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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 IC works as a DC amplifier with gain set by R3 and R2. The gain should be above the minimal value and appropriate external frequency compensation should be used. The problem with the DC configuration is that the IC amplifies its DC offset.

The internal offset depends on the temperature. In most cases that is not important but in all cases it should be taken into consideration. In figure 11 the output voltages are adjusted in large scale with the trimmer potentiometer P1 and that is one of the advantages of that VS. The gain of the IC is calculated with the formula below:

Av = 1 + R3/R2.

In order to improve the stability of that and similar VSs we may need to put a small high-current inductor in parallel with the resistor in series with the output (in this case the resistor is R4*).

Sometimes we are in need of two or more DC power supplies that use the ground line of the input voltage. In these cases we can use several single amplifiers or dual, triple or quadruple PAAs or OAs. Figure 12 shows the circuit diagram of an adjustable power supply that has three output power suppliesV1, V2 and V3that share a common ground GND.

Figure 12: Adjustable power supply which has three output power supplies V1, V2 and V3 which shares a common ground GND.

In fact this is a VS from the second type (figure 1b). That circuit is built around the dual low-power audio amplifier TDA2822M. The TDA2822M features PNP input transistors and an internally fixed AC gain of around 100 (36 to 41 dB), but here the IC is used as a dual DC amplifier. At a power supply of 6V the quiescent output voltage at each output is typically 2.7V. We may adjust the output voltages V2 and V3 with the trimmer potentiometers P1 and P2. The Jumpers J1 to J4 select the mode of operation of the VS.

Voltage splitters based on audio operational amplifiers
Many modern electronic systems require power supply currents well below 50mA. And we are in need of short-circuit protection of these voltages. Audio operational amplifiers (AOAs) can be a good choice for VSs in that case. Modern industry offers a large variety of single, dual and quadruple OAs applicable in these VSs. Table 2 gives some operational amplifiers appropriate for VSs.

Table 2: Some high current, high-voltage or high-power operational amplifiers appropriate for voltage splitters. *The gain is set externally in wide range. **approximate value, please see the data sheet.

Figure 13 presents the circuit diagram of a VS based around dual paralleled OAs.

Figure 13: A VS based around dual paralleled op amps.

We may use practically any dual op amp with a current limiting function that is stable at unity gain and stable with a high capacitive load. The IC is selected according to the required output voltages, current and power dissipation. The output voltage is adjusted with the trimmer potentiometer P1. The equalisation resistors R3 and R4 are obligatory and depend mainly on the stability of the OAs when driving capacitive loads.

If the current provided by two paralleled OAs is not enough, we may use three or four paralleled OAs under the condition that the power dissipation of the package of the IC is not exceeded. Figure 14 gives the circuit diagram of a VS based around quadruple paralleled OAs.

Figure 14: A VS based around quadruple paralleled OAs.


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