scott Charles;
(Maple Groves, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FELPS; JIMMIE DOYLE
Heupel; Scott Charles |
Colorado Springs
Maple Groves |
CO
MN |
US
US |
|
|
Assignee: |
MotoAlliance
Rogers
MN
|
Family ID: |
67106481 |
Appl. No.: |
15/863273 |
Filed: |
January 5, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B66D 1/12 20130101; B66D
1/485 20130101; H02P 7/04 20160201; B66D 1/46 20130101; H02P 7/285
20130101; H02P 7/29 20130101; H02P 7/292 20130101 |
International
Class: |
B66D 1/48 20060101
B66D001/48; B66D 1/12 20060101 B66D001/12; H02P 7/03 20060101
H02P007/03; H02P 7/29 20060101 H02P007/29; H02P 7/292 20060101
H02P007/292 |
Claims
1. An electronic winch control system, comprising: a driver control
comprising: a voltage measuring circuit to determine whether a
voltage from a vehicle ignition switch is above a minimum threshold
of 8 volts, the driver control to activate a winch contactor in
response the voltage from the vehicle ignition switch being
determined to be above the minimum threshold of 8 volts; a logic
latch to debounce an IN signal and an OUT signal from a winch
control switch; an OR gate coupled with the IN and OUT signals to
trigger slow start circuitry and allow winch activation; a
retriggerable one shot coupled with an oscillator to create a slow
start for a winch motor by generating a drive waveform, to be
coupled to the winch motor, of approximately 20% on time duty cycle
and approximately 9.5 kHz frequency to drive the winch motor at the
beginning of each IN cycle and each OUT cycle, the drive waveform
lasting approximately 650 milliseconds before switching to a
constant battery voltage; a one shot to increase an off time of the
drive waveform from approximately 25 microseconds to approximately
100 microseconds in response to a detection of an over current
event; an over-current protection circuit to cause the drive
waveform to be off for a first extended period of time in response
to over current events being detected more frequently than a
selected threshold amount; an over-temperature protection circuit
to cause the drive waveform to be off for a second extended period
of time when at least two metal oxide semiconductor field effect
transistor's (MOSFET's) that are to apply the drive waveform to the
winch motor temperature reach an elevated temperature threshold
limit of approximately 85 degrees centigrade; control logic
circuitry coupled to the OR gate, the oscillator, the one shot, the
over current protection circuit, and the over-temperature
protection circuit to determine whether winch drive is enabled; a
current limit reference circuit to provide a variable winch current
limit; and light-emitting-diode (LED) indicators to display at
least two winch contactor states; a motor driver comprising: a
motor driver integrated circuit to control the at least two MOSFETs
that are to apply the drive waveform to the winch motor, the motor
driver integrated circuit including electronic brake circuitry to
cause a shorting of at east one winch motor winding at the end of
each IN cycle and each OUT cycle, a current sense resistor to
measure winch motor current, winch current measurements to be
coupled to the motor driver integrated circuit the over current
protection circuit, and a boost circuit; and a reverse battery
protection circuit to turn off at least one reversed, N-channel
MOSFET when a polarity of a connection to a battery voltage is
reversed, the reversed N-channel MOSFET also to be turned off when
the maximum voltage of the drive waveform is boosted; the boost
circuit, comprising: a winch current sense monitor amplifier to
amplify a voltage across the current sense resistor; a window
comparator to determine if the winch is unloaded, the window
comparator to be selectively controlled to have at least three
upper thresholds, a first upper threshold for when the maximum
voltage of the drive waveform is not boosted, a second upper
threshold for when the maximum voltage of the drive waveform is
boosted, and a third upper threshold for when the drive waveform is
transitioning between being not boosted to being boosted; a delay
block, coupled to a boost MOSFET and a fast turnoff MOSFET; the
boost MOSFET switch to be controlled by the delay block to turn on
the boost power supply; the fast turnoff MOSFET switch and series
resistor to reduce a delay time of the delay block to turn off the
boost power supply when a winch load is detected; a transition
timing one shot to control the window comparator to have the third
upper threshold and to temporarily turn off the reversed N-channel
MOSFET to allow the boost power supply to turn on; and a resistor
and PNP transistor to determine whether the drive waveform applied
to the winch motor has risen above the battery voltage, and to
allow the maximum voltage of the drive waveform to continue to be
boosted after the transition timing one shot has timed out, and to
inhibit the reversed N-channel MOSFET from being turned back on. a
boost power supply to generate, from the battery voltage, a boosted
maximum voltage of the drive waveform.
2. The electronic winch control system of claim 1 having a slow
start period during a beginning of each IN cycle and each OUT cycle
that provides lower winch motor torque and speed.
3. The electronic winch control system of claim 1 having a fast
winch speed for unwinding and rewinding a winch rope when the winch
motor is determined to be unloaded.
4-11. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to motor vehicle
electrical systems, and more specifically, to a winch control
system that incorporates an electronic winch contactor and a boost
power supply to provide three different speeds for driving the
electric winch.
BACKGROUND OF THE INVENTION
[0002] Electric winches have long been used, especially on utility
type, off-road vehicles, for various pulling and lifting tasks. The
first shortcoming of prior art has been the personal danger and
possibility of winch damage when trying to "park" the winch hook
and the inability to "sneak" up on a load. A second shortcoming is
the length of time it takes to unwind and rewind the winch rope
when there is no load. A third shortcoming is the risk of tangling
the winch rope when winching a vehicle that is stuck and suddenly
gets traction, causing sudden slack in the winch rope. A fourth
shortcoming is the lack of adequate protection features and
reliability for the winch motor and/or the electro-mechanical relay
control module (i.e. contactor) that powers the winch motor and
also reverses the direction of the winch drum. This invention
overcomes the first shortcoming by employing a "slow start" mode
(or "creep" mode) which automatically switches to a normal winch
speed after a short period of time. The second shortcoming is
overcome by detecting when the winch is unloaded and after a
pre-determined period of time automatically switching to a faster
rope speed (boost mode). The third shortcoming is overcome by the
fast speed that minimizes the risk of getting a loose rope. The
fourth shortcoming is minimized by the many features employed in
this invention which include over-current-protection,
current-range-adjustment, over-temperature-protection, various
protection modes for the external drive, metal oxide semiconductor
field effect transistors (MOSFETs), low-battery-protection and
reverse-battery-protection.
[0003] Prior art to offer multiple winch speeds has been done by
changing gear ratios (in the winch gear box) by U.S. Pat. No.
5,927,691 (Otteman), U.S. Pat. No. 4,453,430 (Sell) and U.S. Pat.
No. 4,161,126 (Winzeler). Changing gear ratios has a disadvantage
because it increases the winch torque by the same ratio as the gear
ratio increase, resulting in an increased risk of personal injury
and/or winch system damage. One with ordinary skill in the art will
readily recognize how gearing affects winch load rating as
demonstrated when using a "snatch block" where the winch rope is
doubled between the load and the winch. This will cut the retrieval
speed in half but also doubles the winch power (e.g. you get
approximately 10,000 pounds of pull from a 5,000 pound winch).
[0004] Another method to offer multiple winch speeds is by using
multiple stator windings with different numbers of poles in an
alternating current (AC) motor as used in a shop winch in U.S. Pat.
No. 4,145,645 (Price, et al.). This approach is a result of
recognizing the benefits of having multiple winch speeds,
especially a "creep" mode, but is not automatic and is not
practical for a vehicle winch because AC voltage is not typically
available. Trolling motors used for fishing have multiple speeds to
allow a fisherman to change the speed of the boat. An early method
of accomplishing this was to have up to five discrete speeds by
using multiple windings and resistors in the winch motor which were
selected by switches. More recent trolling motors use
pulse-width-modulation (PWM) to power the motor. PWM is the use of
a rectangular waveform where battery power is applied to the
trolling motor for a period of time and then removed for the
balance of the waveform cycle. The duty cycle of this PWM waveform
is varied to achieve different motor speeds. Prior art trolling
motor speed control is practical but complex, expensive and more
difficult to accomplish at the high currents (up to 300 amps and
more) required to drive a winch motor.
[0005] Yet another prior art that has been used to increase the
speed of direct current (DC) motor is to simply apply a higher DC
voltage to the motor winding. Such was a common practice in
converting antique tractors or other antique vehicles from 6 volt
electrical systems to 12 volt electrical systems. The 6 volt
starter motor was seldom rewound for 12 volts. It would simply run
faster on 12 volts because of the higher torque (since the torque
of a DC motor is directly proportional to the motor's armature
current), and consequently, make it easier to start the vehicle's
engine. This approach is used in the present invention and
automatically controlled.
[0006] One prior art, U.S. Pat. No. 8,958,956 (Felps) uses
electronic control (i.e. solid state) for driving a vehicle winch
but has only one winch speed and still uses an electro-mechanical
contactor for energizing the winch and reversing the drum
direction.
SUMMARY OF THE INVENTION
[0007] In a preferred embodiment of the present invention, when the
winch is activated via an IN or OUT signal, a low duty cycle
pulse-width-modulated (PWM) waveform powers the winch motor for 650
milliseconds to provide a "slow start" mode before switching to a
continuous 12 volt mode for normal operation. If the IN/OUT switch
is cycled before the low duty cycle PWM waveform ends, slow start
will repeat. If IN or OUT is initiated and if no load has been
detected on the winch for 1.5 seconds, the winch motor drive
voltage of 12 volts is boosted to 24 volts to increase the winch
drum speed. When the winch is running in the fast speed mode and a
load is suddenly detected on the winch, the boost power supply is
immediately turned off.
[0008] By using a 20% duty cycle, 9.5 kHz drive waveform to produce
slow start, the winch torque is reduced from what it is during the
normal speed because the winch motor's armature current is
decreased. In practice (i.e. using this slow start drive on a
MotoAlliance 12 volt Viper Elite 5000 pound electric winch on its
outer layer of winch rope), the armature current for slow start is
typically 6.76 times lower than normal speed, resulting in a
typical reduction of winch load rating from 5000 pounds to 740
pounds. Not only does this greatly reduce risk of personal injury
or damage to the winch system, but also makes it easy to stall the
winch when parking the hook or sneaking up on a load, and resulting
in no undue stress on the winch rope. On the outer layer of the
winch rope, typical winch rope speeds observed was 0.85 inches per
second for slow speed, 6.6 inches per second for normal speed and
10.5 inches per second for fast speed.
[0009] If desired, the present invention can also be used without
the boost feature, eliminating the need for the boost power supply.
Eliminating the boost feature also allows the winch contactor to be
used with 24 volt vehicle electrical systems.
[0010] The motor driver integrated circuit (IC), DRV8701 E, used to
drive the winch motor provides electronic braking by shorting the
winch motor winding as soon as IN or OUT is terminated. Protection
features in the winch contactor protect it, and indirectly, protect
the winch against over-current and over-temperature. Reverse
battery protection prevents damage to the solid state winch
contactor in the event the battery connections are reversed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The drawings presented in the present disclosure provide a
better understanding of the present invention, but are not intended
to limit the scope or use of the invention. The components in the
drawings do not necessarily adhere to conventional symbols,
emphasis being placed upon clearly illustrating the principles of
the present invention. Some components such as capacitors and
transient voltage surge protectors used for filtering and/or
voltage surge protection are not shown since they are not pertinent
to understanding the operation of the invention. Moreover, in the
drawings, a tilde character (.about.), indicates a "not true"
polarity of a logic signal. Like reference numerals designate
corresponding parts throughout the several views and in which:
[0012] FIG. 1 is a simplified schematic of a typical vehicle
electrical system equipped with an electric winch that is being
driven by a preferred embodiment of the present invention
comprising a solid state winch contactor and a boost power
supply;
[0013] FIG. 2A is a schematic of the driver control for winch
contactor 18 in FIG. 1 (100 series numbering);
[0014] FIG. 2B is a schematic of the motor driver for winch
contactor 18 in FIG. 1 (200 series numbering) being simplified by
showing MOSFETs 218-226 and resistor 228 as single devices when in
fact they are multiple devices in parallel; and
[0015] FIG. 2C is a schematic of the boost control for winch
contactor 18 in FIG. 1 (300 series numbering).
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present disclosure describes how this preferred
embodiment of the present invention operates, but is not intended
to limit the scope, other applications or uses of the present
invention. The present disclosure is primarily for off-road
vehicles, but is not limited to these vehicles, nor limited in its
chosen signal timings for various features or limited in its chosen
output current or voltage capabilities. All logic circuit timings
and duty cycle percentages, circuit voltages and temperatures are
approximate.
[0017] To begin, refer to FIG. 1, a block diagram for the portion
of a vehicle's electrical system required when a winch control
system using the present invention has been added. Battery 12 is
the vehicle battery which is typically a flooded, lead-acid
battery; switch 14 is part of the vehicle's ignition switch and is
wired to enable winch operation only when the ignition switch is
on; switch 16 is a winch control switch with a center off position
and momentary positions for IN and OUT; winch contactor 18 is a
solid state winch controller that provides functions necessary to
drive and protect winch motor 22; and when winch motor 22 is
unloaded, boost power supply 20 boosts winch contactor 18 motor
voltage from 12 volts to a regulated 24 volts for driving winch
motor 22 at a faster speed.
[0018] In the present invention an output current of 40 amps was
chosen for boost power supply 20 which is sufficient for many
unloaded, winch motors 22, especially those having load ratings up
to 5000 or 6000 pounds. Lower output currents as well as higher
output currents for boost power supply 20 may apply to other winch
motor 22 sizes and/or brands. Winch contactor 18 and boost power
supply 20 should be waterproof units to withstand the elements of
nature.
[0019] Referring to FIGS. 2A, 2B and 2C, driver control, motor
driver and boost control, respectively, these three schematics
combine to perform the functions of winch contactor 18. Part of
connector 100 in FIG. 2A (three terminals) provides the interface
for IGN (ignition), IN and OUT signals from switches 14 and 16 in
FIG. 1. The other part of connector 100 in FIG. 2C (one terminal)
provides an output, .about.BOOST, to activate boost power supply 20
in FIG. 2C.
[0020] Referring to FIG. 2A (driver control), under voltage 114
activates integrated circuit (IC) DRV8701 E 202 in FIG. 2B via the
.about.SLEEP signal and lights the ON light-emitting-diode (LED)
(green) in indicators 138, provided battery 12 voltage in FIGS. 1
and 2B is above 8 volts. If the voltage is below 8 volts or switch
14 in FIG. 1 is off, no LEDs will be lit in indicators 138.
Resistors 108 and 110 are pull-down resistors for when IN or OUT is
not selected. Resistors 104 and 106 limit the current into latch
118 and OR gate 124. Latch 118 selects the phase, PH, of the drive
to winch motor 22 in FIG. 2B through IC DRV8701 E 202 in FIG. 2B.
OR gate 124 triggers one shot 128 when IN or OUT is selected. Latch
118 and OR gate 124 have Schmitt trigger inputs for slow rise and
fall times. Latch 118 also debounces the IN and OUT signals.
[0021] One shot 128 has a pulse width of 650 milliseconds. When one
shot 128 is triggered, oscillator 132 begins to oscillate at 9.5
kHz with a typical 20% duty cycle (percentage of low level time).
The low oscillator frequency of 9.5 kHz was chosen because of the
large, power MOSFETs 220-226 in FIG. 2B. The output of OR gate 134
(having one inverted input) has to be low to drive winch motor 22
in FIGS. 1 and 2B. If the other inputs to OR gate 134 and NOR gate
136 allow oscillator 132 to determine the enable signal, EN, the
signal EN will be high for 20% of its period, generating a slow
start drive for winch motor 22. When EN is high the IN/OUT LED
(orange) in indicators 138 is lit, but is dim during slow start.
Each time IN or OUT is selected, the complete 650 millisecond
period occurs at one shot 128 even if one shot 128 has not
previously timed out (i.e. retriggerable). This feature is
especially useful when parking the hook because it allows an
extended slow start.
[0022] SNSOUT is a signal from IC DRV8701 E 202 that occurs when an
over current event occurs on winch motor 22 which results in winch
motor 22 no longer being driven and the IN/OUT LED (orange) in
indicators 138 is no longer lit. SNSOUT is generated as a means of
current regulation for winch motor 22 referred to as "current
chopping," which is a "fixed-off-time" regulation scheme with a
variable time to be on and to stay on until current chopping occurs
again. Again, because of large, power MOSFETs 220-226, this off
time pulse needed to be increased from its 25 microseconds. So one
shot 112 pulse width was chosen to be 100 microseconds. One shot
112 extends the off time of winch motor 22 through an input in NOR
gate 136.
[0023] Even though IC DRV8701E 202 and one shot 112 combine to
provide current regulation for winch motor 22, the rate at which
current chopping occurs is a function of how much current overload
exists in winch motor 22. If current chopping is occurring more
frequently than every 3 milliseconds, over current 126 will shut
down drive to winch motor 22 through an input of OR gate 134 for a
period of 5 seconds and lights the over current LED (blue) in
indicators 138. Over current shutdown can occur in less than 100
milliseconds for very high, current overloads.
[0024] Over temperature 130 senses the temperature of MOSFET 226 in
FIG. 2B (which is on during an IN operation and at which time winch
motor 22 can be heavily loaded) and shuts down drive to winch motor
22 when the temperature reaches 85.degree. C. Shutdown lasts 14
seconds to allow cool down of MOSFETs 218, 220 and 226. This event
lights over temperature LED (red) in indicators 138. All protection
shutdown modes for winch motor 22 last sufficiently long to alert
the operator that a protection feature has taken over control of
winch motor 22.
[0025] Reference voltage 102 provides a 2.5 volt reference for
differential amplifier 116 that has a gain of 0.2. The result is a
VREF that ranges from 750 millivolts (300 amp upper current limit
for winch contactor 18) at the top of potentiometer 120 and 250
millivolts (100 amp lower current limit) at the bottom, plus an
offset voltage of up to 330 millivolts (130 millivolts typically)
set by potentiometer 122 to compensate for output offset voltage of
the current sense amplifier output signal, SO, in IC DRV8701 E 202
when IN or OUT is not activated.
[0026] Referring to FIG. 2B (motor driver), IC DRV8701 E 202
contains a charge pump to create charge pump voltage, VCP, which is
typically 9.5 volts above winch motor supply voltage, VM, so
N-channel, enhancement mode, MOSFETs 220 and 224 could be used. The
charge pump in IC DRV8701 E 202 can deliver only enough current to
support MOSFETs 220 and 224 that have a maximum total gate charge,
Qg, of 200 nanocoulombs at 38 kHz. Therefore, the timing on
oscillator 132 and one shot 112 in FIG. 2A was chosen to be
compatible with the chosen MOSFETs 220 and 224 that have a maximum
Qg of 578 nanocoulombs. And, the programming on IC DRV8701 E 202
for IDRIVE (not shown) was chosen to be the maximum rating of 150
milliamps for high-side MOSFETs 220 and 224 and 300 milliamps for
low-side MOSFETs 222 and 226. Capacitor 206 is the charge pump
capacitor. Charge pump voltage, VCP, is also used to provide gate
bias voltage for MOSFET 218.
[0027] Many protection features are included in IC DRV8701 E 202
for MOSFETs 220-226 including excessive drain-to-source voltage (an
indication of excessive drain current), undervoltage for motor
supply voltage, VM, undervoltage for charge pump voltage, VCP,
winch motor 22 current limiting, and delays for turning high side
MOSFETs 220 and 224 on only after low side MOSFETs 222 and 226,
respectively, have turned off, and vise versa. When MOSFETs 220 and
226 are on, the voltage at VM+ terminal 234 is positive and the
voltage at VM- terminal 236 is negative and winch motor 22 is in
the rewind mode, IN. And vise versa, when MOSFETs 224 and 222 are
on, the voltage at VM+ terminal 234 is negative and the voltage at
VM- terminal 236 is positive and winch motor 22 is in the unwind
mode, OUT. The positive voltage, VB+, from battery 12 goes through
reverse-battery-protection MOSFET 218 before supplying power to IC
DRV8701E 202. If when installing battery 12 in the vehicle, the
positive terminal of battery 12 is connected to VB- terminal 236
(ground) and the negative terminal of battery 12 is connected to
the VB+ terminal 230, the reverse-battery-protection circuit
consisting of diode 216, NPN transistor 212 and resistors 210 and
214 will turn MOSFET 218 off and not allow the voltage on VM
terminal 234 to be negative with respect to VB- terminal 238 and
lights a reverse-battery-protection LED (red) in indicators 138 in
FIG. 2A. During this event no other LEDs in indicators 138 are lit.
Boost power supply 20 in FIG. 2C must also have
reverse-battery-protection to prevent damage to boost power supply
20 and possibly to winch contactor 18 in FIG. 1 via the VM terminal
232. If boost power supply 20 does not have reverse battery
protection, then boost power supply 20 must be disconnected from
the vehicle electrical system 10 in FIG. 1 until battery 12 is
installed correctly as determined by winch contactor 18.
[0028] Resistor 204 and opto-coupler 208 can also turn MOSFET 218
off (via OPTO-DRV) to allow voltage, VM, to be boosted to 24 volts
by boost power supply 20.
[0029] Resistor 228 senses current of winch motor 22 for the
purpose of over-current-protection performed by IC DRV8701 E 202
and for determining (via boost control circuitry in FIG. 2C) when
winch motor 22 is unloaded.
[0030] Output voltage, 4.8V, from IC DRV8701 E 202 provides power
for winch contactor 18 in FIGS. 2A-2C. Output voltage, 3.3V, from
IC DRV8701 E 202 is only used to power the fault LED (red) in
indicators 138, the FAULT signal being an output of IC DRV8701 E
202, being low active during any of the many protection features
built into IC DRV8701 E 202 and recovering automatically when the
fault ceases.
[0031] Referring to FIG. 2C (boost control), current sense
amplifier 300 monitors the voltage across resistor 228 in FIG. 2B
(SP minus SN), and amplifies it by a factor of 500 and sends the
result to window comparator 314 which determines if the result lies
between the range of 8 amps and 25 amps (the current range selected
before boost). The output of window comparator 314 goes to digital
delay block 318 where the output, BOOST, does not go high until
window comparator 314 output remains high continuously for 1.5
seconds (set by resistor 322 and two programming resistors 316 and
320 for delay block 318). Slow start one shot 128 in FIG. 2A sends
signal, SSOS, to delay block 318 input, INH, which inhibits the 1.5
second timing of delay block 318 until slow start ends. When the
output of delay block 318, BOOST, goes high, it goes to MOSFET 328
which generates signal, .about.BOOST, to turn on boost power supply
20, selects the 40 A current threshold in reference switch 306
(provided it is not over-ridden by one shot 302) and triggers one
shot 302.
[0032] The pulse width of one shot 302 is 550 milliseconds for the
purpose of essentially disabling the upper reference current for
reference switch 306 (i.e. making it >40 A to allow the start up
surge current in winch motor 22) and for turning off the
reverse-battery-protection MOSFET 218 in FIG. 2B via output,
OPTO-DRV, through resistor 308 and buffer 312. The pulse from one
shot 302 allows time for PNP transistor 310 to detect motor
voltage, VM, has become 1.0 volt higher than battery voltage, VB+
in FIG. 2B, and thus allows boost to continue after one shot 302
times out. Transistor 310 also prevents MOSFET 218 from being
turned on again until motor voltage, VM, drops back down to within
1.0 volt of battery voltage, VB+. This prevents MOSFET 218 from
having to discharge the output capacitors in boost power supply 20
when it has a high drain-to-source voltage (up to 16 volts) on it
which would likely exceed the pulse power capability of MOSFET
218.
[0033] Resistor 304 limits the current through the base of
transistor 310 and into the input of buffer 312. When one shot 302
times out, the signal, BOOST, switches reference switch 306 to
select the 40 amp upper reference current for window comparator
314. This higher reference current (40 A versus 25 A) is for the
purpose of allowing a higher winch motor 22 current that results
when 24 volts is applied to winch motor 22. BOOST going high also
switches in resistor 324 via MOSFET 326 to reduce the delay time to
turn off delay block 318 to <300 milliseconds.
* * * * *