Dragon Tamer
Member
can someone please give me a brief description on how to use JFETs and MOSFETs?
plz provide pictures, thx
plz provide pictures, thx
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
1.) MOSFETS are often used in power applications where the voltage is typically 100V or less. But some can be used up to several hundred volts.what I was looking for specifically was an equivalent circuit, and some ideas on how do not destroy them with heat or over voltage. Lets try this:
1.) What voltages are MOSFETs used for (most of the time)?
2.) Are MOSFETs designed for use in AC circuits?
3.) What is the equivalent circuit for a MOSFET?
4.) What is the equivalent circuit for a JFET?
Generally a resistor is used on the gate to prevent ringing. Since their usual state is digital (on/off) you don't want a ringing signal on the gate putting them in the linear region.
Care should be exercised not to exceed the gate-to-source maximum voltage rating. Even if the applied gate voltage is kept below
the maximum rated gate voltage, the stray inductance of the gate connection, coupled with the gate capacitance, may generate
ringing voltages that could lead to the destruction of the oxide layer. Overvoltages can also be coupled through the drain-gate
self-capacitance due to transients in the drain circuit. A gate drive circuit with very low impedance insures that the gate voltage
is not exceeded in normal operation. This is explained in more detail in the next section.
The most difficult task in direct gate drives is to
optimize the circuit layout. As indicated in Figure
8, there might be considerable distance between
the PWM controller and the MOSFET. This
distance introduces a parasitic inductance due to
the loop formed by the gate drive and ground
return traces which can slow down the switching
speed and can cause ringing in the gate drive
waveform.
I keep hearing people say this, but I think it's only specific to amplifiers, not switching circuits.
If you charge a cap, is there ringing? Why would there be ringing by charging a gate? I've looked with a scope and the only ringing is a bit from the driver itself, but it gets smoothed out by the gate capacitance usually.