One of the problems of directly connecting LEDs to the output of an amplifier is the low voltage available. In fact, given that P = V2 / I, we see that with a 4 ohm load, the minimum power that results in 1.6 V to light a red LED is approximately 640 mW. And even if we have power sufficient, more LEDs need more power.
An interesting way to operate LEDs with small power without stealing it from the amplifier is with the help of a transformer. With the circuit we have described we can drive up to 10 LEDs with 5 to 100 W amplifiers, no problem. In figure 1 we have the circuit for that.
The resistor Rx depends on the power of the amplifier with which the system will work, according to the following table:
The transformer has a 5 to 9 V secondary with a current of 100 to 300 mA and the LEDs must be the same, but can be any color.
Material list
LED1, LED2, LED3 - Common LED of any color
D1 - 1N4004 - Silicon Diode
Rx - View Text
R1 - 2.2k ohm x 1/8 W - resistor - red, red, red
Miscellaneous: wire, solder, terminal bridge, screw bridge, mounting box, etc.
| Power
|
|
| Rx | |
| 5 to 25 W
|
|
| 10 ohms x 1 W | |
| 25 to 50 W
|
|
| 22 ohms x 2 W | |
| 50 to 100 W
|
|
| 47 ohms x 2 W |
