Projecta IM2000 Instruções de Operação descarregar pdf (Página 18)

The IM2000 outputs both sine and cosine data simultaneously when applying a

step clock input. Dual internal look-up tables are used to output a unique

position for every step clock input to enhance system performance.

Dual PWM Circuit

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.

Recirculating

In a recirculating PWM, the

current 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 inductance 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).

Non-Recirculating

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

features of both by combining recirculat-

ing and non-recirculating current control.

On the rising edge of the sine/cosine

waveform, the PWM will always be in a

recirculating mode. This mode allows the

driver to run at peak efficiency while

maintaining minimum current ripple even

Figure 4.3: Non-Recirculating PWM

DRIVE CURRENT

RECIRCULATION

Figure 4.2: Recirculating PWM

DRIVE CURRENT

RECIRCULATION

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 76 77

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