| Simple circuit using the
LM3915. It does not differ in a lot of points from other applications with
same IC. The circuit is a Vu meter that will be connected in the exit of
power amplifier. It can be adapted in it's sensitivity so as to it
works with amplifiers that have different out power, we change the R1 value
of according to Table 1. The value that will be found if it does not
correspond in standard resistance price, it should selected the next
standard value or if you want the biggest precision it should you put
resistances in series or parallel so that you achieve the value. You can use
various types Leds round or square, so that you take the optical and
cosmetic result that you want. With switch S1 selects if the Vu meter works
as bar or dot. In the place ON [switch closed] the operation is bar and in
place OFF [switch open] the Led operation is Dot. In the Bar mode the power
consumption goes up, because all the Led's it can reach up to 150mA. For
amplifier with two channels obviously it's that it will be supposed made two
same circuits, one for each channel. The voltage circuit supply is +12Volts.
The source for this supply should become from the existing power
supply of power amplifier. Usually the power amplifiers work with supply
bigger than +12Volts that it needs the circuit. For this reason added one
stage of voltage +Vp attenuation in +12Volts. This becomes with the stage
that is found in the line and with the IC2. That is a regulated
stabilizer. The use of small heatsink is essential because the voltage
differences of input / output are big so that we have increase of high
levels of temperature. The use of R5 helps in the fall of voltage so that
goes down the voltage in the IC2 input in lower levels. The calculation of
this resistance value is simple using the Ohm law. The voltage in the IC2
input should it is bigger than +16Volts. For example if the voltage of power
amplifier is for example +50Volts it will be supposed we have voltage fall
50-16=34 Volts above in R5. For current with mean 50mA that it wants circuit
[can reach until 150mA] the price of R5= V/I=34V/0.05A=680 ohms 2W. Perhaps
it needs boost or decrease this value after tests. Because of the resistor
heat is it placed in some distance from PCB. The regulation process of
IC2 with the TR1 is a simple adjustment. If you have benefit possibility of
continuous voltage +12V from some point of power amplifier, leave out the
R5, the IC2 and the components that are found in the power line. |
