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L292

SWITCH-MODE DRIVER FOR DC MOTORS

STMicroelectronics 

Figure 7. Open Loop Frequency Response

L292

CLOSED-LOOP SYSTEM STEP RESPONSE

a) Small - signals analysis.

The transfer function (3) can be written as follows:

1 + ------s-------

I--M---

VI

(

s

)

=

0----.-0----4---4--

Rs

--------------2----ξ----ω----o-----

1 + 2----ξ----s----+-----s---2-

(7)

ωo ωo2

where

wo =

-------G-----m----o---R-----s---

R4 C RF CF

is

the

cutoff

frequency

ξ = ----------------R-----4---C-------------- is the dumping factor

4 RF CF Gm o Rs

By choosing the ξ value, it is possible to determine the system response to an input step signal.

Examples :

1) ξ = 1 from which t

IM (t )

=

0----.--0---4----4-





RS





–---------t---------

1–e

2

RF

CF





1

+

4----R-----Ft---C-----F-



⋅ Vi



(where Vi is the amplitude of the input step).

2) ξ = ---1--- from which

IM (t )

=

2

0----.-0----4---4--

Rs









1

–

cos

---------t---------

2RFCF

e – -2---R-----Ft---C-----F- 



V

i

9/13

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