The main objective of a BTL configuration is to enable a two way operation of the load which in turn helps to increase a two fold increase in the efficiency level of the system. It's equivalent to a full bridge network which we normally find in inverters.
Image Courtsey: Elektor Electronics
The complete circuit diagram for the proposed BTL 120 watt amplifier circuit using two TDA 2030 ICs can be seen in the above diagram.
IC1 and IC2 are the two TDA2030 ICs rigged in a bridged tied load configuration which means the these two IC s now conduct in tandem in response to the high and low amplitudes of the input frequency and drive the loudspeaker in a powerful push pull mode.
For example when IC1 output may be delivering a high output to the speakers, IC2 simultaneously would be delivering a low output and vice versa enabling the required push pull action on the loudspeaker. This means the loudspeaker would be alternately operated with maximum positive and negative supply levels, causing the loudspeaker to work with double efficiency level compared to the normal amplifiers which are not BTL based.
The BJTs T1---T4 are included to boost the current level of the amplifier upto the specified 120 watt RMS, since the IC1, IC2 alone wouldn't be able to do this.
The NPN/PNP output BJTs also complement the BTL topology and help the ICs to achieve the specified amount of power on the loudspeakers.
The various resistors and capacitors around the speaker are introduced to suppress and filter the final outcome on the speaker, and to produce a clean and distortion free audio on the speaker.
Dual Power Supply for the Amplifier
The power supply for this 120 watt BTL amplifier using TDA2030 ICs is derived from a 12-0-12V / 7 amp transformer. whose output is rectified using a bridge rectifier and filtered using the indicated capacitor C8---C11.
The power supply produces a dual +/- 20V / 7 amp output which is mandatorily required for most BTL based amplifier circuits.