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# What is the difference between Vcc, Vdd, Vee and Vss

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I came across a lot of circuit diagrams, on devices connected to a computer, where Vcc and Vdd are interchangeable.

• I know that Vcc and Vdd are used for positive voltage, and Vss and Vee for common line (ground), but what is the difference between each of the two options in pairs?
• Do C, D, S and E mean anything?

And in addition: why Vdd and not just Vd?

Vcc, Vee, Vdd, Vss – where do these designations come from?

The designations of power circuits stem from the field of analysis of circuits on transistors, where, usually, a circuit with a transistor and resistors connected to it is considered. The voltages (to ground) across the collector, emitter, and base are denoted Vc , Ve , and Vb . The resistors connected to the terminals of the transistor will be designated Rc , Re and Rb . The voltages at the far (from the transistor) terminals of the resistors are often referred to as Vcc , Vee , and Vbb .

In practice, for example, for an NPN transistor with a common emitter, Vcc corresponds to the plus, and Vee to the minus of the power supply. Accordingly, for PNP transistors, it will be the other way around.
Similar reasoning for N-type FETs and common-source circuits gives an explanation of the notation Vdd and Vss (D – drain; S – source, source): Vdd – plus, Vss – minus.

Designations of voltages at the terminals of vacuum tubes can be as follows: Vp (plate, anode), Vk (cathode, namely K, not C), Vg (grid, grid).

As described above, Vcc and Vee are used for bipolar transistor circuits (Vcc is positive, Vee is negative), and Vdd and Vss are used for FET circuits (Vdd is positive, Vss is negative). This designation is not entirely correct, since microcircuits consist of complementary pairs of transistors. For example, in CMOS microcircuits, the plus is connected to the P-FET sources, and the minus to the N-FET sources. However, this is the traditional, well-established designation for power circuits, regardless of the type of conductivity of the transistors used.
For bi-polar circuits, Vcc and Vdd can be interpreted as the most positive, and Vee and Vss as the most negative voltage in the circuit with respect to ground.

For microcircuits powered from one or more sources of the same polarity, minus is often denoted GND (ground). The ground can be different, for example, signal, ground connection, ground.

I do not know if it is allowed to specify third-party resources, but it seems to me it would be dishonest to keep silent about the author. RadioKot

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