Advice 1: How to choose the transistor

Transistors differ from each other in a number of parameters: structure, maximum power dissipation, current in the open state and the voltage in the open etc. Only a well-matched transistor will be long in the scheme into which it is installed.
Instruction
1
The load transistor is included between the power bus and the collector of the device. If the voltage on the positive bus, use the transistor structure of n-p-n, and if negative - structure p-n-p. Note that the control signal supplied to the base must have the same polarity as the supply voltage.
2
If the transistor will operate in analog mode, split the voltage in half and multiply by half the maximum load current. This will be the power dissipated on the device in the most adverse conditions - when it is open exactly half. If he works in a key mode, the maximum power dissipated on it will be much less. To find out, multiply the voltage drop on the transistor in the fully open position (typically it is only a few tenths of a volt) at nominal load current. Guided by the maximum power dissipation, decide whether you want the instrument radiator.
3
For maximum current in the open state take the maximum current consumed by the load, and the maximum off-state voltage - the voltage of the power supply. These parameters of the transistor must exceed the values that occur in the schema, at least in half.
4
The current transfer ratio select, depending on what should be the relationship between control current and load current. For example, if the rate is equal to 50, the load current can exceed the current control at least 50 times. Based on this, pick up the value of the resistor in the base circuit.
5
If the load is inductive, parallel to it, turn on the diode in polarity opposite to the similar indicator of the power supply.
6
Find it in the reference transistor, all of which specifications with some margin exceeds the chosen. Do not allow operation of the device in two or more of the limiting values of the parameters. Setting a selected transistor device, let it run for several hours, then switch off, discharge in the capacitors and measure the temperature of the transistor. It should not exceed 50 degrees.

Advice 2 : How to choose diode

Diodes are used in engineering for different purposes: rectification, detection, isolation, etc. They differ from each other by a number of parameters. Selection of the diode should be implemented depending on the requirements.
Instruction
1
Regardless, to perform which operation you will use the diode, when it is selected be sure to include such basic parameters as the maximum allowable forward current and reverse voltage. If the value of the pulsed direct current is much higher than the average, account for it, especially if the diode is a semiconductor.
2
If you need to straighten the currents of significant frequencies, note also the performance of the diode. Point semiconductor diodes have less capacitance than planar, and therefore, right currents a significant frequency. But they are very thin. The same property with a much larger capacity, and have a Schottky diode.
3
Correctly select the physical principle of operation of the rectifier. If the diode requires a complete absence of reverse current, but the efficiency is unimportant, use of the vacuum-tube diode. He's good that starts to straighten with a small voltage value.
4
Coproxy rectifier also open at low voltage but very high reverse current, low power, and performance, it is relatively small. Use it to straighten small alternating voltage of low frequency prior to measurement.
5
A germanium diode is opened when a slightly larger voltage, but the reverse current it has less. Use it, in particular in detectors of amplitude-modulated signals.
6
From selenium rectifier voltage large opening and little permissible reverse voltage, therefore, for rectifying significant voltage connect them in series. Appreciable reverse current allows to exclude the equalizing resistors. These rectifiers can withstand momentary short circuit, but after a long work break down for no apparent reason. Use such devices only in instances when no other diodes to replace them is impossible.
7
Silicon diodes are the most common today. They almost replaced the rectifiers of other types. Among them you can choose the instrument with virtually any necessary parameters. Try to apply them in all cases when possible.
8
Having defined the requirements for the diode, find the suitable for all parameters of the device in the directory.

Advice 3 : How to open the transistor

A bipolar transistor may be open or closed condition, and in any of a plurality of intermediate States. To control the state of the transistor serves as its electrode, called the base or base.
Instruction
1
Remember that a bipolar transistor, in contrast to the field, as well as electronic lamp, is not controlled voltage and current. The device structure of the n-p-n the current should pass in the direction from the base to the emitter (i.e., a plus to the database). If the transistor has a structure p-n-p, it skip the current in the opposite direction.
2
Before controlled by a transistor load, it must be correctly connected. The emitter of the transistor connect directly with the common wire, and the collector through the load to a power source. If you use the structure of n-p-n, this source should produce a positive voltage relative to the common wire, and if the structure p-n-p is negative.
3
Decide which mode is supposed to work: analog or key. In the first case, you will need a much larger heat sink. This is due to the fact that using fully enclosed transistor a very small current flows and completely open to a very small applied voltage. When the device is partly open, high, albeit not maximum, the values of both tension and current. For this reason, most power is allocated to the transistor when it is not fully opened.
4
Calculate what current must flow through the base-emitter transition of transistor to through the load began to pass a certain current. To do this, the desired load current divide on the dimensionless parameter of an instrument called current transfer ratio.
5
Realizing further increase in the current database, you will find that the current load is not growing. This means that the transistor is saturated. The greater the load current, the greater the saturation of the transistor of the same type the required base current. If you want to use the transistor in a key mode, always convert the mode to saturation, and heat it in the open state will be minimal. Do not, however, the base current is too large for the device began to heat up from this current.

Advice 4 : How to turn on the transistor

Bipolar transistors are of the structure n-p-n and p-n-p. It is most convenient to include them on the circuit with common emitter. Depending on application, transistor can be made to work in key or linear mode.
Instruction
1
Regardless of which mode will operate the transistor, connect the emitter to ground directly, and the collector to the power bus through the load. If the device has the structure n-p-n, the power bus should be a positive voltage, and if the p-n-p - negative. Make sure that the parameters of the transistor (the permissible current in open state, a valid off-state voltage, dissipated power) is sufficient to control the load that is connected to it.
2
To open the transistor in a key mode, take its base voltage through a resistor. Its resistance choose from so that the base current slightly higher than the number that happens if the nominal load current divided by the gain of the transistor. Insufficient base current, the device will overheat because it will not fully open, and when too large, from the current base.
3
For the transfer transistor in an analog mode, apply the base offset. It will also connect it to a power source through a resistor, but this time pick up the resistance so that the voltage at the collector of trnasistor relative to the common wire was equal to the half the supply. Then about 50% of the power will be dissipated on the load and the remaining 50% - on the instrument. To avoid overheating, use cooler.
4
During operation of the transistor in terms of change of temperature in a wide range of have to ensure the stabilization of his regime. For this, the upper output bias resistor not connect to the power bus and the collector.
5
At the base of the transistor working in the linear mode, the variable control signal feed through capacitor. If the cascade is the output, the load use a resistor, and the output signal remove the collector via a capacitor. In this form it can be submitted to the next stage.
Note
All perepiski engage when the power is off. Avoid overheating of the transistor.
Search