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參數(shù)資料
| 型號： | L497B |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | HALL EFFECT PICKUP IGNITION CONTROLLER |
| 中文描述： | 霍爾效應(yīng)皮卡點火控制器 |
| 文件頁數(shù)： | 6/11頁 |
| 文件大?。?/td> | 106K |
| 代理商： | L497B |
DWELL ANGLECONTROL
The dwell angle control circuit calculates the con-
ductiontime D forthe outputtransistorinrelationto
the speed of rotation, to the supply voltage and to
the characteristicsof the coil.
On the negativeedge of the Hall-effectinputsignal
thecapacitorC
W
beginsdischargingwithaconstant
currentl
11D
. Whenthesetpeakvalueof thecoilcur-
rent is reached, this capacitor charges with a con-
stant currentI
11C
= 13.3x I
11D
, andthe coil current
is keptconstantby desaturationof the drivenstage
and the externaldarlington.
The capacitor C
T
starts charging on the posi-
tive.edge of the Hall-effect input signal with a con-
stant current I
10C
. The dwell angle, and conse-
quentlythestartingpointof thecoilcurrent conduc-
tion,isdecidedbythecomparisonbetweenV
10
and
V
11
.
A positivehysteresis is added to the dwell compa-
ratorto avoidspuriouseffectsandC
T
is rapidlydis-
charged on the negative edge of Hall-effects input
signal.
In thisway the average voltage on C
W
increasesif
the motor speed decreasesand viceversa in order
tomaintainconstanttheratiot
Tatanymotorspeed.
t
d
T
is kept constant(and notD
T
= cost) to control
the powerdissipationand to have sufficienttime to
avoidlow energysparks duringacceleration.
DESATURATIONTIMESIN STATIC
CONDITIONS
In staticconditionsandifC
T
=C
W
asrecommended
andif thevaluesoftheapplicationcircuitoffig.4are
used.
t
d
T
=
1
+
I
11C
/ I
11D
1
DESATURATIONTIMESIN LOWAND HIGH
FREQUENCY OPERATION
Dueto theupperlimit of thevoltagerangeofpin11,
if the components of fig.4 are used, below 10 Hz
(300 RPM for a 4 cylinder engine) the OFF time
reachesits maximumvalue(about50 ms)andthen
the circuit graduallylosescontrol ofthe dwellangle
becauseD = T – 50 ms.
Over200Hz(6000RPMfora 4cylinderengine)the
availabletimefortheconductionislessthan3.5ms.
Iftheusedcoilis6 mH,6A,theOFFtimeis reduced
to zeroandthecircuit losesthe dwellanglecontrol.
TRANSIENT RESPONSE
The ignition system must deliver constant energy
evenduringtheconditionofaccelerationanddecel-
erationofthemotorbelow80Hz/s.Theseconditions
can be simulated by means of a signal gene-rator
with a linearly modulated frequency between 1 Hz
and200Hz (thiscorrespondsto achangebetween
30 and 6000 RPM fora 4 cylinders engine).
CURRENT LIMIT
Thecurrentin thecoilismonitoredbymeasuringthe
I
sense
current flowing in the sensing resistor R
s
on
theemitterof theexternaldarlington.I
sense
isgiven
by :
I
sense
= I
coil
+ I
14
WhenthevoltagedropacrossRsreachestheinter-
nalcomparatorthresholdvaluethefeedbackloopis
activatedandI
sense
keptconstant(fig.1)forcing the
externaldarlingtonin the active region. In this con-
dition:
I
sense
= I
coil
WhenaprecisepeakcoilcurrentisrequiredR
s
must
be trimmedor anauxiliaryresistordivider(R
10
, R
11
)
added:
Icpeak
(
A
) =
0.320
RS
)
R10
R11
+
1
SLOWRECOVERYCONTROL (fig. 2)
If I
sense
hasnot reached94 % of the nominal value
justbeforethenegativeedge oftheHall-effectinput
signal, the capacitor C
src
and C
W
are quickly dis-
chargedaslongasthepick-upsignalis ”low”.Atthe
next positive transition of the input signal the load
currentstartsimmediately,producingthemaximum
achievable T
desat
; then the voltage on C
SRC
in-
creaseslinearlyuntilthestandbyis reached.During
thisrecoverytimetheC
SRC
voltageis convertedinto
a current which, substrated from the chargingcur-
rentof thedwellcapacitor,producesa T
desat
modu-
lation. This means thatthe T
desat
decreasesslowly
untilitsvaluereaches,afteratimeT
SRC
,thenominal
7% value.
The time T
SRC
is givenby:
T
rsc
= 12.9R7C
SRC
(ms)
whereR
7
isthebiasingresistoratpin12(inK
)and
C
src
thecapacitorat pin8 (in
μ
F).
L497
6/11
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