Transcript Drive circuits

Drive Circuit
What is “drive circuit”?
Circuits that are constructed to turn on/off power devices/switches
Control circuit
Gate driver
• Provides an interface between the control signal (small signal
electronics) and power circuits
• Sometimes called ‘gate drivers’
Why do we need drive circuit?
To amplify control signals to level required to drive the power
switches and also to ensure fast turn-on and turn-off
•
MOSFET/IGBT typically require voltages between 10V - 20V to ON and initial high
current to charge parasitic input capacitance. The capacitor need to be
discharged during turn off
•
BJT require continuous current to ON – initial high current is needed to reduce
turn on time.
Provides electrical isolation between control circuit (small signal) and power
circuit
•
Require for safety reasons and elevated emitter (or source) of the transistor in
bridge configuration
Some examples of drive circuits
Gate drive with totem-pole configuration
Some examples of drive circuits
Electrical isolation methods
• Transformer isolation
• Opto-coupler isolation
• Isolated dc power supplies
for drive circuits
Some examples of drive circuits
•
Negative half cycle of vs(t) - positive dc
rail near safety ground potential. Temitter potential large and negative with
respect to safety and logic ground
• Postive half cycle of vs(t) - negative dc
rail near safety ground potential. T+
emitter substantially positive with espect
to safety ground if T- is off
• Variation in emitter potentials with
respect to safety and logic ground means
that electrical isolation of emitters from
logic ground is needed.