I am trying to get a handle on some electrical circuit diagrams I've been encountering as I try to get back into electronics and building electronic gadgets. I've encountered a number of terms for voltage, and I am not sure what they all mean, so I was hoping someone could explain them to me. Here they are, along with what I believe they mean (if I think I know):

  • Vpp (Voltage peak power?)
  • Vp
  • Vcc
  • Vc
  • Vr
  • Vdd
  • Vi
  • Va
  • Vt
  • V0 or 0V (Negative or common "terminal", source of lowest potential?)

There are also the common Vin and Vout designations, which are pretty self explanatory. I've also seen positive and negative voltage indicators in AC circuits, but that is also self explanatory.

Are some of these simply context specific, with meanings only valid within a given circuit? Are they all commonly used?

  • \$\begingroup\$ Related and this one too. \$\endgroup\$ Aug 4, 2014 at 1:01
  • \$\begingroup\$ Thanks, Nick. The first link was quite useful for a number of other terms as well. \$\endgroup\$
    – jrista
    Aug 4, 2014 at 4:47

4 Answers 4


As suggested by other answers, most of this is pretty arbitrary anyway

  • Vpp : peak-to-peak voltage (for AC waveforms), historically this would also be used for the programming voltage for EEPROM or flash memory (particularly those devices that did not generate their own programming voltage on-chip).
  • Vp : peak voltage (again, for AC) referenced to system ground, or 0V. May also be used for pull-up voltages (which could also be Vpu).
  • Vcc : positive power supply for many IC's, traditionally this referred to BJT based ICs, the 'cc' referring to the collectors of the integrated transistors. Often this was matched with a negative supply, Vee ('ee' referring to the emitters of the transistors).
  • Vc : Collector voltage for a BJT, similarly Ve, Vb may also be used for the emitter and base while Vs, Vd and Vg may be used for the source, drain and gate of FETs.
  • Vr : reverse voltage, particularly when referenced to diodes. You may also encounter Vz used to indicate a zener voltage. Vf is used to indicate the forward voltage drop of the diode.
  • Vdd : positive power supply for many IC's, traditionally this referred to FET (NMOS, PMOS, CMOS) based ICs, the 'dd' referring to the drains of the integrated FETs. Often this was matched with a negative supply, Vss ('ss' referring to the sources of the FETs).
  • Vi : input voltage.
  • Va : used to indicate an internal analogue voltage point.
  • Vt : May be used for the Thevenin equivalent voltage, or as suggested by WhatRoughBeast the threshold voltage (for a comparator or similar for example), or the termination voltage (also known as Vtt in the case of DDR=type memories).
  • Vo : Output voltage for op-amps and the like.
  • 0V : Zero-volts, not to be confused with Vo, refers to the system ground. Also,
  • Vhsys : may be used for the hysteresis voltage of a comparator type circuit.
  • \$\begingroup\$ Thanks! I think this covered everything nicely. Clears up a lot of questions I had about quite a number of circuit diagrams. \$\endgroup\$
    – jrista
    Aug 4, 2014 at 1:39
  • \$\begingroup\$ Alternatively, Va : anode voltage. Usually seen alongside Vg : grid voltage (now gate voltage) and Vk : cathode voltage. Usually on older (MUCH older circuits! with tubes) but you sometimes see Va,Vk on diodes, e.g. photodiodes \$\endgroup\$
    – user16324
    Aug 4, 2014 at 10:20

Most of that notation is going to be arbitrary. However, Vdd and Vcc are commonly references to your negative supply and positive supply, respectively (some devices require such configuration, like an op-amp for example).

Vpp is actually Voltage peak-to-peak, which has relevancy when speaking about time-varying voltage signals or output voltage ripple (like pulse signals or sinusoidals).

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Vo is commonly read as Voltage-Out and is typically the voltage of interest if labeled as such.

  • 5
    \$\begingroup\$ No, Vdd and Vcc are both generally positive, but refer to different technologies: Vdd is for FET circuits (d = drain), while Vcc is for BJT circuits (c = collector). The corresponding negative supplies are Vss (s = source) and Vee (e = emitter), but these are usually just called "Gnd". \$\endgroup\$
    – Dave Tweed
    Aug 4, 2014 at 0:53
  • \$\begingroup\$ Agreed, what you've said is wrong and confusing. Related, a lot of people say VCC for any power supply voltage, regardless of whether or not it has anything to do with BJTs. \$\endgroup\$
    – benjwy
    Aug 4, 2014 at 5:02

sherrelbec's explanations look OK to me. Of the remaining,

Vp usually refers to a peak voltage

Vr is commonly a reverse voltage used, for instance, to indicate a threshold or breakdown voltage

Vi might equally be an input voltage, or the voltage appearing on a current sensor

Vt can equally be a threshold voltage or the voltage produced by a termination network


I've seen Vcc defined as the collector supply voltage, and Vc as the actual voltage at the collector (corresponding definiitions for Vss/Vs, Vdd/Vd, etc.)


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