Conex Club Magazine - no.1 - 2004

Conex Club Magazine - no. 1 - 2004 - Supply with distributed stabilization

Reading time: 2 minute

The main topics presented

1. Digital thermostat with K probe

The thermostat is made with the microcontroller AT90S4433 from Atmel and accepts at the entrance temperatures between 0 and 1000C.

The sensor is a K-type probe (thermocouple), and the temperature adjustment is done bipositionally, by closing or opening the contacts of a relay.

It, in turn, switches on or off a heating element, thus maintaining the temperature between two thresholds, the values ​​of which are entered from the keyboard.

General characteristics:

  • User interface
  • LED display, red color, 3 digits + a digit that forms the characters "° C";
  • 4-button keyboard;
  • Measurement method: A / D converter with successive approximations, 10 bits;
  • Measuring range: 0 - 1000 ° C:
  • Acquisition rate: three readings per second;
  • Sensor: K-type thermocouple;
  • Output: relay, max. 10 / 250V;
  • Dimensions: 125 x 66 x 47mm (without housing);
  • Housing: a box type G1098 is recommended,
  • Power supply: 220V / 50Hz.

2. Power supply with distributed stabilization

When it is necessary to supply a large number of electronic modules with a stabilized voltage, a single, high-power source can be used for the whole assembly, but there are problems with the distribution of high currents on the interconnection bus, and the stabilization leaves much to be desired.

In addition, once the power source or a short circuit board fails, the entire equipment is shut down.

A pre-stabilization circuit (switching) is recommended followed by many stabilizers (linear or switching) distributed on each module.

The need for such a solution arises, for example, in the drawers with plates, powered by an unstabilized DC voltage source (possibly with a battery backup circuit) of relatively high voltage - 48V. For such a voltage a usual range of variation is between 38V and 58V.

3. LA4445 - Dual AF power amplifier

LA4445 is a monolithic linear integrated circuit, double power amplifier in the field of audio frequencies, capable of delivering 5.5W / 4 Ohm, on each channel.

Some of the main features are:

  • 4 Ohm load output power for each channel: 5.5W;
  • requires few external components;
  • low start / stop noise;
  • rejection of the supply voltage ripple: 46dB (typical);
  • smooth crosstalk attenuation;
  • thermal protection.

4. uA78S40 - 40V / 1.5A switching voltage stabilizer

The uA78S40 integrated circuit is a switching voltage stabilizer capable of supplying output up to 40V, at a max. of 1.5A. It is produced by several companies, such as: Motorola, Fairchild etc.

Having a very low consumption (approx. 5.5mA) and a very good efficiency, the circuit is very suitable for applications in portable equipment, powered by batteries. But it can provide a significant output current, as pointed out, of 1.5A, accepting a input voltage between 2.2V and 40V.

If we also consider reasonable purchase prices, there are all the prerequisites to work with this integrated circuit.

5. 3 1/2 digit digital voltmeter

The assembly is a 3 and 1/2 digit digital voltmeter built around the integrated circuit 7107 digital analog converter (CAD) which also contains decoders for display.

The integrated circuit was used as the reference voltage source ICL8069 (LM385). The required negative voltage for the correct operation of the A / D converter is obtained with the help of the integrated circuit 4049 which buffers the clock oscillator. The signal thus obtained is rectified (D1, D2) and filtered (C7).

The decimal points can be lit, as needed, by connecting the corresponding pins to the ground.

The kit can be used as measuring instrument individually or in complex measuring and control equipment.


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