AN1857 Freescale Semiconductor / Motorola, AN1857 Datasheet - Page 21

• Manufacturer Part Number: AN1857
• Description: A 3-Phase ac Induction Motor Control System Based on the MC68HC908MR32
• Manufacturer: Freescale Semiconductor / Motorola

Power Switch
Driver Circuitry
AN1857
MOTOROLA
For a better understanding of the power stage, a description of several
of its circuits follows.
Figure 12
driver circuitry. The IGBT drivers, IR2112S, provide control of the power
IGBT power switches by shifting and transforming the PWM logic level
control signals to the levels necessary to control the power switches.
The turn-on time of the IGBT power switch is controlled by resistors
R401 and R402 which are connected to the power switch gates. Diodes
D402 and D404 aid in a fast turn off of the IGBT power switches by
providing a low-impedance path back to the IR2112S to discharge the
power switch’s gate. D401 protects the power supply and any other
circuits connected to it by preventing high voltage that could flow out of
the VB power input (pin 7) to the IR2112S.
If an overcurrent situation should occur, the overcurrent circuit on the
power module will supply a shut down signal to the IR2112S, turning off
its outputs, thus protecting the power switches. At the input, pull down
resistors, R403 and R404, set a logic low in the absence of a signal.
Open input pull down is important for gate drive signals, where it is
desirable to keep power transistors off in case of either a broken
connection or absence of power on the control board.
CONTROL
TO/FROM
SIGNALS
BOARD
Freescale Semiconductor, Inc.
HV POWER
INPUT
For More Information On This Product,
is a schematic diagram of the basic design of the power switch
Go to: www.freescale.com
Figure 11. Power Module Block Diagram
ID BLOCK
BOARD
POWER SUPPLY
SWITCH MODE
DRIVERS
GATE
PHASE CURRENT
PHASE VOLTAGE
BUS CURRENT
BUS VOLTAGE
IGBT POWER
MONITOR
MODULE
BACK-EMF SENSE
ZERO CROSS
PFC CONTROL
dc BUS BRAKE
Application Note
Power Stage
3-PHASE AC
MOTOR
TO
21