Curtis 1205 Guide de dépannage télécharger pdf (Page 46)

Curtis 1204/1205 Manual, Rev. C

use with PM motors only, the plug diode and A2 terminal are omitted; however, the Functional

Description is written in terms of series motors.

LOGIC SECTION

B- is the ground return for all of the logic circuitry. For systems over 12 volts, the battery supply

is regulated down to 14 volts to power the logic circuitry. The output of the 14 volt regulator is

switched on and off (switch) by the keyswitch input (KSI) to power up the control circuitry when

the vehicle is in use and to power it down (shutdown) when the vehicle is not in use.

The speed control input (throttle input) is usually a 5000 ohm, two-wire pot, but other types

can be accommodated, so a ﬂexible throttle input scaling circuit conditions the control input to

a standard level. This standardized throttle input goes to the acceleration circuit which limits the

rate at which the controller output can increase. The acceleration rate is set by a resistance, and is

adjustable via a user accessible trimpot (acceleration ramp adjust

The output of the throttle input scaling also goes to a pot fault circuit which turns the controller

output off in the event of inputs (e.g., broken wires) which would otherwise cause a runaway. An

optional protective feature, high pedal disable (HPD), inhibits controller output if the controller is

turned on with the throttle applied. After an interval measured (start-up timer) from the moment

the KSI input is turned on, the HPD circuit checks the throttle position. If an applied throttle

condition is detected, controller output is held off until the throttle input is returned to zero and

then normal operation is allowed.

The control signal then goes to the limit integrator which reduces the controller output in response

to undervoltage or overcurrent. The time-averaged response of this circuit gives a stable limit

ing action. The undervoltage detector gives an output when the battery voltage is too low. The

reduction in output allows the battery voltage to recover and an equilibrium to be established at

a voltage high enough to allow the controller to function properly. The current limit function is

explained in more detail below.

The heart of the logic circuitry is the pulse width modulator in which the control input derived

from the previous stages is compared in magnitude to a 15 kHz sawtooth wave from the

oscilla-

tor. The resulting pulse output can be smoothly varied between full off and full on. These pulses

become the input to the controller’s main power MOSFET switch via a gate drive circuit that

provides the high pulse currents needed to turn the power MOSFETs on and off (see Fig. B-1).

The shape of the sawtooth wave may be altered so that most of the pulse width change occurs in

the earlier or in the latter part of the control input range, giving more sensitive throttle response

at high or at low speeds.

Current limiting is done by sensing the voltage drop across the main power MOSFET switch when

it is on. This voltage is compared (current limit comparators) with a current limit reference; when

it exceeds the reference, an overcurrent signal acts on the limit integrator to reduce the controller

A-2

APPENDIX A: FUNCTIONAL DESCRIPTION

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Curtis 1205 Guide de dépannage Page 46