Dual Pwm Circuit; Figure 4.2 Recirculating Pwm; Figure 4.3 Non-Recirculating Pwm - Intelligent Motion Systems IM805 Operating Instructions Manual

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 accu-
rately 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 cur-
rent in the windings is contained
within the output 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 induc-
tance motors, but lacks response
because 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, espe-
cially in lower inductance motors (See Figure 4.3).
The IM2000's PWM utilizes the best features of both by combining recir-
culating and non-recirculating current control. On the rising edge of the sine/
DRIVE CURRENT
RECIRCULATION
Figure 4.3: Non-Recirculating PWM
DRIVE CURRENT
RECIRCULATION
Figure 4.2: Recirculating PWM
cosine waveform, the PWM will
always be in a recirculating mode.
This mode allows the driver to
run at peak efficiency while main-
taining 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 recirculating mode to increase
efficiency and reduce current
ripple.
IM805 Operating Instructions Revision R032306 17