Some precautions for paying attention to using MOS tubes in work

2022/04/08

  Author :Iflowpower – Portable Power Station Supplier

The advancement of human society is inseparable from all walks of life, and the update of various electronic products will not open our designer's efforts. In fact, many people will not understand the composition of electronic products, such as MOS. Tube.

MOS tube is involved in conductive from most carriers, also known as single-pole transistors. It belongs to voltage control semiconductor devices. Has high input resistance (10 ^ 7 ~ 10 ^ 12Ω), low noise, low power consumption, large dynamic range, easy integration, no secondary breakdown phenomenon, safe work area width, etc.

, is now a bipolar transistor and Power transistor's powerful competitor. MOS tubular diode (also known as parasitic diode) found in a single MOS tube device, but there is no in the integrated circuit. The diode can be used in reverse protection and continuation of high current drive and inductive load.

Usually, the forward pressure drop is about 0.7-1V. Since the diode is present, the MOS device cannot simply understand the use of the switch in the circuit.

For example, in the charging circuit, charging is completed. After disconnecting the power, the battery will reverse. Precautions for using MOS (1) In order to safely use MOS tubes, the limit value of its dissipation power, maximum drain-source voltage, maximum gate-source voltage, and maximum current is not exceeded in the circuit design.

(2) When using various types of MOS transistors, they must be connected to the circuit in strict accordance with the required bias, and must pay attention to the bias polarity of MOS transistors. For example, there is a PN junction between the source and the drain of the MOS tube, and the gate of the N-channel tube cannot be pressed. The gate of the p-channel tube cannot be negatively biased, and this kind of push.

(3) Since the input impedance of the MOSMOS transistor is extremely high, the pin must be shorted during transportation and storage, and metal shield packaging must be used to prevent external induction potential breakdown gate. It is important to note that the MOSMOS tube cannot be placed in a plastic box. It is best to store it in a metal box.

At the same time, pay attention to the moisture resistance of the pipe. (4) In order to prevent the induction breakdown of the MOS pipe gate, all test instruments, workbenches, soldering iron, and circuit itself must be well grounded; when welding, please be welded first. Before the connection circuit, the end of the tube should be shorted to each other, and the short-circuit material is removed after welding; when the tube is removed from the assembly frame, ensure that the human body is grounded in an appropriate manner, for example using a ground ring.

Of course you can use. Advanced gas heating electric iron is more convenient to weld the MOS tube to ensure safety; when the power is not closed, the lamp is inserted into the circuit or from the circuit. You must pay attention to the above security measures when using MOS.

(5) When installing the MOS tube, pay attention to the installation position to avoid close to the heat generating element; in order to prevent the tube vibration, it is necessary to fix the lamp housing. When the pin lead is curved, its diameter should be larger than the root size of 5 mm to prevent the needle to bend and lead to air leakage. (6) When using the VMOS, a suitable heat sink must be added.

Take VNF306 as an example, after installing 140 × 140 × 4 (mm) radiator, the maximum power can reach 30W. (7) After connecting a plurality of tubes in parallel, since the capacitance between the electrodes and the distribution capacitance, the high frequency characteristics of the amplifier degraded, and the high frequency parasitic oscillation of the amplifier is easy to occur. Caused by feedback.

Therefore, it is usually not more than 4 composite tubes in parallel, and the parasitic oscillation resistor is connected to the bottom or gate of each tube. (8) The gate-source voltage of the MOS tube cannot be reversed, which can be stored in the open state. When the insulated gate MOS tube is not used, due to its high input resistance, each electrode must be shorted to prevent external electric fields.

Damage to the effect of the pipe. (9) When welding, the outer casing of the soldering iron must be equipped with an external ground wire to prevent damage to the tube due to electric iron. With regard to a small amount of welding, you can also heat the soldering iron before welding and pull out the plug or turn off the power.

In particular, when welding the insulated gate MOS tube, welding should be performed in the order of the source leak gate, and the welding should be cut off. (10) When sold with 25W soldering iron, it should be fast. If you use 45~75W soldering iron, use the tweezers to clamp the roots of the pin to help heat dissipation.

The MOS tube can be used to qualitatively check the quality of the tube by the meter resistance file (check the positive and reverse resistance between each PN junction and the resistance between the drain), and the insulated gate field effect tube cannot be checked for the use of the multimeter, must be used Tester. Moreover, short-term routes for each electrode can only be removed after connecting the tester. When disassembling, you should short it, then remove it.

The key is to prevent the door from floating. In summary, make sure MOS management safety use, it is necessary to pay attention to a variety of safety measures to be a variety, vast majority of professional technicians, especially the majority of electronic enthusiasts, must start according to their own actual situation, Take a practical way, safe and effective use of MOS tube. .

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