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WHAT'S YOUR ENGINEERING QUOTIENT?

Problem 5— The Zetex ZHB6718 is a full H-Bridge chip implemented by BJTs. The VCE(sat)s (saturation voltages across the collector and emitter) of the PNP and NPN BJTs are -0.2V and 0.15V respectively.

The Fairchild NDS8858 is a half H-Bridge chip implemented by MOSFETs. The RDS(on)s (drain to source resistance at on-state) of the P-Channel and N-Channel MOSFETs are 0.10 and 0.055 Ohms respectively.

Using a DC motor operating at 6V (assume constant voltage) and coil resistance of 12 Ohms, compute the following:

ý Stall current of the DC motor switched by the Zetex chip (10 mgp)
ý Stall current of the DC motor switched by the Fairchild chips (two half H-bridges make one full H-bridge) (10 mgp)
ý Power dissipated at the Zetex chip when the motor is stalled (6 mgp)
ý Power dissipated at the Fairchild chips when the motor is stalled (6 mgp)

ANSWER

Problem 6—For many electrical engineers, motors are a lost art. Can you define the following terms as they apply to rotating machinery?

Rotor
Stator
Brush
Commutator
Generator
Alternator
Armature
Field
Windings
Universal Motor

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