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Utilise audio amps for voltage splitting (Part 3)

Posted: 16 Apr 2014 ?? ?Print Version ?Bookmark and Share

Keywords:voltage splitters? power audio amplifiers? PAA? op amps? transistors?

The reference input voltage of around 1.2V is obtained from an LM385-1.2. In that case the internal gain of the LM386 is 20; the minimal gain of that IC is around nine. The adjustment of the output voltage is made with the trimmer potentiometer P1. The jumpers J1 and J2 are used to apply the reference voltage to the inverting or non-inverting input of the PAA. The resistors R3, R4 and R5 are not obligatory, but improve the parameters of the VS.

The IC TBA820M also provides several options to create adjustable and non-adjustable VSs. That IC has the possibility to externally adjust the voltage gain and the frequency compensation. Figure 9 presents the circuit of a simple VS around the TBA820M.

Figure 9: A VS circuit using the TBA820M.

The input pin 3 of the IC can go to the ground. That input is protected with an internal resistor of around 2k. The AC gain of the IC should be set to the minimum in order to reduce the noise at the output of the IC. The frequency compensation is adjusted with C4. If needed, the output voltage is adjusted with the trimmer potentiometer P1. Only one of the jumpers J1 and J2 should be closed, depending on the required mode of operation.

If we are in need of more current and power in single polarity applications we can use a VS based on single power audio amplifiers such as the TDA2002 (10W) and TDA2003 (10W) and dual PAAs such as the TDA2004R (6W+6W), TDA2005R/M/S (11W+11W), TDA2009/A (12W+12W) and similar.

The DC test circuit of these ICs can be used as simple DC non-adjustable VSs. Here we will examine one of these cases. Figure 10 presents the circuit of a VS based around a TDA2003. The circuit also works with the older and less popular now TDA2002.

Figure 10: A VS with the TDA2003 or older and less popular now TDA2002.

For a power supply of 14.4V the output voltage of the IC is between 6.1V and 7.7V. The inputs of the IC are connected to single internal NPN transistor. The negative feedback between the output of the circuit and the emitter of the input transistor is accomplished by R2 and R3. The voltage gain of the IC should be set to minimum in order to have minimum output noise. The output voltage is adjusted with the trimmer potentiometer P1.

PAAs such as the TDA2030/40/50, LM1875, LM1876 (dual PAA), LM1877 (dual PAA) can be considered as some sort of power operational amplifiers with differential inputs, but nevertheless there are some significant differences among these PAAs. E.g., the input stage of the TDA2030/40/50 uses input PNP transistors while the input stage of the LM1876 and LM1877 is with NPN transistors.

Care should be taken about the maximum differential input voltages of the ICs and if needed we should add external protection with resistors, diodes and capacitors. For example, the maximum input voltage of some ICs can be very low, e.g., only 0.7V.

Figure 11 presents the circuit of a VS using a TDA2030, TDA2040 or TDA2050.

Figure 11: A VS with a TDA2030, TDA2040 or TDA2050.


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