Amplifier specifications
output power: 2 × 100 W
compatible with speakers with a resistance of 2 W
integrated short circuit protection and thermal protection
voltage controlled standby and mute
small board sizes
power supply: +/- 27 V DC
Description of amplifier circuit
The TDA8920 Integrated Circuit is a built-in Class D stereo amplifier with 100 watts per channel and very low heat dissipation. A wide range of supply voltages from +/- 12.5 V to +/- 30 V and a high class D efficiency mean that the amplifier is widely used in room sound, car audio, and in expanding home audio systems. In an automotive audio system where high efficiency is important due to low supply voltage and high currents, the system will work perfectly with a switching voltage converter. The soft start function protects the speakers from harmful “bumps” when the power is turned on, very high efficiency minimizes the case and the radiator. From the amplifier you can get 110 watts of power for an impedance speaker of 3 W or 86 watts for a speaker of 4 W with a power supply of +/- 27 V. The amplifier can also work in bridge mode (mono). With this configuration, the output power of the 6-watt speaker reaches 210 watts.
The amplifier circuit in a stereo configuration is shown in Fig. 1.
An analog input signal is converted to a digital signal with a modulated duty cycle (PWM). Power output transistors controlled by this signal open and close without intermediate states with a frequency in the range of 300 ... 350 kHz. With this setting, the steep rising and falling edges of the output signal contain a very wide range of unwanted signals that can interfere with radio devices. To fix this, you need to use LC low-pass filters.
The values of the L and C elements of the output filter should be selected for this column impedance value. Table 1 shows the meanings of these elements. Inductors L1 and L2 must be wound with a wire with a diameter of at least 1 mm, since the current flowing through them is approximately 8 A.
The amplifier can operate in three modes:
- Waiting - in this state, the system receives a very low current and is in a sleep state,
- Mute - in this state, the system is active, but there is no signal at the output,
- It works - the system is turned on. This is a working condition.
To set the mode, set the switches S1 and S2 (Table 2).
table 2 | S1 | S2 | Mode of operation |
| Closed | Closed | Expectation |
| Closed | Open | Expectation |
| Open | Closed | Mute |
| Open | Open | Works |
The circuit has thermal protection and overload protection. Thermal
protection shuts off the power source when the temperature of the
structure reaches 150ºC, and turns it on when it drops to 130ºC. Short circuit protection monitors currents flowing through power transistors. When
the current reaches 8 A, the amplifier does not turn off, it only
changes the bias of the transistors, which reduces the power supplied to
the speakers. The
system checks the status of the output every 100 ms and tries to
restart it until the cause of the too high output current is eliminated. For the amplifier to work in bridged mode (mono), remove the components R11, R12, C26, C28 and C29, and then short-circuit the output
circuit of the U1 chip: 2 of 21 and 3 of 22. In this mode, the speaker
must be connected between the outputs OUT1P and OUT2M. The values of the elements L and C of the output filter are presented in table. 3 .
If less power is required, then you can use the TDA8922 chip, which differs from the TDA8920 only with an output power of 2 × 25 watts. Other parameters are the same. The assembly diagram is shown in Fig. 2.
After assembly, the amplifier does not require any settings. Install the U1 chip with a small heatsink.
