Field effect tube to note what

( 1) for safe use of field effect tube, the circuit design of power dissipation can not exceed the maximum pipe, drain to source voltage, maximum gate voltage and maximum current and other parameters of the limit value.
( 2) MOS field effect tube as the input impedance is very high, so the transport, storage must be leading-out feet short, use the metal shielding packaging, to prevent the external gate breakdown induced potential. Pay attention to, not MOS field effect tube into the plastic box, saving best placed in a metal box, also want to pay attention to the moisture barrier tube.
( 3 ) the use of VMOS must be added the right radiator. In the case of VNF306, the pipe installation of 140 x 140 x 4 ( mm ) of the radiator, the maximum power can reach 30W.
( 4) the type field effect tube when in use, are in strict accordance with the requirements of the biasing access circuit, to abide by the FET bias polarity. Such as the JFET gate source and drain is a p-n junction, N channel tube grid not with positive bias; P channel tube grid with negative bias, etc..
( 5) in order to prevent the FET gate induced breakdown, all test equipment, workbench, electric iron, the line itself must have a good grounding pin; when welding, welding source; in the connected into the circuit before, of all lead end keep each other short connected condition, after welding the shorting material removed from components; shelf tube, should be appropriately ensure the ground such as the use of grounding ring; of course, if the use of advanced gas heating type electric iron, welding field effect tube is more convenient, and ensure the safety of; without power off time, absolutely can't put tube inserted or pulled out from the circuit circuit. The above safety measures in the use of field effect tube must note.
( 6) mounted on the field effect tube, pay attention to the installation position to avoid close to the heating element; in order to prevent pipe vibration, it is necessary to tube shell fastened together; pin lead bend, shall be greater than the root size 5 mm, in order to prevent breakage and leakage caused by tube feet.
( 7) welding, soldering iron shell must be fitted with an external ground wire, in order to prevent the electric soldering iron is charged and damage to the tubes. For a small electric iron welding, can also be hot after pull the plug or power off after welding. Especially in the welding of insulated gate field effect tube, according to the source / drain and gate sequence welding, and welding power.
( 8) multi-pipe parallel connection, because the interelectrode capacitance and the distributed capacitance of a corresponding increase, make the amplifier performance deterioration, through feedback is easy to cause the amplifier high frequency parasitic oscillation. For this purpose, the parallel composite pipes are generally not more than 4, and in each tube base or gate in series connection parasitic oscillation resistance.
( 9) JFET gate to source voltage can not be reversed, can be in the open state of preservation, and the insulated gate type field effect tube when not in use, due to its very high input resistance, to each electrode short circuit, so as to avoid the effect of external electric field and the tube damage.
( 10) 25W electric soldering iron welding should quickly, if use 45～ 75W electric soldering iron, used a pair of tweezers to clamp the tube foot root to help dissipate heat. Junction type field effect tube available sheet resistance profile of qualitative check the quality ( check the PN junction is reverse resistance and leakage between the source and the resistor value ), and the insulated gate field effect tube can not use a multimeter to check, must use the tester, and the tester can remove the access of each electrode shortest route. When removed, you should first short circuit is removed, the key to avoiding gate hanging.
The requirements of high input impedance occasions when in use, must take measures to avoid the influence of the temperature moisture, so that the FET input resistance decreased. If the four lead in the field effect tube, the substrate should be grounded wire. Ceramic encapsulated sesame tube having photosensitive properties, attention should be paid to avoid light use.
For power MOSFET, want to have good heat dissipation condition. Because the power MOSFET in the high load condition use, must be designed to ensure adequate radiator, shell temperature does not exceed the rated value, enabling the device to long-term stable and reliable work.
In short, to ensure the safe use of field effect tube, matters needing attention are diverse, safety measures is various, the majority of professional and technical personnel, especially the majority of electronic enthusiasts, according to its own actual situation, take practical and feasible method, the safe and effective use of field effect tube.

Field effect tube electrical characteristics

Field effect transistor and transistor in the electrical characteristics of the main difference is the following:Patch FET1: the field effect tube voltage control device, the conductive case depends on the gate voltage. Transistor is the current control device, the conductive case depends on the size of the base current.2: the field effect tube current IDS and the grid UGS Gm decided by the relationship between the transconductance, transistor current Ic and Ib by the relationship between amplification coefficient βdecision. That is to say, the field effect tube capable of amplifying Gm measure, transistor capable of amplifying the use of βmeasure.3: FET input impedance, input current is small; the transistor input impedance is very small, in the conductive when larger input current.4: the FET drain source static volt-ampere characteristic with gate voltage UGS variables, transistor characteristic curve to the base current of Ib variables.5: general field effect tube with small power, high power transistor.