Classification and measurement methods of field effect transistors (MOS tubes):
1. Symbol: “Q, VT”, FET referred to as FET, is another semiconductor device that controls the output current by voltage. It is a voltage control device.
FET three poles:
D extremely drain (current electrode)
S extremely source electrode (output electrode)
G extremely gate (control electrode)
D and S poles are used interchangeably to
two, classification FET:
field The effect tube can be divided into N-channel and P-channel tubes according to the channel division (the direction of the arrow in the middle can be seen in the symbol diagram).
According to the material, it can be divided into junction tube and insulated grid tube. The insulated grid type is divided into depletion type and enhanced type. Generally, most of the main board is insulated gate type tube, referred to as MOS tube, and most of them adopt enhanced N-channel. Second, the enhanced P-channel, the junction tube and the depletion tube are almost unused.
Third, the characteristics of the effect tube:
1, working conditions: D pole must have power supply, G pole must have control voltage
2, the field tube N-channel on the motherboard, the higher the G pole voltage, the higher the S pole output voltage
3, When the field tube G voltage on the main board reaches 12V, the DS is fully turned on, and the 5V on the individual boards is turned on.
4. The DS function of the field tube can be interchanged
with the on-off voltage of the N-channel field tube:
conduction condition: VG>VS When VGS=0.45--3V, it is in the on state, and the larger the VGS is, the larger the ID is. The
cutoff condition is: VG<VS, the ID has no current or has a small current.
4. The effect of the FET:
Amplification, modulation, resonance, switch
five, measurement and quality determination of the FET
1, measurement
polarity and tubular Analyzing
red pen then S, then D is black pen (300-800) are N-channel
red pen then D, then the black pen is S (300-800) is a p-channel
if the first is not G, D and nothing S, D president ring, and G on the leads connected to the discharge shortest foot, then a long ring if a breakdown
paste The field tube and the triode are indistinguishable. First, the triode is not used. If it is not measured by the
field tube, it is best to take it down. The measurement on the main board will not be allowed.
2. The
D and S values are judged . (300-800) is normal. If "0" is displayed and the sound is long, the field tube is broken. If "1" is displayed, the field tube is open-circuited with
soft breakdown (measurement is good, it is bad to switch to the motherboard), The field tube output is not controlled by the G pole.
Sixth, the FET replacement principle (only for the main board)
Field tube replacement only needs the same size, distinguishing the N-channel P-channel. The
power
