500W power amplifier output circuit that can be used for high-power unipolar power supply

500W power amplifier output circuit that can be used for high-power unipolar power supply

Function of the circuit

This circuit is the output circuit of the power amplifier, with a load of 8 ohms, an effective output of 500W, an output voltage of 180VP-P, and an output current peak value of more than 10A, so it can also be used for high-output unipolar power supplies. The power supply voltage is positive or negative 95V, and there is no need to change the circuit parameters even if it is lower.

How the Circuit Works

When the load is 8 ohms, in order to output 500W of power, according to VCC=√8RLP, VCC should be 179V, and taking the loss voltage into account, a positive and negative 95V bipolar power supply can be used. The total collector current IO (MAX) flowing into the four parallel connections
is about 11.2A according to the formula IO (MAX) = √2PO/RL, and a power supply that can supply such a current should be equipped.

If the DC current amplification factor HFE2 of each transistor of TT5~TT12 is at least 50, then a base current of 224mA flows through it. If HFE1 of TT3 (TT4) is also 50, then the emitter current of TT1 (TT2) is about 4.5mA, and the circuit can easily work under such a current. This connection method with HFE as the multiplication result (HFE1*HFE2) is called Darlington connection.

Notes

Positive and negative bipolar power supply circuits and power supply capacity

Since the power amplifier omits the output capacitor, a bipolar power supply circuit is often used. Figure 1 shows the rectification and filtering circuit, and Figure 2 shows the regulation curve (the curve of the DC output voltage V changing with the load current IC) and the pulsation (pulse wave content) curve.

According to the required DC voltage VCC, the approximate value of the secondary voltage VCC of the power transformer is calculated, that is, VCC≈VCC*1.25 (when there is no load, VCC=√2*VCC). The current is determined by the output power and the load resistance. The average DC current IDO is calculated by the formula IDO=2IO(MAX)/π, where IO(MAX) is the maximum collector current of the output stage. The AC IAC is determined by the filter capacitors C1 and C2, which is roughly IAC=（√2~2）IDO.

The parallel capacitors C3 and C4 are used to correct the high-frequency impedance of the filter capacitor. Their capacity and type are determined according to the bandwidth to be amplified. In high-power circuits, the current flowing through is large, so pay attention to the wiring of C1 and C2. The . symbol in the figure can be used as a terminal for wiring, and try to use thick wires.