Week #12: (11/23-27) SCRs (Intro), BJT Amplifier Types, JFETs & MOSFETs

[rjagodowski]

We will revisit Week #10 with emphasis on amplifier classification: Class A, Class B, Class AB and others.

Once that has been completed, we'll take an ever-so-slight detour to discuss SCRs. This is in preparation for your next lab which can be found here.

http://www.wisc-online.com/Objects/View ... ID=SSE4803 and http://www.wisc-online.com/Objects/View ... ID=SSE4903,

Shockley Diodes here and Here. The second link shows the two common applications of the Shockley diode as a Relaxation Oscillator and a Trigger Switch.

SCRs from AllAboutCircuits.com


Then, we'll resume our discussion of FETs with:

JFET Tutorial.

JFETs from Wisc-Online

JFET Amplifiers and their similarity to BJT amplifier circuits (from Wisc-online).

MOSFET Tutorial

MOSFET Vocabulary from Wisc-Online.

E-MOSFETs - The Ohmic Region.

2N7000-D_MOSFET DataSheet.PDF

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NTB5860NL N-Channel Power MOSFET. Make special note of the low "ON Resistance" of approximately 0.003 Ohms!!! 3 milli-ohms! Three thousandths of an ohm. That is LESS than most mechanical switch contacts. That resistance isn't even measurable with normal DMM. When you short the leads on your DMM, sometimes it might show 0.1 ohms. That is the lowest non-zero resistance the DMM can display. 0.1 ohms is equal to 100 milli-ohms. That is 30 times larger than the ON resistance of this MOSFET. Typical "OFF Resistance" between the Drain and Source is in the tens if not 100's of Mega-Ohms, which would read "Infinite" on most DMM's. These ON and OFF characteristics help explain why MOSFETs are commonly used to replace mechanical relays and contactors in electrical control equipment. Being solid-state with no moving parts, they do not wear out. The MAY be susceptible to voltage spikes, however, so flyback diodes should always be properly installed around any inductive components used with FETS and Transistors.

The MOSFET as a Switch.

MOSFET Switching Tutorial Make special note of the H-Bridge which is commonly used for DC Motor Control.

MOSFET H-Bridge

In the link above there is a good video showing the H-Bridge circuit in operation. Note the display on the scope showing the PWM (Pulse-Width Modulated) signal being applied to the DC Motor. Wide pulses result in high motor speed, thin pulses result in slow motor speed. With PWM modulation, not that even with the thin pulses, the motor is still receiving the FULL VOLTAGE, which gives the DC motor maximum torque. This is much more efficient than using a resistive element to control motor speed as the resistance "dissipates" the voltage that would otherwise be used by the motor. With reduced voltage to the motor, the motor won't be able to work at slow speeds as is possible with a PWM driver. The mechanical switch is used to reverse direction of the motor, but that could easily be converted to automatic control, if needed.

FQP30N06L_60V_32A_MOSFET.pdf

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Infineon Power MOSFETs