Conex Club Magazine - no.12 - 2000

Conex Club Magazine - no. 12 - 2000 - MIC2754 / 3 - Supply voltage supervisor

Reading time: 4 minute

The main topics presented

1. MIC2754 / 3 - Supply voltage monitor

Componententele MICREL, MIC2753 and MIC2754 provides surveillance and overvoltage protection of processors that are sensitive to voltage peaks from power supplies, whether linear or switching.

A protection interface is able to detect overvoltages and reset the system in less than 140ms.

The maximum supply voltage is 7Vand consumption of only 30uA, the components being recommended for use in stationary or portable devices.

With five preset voltage levels, the circuits shown allow the control of several standardized supply voltages for digital systems. They are available in SMD capsules type SOT23-5.

2. LT1638 / 9 - 1.2MHz operational amplifier, 0.4 / us

Note that this operational amplifier can work with input signals that have the amplitude above the supply voltage (up to 44V).

The four standard capsule amplifiers, DIP or SMD with 8 pins, can be powered (single or differential) with 2.5V up to 44V, maximum consumption 230mA on the amplifier and has protection when the battery is connected (up to 18V).

The gain-band product is 1.2MHz, and Slew Rate 0.4V / us.

It is used for monitoring in systems powered by batteries or solar cells, for instrumentation and conditioning of measurement sensors, for low power active filters.

3. TPA2000D2 - Audio amplifier for media systems

The PDA2000D2 produced by Texas Instruments is a class D audio amplifier circuit offers 2W per channel (3 Ohm load) and does not require an output filter.

Low level audio signals are converted to time modulated pulses (PWM).

It has thermal and overcurrent protection and goes into standby mode when the supply voltage decreases. The power supply is made with + 5V, the standby consumption being 1 uA. It is offered in a 24-pin SMD capsule.

4. Transmitter - receiver for remote control

The transmitter-receiver assembly presented offers various practical applicability, such as: control of doors and / or anti-theft device of a vehicle, remote opening of doors, electrically operated doors with motors (from yards, garages, etc.) or control indoor or outdoor lighting. The maximum operating distance is 15m.

5. TL497 - Switching voltage regulator

For the construction of switching voltage sources, Texas Instruments made the circuits TL497AC and TL497AI which integrates on a single face the functions necessary for this purpose.

With these circuits you can configure sources in type switching Buck, Boost or inverters (of polarity) with high efficiency (over 60%).

TL497AC operates at normal parameters in the temperature range 0… 70 ° C, and the TL497AI in the range -40 °… 85 ° C. The significance of the 14-pin capsule terminals is shown in Figure 2 (from the article).

6. Battery protection

The battery protection device with lead plates presented in the article is used in the field of communications.

The discharge of batteries, in general, below the limit value provided by the manufacturer leads to the appearance of irreversible electrochemical processes, which result in a decrease in electrical capacity or even their destruction.

The manufacturer specifies in the technical documentation, the minimum and maximum voltages at the battery terminals and these depend on the following factors:

  • battery type;
  • battery capacity;
  • ambient temperature;
  • discharge current, respectively charging;
  • unloading time, respectively loading.

Thus, recommended minimum and maximum voltages can reach the following values:

  • minimum voltage: 1.00V… 1.75V per element;
  • maximum voltage: 2.27V… 2.40V per element.

In the case of the presented device, the control is made only on the minimum voltage, by disconnecting the batteries and protecting them when discharging below the minimum recommended voltage.

To determine this voltage, the following hypotheses are taken into account:

  • a number of 4 batteries with lead and acid electrolyte, without maintenance, dryfit type A400, manufactured by Sonnenschein, connected in series, are used to obtain the nominal voltage of 48V;
  • ambient temperature located in the range 15C… 25C (in this case there is no need for additional correction of the resulting voltage value);
  • average discharge current of 1 x I20 where I20 = Battery capacity / 20h.

7. Balance indicator

In Hi-Fi stereo amplifiers, often the signal on one channel cannot be compared correctly with the signal on the other channel.

This inconvenience can be removed by using a montage to compare the two signals and at the same time to warn, by means of two LEDs, the equality or inequality of the signals.

During operation, the LED corresponding to the channel with the higher signal will illuminate, the equality of the signals determining the activation of both LEDs.

The indicator allows the comparison of two signals whose amplitude is within the limits of 0.4… 10V. The maximum supply voltage is 12V, and consumption below 20mA.

8. Dynamic light

On the eve of the winter holidays and motivated by the many possibilities of decoration that the installation "Dynamic Light" can suggest to the user (even at the Christmas tree), the magazine briefly resumes its presentation, in the December 1999 issue (at the pages 30-31) of the magazine, but with additions regarding the way of interfacing with the power electronics part.

The ensemble can also be used for companies or illuminated advertisements. The system developed by Conex Electronic consists of a control and monitoring module with 8 + 1 LEDs and an eight-channel power module for (especially) resistive loads, for example, incandescent lamps powered by the single-phase AC mains 220V.

The two modules are interconnected according to the block diagram shown in figure 1 (from the article).

The command and monitoring part is done with 74Th series TTL integrated circuits and obligatorily its supply must be made from a source stabilized by + 5Vdc. Consumption is maximum 100mA.

9. RxTx - 29MHz

Agglomeration of the 144… 146MHz requires for local communications (primarily) the use of other frequency bands allocated to amateur radio traffic.

Higher frequency bands are generally targeted, as is the case with 432MHz or 1296MHz. The technical equipment for traffic in these lanes is more special, but easy to purchase when the amateur radio has the financial means.

The situation is more complicated in YO where Home Made constructions are the majority. A practical solution is to use the 10m band in the immediate vicinity of the frequency of 29MHz.

The presented transceiver, fruit of the experiments made by Y03HZ has a modern technical conception, being able to be reproduced without great difficulties.

Use of specialized integrated circuits (AN7205P) gives it a high degree of miniaturization but also a pronounced reliability.


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