The main topics presented
1. Electronic components for SMT technology (III)
The presentation of SMD components reached the chapters dedicated to inductors, connection / switching elements and discrete active components - diodes and transistors.
Surface-mounted inductors are generally used in applications where a high density of equipment is required. In some high frequency applications, surface-mounted inductors can provide similar performance to THT inductors.
Of course, SMD components being limited in size, very high values of inductance or quality factor cannot be obtained.
Currently, there are two variants of making inductors in the SMD variant: inductors with coiled conductor and multi-layer inductors.
The most commonly used SMD inductors today are of the classic type, with coiled wire. For high inductance values, the winding on a ferrite core is used, most often in the form of a spool.
For use at high frequencies, a non-magnetic material is used as a support, usually alumina.
With the wide use of SMD passive components, in order to have a certain homogeneity of the technological assembly process, active components in the SMD variant were required by the industry.
The diodes were components easily adapted for surface mounting and various constructive variants were made for this purpose, some variants being derived from the components used in hybrid circuits.
Over time, some of the capsules came into use. These are shown in Figure 5 (of the article).
MELF cylindrical capsule - Metal Electrode Face is similar to that used for resistors. In the case of MELF diodes, the capsule has a glass body with metal electrodes at the ends, for soldering, as can be seen in figure 6 (from the article).
The two metal electrodes also contact the silicon structure which is provided with solder bombs. For MELF diodes there are two variants, identified as MLL 34 (SOD-80) and MLL 41 (SOD 87).
Small Outline Transistors (SOT)
"Small Outline" transistors were among the first active components used for surface mounting. The transistors are available in capsules with three or four terminals, identified as SOT (Small Outline Transistor).
The most common capsules with three terminals are SOT 23 (EIA TO 236) and SOT 89 (EIA TO 243). Of the four-terminal capsules, the most commonly used is the capsule SOT 143 (EIA TO253).
All these capsules can be used for both transistors and diodes. The construction of the SOT 23 capsule is shown in figure 10 (from the article).
SOT capsule 23 there are three variants with different heights (profiles) from the substrate: small, medium and large, as can be seen in Figure 11 (from the article).
The low profile variant (low - engl.) Is optimized for adhesive deposition and gluing in the wave, the one with high profile (high - engl.) Being preferred for reflow gluing allows a better cleaning. The medium profile variant is a compromise and can be used in both gluing processes.
2. Universal board with two relays
Cards with relays, triacs, thyristors or other semiconductor elements of switching power are universal execution elements of a real practical utility in industrial automation applications.
A new realization at Conex Electronic, the universal board with two relays is designed in two variants, respectively for relays of 12V or 24V for a current in charge of 8A.
The board with two relays can be used as interface between the electronic control part and the force part (of the execution elements).
The assembly made in the Conex Electronic kit represents a universal board with two relays. These are controlled by low current transistors. The order is made on the base, with a "high" signal (positive to the table).
The current absorbed by the control inputs, IN1 and IN2, respectively, is small. The peculiarity of the installation consists in the possibility to mount on the printed wiring, or relays with nominal supply voltage of 12V, or 24V, the physical dimensions and the location of the pins being the same.
The relays have two pairs of NI / ND contacts, noted in the diagram in figure 1 (from the article), K1 and K2, respectively K3 and K4. The relays support a load current of 8A. The relay board is powered by 12Vdc or 24Vdc, depending on the type of relays used, from the K6 connector.
3. ZCD - Zero Cross Detector - Detector with zero crossing of the network voltage
Zero voltage detectors it is mainly used in power rectifiers, whose switching devices are thyristors.
They generate the control signals with a well-determined delay compared to the zero crossing of the mains voltage, determining the entry into conduction of the power semiconductor devices.
However, other applications can be listed: measuring the network frequency with a very high precision, measuring the phase shift between voltage and current for the case of resistive loads - inductive or capacitive, etc.
The zero crossing detector presented in this article is made with an industrial microcontroller from the C51 series, AT 89C2051, in order to obtain a high precision and the possibility to connect to a personal computer through the serial port, using a classic RS232 interface.
4. Methods for virtual characterization of digital systems
The virtual characterization of "high-speed" digital systems involves the use of an appropriate modeling and simulation environment, which allows to take into account the parasitic effects that negatively influence their operation.
In this article, the authors have chosen (to highlight the subtle undesirable effects) a program considered to be among the best in the field of signal integrity analysis.
HyperLynx (the trade name of the software presented) is an environment for evaluating digital projects at the layout level and proves to be a extremely useful tool for specialists involved in the development of new products, with a focus on the design and manufacture of PCB modules.
5. PIC microcontroller programmer and I2C memories
Physical programming of microcontroller memory is a simple step in the entire development chain of an application and is done with the help of a programmer.
PIC series microcontrollers are manufactured by Microchip and are often used in a wide variety of applications, being preferred by many application developers.
They are relatively cheap compared to other types of processors, easy to program, with a reduced set of instructions, have low consumption, can be made fast applications, being designed in a RISC architecture, benefit from very rich and mediated information support from part of the manufacturer etc.
The programmer presented as a practical application facilitates the programming of the most common microcontrollers produced by Microchip. In addition, just as common memories can be programmed as those in the l2C - 24Cxx series.
In commercial and industrial applications the power supply of PIC microcontrollers is made with low voltage, 2… 6Vdc.
6. TV modulator for mini video cameras
There are often cases when we are in possession of a miniaturized video camera or a VCR and we want to send the complex video signal either via a coaxial cable or over the air, to a TV that has no AV input.
Conex Electronic has developed a TV modulator that interconnects a surveillance video camera with either a cable or radio TV. The assembly ensures a good frequency stability as well as a quality amplitude modulation.
In order to ensure this desideratum, the variant presented in figure 1 (from the article) was used. The oscillator block is made with a type transistor BRF93A (SMD type) whose oscillation frequency is twice lower than that of the signal at the output of the assembly.
It is mentioned that the modulator works in the ultra high frequency (UIF) range and can be adjusted (as a frequency) to cover the range of 24… 40 TV channels. This means that the frequency range can be used 500-630MHz.
7. STK 401 - XXX - Dual power audio amplifiers with symmetrical power supply
SANYO has recently developed a new family of hybrid integrated circuits for audio power amplifiers, whose major feature is the pin-to-pin compatibility of all types in the series as well as in different series.
This allows the manufacturer of different power amplifiers to design and use a single type of printed circuit board.
Among the notable characteristics of the circuits from the STK401 - xxx series are the following:
- pin compatibility with STK 400 - XXX series (3 channels per capsule);
- load impedance from 3 to 6 Ohm;
- a new assignment of the pins on separate functional blocks (inputs, outputs, power supply) which determines the minimization of the degradation of the electrical parameters due to the printed circuit;
- requires few external components (no more resistors and bootstrap capacitors are needed).
8. Power relay - Solid State 220Vac / 13A
This static power relay can switch various loads, powered to 220Vac which have a consumption of up to 13A. The switch element is a triac, and the command is made in voltage (12… 24V, continuous or alternative) by optical isolation with optotriac.
The practical realization allows the mounting on a DIN frame of electrical panel. The voltage control of the semiconductor power relay is used due to the low current consumed on the control input.
Another advantage is the lack of "moving" components, which eliminates problems such as extinguishing the electric arc.
Interesting in the presented application is the fact that optotriac (type MOC3042) provides trigger (gate command) with Zero Crossing Circuit;