Conex Club Magazine - no.10 - 2000

Conex Club Magazine - no. 10 - 2000 - Toroidal transformers

Reading time: 3 minute

The main topics presented

1. LM3647 - Controller for monitoring battery charging

Made in an S0-20 capsule, the LM3647 integrated circuit is specially designed to assist the process of charging batteries Ni-Cd, Ni-MH and Li-Ion.

Three LEDs and a buzzer provides information about the condition of the battery (advanced state of wear, its short circuit).

The integrated circuit monitors the temperature of the battery, the voltage drop at its terminals, the charging current and of course, for a normal charging, it discharges it beforehand.

They can be charged simultaneously two to eight Ni-Cd or Ni-MH elements or one to four Li-Ion elements.

2. LM2677 - Switching regulator - 5A

LM2677 belongs to a family called generic "simple switcher" of the National Semiconductor company. The regulator is made in three variants (for the output voltage): 3.3V - variant LM2677-3.3, 5V - variant LM2677-5.0 and 12V - variant LM2677-12.0.

The yield is higher than 90%. Control pin 7, allows access to the operation of the converter, it being active in logic 1.

The internal oscillator works on 260kHz. At pin 5, with a capacity of 100pF, the circuit is synchronized externally (optional) with a rectangular signal with a frequency of 280 - 400kHz.

Voltage in the range can be applied at the input 8… 40V. Standby consumption is 50uA. It is made in a capsule TO-263 (7 pins) or TO-220 (7 pins).

3. LT1959 - DC / DC regulator - 4.5A

Made at Linear Technology in the SO-8 capsule (8 pins) is the converter DC / DC Buck LT1959. Working frequency is higher - 500kHz, which gives the assemblies with this integrated circuit a very small size.

The number of external components is reduced to a minimum: the filter capacitors, the resistive divider for the reaction voltage and, the basic element, the coil of only 5uH.

It has a activation pin (/ SHDN). Like most modern integrated regulators it is made in several variants: for 1.8V, 2.5V and 3.3V. The input voltage can take values ​​between 4V and 16V.

4. TDA2320A - applications

The most accurate playback of music programs (magnetic, optical, etc.) involves the use of quality components in the amplification chain.

For quality auditions, electronic component manufacturers are looking to make devices (especially integrated circuits) that produce as little audio signal distortion as possible, to generate their own low noise, to have low energy consumption, to have a wide voltage range ( voltages) its supply

Made with ST Microelectronics, the TDA2320A integrated circuit meets the qualities presented above. It is a double preamplifier in class A operation, offered in an 8-pin DIP capsule.

The circuit is supplied with electrical voltage in the range 3 - 36V, the consumption being 0.8mA.

5. Electronic switch

The electronic switch shown is an application of the integrated circuit CD4532 which can be used in any assembly that requires the presence of a mechanical switch with 16 positions randomly actuated.

The assembly can be used in devices such as: function generator, step voltage stabilizer, remote control, TV keyboard, programmer for radio devices operated with varicap diodes, voltage controlled oscillators, audio mixers and switches, etc.

6. Toroidal transformers

The frequent use in electronic equipment for the production of toroidal transformers is justified by their advantages compared to the classic constructions that use E + I sheet metal.

The characteristic of a toroidal transformer consists in the toroidal geometry (from where it got its name), and this ensures a efficiency that frequently reaches 97-98% at high powers.

Compared to E + I interwoven sheet metal transformers, toroidal transformers also have the following advantages:

  • half the size and weight at the same power;
  • reduction of approx. 8 times the noise produced;
  • one tenth of the electromagnetic field radiation to the outside;
  • easy and fast installation in electronic equipment;
  • low thermal radiation.

7. Protection of power supplies over voltage

Many power supplies must provide a stabilized voltage for particularly demanding loads: industrial transceivers, expensive integrated circuit boards, etc.

Any overvoltage applied to them can cause considerable damage. In the case of voltage stabilizers, the mechanism of ensuring a constant voltage at the output is based on the existence of a higher voltage regulator upstream.

The protection scheme presented in the article is based on the permanent sensing of the voltage on the load and, in case of an overvoltage, the input voltage in the stabilizer is short-circuited, thus activating the short-circuit protection (either by fuse safety or by other methods).

The method is called in the literature "crowbar" (crowbar, ad hoc short-circuiting element).

A specialized integrated circuit is used, dedicated to this type of protection - MC3423P. The circuit contains a reference source, of good quality, with low thermal drift, which has the voltage of 2.5 - 2.6V, a timing circuit designed on the basis of a constant current generator that charges an external capacitor, two special comparators and an output circuit.

8. Tester for RS232 networks

The presented tester is connected in series on an RS232 network that has defects in data transmission and allows, with the help of straps handled by the service provider, to perform checks, such as: interruption or not of the cable, or forcing levels of voltage of some signals on 1 or 0 logic, for this purpose bicolor LEDs are used which indicate the logic level.

Two DB9 plugs are used for the father and the mother, respectively.


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