03-11-2016, 06:41 PM
(This post was last modified: 03-11-2016, 06:45 PM by Mike Watterson.)
Power FETs can usefully use load lines, so actually can bipolar!
Many bipolar transistors have a pentode like Ic vs Vc (instead Ia, vs Va), i.e. a relatively constant current vs supply voltage above the "knee" and many FETs are more like triodes, or power VMOS types more often like voltage controlled resistors (linear output current vs supply voltage).
Loads on valves are usually resistors, transformers or inductors, except for cascode circuits. Transistor "loads" can additionally be totem pole (rare on valves) or complementary driving resistive load with centre tap supply or simulated via output coupling capacitor. A load line is most meaningful for Class A, which is very rare on transistor o/p stages, as they are usually push pull (yes transformers on pocket radios to amps for 100V line PA), totem pole/quasi complementary or complementary class B or AB. Valve push pull seems to be more often AB (usually transformer), though I've seen SOME class A and class B.
Yes, you can plot gm vs Ia (or anything else) on a spreadsheet from the data from uTracer. It allows you to save text files of all the data captured, though the built in graphs are pretty clever. It may even plot gm vs Ia directly, I don't remember. It can display user defined load line.
Many bipolar transistors have a pentode like Ic vs Vc (instead Ia, vs Va), i.e. a relatively constant current vs supply voltage above the "knee" and many FETs are more like triodes, or power VMOS types more often like voltage controlled resistors (linear output current vs supply voltage).
Loads on valves are usually resistors, transformers or inductors, except for cascode circuits. Transistor "loads" can additionally be totem pole (rare on valves) or complementary driving resistive load with centre tap supply or simulated via output coupling capacitor. A load line is most meaningful for Class A, which is very rare on transistor o/p stages, as they are usually push pull (yes transformers on pocket radios to amps for 100V line PA), totem pole/quasi complementary or complementary class B or AB. Valve push pull seems to be more often AB (usually transformer), though I've seen SOME class A and class B.
Yes, you can plot gm vs Ia (or anything else) on a spreadsheet from the data from uTracer. It allows you to save text files of all the data captured, though the built in graphs are pretty clever. It may even plot gm vs Ia directly, I don't remember. It can display user defined load line.
