20 .- What are the differences in the characteristics of gate BJTs and MOSFETs?
The high power bipolar transistors are common in power converters at frequencies below 10 kHz. And its application is effective in the specifications of power up to 1200 V, 400 A. a bipolar transisor has three terminals: base, emitter and collector. It usually operates as a switch in the common emitter configuration.
While the base of an NPN transistor that a potential higher than the emitter and the base current is large enough to drive the transistor in the saturation region, the transistor will remain turned on whenever the junction of the collector to transmitter is properly polarized.
The forward drop of a driving transistor is in the range of 0.5 to 1.5 V. If the excitation voltage of the base is removed, the transistor remains non-conducting mode. (Ie disabled).
Power MOSFETs are used in power converters, high speed and are available in a relatively low power specification in the range of 1000V, 50 A, in a frequency range of several tens of kHz.
21 .- What is the characteristic of an IGBT gate?
The IGBT power transistors are voltage controlled. By nature, they are faster than the BJT, but still not as fast as the MOSFET. However, they offer excitement and features of much higher output at high currents and frequencies up to 20 kHz. IGBTs are available up to 1200 V, 400 A.
22 .- What is the characteristic of an MCT gate?
An MCT can be activated by a small negative voltage pulse on the MOS gate on its anode), and by pulse descativar small positive voltage.
23 .- What is the characteristic of a SIT gate?
A SIT is a high-power and high frequency. It is essentially solid-state version of a triode vacuum tube, and is similar to a JFET. It has a power capacity of low noise, low distortion and high frequency audio. The activation and deactivation times are very short, typically o.25 usec.
The characteristic of normally active and high voltage drop limit their applications for conversion of utility power. The specification of current use of SIT may be up to 1200V, 300 A, and the speed of interruption can be as high as 100kHz.
The SIT is suitable for high power, high frequency (ie, audio, VHF / UHF and microwave amplifiers).
24 .- What are the differences between a BJT and IGBT?
-The IGBT power transistors are voltage controlled
'They're faster than BJT
-The IGBTs are suitable for high voltages, high currents.
-Manage frequencies up to 20Khz.
-IGBTs are available up to 1200V, 400 A.
-The BJT power transistors are current controlled.
-They are less rapid than BJT
-Not suitable for high voltages, high currents.
-Manage frequencies below 10 kHz
-It can handle voltages up to 1200V and currents up to 400 A
25 .- What are the differences between MCT and GTO?
-The GTO is activated by applying a brief positive pulse gates.
-The GTO-energize by applying a short negative pulse gates.
-Do not require any switching circuit
-They are very attractive for switching converters forced
-Are available up to 400V, 3000 ª.
-The MCT can be energized by a small negative voltage pulse on the MOS gate (with respect to its anode).
-The MCT-energize through a small pulse of positive voltage.
Energization-gain is very high.
-MCTs are available up to 1000V, 100A.
26 .- What are the differences between the Sith and the GTO?
-The GTO thyristors and self SITH are disabled.
-The GTO and the Sith are energized by applying a brief positive pulse gates.
The GTO-SITH-energize and by applying a short negative pulse gates.
-The Sith differ from the GTO in its specifications and the Sith are available up to 1200V, 300A. and are available 4000V GTO, 300 A.
-The Sith apply to medium power converters.
-The Sith handle frequencies of several hundred kHz. Beyond the frequency range of the GTO.
Types of power diodes: diodes standard for general use, quick recovery, shottky.
Leakage current of diodes: When the anode potential is positive to the cathode is said that the diode is forward biased and conducts. When the potential of the cathode is positive with respect to the anode, said that the diode is reverse biased (tmb known as leakage current) in the range of mA and uA, whose magnitude increases as a function of reverse voltage, until the voltage avalanche or zener.
Reverse recovery time of the diodes: the time interval between an instant when the current passes through zero during the change of driving directly to the reverse blocking condition and when the reverse current is reduced to 20 % of its peak value irr, trr depends on the junction temperature, the rate of abatement of direct corriende and direct current before switching.
The reverse recovery current of diodes is the current flowing q due to minority carriers when the diode is in a condition of reverse bias.
The softness factor of the diodes is the ratio tb / ta ta which is generated by storing charge in the depletion region of reverse peak union irr; TB is due to charge storage in the material of the semiconductor.
Types of recovery diodes, fast recovery diodes are under less recovery time 5ms q, are used in converters circut ca cd cd cd and where the speed of recovery is often of critical importance. Epitaxial diodes provide higher switching speed than the diffusion diodes. For specifications of voltage above 400V fast recovery diodes are fabricated by diffusion and recovery time is controlled by diffusion of gold or platinum.
Cause of the reverse recovery time of a pn diode, current-biased diode is the net effect of the majority and minority carriers. When a diode is in forward conduction mode and current is reduced to zero, the diode continues to conduct due to minority carriers that remain stored in the pn junction.
Effect of reverse recovery time: it limits the rate of rise of forward current and switching speed.
Why is it necessary to use fast recovery diodes for high speed conversion? As q increases the speed of recovery.
What is direct recovery time? Q It takes time to recombine the charges in the pn junction.
D Difference between the pn junction diodes and shottky: a diode can be eliminated shottky the storage problem of loading a pn junction. The diode recovered charge shottky is much lower than that of a pn junction diode. The leakage current of a diode shottky is greater than a pn diode. Shottky diode with a voltage driving a relatively low leakage current is relatively high and vice versa.
Limitations of D shottky: Your permission is limited to Vmax 100v. The current ratings vary from 1 to 300 A. They are ideal for power supplies, high current, low voltage direct current. They are used in low power supplies current to greater efficiency.
Typical reverse recovery time d general purpose diodes: they have a reverse recovery time relatively high, typically 25US and are used in applications where speed Vaha recovery time is not critical,
Typical reverse recovery time of fast recovery diodes: they have a low recovery time, usually less than 5US. Converter circuits are used in cd cd cd ca, where the level of recovery is of critical importance.
What are the problems d diodes connected in series and what are the possible solutions? In many applications, high voltage diode can not be commercially available voltage to the specification required, so that the diodes are connected in series to increase reverse blocking capabilities.
Steps Involved in the tell a potecia electronic equipment, can be divided into 4 parts, 1 .- design of power circuits, 2 .- Protection of power devices, 3 .- Determination of the control strategy, 4 .- logic circuit design and control.
Peripheral effects of electronic equipment to power: the operations of power converters based on switching power semiconductor devices and as a result, the drives introduce harmonic current and voltage in the power supply and output converters . It is usually necessary to introduce in the output filter and the input of a converter system to reduce a magnitude acceptable level of harmonics.
Differences between the characteristics of the GTO gate and the thyristors, in which the thyristors are not disabled by the GTO gate and if they apply a negative pulse or the gate can be disabled mode of operation.
19 Differences between the characteristics of gate thyristors and transistors, the transistors are activated by current and voltage thyristors through.
Power Electronics:can be defined as the application of solid state electronics for controlling and converting electrical power.
Types of thyristor, phase control thyristor SCR, fast switching SCR, GTO gate deactivation of SCR bidirectional triode, RCT reverse conduction, induction static SITH, silicon-controlled rectifier LASCR light-activated, controlled by FET FET -CTH, controlled by MOS MCT.
Circuit switching: q that polarizes the gate of a thyristor (DIAC, TRIAC, SCR, FET) to ensure passage of current from anode to cathode.
Conditions for driving a thyristor: a thyristor has 3 terminals, an anode, cathode and gate. When a small current passes through the terminal gate to the cathode, the thyristor conducts long as the anode terminal to a potential higher q the cathode.
How to disable a thyristor in conduction: making the anode potential is equal to or less than the potential of the cathode. The thyristors are switched off online because of the nature of the input voltage sine wave and in forced commutated thyristors are turned off because of the nature.