Dual Power Supply Board for Audio power amplifier

A good power supply determines the quality of an audio power amplifier output. GEOES INDIA makes good quality Dual Power Supply boards especially made for the audio power amplifiers. The board uses high quality capacitors as filters. The board's maximum output voltage limited is according to the voltage specified on the capacitor. So it's very important to choose the right power supply for your amplifier needs. 

Important information to take care of the amplifier power supply selection

  1) Transformer Selection

Suppose the amplifier demands a +/- 35VDC 5A power supply for its proper functioning, then the transformer should have the capability to handle this power requirement. Here in this scenario a +/- 35VDC is the maximum allowed DC voltage for the specific board, this doesn't mean that we have to choose a 35-0-35 transformer. Normally the voltage specified for the transformer is the RMS (Root mean square) value. So here a 35-0-35 transformer will have a  49.5 (35x √2) at its peak.

       This peak voltage is going through a full bridge rectifier for rectification. In this stage, each cycle will go through 2 diodes during the forward biasing. Suppose we consider a 0.7V as the theoretical diode voltage drop, then a total of 1.4V drop will occur in each cycle. So the effective RMS voltage at rectifier output will be around 35-1.4 = 33.6V RMS. And its peak voltage will be around 47.5V (33.6x√2) .

      After the filtration by the capacitors, the output DC voltage will climb to this peak voltage itself, ie,  47.5VDC.  In general, for a +/- 35VDC required amplifier board, if you selected a 35-0-35V AC transformer, then approx. +/-47.5V DC will reach the amplifier, which probably may damage the amplifier board. 

 So how much Voltage should we select, obtain +/-35VDC out?

a) Required Out ie after Filter: Vout :  +/-35VDC

b) R.M.S value : 35/√2 =  24.75V

c) Consider a 1.4V diode drop, in the theoretical case, But in the reality, it differs according to the current flowing through it. In this case, we are using a 6A10 diode, which will support the 6A average current flow. The Datasheet says that at 6A current flow, the forward drop voltage can be in the range of 0.9V for a single diode, then a total 1.8V drop. So transformer output voltage should be as follows

In case of 1.4V drop,   24.75V + 1.4 = 26.15V   ~= 26V

In case of 1.8V drop,  24.75V + 1.8 =  26.55V ~= 27V

So a 27-0-27 transformer is required to obtain this voltage rating. The current rating can be determined according to the amplifier demands. The important thing to be considered is that transformer's quality and regulation are also heavily affected to achieve these parameters. Which is determined by the Core materials, core cross-sectional area, and winding wire gauges. 

      For better filtering and current requirements, good-grade capacitors are required. Those should meet the amplifier's sudden demands. In this board, we ensure this by using high-quality capacitors. Each supply rail is connected parallel with 2x 4700uF, ie 9400uF per rail. Which is good enough to meet the normal medium-range amplifiers.

         Another important thing to consider is the voltage rating of the capacitors. Even though the good quality capacitors will withstand up to the specified voltage ratings, while considering the long-running life of the components, it's always recommended to consider some headroom, for accommodating any extreme situations. It's better to keep at least 10% headroom. For eg: for a 50V rating cap, limit the requirement up to 45V   

So consider all these cases, while selecting the correct power supply for your amplifier.