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參數(shù)資料
| 型號： | LM1893 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | LM1893/LM2893 Carrier-Current Transceiver |
| 中文描述： | LM1893/LM2893載波電流收發(fā)器 |
| 文件頁數(shù)： | 11/24頁 |
| 文件大小： | 576K |
| 代理商： | LM1893 |
Component Selection
(Continued)
power capability than standard avalanche diodes rated for
equal DC dissipation. Metal oxide varistors have not proven
useful because of their inferior clamping coefficient and are
not recommended. Specifications for an example minimum
diode are given in Figure 13.
Breakdown Voltage
44–49V
@
1 mA
1
m
A
@
40V
300 pF
@
BV
64.5V
@
7.8A
Maximum Leakage
Capacitance
Maximum Clamp Voltage
Peak Non-Repetitive Pulse Power
10 kW for 1
m
s
(REA Standard Exponential Pulse)
Surge Current
70A for 1/120s
FIGURE 13. Key specifications for a recommended
transient suppressor Z
T
available from General
Semiconductor, 2001 West Tenth Place, Tempe, AZ
85281, 602–968-3101, part no. SA40A
R
T
R
T
acts as a voltage divider with Z
T
, absorbing transient
energy that attempts to pull the Carrier Input pin above 44V.
Make the resistor a carbon composition 1/4W. When exper-
iments discharging C
C
charged to the peak-to-peak 620V
AC thru a 1
X
power line were carried out, film resistors blew
open-circuit.
D
T
This Schottky diode is placed in parallel with the CCT chip’s
substrate diode to pass the majority of the current drawn
from ground when the Carrier Input or Carrier Output is
pulled below ground by a larger-than-twice-the supply-swing
on the tank. Note that Z
T
is in parallel with the substrate
diode, but is ineffective due to its high forward voltage drop
and high diffusion capacitance caused by its low forward
speed. Tests proved that a 1N5818 kept a receive-path
functional with a 20X boost transmitter with a 7:1 transform-
er attempted to swing the receiver’s Carrier I/O to
g
100V
(300 mA peak ground current in the receiver). Without D
T
,
the receiver momentarily stops functioning at a 100 times
lower ground current.
This diode is not needed if the Carrier I/O never swings
below ground. If your CCT systems all run on the same
regulated voltage with all matched transformers and turns
ratios, it is not needed. Otherwise, it is.
THE RECEIVER
The receiver and transmitter share components C
C
, T
1
, C
Q
,
R
T
, Z
T
, C
O
, R
O
, and peripheral supply and bias components
that are not in need of change for RX mode operation. Val-
ues for the balance of the components are now found.
Line-Frequency Rejection
To use the ultimate sensitivity of the device, fully 110 dB of
115 V, 60 Hz attenuation is required between the line and
the limiter amplifier output. Using the circuit topology ofFig-
ure 4, the combined attenuation of the C
C
/T
1
highpass, the
tuned transformer, and the bandpass filter attenuation of
the limiter amplifier give far more line rejection than the
above-stated minimum. However, if some other CCT line
coupling circuit is used, line rejection will become important
to the system designer.
Receiver input power supply rejection (PSRR) and common-
mode rejection (CMRR) are one-in-the-same using the sup-
ply-referenced signal input of Figure 4. Ripple swings both
differential inputs of the Norton amp. equally, while the sin-
gle-ended input signal swings only the positive input. Overall
PSRR consists of the input CMRR (set by the input stage
component matching) and the ripple-frequency attenuation
of the input amplifier bandpass response that passes carrier
frequency but stops low frequencies. A typical 1% resistor
and 1 mV n-p-n mirror offsets give 26 dB of attenuation, the
bandpass gives 54 dB 120 Hz attenuation, for an overall 80
dB PSRR to allow tens of volts of ripple before impacting
ultimate sensitivity.
C
C
A value was chosen earlier. Knowing T
1
’s secondary induc-
tance allows a check of LC line attenuation usingFigure 14.
C
L
The Norton input limiter amplifier has a bandpass filter for
enhanced receiver selectivity, noise immunity, and line fre-
quency rejection. The nominal response curve for F
O
e
50
kHz is shown inFigure 15. The 300 kHz pole is fixed. The 50
kHz pole is set by C
L
’s value. After C
L
is found, the resulting
line frequency attenuation is found for the bandpass filter.
Use Figure 15 to find a C
L
value given for F
O
. The approxi-
mate line frequency attenuation of the bandpass filter may
then be found inFigure 16.Figure 15 returns a value for C
L
33% larger than nominal, giving a low frequency pole 33%
low to allow for component tolerances.
TL/H/6750–15
FIGURE 14. The 60 Hz line rejection of the highpass
filter made up of C
C
and T
1
’s line-side winding
(neglecting capacitive coupling)
TL/H/6750–16
TL/H/6750–17
FIGURE 15. Given F
O
, C
L
is found. Also shown is the
input amplifier’s small signal amplitude response
11
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| LM1893N | RES 250K-OHM 1% 0.125W THICK-FILM SMD-0805 5K/REEL-7IN-PA |
| LM2893M | LM1893/LM2893 Carrier-Current Transceiver |
| LM2893N | LM1893/LM2893 Carrier-Current Transceiver |
| LM2895 | AUDIO POWE RAMPLIFIER |
| LM1895 | AUDIO POWE RAMPLIFIER |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM1893 WAF | 制造商:Texas Instruments 功能描述: |
| LM1893N | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:LM1893/LM2893 Carrier-Current Transceiver |
| LM1893N/A+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Carrier/Multi-Wire Interface |
| LM1893N/B+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Carrier/Multi-Wire Interface |
| LM1894 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dynamic Noise Reduction System DNR |
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