Freescale Semiconductor 33395, Справочное руководство

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Design Considerations
Brake Control
33395 Evaluation Motor Board DRM33395 Designer Reference Manual
Design Considerations 41
5.6 Brake Control
A brake circuit is included to dissipate re-generative motor energy during
periods of active deceleration or rapid reversal. Under there conditions,
motor Back-EMF adds to the dc bus voltage. Without a means to
dissipate excess energy, an over-voltage condition could easily occur.
The circuit shown in Figure 4-5 connects R403 across the dc bus to
dissipate energy. The transistor Q401 is turned on by software when the
bus voltage sensing circuit in
Figure 5-1 indicates that the bus voltage
could exceed safe levels. On-board power resistor R403 will safely
dissipate up to 5 watts continuously or up to 50 watts for 5 seconds.