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參數(shù)資料
| 型號： | AND8067 |
| 廠商： | ON SEMICONDUCTOR |
| 英文描述： | NL27WZ04 Dual Gate Inverter Oscillator Increases the Brightness of LEDs While Reducing Power Consumption |
| 中文描述： | NL27WZ04雙門變頻振蕩器的提高，同時降低功耗的LED亮度 |
| 文件頁數(shù)： | 4/8頁 |
| 文件大?。?/td> | 62K |
| 代理商： | AND8067 |
AND8067/D
http://onsemi.com
4
Figure 8. “ON” Time Oscillator Subcircuit
U
1A
R
2
12 k
C
2
0.01
μ
F
V
4
V
1
V
2
Figure 9. “OFF” Time Oscillator Subcircuit
U
1B
R
1
12 k
C
1
0.1
μ
F
V
2
V
3
V
4
The equations are developed to predict the time it takes the
RC circuits to discharge to the threshold switching voltage
of the inverter. The threshold voltage of the inverters will be
assumed to be one–half the supply voltage, which is equal
to the average of the High–Level–Input Voltage (V
IH
) and
the Low–Level Input Voltage (V
IL
). The NL27WZ04
specifies V
IH
as 0.7
×
V
CC
(minimum) and V
IL
as 0.3
×
V
CC
(maximum). In addition, the initial voltage or the output
“High” voltage (V
OH
) of the inverter is assumed to be equal
to V
CC
. The actual V
OH
value is a function of the output
current and decreases as the output current increases.
The general equation for a RC circuit discharging to a
logic switching threshold voltage (V
th
) with an initial
voltage (V
i
) is as follows.
Vth
Vi
e
–t
R
C
These assumptions result in the equation listed below that
can be solved for time (t).
Assume
Vth
0.5
V
and
Vi
VOH
VCC
Then
t
RCln
Vth
VCC
RCln0.5
VCC
VCC
0.693
RC
LED “ON” Time
The LED’s “ON” time is controlled by the discharge time
t
1
at inverter U
1A
, as shown from the equation listed below.
t1
0.693
Substituting values into the equation yields:
R2C2
t1
0.693
(12000
)(0.01 F)
83.2 s
LED “OFF” Time
The LED’s “OFF” time is controlled by the discharge time
t
2
at inverter U
1B
, as shown from the equation listed below.
t2
0.693
Substituting the values into the equation yields:
R1C1
t2
0.693
(12000
)(0.1 F)
832 s
LED Oscillation Frequency
The time period (T) of the oscillator is equal to the sum of
the charge times in the first and second RC stages. Note the
propagation delay of the inverters can be ignored at the LED
circuit’s oscillation frequency of 1 kHz.
T
T
t1
83.2 s
t2
832 s
915 s
f
1
T
1
915 s
1.09 kHz
LED Duty Cycle
The duty cycle (DS) for the oscillator at V
1
is given by the
equation:
DSV1
t1
t2
100%
The duty cycle of the oscillator is proportional to the ratio
of the two time constants that are set by capacitors C
1
and C
2
.
The LED oscillator has a duty cycle of ten percent as shown
below.
DSV1
83.2 s
832 s
100%
10%
Experimental Results
The operating characteristics of the pulsed LED oscillator
circuit were compared to the DC circuit shown in Figure 10.
The DC circuit’s current limiting resistor R
5
was selected so
the current through the LED was equal to the average (RMS)
current of the oscillator circuit’s LED. A high efficiency
green GaP/GaP LED from Chicago Miniature Lamp (part
number CMD64531) was used to evaluate the circuits. The
resistor and capacitor values are listed below.
Component Values
LED Oscillator Circuit (Figure 1):
R
1
= R
2
= 12 k
R
3
= 39
R
4
= 1 M
C1 = 0.1
μ
F
C2 = 0.01
μ
F
DC LED Circuit (Figure 10):
R
5
= 680
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