POWER AMPLIFIER WITH IC LM4780
(16 January 2006)
Croatian version
This IC is, in fact, a double LM3886 in one package and its properties are similar to those of the LM3886. The advantages of the LM4780 are its compact design and a better match between two amplifiers, which is of special importance in parallel and bridge circuits. The amplifier’s schematic is shown in Figure 1.
Figure 1
Parts list:
| R1, 2 | 1 kΩ |
| R3, 4 | 47 kΩ |
| R5, 6, 8' | 4k7 |
| R7, 8 | 100 kΩ |
| R9, 10 | 0.1 Ω/3-5W |
| R11 | 10 kΩ |
| C1, C2 | 2200uF/50V |
| C3, C4 | 220nF/50V |
| IC | LM4780 |
Our design of the LM4780 incorporates jumpers (CON 4) whereby any of the three available modes of operation can be selected quickly and easily: stereo, parallel-mono and bridge-mono.
In the stereo mode, the jumpers should bridge pins 5-6, 9-10 and 11-12. This will set both amplifiers in the same mode of operation, resulting in two non-inverting amplifiers whose gain is equal to 1+R7/R5 or 1+R8/R6, respectively. The input of the right amplifier will thus be connected to the right input pin (CON 2-3) whereas the speakers should be connected to outputs OUT L and OUT R.
In the parallel-mono mode, the jumpers should bridge pins 3-4, 9-10 and 11-12. Again, this will set both amplifiers in the same mode of operation, giving two non-inverting amplifiers whose gain is equal to 1+R7/R5 or 1+R8/R6, respectively. However, the input of the right amplifier will now be connected to the left input pin (CON 2-1). The speaker should be connected to output OUT L whereas outputs OUT L and OUT R should be paralleled.
Finally, in the bridge-mono mode, the jumpers should bridge pins 1-2 and 7-8. This will set the right amplifier in the inverting mode of operation, with the gain equal to (R8 + R8 ') / R6. The speaker should be connected between outputs OUT L and OUT R.
The choice of the power transformer and heat sinks will depend on the desired power and mode of operation. The comments given in the LM3886 article regarding the power transformer and cooling also apply here.
Figure 2 shows the bare LM4780 printed circuit board.
Figure 2
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