April 2007 - Do It Easy With ScienceProg

DIY 4x22W car audio amplifier based on TDA7384

I decided to make a pretty simple but powerful enough audio amplifier. For this, I’ve chosen quad-bridge car audio amplifier IC – TDA7384, which has four input and four output channels with a power capability of 4x35W. If connected to a car battery where the operating voltage is about 13.2V, then each channel can give 22W what is more than enough for me. This amplifier I probably will use to test audio processor TDA7313, which is still in the development phase. I didn’t find much information about this chip on the internet, so I decided to build it and try it independently.

Programming microcontrollers AduC70xx using boot-loader and ARMWSD utility

Firmware for AduC70xx ARM microcontrollers can be uploaded using a built-in boot-loader. To work with boot-loader, Analog Devices offer a small free program, ARMWSD working under the windows system. The program doesn’t require installation. ARMED communicates with AduC70xx via COM-port. Simple programming steps looks like this: Connect target board to PC COM port; Go to Configure->Parts and select AduC part: Then go to Configure->Comms and select serial port and baud rate:

Integral Hall sensors

Hall sensors are common sensors of many measuring devices, including linear or angular motion, magnetic field, current, etc. The main convenience of hall sensors is that they don’t have to be mechanically connected to objects. They are also simple, cheap, which makes them attractive in the automotive, manufacturing, and aviation industries. Many manufacturers produce hall sensors: Honeywell, Melexis, Allegro Microsystems, Micronas Intermetall, Siemens, Analog Devices, etc. A typical circuit for connecting Hall sensors One of the simplest is linear Hall sensors that are used for measuring magnetic field strength. Integral hall sensors include a sensor signal amplifier, also temperature compensation, and supply stabilization circuits. Sensor output signal voltage and polarity depend on magnetic field strength and direction. If there is no magnetic field near the sensor, then output is equal to zero. To achieve this differential amplifier has to be used, characteristics will be corrected to be output voltage zero when there is no magnetic field. Other groups of hall sensors have comparator built-in. This allows having digital level signals on output. There can be two types of such hall devices: switches and triggers.

Protection circuits for operational amplifiers

In the specifications of operational amplifiers, there are maximum limits of allowed voltages on pins. Maximum currents are limited as well. So voltage and current they both limit allowed dissipated power Pmax=Umax*Imax. In well-designed circuits, Op Amps should have protection circuits from various overloads like a short circuit, high common phase voltage level in differential inputs, electrostatic charges, etc. Earlier operational amplifiers didn’t have built-in protection circuits, while modern ones have. Today popular operational amplifiers have internal protection circuits built-in, and this makes designers’ life much easier. But protection elements lowers some operational amplifiers like operation speed, dynamic range, and output signal swing level. Because of this, some operational amplifiers may not have internal protection circuits. In this case, you have to take care of it.

Switching step-up and step-down regulators

All regular voltage regulators (like 7805) have several disadvantages like output voltage is always lower than input, and some power is dissipated in the control element. Dissipated power is approximately equal to I(Vin-Vout). There is another way to generate a regulated voltage. The method is different from the previous one. A transistor operates as a saturated switch in a switching regulator, which periodically applies the full unregulated voltage across an inductor in short intervals. During each pulse, inductor current builds up, storing energy on its magnetic field: Inductor also smooths the output voltage. Feedback circuit with comparator compares the output voltage with reference and this way changes oscillators pulse width or frequency.

Dual polarity power supply source

Most op-amp circuits run from the symmetrical bipolar supply source, let’s say ±15V. The simplest way to generate symmetrical split supplies is to use a pair of 3 terminal voltage regulators. For instance, let’s take two voltage regulators: 7815 and 7915. If you need an adjustable variant of dual polarity regulated voltage source, you can use 317 and 337 adjustable regulators, where you can trim voltage with a voltage divider, which consists of two higher accuracy resistors: