AN1857 Freescale Semiconductor / Motorola, AN1857 Datasheet - Page 25

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

dc Bus Brake
AN1857
MOTOROLA
Brake_control
CAUTION:
10 k
R202
GND
C212
1 nF
Under certain operating conditions, a motor can act as a generator,
delivering high voltage back into the dc bus through the inverter’s power
switches and/or the power switch source-drain recovery diodes. That is
a very undesirable condition and can damage the power transistors and
other components in the inverter. The excess energy must be
dissipated; otherwise, the dc bus voltage will rise above a safe limit. The
power module contains an IGBT and current limiting resistors, placed
across the dc bus to act as a dc bus brake and dissipate the excess
energy.
When using the brake, care must be taken to not exceed the power
dissipation of the brake transistor and its current limit resistors.
Provisions are made on the power board for the user to install an
additional brake resistor across the one composed of R6–R9, allowing
for additional bus brake current to be imposed on the system. Again,
care must be taken not to exceed the ratings of the IGBT brake transistor
when an additional brake resistor is installed in the system. Typically, the
system software will pulse-width modulate the brake to dissipate the
excess voltage until it is brought down to an acceptable level.
Under certain operating conditions, a motor can act as a generator,
delivering high voltage back into the dc bus through the inverter’s power
switches and/or the power switch source-drain recovery diodes. This
can damage the power transistors and other components in the inverter.
U202
Figure 16. dc Bus Brake Circuit Schematic
4
2
1
NC
InA
InB
Freescale Semiconductor, Inc.
+15V_D
MC33152D
For More Information On This Product,
VCC
6
3
Figure 16
GND
10 F/35 V
100 nF
OutA
OutB
C202
C203
+
NC
Go to: www.freescale.com
8
7
5
GND
100
R204
is a schematic of the dc bus brake control circuitry.
GND
D201
MMSZ5251BT1 DC Bus –
DC Bus +
Brake_Res
250
250
R6
R7
R9
R8
250
250
Q7
SGB04N60
Application Note
DCB_Cap_Neg
DCB_Cap_Pos
D11
HFA04TB60S
Power Stage
25