Amplifier current negative feedback TDA7294 DC Servo

In the field of consumer reports electronics products reviews, product size, weight is toward smaller, lighter direction, high-power single-chip audio power amplifier needs of increasingly prominent, TDA7294 is currently the best performance, the biggest single-chip audio power amplifier One.

It consists of the European SGS-THOMSON Italian-French company in accordance with discrete components A and B audio amplifier circuit design from classic. Its former low-level noise, low distortion of the bipolar transistor circuit, at the end of a high-pressure, high current DMOS output of the buffer, it has bipolar circuit sounds pure merit, have large current high voltage FET Driver output characteristics.

Since 1998 TDA7294 introduced to China so far, I believe that many enthusiasts have been TDA7294 delicate taste, natural sound. Regrettably, however, is that they have heard only negative feedback is standard voltage of the voice amplifier.

And negative feedback amplifier voltage than current negative feedback amplifier as excellent transient nonlinear distortion and intermodulation distortion characteristics, the frequency amplifier curve flat, high and low frequency response more exhibition wide; more important is that circuit Will load impedance into the feedback network, it can change the speakers of such fierce resistance to the load compensation, coupled with stable and reliable performance, than the negative feedback voltage amplifier has more advantages, the current negative feedback current amplifier is widely For the modern high-fidelity audio amplifier.

Figure 1 circuit is an excellent performance, improve the design of the fever-100 W × 2 DC Servo Amplifier current negative feedback stereo amplifier, formed by the two TDA7294, the frequency response of 10 Hz ~ 100kHz. The use of sophisticated audio Yun-double as the two-channel amplifier DC Servo Amplifier output. Speakers from the protection of ASIC μPC1237HA driver completed the relay switch-mute and amplifier output DC offset protection, and other speakers. When the AC power plug, the relay will be delayed for some time speakers access amplifier; disconnecting the AC power when, μPC1237HA detected exchange loss, immediately disconnect the speaker to relay, the amplifier is the complete elimination of the set, Shutting down the transition process the impact of noise on the speakers.

In actual use, taking into account the electricity grid fluctuations Rectifier amplifier output voltage ± Vs volatile, in order to avoid over-voltage and high temperature in the state of damage TDA7294 (Note pressure in the temperature of 25 ℃ under the conditions, if the temperature exceeds 25 ℃, TDA7294 the value will subsequently reduce the pressure), the exchange recommended power supply voltage transformer CT-AC26V × 2.

Listen:

Speaker to use B & W601, CD machine Marantz CD-19, compared TDA7294 amplifier for the negative feedback standard voltage lines. Software programs at Cai Qin, "the film" test the human voice, Mutebutsi trial String, RRs "Tutti" dynamic test, Rubinstein "Chopin Nocturne" trial piano.

The results are as follows:

In a dynamic sense of speed, the two amplifier very close, but the sound on the current negative feedback is obviously more sweet; the string, the human voice like the rendering software for a warmer, the details of the re-orientation; due to current negative feedback circuit Impedance of the compensation, the low-band high-impedance output has been strengthened, so dive in the low-frequency and intensity of the depth occupied obvious advantage.

Current negative feedback in addition to direct stereo amplifier for CD, VCD, DVD, and other music source amplifier, but also with audio processing unit for use by different combinations of the playback effect.

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Negative Output Switching Regulator

There are only a limited number of switching regulators designed to generate negative output voltages. In many cases, it’s thus necessary to use a switching regulator that was actually designed for a positive voltage in a modified circuit configuration that makes it suitable for generating a negative output voltage. The circuit shown in Figure 1 uses the familiar LM2575 step-down regulator from National Semiconductor (www.national.com). This circuit converts a positive-voltage step-down regulator into a negative-voltage step-up regulator. It converts an input voltage between –5 V and –12 V into a regulated –12-V output voltage.

Note that the output capacitor must be larger than in the standard circuit for a positive output voltage. The switched current through the storage choke is also somewhat higher. Some examples of suitable storage chokes for this circuit are the PE-53113 from Pulse (www.pulseeng.com) and the DO3308P-153 from Coilcraft (www.coilcraft.com). The LM2575-xx is available in versions for output voltages of 3.3V, 5 V, 12 V and 15 V, so various negative output voltages are also possible. However, you must pay attention to the input voltage of the regulator circuit. If the input voltage is more negative than –12 V (i.e., Vin <–12 v), the output voltage will not be regulated and will be lower than the desired –12 v.


The LM2575 IC will not be damaged by such operating conditions as long as its maximum rated input voltage of 40 V is not exceeded. High voltage (HV) types that can withstand up to 60 V are also available. Although the standard LM2575 application circuit includes circuit limiting, in this circuit the output current flows via the diode and choke if the output is shorted, so the circuit is not short-circuit proof. This can be remedied by using a Multifuse (PTC) or a normal fuse. There is also an adjustable version of the regulator with the type designation LM2575-ADJ (Figure 2). This version lacks the internal voltage divider of the fixed-voltage versions, so an external voltage divider must be connected to the feedback (FB) pin. The voltage divider must be dimensioned to produce a voltage of 1.23 V at the FB pin with the desired output voltage. The formula for calculating the output voltage is:

Vout = 1.23 V × (1 + [R1 ÷ R2])

The electrolytic capacitors at the input and output must be rated for the voltages present at these locations.
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