Re: Chopper circuit

Hi Wayne,

More than happy to help.

The Vf and the reverse recovery time (trr) of the diodes does make a
difference. We have tested enough manufacturers over the years to
prove this. If you can get a good priced one with a Vf of 0.5 to 1V
and trr of <100nS then you will be saving energy (in these
environmentally conscious times !!). In our 3.5A drive we use a
General Instruments diode rated at Vf 0.95V at 5A and trr of 35ns
max, part # EGP50B.

24V PSU is great, but may limit the top speed of your motor. If you
want higher speeds go for your 36V with a max peak of 40V, and the
L298's should remain in one piece ;-)

0.1uF ceramics are good across each L298, and again across the L297.
Keep signal tracks/components short around the L297 (Osc; Vref;
Isense etc). Use one low ESR electrolytic (100 to 470uF) across
motor power circuit (or 2 smaller ones across each L298..... depends
on your PCB layout).

As L298's are bipolar transistors with a high Vce Sat they need a lot
more heatsinking than their mosfet counterpart (L6203). For our 3.5A
drive a 2 deg C (3.6 F) per Watt heatsink keeps everything within
spec with normal convection cooling (use a fan if you have a good
cheap source as it should extend the MTBF of the silicon).

All the best with your project.

Paul