參數(shù)資料
型號(hào)： KA3902
廠商： FAIRCHILD SEMICONDUCTOR CORP
元件分類： 運(yùn)動(dòng)控制電子
英文描述： DC FAN Motor Controller
中文描述： BRUSH DC MOTOR CONTROLLER, 0.8 A, PDIP14
封裝： 0.300 INCH, DIP-14
文件頁(yè)數(shù)： 9/14頁(yè)
文件大?。?/td> 127K
代理商： KA3902
FAN8902(KA3902)
9
In the steady state, the terminal voltage on a motor is consisted of a back EMF and the voltage drop on the armarture resistors.
When the motor happens to be stalled, the back EMF becomes zero, and the motor current (I
M
) is quickly increased until a
maximum values.
Therefore the duty of the pin #12 output becomes lower because of the increase of the sense voltage (V
RS
). Also it makes the
voltage (V
La
) be lowered, then it makes the duty become lower again.
This mechanism makes the motor current hold very low value in the stalled motor state.
The voltage on pin #14 (V
La
) ia calculated as follows:
We can choose the ratio of the resistors, R2 and R3, as follows:
- Applied the rated voltage on motor, and then measured the current IRAT
- Matched the maximum command current, V
CMD,MAX
to I
RAT
.
V
CMD,MAX
= V
La,MAX
= R
S
×
I
RAT
×
5
×
5
for example, if R
S
= 10m
and I
RAT
= 20[A] at V
BAT
= 13[V],
V
CMD,MAX
= V
La,MAX
= 10m
×
20
×
25 = 5V
- V
La,MAX
= 5V = V
BAT
×
1
×
R3 / (R2 + R3)
Ratio = R3 / (R2 + R3) = V
CMD,MAX
/ V
BAT
= 5 / 13
Therefore, R2 : R3 = 8 : 5
The buffer OP-amp selects the lower command between V
CMD
and V
La
so as to limit the stalled motor current to very low in
the above figure. Because of much larger V
La
than V
CMD
, the motor operating point stays at A. But the point gradually moves
toward B’ and then B” through the curve from the instance of stall as the below figure.
V
La
V
BAT
D
×
+
R2
R3
---------------------
×
=
Assumed the saturation voltage of Q1 is zero.
VLa curve
×
(1 / R)
The voltage drop
on the amarture resistance
V
LA
V
CMD
I
RAT
V
MOTOR,STALL
V
BAT
V
LA
V
LA
V
MOTOR
Operating curve
A
B
B
’
B
”
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