Discussion
Why do we need a ULN2003 in driving a stepper motor from 8051 port ?
Answer: B
The ULN2003 is needed for increasing the current.
An 8051 port pin can supply or sink only a few milliamperes, far too little to drive a stepper motor winding that needs hundreds of milliamperes. The ULN2003 contains seven Darlington transistor pairs, each able to sink about 500 mA, with built-in suppression diodes for inductive loads. The port drives the Darlington inputs and the Darlingtons carry the winding current.
Switching the windings on and off in sequence is done by the 8051's program; the ULN2003 only amplifies the current. 'Increasing the power' is less precise, since the supply voltage is unchanged and the driver's role is current gain. The ULN2003 has no short-circuit shut-off.
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