Supose I wanted to use the LD1014d as a 2w class A source follower using a 24v power supply and a .5A ccs with about 12v D to S with no single input how do I calculate the input capacitence. I believe Nelson made a point in one of his articles that at least a Fet source follower had a an input capacitance lower than the Ciss figure from the data sheet. So is there an easy way to calculate this ?
LD1014D pdf, LD1014D description, LD1014D datasheets, LD1014D view ::: ALLDATASHEET :::
LD1014D pdf, LD1014D description, LD1014D datasheets, LD1014D view ::: ALLDATASHEET :::
One way to estimate the effective input capacitance of a MOSFET source follower stage, as seen by the circuit driving it, is the following
Where "Gain" is the incremental (dVout/dVin) gain of the source follower stage. It is just a wee bit less than one; Gain=0.92 might be a typical figure.
As Nelson Pass and countless EE textbooks have observed, the gate-to-source capacitance CGS is bootstrapped: both plates move together. If Gain were exactly equal to 1.0000 then CGS would have no effect whatsoever.
By the way, for those who don't wish to fight against the alldatasheet website anti-privacy machine, I've attached the datasheet in pdf format, below.
- Ceffective =approx= CGD + {CGS * (1 - Gain)}
As Nelson Pass and countless EE textbooks have observed, the gate-to-source capacitance CGS is bootstrapped: both plates move together. If Gain were exactly equal to 1.0000 then CGS would have no effect whatsoever.
By the way, for those who don't wish to fight against the alldatasheet website anti-privacy machine, I've attached the datasheet in pdf format, below.
The datasheet shows abolute maximum Vds as 24V
How did you arrive at a supply voltage of 24Vdc?
If you set your single ended amplifier/follower Id to 0.5A then the maximum output current will be 0.5Apk
The maximum ClassA output is also 0.5Apk
The maximum output power into 8ohms is 2W as you have stated.
But the maximum swing into an 8ohm load is only 4Vpk, or 8Vpp.
Your supply should be somewhere between 2V and 5V above the swing in each direction.
That gives a PSU range of somewhere around 8+2*2 to 8+2*5 = 12Vdc to 18Vdc, not 24Vdc.
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