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參數(shù)資料
| 型號(hào)： | GFW |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | Push-Pull Four Channel Drivers(推挽式四通道驅(qū)動(dòng)器) |
| 中文描述： | 推挽式四通道驅(qū)動(dòng)器（推挽式四通道驅(qū)動(dòng)器） |
| 文件頁數(shù)： | 6/8頁 |
| 文件大小： | 101K |
| 代理商： | GFW |
CHOPPER CIRCUIT OFFERS MORE EN-
HANCEMENTS
Addingachoppercircuittomaintainaconstant-ave-
rage phasecurrent improves performanceand effi-
ciency.Fig.3 shownasimpleconstant-currentdrive
that employs a dual bridge,dual comparatorand a
few passive components. This circuit requires an
L293E,becausethisdual-bridgeICoffersaccessto
the loweremitterconnections,thuslettingyouinsert
current-sensingresistors.
Operationof this fixed-ripple chopperdrive is strai-
ghtforward. When the
μ
C or translator activates a
bridge,theincreasingloadcurrentraisesthevoltage
across the sensing resistor until it equals the com-
parator’s reference voltage. The comparator then
switches, clamping the translator signals through
the diodesto deactivatethe bridge. As the current
decays,the voltage across thesensing resistor de-
creases untilit equals thecomparator’slower thre-
shold. The comparatorswitches again,allowingthe
μ
C or translatorto activate a bridgeand restart the
cycle.Aslongasthetranslatordrivesthebridge,this
sequence repeats to provide a constant-average
phasecurrent with fixed ripple.
V
ref
adjuststhelowercurrent limit, while the compa-
rator’s hysteresis sets the ripple, and hence the
peakcurrent. Althoughadividerestablishestheva-
lueof V
ref
inthiscase,youcanemploythedual-sup-
plydesignapproachandswitchV
ref
toa lower value
whenthemotoris idle.In addition,useofaD/A con-
verter establishes V
ref
for micro-stepping applica-
tions. This drive circuit, with its fixed-ripple current
characteristics,is well suited for such service.
FIXED-FREQUENCY CHOPPER IS MOTOR
INDEPENDENT
Fig. 3’s drive has some disadvantages. First, the
chopper frequency dependson motor characteris-
tics, and these parametersvary from unitto unit. In
addition, it’s impossible to synchronize the chop-
pers,andthis shortcomingcancausetroubleonthe
groundplane.
Usinga flip flop/comparatorarrangement (fig.4) to
developa fixed-frequencychopperovercomesthe-
se problems. In thiscircuit, the NE555 timer gene-
rates negative pulses that reset the flip flops to
enablethephase-controlsignalsfromthetranslator.
If these signals are set to energizea winding, the
Figure 4 :
This Fixed-frequencyConstant-currentChopper Driver Enablesthe Synchronizationof Several
Drives, thus Minimizing PotentialGround-planeProblems.
APPLICATION NOTE
6/8
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