Sample Application Circuit
Note : Input signal of approximately 110 mVrms causes D8 (0 dB display) to light.
Unit (resistance:
, capacitance: F)
For sample application circuit:
1.
The LB1412 consists of the following blocks.
.
Input amp 1 : Amplification of input signal, variable with external constants
.
Input amp 2 : Amplification of signal (fixed, double), detection of signal
.
Reference voltage : Reference voltage of comparator, constant-current drive of LED
.
Comparator : Comparison of input voltage
.
LED driver : LED drive, D1 to D7 : Constant-current drive
.
Peak hold circuit : Hold of highest-order point of high-order 5 points (D8 to D12)
.
Oscillator for peak hold reset : Peak hold circuit reset
2.
Description of constants of each block
2-1 R3, R4 (R11, R12)
The gain of amp 1 depends on R3, R4. Gain of amp 1 = R3/R4 times. The gain of amp 1 must not exceed 4 times
(12 dB).
R3+R4
6 100 k (C4 = 4.7 F)
2-2 C2, C3 (C5, C6)
C3 is for coupling amp 1 with amp 2 and its value is 1 F. C2 is for controlling the time to turn off LED.
2-3 R2 (R10)
The current of LEDs connected to D1 to D7 depends on R2. The current is stabilized to be approximately 17 mA at R2
=3k
and approximately 11 mA at R2 = 4.7 k.
2-4 R5 to R9 (R13 to R17)
The current of LEDs connected to D8 to D12 depends on these resistors. D8 to D12 pins are collectors of Darlington
transistors.
ID8 to D12 =
VCC –Vsat D8 to D12 –VFLED
R5 to 9
6
VCC – 3.5 V
R5 to 9
ID8 to D12 is approximately 4 mA at R5 to 9 = 2.2 k
R5 2.2 k
R6 2.2 k
R7 2.2 k
R8 2.2 k
R9 2.2 k
10
to
16
V
LB1412
No.1218-4/5