Hardware Reference
In-Depth Information
Protection Diodes
No inductive driver circuit is complete without protective diodes. When the applied
voltage is suddenly removed from the motor coil, the magnetic field collapses, producing
an electric current. Recall in Chapter 6 that the reverse-biased diode was used to bleed off
the inductive kick in the unipolar motor drive.
Figure
7-2
shows the L298 with the external protective diodes wired in (these are
not included in the IC). If the current flow was as shown in the earlier block diagram, the
sudden off would cause the current to flow through diodes
D
3
and
D
2
. The SGS-Thomson
Microelectronics datasheet specifies that these should be 1A fast-recovery diodes (
t
rr
£
200
ns
). A slow-reacting diode can allow the voltage to spike into the surrounding circuit.
Figure 7-2.
L298 with protective diodes
L298 PCB
You could build your own L298 driver circuit, but with the availability of PCBs around $4
on eBay, you'd have to have a good reason to bother. Figure
7-3
shows the unit that
I purchased and used for this project.
