Switch triode - adomain

a circuit diagram

is connected directly across the load resistor between the collector of the power transistor, while the transistor among the main current loop, the input voltage V _in turn the control transistor switch (open) and closed (closed) operation, when the transistor was turned on, the load current will be blocked, and vice versa, in a closed state when the transistor, current can flow.

In detail, when V _in is a low voltage, since no base current, nor a current collector, so that the load is connected to the collector terminal also no current , corresponding to the activation of a switch (closed state), the work in this case is the transistor turned off (cut off) area.

Similarly, when the voltage Vin is high, since the base current flows, so that the collector current flowing through the greater magnification, so the load circuit will be turned on, and the switch is closed is equivalent to (connected state), when the transistor operates in the saturation region is the (saturation).

works

off-state

When applied to the transistor emitter voltage is less than the turn-on voltage of the PN junction, a zero base current, the collector current and emitter current is zero, transistor current amplification lost time, corresponding to the switching off state between the collector and emitter of the transistor that is turned off. Wherein the switch transistor is in an off state emitter, each collector junction is reverse-biased.

ON state

When applied voltage is higher than the ON voltage of the PN junction of the transistor emitter, base and when the current is increased to a certain level, the collector current is not with further increase in base current is increased, but in no change in how close to a certain value, then the loss of current amplification transistor, the voltage between the collector and the emitter is very small, the collector and emitter corresponds to switch between a conductive state, namely transistor conductive state. Wherein the switch transistor is in the state of saturated conduction emitter, collector junctions are forward biased. And wherein the transistor is in an enlarged state, the emitter junction is forward biased, the collector junction is reverse-biased. It is also possible to use a voltmeter test emitter, collector junction voltage of transistor principle determined operating conditions. It is based on switching transistor switching characteristics of the transistor to work.

operating mode

lot

type transistors, and different models have different purposes. Transistor mostly plastic package or metal package, the appearance of the common transistor, an electrode is the emitter of an arrow, the arrow facing the NPN transistor, and the arrow toward a PNP type. Indeed direction of the arrow shows a direction of the current.

FIG. 1

bipolar junction transistor two types: NPN and PNP

NPN type comprising two n-type region and a p-separating them type region; the PNP type contains two p-type region and a n-type region separating them.

Features Applications

switching transistor having a long life, safe and reliable, no mechanical wear, high switching speed, small size and other characteristics. Switching transistor can be very small current, on-off control of large current, have a broader application. Small power switches may be used in a power supply circuit, a driving circuit, the switching circuit; switching power supply can be used to color TV tube, the communication device; also be used for low frequency power amplifier circuit, the current adjustment; High voltage power switch Color television tube can be used to output pipe.

Shen primes

selection transistor Xuyao understand the main parameters of the transistor. When the hands of a manual best transistor characteristics. Many parameters of the transistor, which must understand the four limit parameters: I CM , BV CEO , P CM , f T, TON TOFF and the like, can be used to meet the needs of more than 95%.

1. I CM is the maximum allowable collector current. When its collector current exceeds a certain value, its current amplification factor β will drop when the triode. Providing that transistor current amplification factor β is not more than the maximum change in the collector current allowable value is called I CM . Therefore, in use, when the collector current IC exceeds ICM not destroy the transistor, but will reduce the value of β, affect circuit performance. .

2 BV CEO is an open base transistor, the collector - emitter reverse breakdown voltage. In situations where the voltage is applied between the collector and emitter exceeds this value, the transistor will likely make a large collector current produced, a phenomenon called breakdown. Cause permanent damage or deterioration after the transistor breakdown.

3. P CM is the maximum allowable collector power dissipation. In operation the transistor collector current generates heat in the heat collector junction of the transistor. If the power dissipation is too large, the transistor will burn out. In use for a long time if the operation of transistor greater than P CM , the transistor may be damaged. Note that the high-power transistor given the maximum allowable power dissipation is supplemented with parameters under certain circumstances specifications radiator. Use must pay attention to this.

4. Characteristic frequencies f T . As the operating frequency increases, amplification capability of the transistor will decrease, corresponding to a β = 1 when the frequency f T is called the characteristic frequency of the transistor.

5. On-time, off-time is an important parameter to measure the response speed of the switch.

Common Switch

switching transistor same shape and appearance ordinary transistor, for switching off and on the main circuit. Because of its complete disconnection or turned action, are widely used in a switching circuit, and having a fast switching speed, long life, and generally for power | regulator circuit, a drive circuit, an oscillator, a power amplifier, pulse amplifier and line output circuit. Because the power switching transistor can be divided into small power switch and power switch.

conventional low power switch are: 8550,8050 like.

conventional high back pressure, with a high-power switch tube: 2SD1556,2SD1887,2SD1455,2SD1553,2SD1497,2SD1433,2SD1431,2SD1403,2SD850 the like, which are the maximum back pressure above 1500V.

Considerations

1, the transistor Select "switching transistor", to increase the switching speed;

2, the circuit design, to ensure that the transistors operate in the "saturated / off "state, can not work in the enlarged region;

3, not to make the transistor in a deep supersaturation, otherwise affect the switching speed off; as off, does not necessarily require a" negative voltage "bias input when the zero on the deadline, otherwise affect the conduction conversion speed.

4, transistor switch as is noted for its reliability; at the base of the man-access to a negative power supply VEE, its reliability can be solved.

5, the transistor switching speed is generally unsatisfactory; to adjust the input frequency signal.