12V BATTERY LEVEL INDICATOR CIRCUIT

This battery level indicator offers (5)
LEDs that light up progressively as the
voltage increases:

• Red: Power Connected (0%)
  
• Yellow: Greater than 10.5V (25%)
  
• Green 1: Greater than 11.5V (50%)
  
• Green 2: Greater than 12.5V (75%)
  

Green 3: Greater than 13.5V (100%)
Of course, you may select your own
colors if desired.
12 Volts Battery Level Indicator
Circuit Schematic

Operation of the battery level
indicator
D1 is the voltage reference zener. Tied
to this is a string of divider resistors
(R2-6) that set the various fixed
voltage levels. R7 & 8 form a voltage
divider to that reduces the battery
voltage by a factor of 3. U1 is an
LM339 quad comparator that
compares the various voltages from
the two dividers. The comparator
sections have open collector outputs
that simply function as switches to
operate the LEDs. D7 protects against
reverse battery connection.
The LEDs are biased to operate at
about 4mA which is quite bright if
modern LEDs are used. This current
can be adjusted simply by varying the
series resistors (R9 through R13). The
overall current drain as shown is
about 25mA which tends to be
wasteful for continuous operation. For
energy conservation, connect to
battery via a pushbutton (Push to
Test).
Printed Circuit Board
I did a www.expresspcb.com SMT
layout using 0805 size components,
1N753 zener and SOIC-14 IC. D7 is in
a SOT-23 package. These components
are about as small as I like to work
with. The layout has not yet been
carefully checked or built. Note that
surprises abound when constructing
prototypes.
The circuit board measures only 0.5” x
1.5”.
download the PCB layout
More recently, I located an
inexpensive SOT-23 zener with a 2%
voltage tolerance—this has not yet
been incorporated.
I have had good results with 0805 size
LEDs purchased from China on eBay.
They are both inexpensive and
BRIGHT!

The 12v battery level indicator unit in
the photo has no reverse polarity
diode and R2 is the calibration
potentiometer.
Source: Elektro symetrics

Class-D Audio Amplifiers with Wide Supply Range and High Switching Rates

Texas Instruments has introduced
three analog-input class-D stereo
amplifiers for use in soundbars, after-
market automotive solutions, portable
audio docks, and LCD televisions. The
TPA3116D2, TPA3118D2 and
TPA3130D2 feature the industry's
highest programmable switching rate
and widest power supply range,
enabling audio output that is both
high quality and highly efficient. The
devices are pin-to-pin and software
compatible and can support a single-
layer printed circuit board (PCB),
enabling cost savings by allowing
designers to reuse a single layout for
multiple designs.
Key features and benefits of the
TPA3116D2, TPA3118D2 and
TPA3130D2:

• Supply range of 4.5 V to 26 V
  enables simultaneous operation of
  line power and battery power on
  the same board for longer battery
  life in soundbars and portable
  audio docks.
  
• Thermally efficient FETs allow 30 W
  x 2 operation without the need for
  a heat sink, or 50 W x 2 with a heat
  sink (TPA3116D2 only).
  
• Programmable switching rates of
  400 KHz to 1.2 MHz allow inductor
  filter-free operation and
  interference avoidance for clear
  audio with no distortions.
  
• Closed-loop design provides
  excellent power supply rejection
  ratio (PSRR) and slower edge rates
  for waveform switching to improve
  electromagnetic interference (EMI)
  performance.
  
• RDS(on) of 120 milliohms at 30 W x
  2 improves efficiency by decreasing
  resistance during operation.

Source: Elektro Projects