IM483H/IM805H Rev. R032206
20
21
IM483H/IM805H Rev. R032206
D u a l P W M C i r c u i t
The IM2000 contains a unique dual PWM circuit that efficiently and accurately
regulates the current in the windings of a two phase stepping motor. The internal
PWM accomplishes this by using an alternating recirculating/non-recirculating
mode to control the current.
R e c i r c u l a t i n g
In a recirculating PWM, the current in the windings is contained within the out-
put bridge while the PWM is in its OFF state. (After the set current is reached.)
This method of controlling the current is efficient when using low inductance
motors, but lacks response be-
cause of its inability to remove
current from the windings on
the downward cycle of the sine/
cosine wave. (See figure 4.1)
N o n - R e c i r c u l a t i n g
In a non-recirculating PWM,
the current flows up through the
bridge and back to the supply
in the OFF phase of the cycle.
This method of controlling
current allows for much better
response but reduces efficiency
and increases current ripple,
especially in lower inductance
motors. (See Figure 4.3)
The IM2000’s PWM utilizes the best fea-
tures of both by combining recirculating
and non-recirculating current control. On
the rising edge of the sine/cosine waveform,
the PWM will always be in a recirculat-
ing mode. This mode allows the driver to
run at peak efficiency while maintaining
minimum current ripple even with low
inductance motors. On the downward
cycle of the sine/cosine waveform, the
PWM operates in a two part cycle. In the
first part of its cycle, the PWM is in a non-
recirculating mode to pull current from the
motor windings. In the second part of the
cycle the PWM reverts back to recirculat-
ing mode to increase efficiency and reduce
current ripple.
The IM2000 will automatically change
Figure 4.2: Recirculating PWM
DRIVE CURRENT
RECIRCULATION
Figure 4.3: Non- Recirculating PWM
DRIVE CURRENT
RECIRCULATION
