100W amplifier driven by TDA7250

When designing a power amplifier circuit, the most troublesome problem is the transistor pairing and zero drift adjustment of the differential circuit. If you are not careful, you may even damage the power amplifier tube... Now it's okay and you can try TDA7250.

TDA7250 is a power amplifier driver IC produced by SGS-THOMSON. Its characteristics are as follows:

• The peripheral circuit is simple and easy to manufacture;
• Support wide voltage range: 2V-90V (±10V-±45V);
• It has a zero drift control circuit that does not require temperature compensation;
• Power transistor overcurrent protection;
• Squelch/standby function;
• Low power consumption;
• Low harmonic distortion: Harmonic distortion = 0.004% when PO = 40W, fo = 1KHz
• Output power: 60W/8Ω, 100W/4Ω.

The following is the application circuit diagram:

From the above circuit, we can see that the overcurrent protection principle of TDA7250 is to detect the voltage of resistors R11, R12, R13, and R14. When the transistor is overcurrent, according to U=I・R, the terminal voltage of the resistor increases accordingly. After reaching a certain voltage, TDA7250 sets the voltage of the transistor base to zero, thereby achieving the function of transistor overcurrent protection. Resistors R14, R15, R16, and R17 form a negative feedback loop. The gain of the entire circuit is determined by the ratio of R14, R15 and R16, R17. The formula is GV=1+R14/R16 or GV=1+R15/R17.

The above circuit has another use for audiophiles: to compare the differences between different power tubes. I happened to have MJ11032/11033, MJ11015/11016, 2SC3055/2955, 2SC4278/A1633, 2SB522/D522, TIP142/147 and other pairs of tubes, so I connected them one by one for debugging. The speaker is a 12-inch box from Feida. The results are as follows:

The first tubes I listened to were MJ11032/11033. The treble of this pair of tubes is transparent and bright, the midrange is round and full, the lip and tooth sounds are clearly audible, and the bass is powerful and elastic. After listening to its bass, I feel that the bass of other tubes is not as good, especially 2SC3055/2955 and TIP142/147 are even more boring; MJ11015/11016 is worse than MJ11032/11033 in high, mid and low frequencies, especially in the strength of the bass and high The timbre of 2SB522/D522 is purer, and the bass volume is worse than that of MJ11015/11016, but the treble overtones are better than those of MJ11015/11016; 2SC4278/A1633 is similar to 2SB522/D522 as a whole, and the treble seems to be better than 2SB522/D522; while 2SC3055/2955 and TIP142/147 are very poor, and I don't know if what I bought is authentic.