Audio Power Indicator with 6 LED Bars

Overview

The circuit has been designed for loudspeakers to provide a monitoring scheme of audio power being supplied which will determine that any setup will not be required without the presence of a power supply.

Part List

Terminology

• BZX79C2V7 – a 500mW hermetically sealed glass Zener voltage regulator with features such as cathode indicated by polarity band, solder hot lead finish, RoHS compliant, all external surfaces are corrosion resistant and leads are readily solderable, compression bonded construction, through-hole device type mounting, DO-35 Jedec package, and 2V to 75V Zener voltage range
• Zener Diode – a special kind of diode that permits the flow of current in just one or forward direction as a normal diode, but will also allow in the reverse direction if the voltage is above or larger than a certain value of the breakdown voltage

Circuit Explanation

The illumination of six LEDs will serves as the means of indicating the instantaneous power output being delivered to a loudspeaker. The circuit may be connected to any loudspeaker output of an audio amplifier. The illumination of the LEDs takes place one after another due to the little by little increase in the values of the voltage. This will provide a visual notion of luminous bars that forms a column while showing the increase and decrease in height in accordance to the output level of the signal.

The 400 V diode D1 is responsible for the rectification of the input signal during the initial stage. The rectified signal is then fed to the six different voltage dividers that are located in each LED. The instantaneous power drilled by the whole loudspeaker cabinet is directly represented in the power display of the LEDs as they start to illuminate. The representation of the six levels of power outputs are displayed by the LEDs in the range of 2W, 5W, 10W, 20W, 40W, and 80W. When the respective LED illuminates at full brightness, each nominal power level indication into 8 Ohms load is reached.

In the event that a 4 Ohms load is driven, the output power indicated by each LED will be doubled. By reducing the number of LEDs and their corresponding voltage regulators, the circuit may be utilized for less powerful amplifiers. Stereo amplifiers would require two identical circuits. For the LEDs to be compacted in bars or columns, a rectangular shape LED will be more suitable although the dimension could be in any form.

Application

The power indicator used for loudspeaker does not only concentrate on the power being supplied. It is also a tool used to verify the integrity of the floor jacks, consoles, or power cabling to be used. When used with commercial and industrial music system, it can be found along with the front panel controls. In some designs, it can be mounted on the grille and can be turned OFF as required with a rear panel switch or it can be connected as rear facing LEDs.

Source : redcircuits.com/Page102.htm