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參數(shù)資料
| 型號： | LT1932ES6#TRM |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.78 A SWITCHING REGULATOR, 1600 kHz SWITCHING FREQ-MAX, PDSO6 |
| 封裝： | PLASTIC, SOT-23, 6 PIN |
| 文件頁數(shù)： | 15/16頁 |
| 文件大?。?/td> | 235K |
| 代理商： | LT1932ES6#TRM |
8
LT1932
Dimming Using a Filtered PWM Signal
While the direct PWM method provides the widest dim-
ming range and the purest white light output, it causes the
LT1932 to enter into Burst Mode
TM operation. This opera-
tion may be undesirable for some systems, as it may
reflect some noise to the input source at the PWM fre-
quency. The solution is to filter the control signal by adding
a 10k resistor and a 0.1
F capacitor as shown in Figure 6,
converting the PWM to a DC level before it reaches the
RSET pin. The 10k resistor minimizes the capacitance seen
by the RSET pin.
Dimming Using a Logic Signal
For applications that need to adjust the LED brightness in
discrete steps, a logic signal can be used as shown in
Figure 6. RMIN sets the minimum LED current value (when
the NMOS is off):
R
V
I
MIN
LED MIN
=
225
01
.
()
RINCR sets how much the LED current is increased when
the NMOS is turned on:
R
V
I
INCR
LED INCREASE
=
225
01
.
()
APPLICATIO S I FOR ATIO
WU
UU
Figure 6. Five Methods of LED Dimming
Dimming Using a DC Voltage
For some applications, the preferred method of brightness
control uses a variable DC voltage to adjust the LED
current. As the DC voltage is increased, current flows
through RADJ into RSET, reducing the current flowing out
of the RSET pin, thus reducing the LED current. Choose the
RADJ value as shown below where VMAX is the maximum
DC control voltage, ILED(MAX) is the current programmed
by RSET, and ILED(MIN) is the minimum value of ILED (when
the DC control voltage is at VMAX).
R
VV
II
ADJ
MAX
LED MAX
LED MIN
=
225
01
–.
–
()
(
)
Regulating LED Current when VIN > VOUT
The LT1932 contains special circuitry that enables it to
regulate the LED current even when the input voltage is
higher than the output voltage. When VIN is less than VOUT,
the internal NPN LED switch (transistor Q2 in Figure 1) is
saturated to provide a lower power loss. When VIN is
greater than VOUT, the NPN LED switch comes out of
saturation to keep the LED current in regulation.
LT1932
RSET
VDC
RSET
4
1932 F06
RADJ
LT1932
RSET
PWM
LT1932
PWM
FILTERED PWM
DC VOLTAGE
LOGIC
RSET
PWM
RSET
4
RPWM
LT1932
PWM
SHDN
PWM
5
RSET
0.1
F
4
10k
RPWM
LT1932
RSET
RMIN
LOGIC
SIGNAL
4
RINCR
Burst Mode is a trademark of Linear Technology Corporation.
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相關(guān)代理商/技術(shù)參數(shù) |
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