Circuit Symbols
Drawing style

Diode symbol

In the diode symbol shown here, the bar end is the cathode (K) and the other end the anode (A). The diode is forward biased when its anode is more positive than its cathode, whichever way the symbol is drawn.⁠Source 1Source 2Source 3

Reference Designator D⁠Source 4

On this sheet

Symbol and what it is doing

applied 0 V
applied 0 V
applied +5 V
applied +12 V
applied −5 V
applied +5 V
applied +12 V
applied −5 V
applied 0 V
applied 0 V
applied +5 V
applied +12 V
applied −5 V
applied +5 V
applied +12 V
applied −5 V
Fig. 1 — Diode, anode-side source 0 V, cathode-side source 0 V: Zero bias (ideal model) Diode, anode-side source 0 V, cathode-side source +5 V: Reverse bias (ideal model) Diode, anode-side source 0 V, cathode-side source +12 V: Reverse bias (ideal model) Diode, anode-side source 0 V, cathode-side source −5 V: Forward bias (ideal model) Diode, anode-side source +5 V, cathode-side source 0 V: Forward bias (ideal model) Diode, anode-side source +5 V, cathode-side source +5 V: Zero bias (ideal model) Diode, anode-side source +5 V, cathode-side source +12 V: Reverse bias (ideal model) Diode, anode-side source +5 V, cathode-side source −5 V: Forward bias (ideal model) Diode, anode-side source +12 V, cathode-side source 0 V: Forward bias (ideal model) Diode, anode-side source +12 V, cathode-side source +5 V: Forward bias (ideal model) Diode, anode-side source +12 V, cathode-side source +12 V: Zero bias (ideal model) Diode, anode-side source +12 V, cathode-side source −5 V: Forward bias (ideal model) Diode, anode-side source −5 V, cathode-side source 0 V: Reverse bias (ideal model) Diode, anode-side source −5 V, cathode-side source +5 V: Reverse bias (ideal model) Diode, anode-side source −5 V, cathode-side source +12 V: Reverse bias (ideal model) Diode, anode-side source −5 V, cathode-side source −5 V: Zero bias (ideal model) Diode, anode-side source 0 V, cathode-side source 0 V: Zero bias, below the 0.7 V offset Diode, anode-side source 0 V, cathode-side source +5 V: Reverse bias, below the 0.7 V offset Diode, anode-side source 0 V, cathode-side source +12 V: Reverse bias, below the 0.7 V offset Diode, anode-side source 0 V, cathode-side source −5 V: Forward bias, above the 0.7 V offset Diode, anode-side source +5 V, cathode-side source 0 V: Forward bias, above the 0.7 V offset Diode, anode-side source +5 V, cathode-side source +5 V: Zero bias, below the 0.7 V offset Diode, anode-side source +5 V, cathode-side source +12 V: Reverse bias, below the 0.7 V offset Diode, anode-side source +5 V, cathode-side source −5 V: Forward bias, above the 0.7 V offset Diode, anode-side source +12 V, cathode-side source 0 V: Forward bias, above the 0.7 V offset Diode, anode-side source +12 V, cathode-side source +5 V: Forward bias, above the 0.7 V offset Diode, anode-side source +12 V, cathode-side source +12 V: Zero bias, below the 0.7 V offset Diode, anode-side source +12 V, cathode-side source −5 V: Forward bias, above the 0.7 V offset Diode, anode-side source −5 V, cathode-side source 0 V: Reverse bias, below the 0.7 V offset Diode, anode-side source −5 V, cathode-side source +5 V: Reverse bias, below the 0.7 V offset Diode, anode-side source −5 V, cathode-side source +12 V: Reverse bias, below the 0.7 V offset Diode, anode-side source −5 V, cathode-side source −5 V: Zero bias, below the 0.7 V offset

Pick the voltage applied to each end and a model. The printed diode never changes; the highlight shows the bias and whether that model lets current through.

Model
Rows: anode-side source. Columns: cathode-side source.
anode-side source down, cathode-side source across +12 V+5 V0 V−5 V
+12 V
+5 V
0 V
−5 V

Zero bias. The applied potentials are equal, so this comparison shows no forward-bias difference. Under the ideal model, zero voltage drop alone does not determine a current.

Reverse bias. The applied anode-side potential is lower: this is a reverse-bias comparison. The ideal diode model blocks reverse current.

Reverse bias. The applied anode-side potential is lower: this is a reverse-bias comparison. The ideal diode model blocks reverse current.

Forward bias. The applied anode-side potential is higher: this is a forward-bias comparison. The ideal model permits anode-to-cathode current in the stated current-limited test; the applied values are not loaded diode voltages.

Forward bias. The applied anode-side potential is higher: this is a forward-bias comparison. The ideal model permits anode-to-cathode current in the stated current-limited test; the applied values are not loaded diode voltages.

Zero bias. The applied potentials are equal, so this comparison shows no forward-bias difference. Under the ideal model, zero voltage drop alone does not determine a current.

Reverse bias. The applied anode-side potential is lower: this is a reverse-bias comparison. The ideal diode model blocks reverse current.

Forward bias. The applied anode-side potential is higher: this is a forward-bias comparison. The ideal model permits anode-to-cathode current in the stated current-limited test; the applied values are not loaded diode voltages.

Forward bias. The applied anode-side potential is higher: this is a forward-bias comparison. The ideal model permits anode-to-cathode current in the stated current-limited test; the applied values are not loaded diode voltages.

Forward bias. The applied anode-side potential is higher: this is a forward-bias comparison. The ideal model permits anode-to-cathode current in the stated current-limited test; the applied values are not loaded diode voltages.

The cathode is a terminal name, not a permanently negative terminal. During forward conduction conventional current leaves it. A cathode can be at +5 V while the anode is more positive.

Zero bias. The applied potentials are equal, so this comparison shows no forward-bias difference. Under the ideal model, zero voltage drop alone does not determine a current.

Forward bias. The applied anode-side potential is higher: this is a forward-bias comparison. The ideal model permits anode-to-cathode current in the stated current-limited test; the applied values are not loaded diode voltages.

Reverse bias. The applied anode-side potential is lower: this is a reverse-bias comparison. The ideal diode model blocks reverse current.

Reverse bias. The applied anode-side potential is lower: this is a reverse-bias comparison. The ideal diode model blocks reverse current.

Reverse bias. The applied anode-side potential is lower: this is a reverse-bias comparison. The ideal diode model blocks reverse current.

Zero bias. The applied potentials are equal, so this comparison shows no forward-bias difference. Under the ideal model, zero voltage drop alone does not determine a current.

A diode is forward biased when its anode potential is higher than its cathode potential, and reverse biased when the cathode is higher. Page orientation does not decide bias; the current also depends on the model and connected circuit.

Zero bias, below the 0.7 V offset. The applied anode-side potential is less than 0.7 V above the cathode-side potential. It is below the offset-model comparison boundary, so this model does not permit forward conduction in the stated test.

Reverse bias, below the 0.7 V offset. The applied anode-side potential is less than 0.7 V above the cathode-side potential. It is below the offset-model comparison boundary, so this model does not permit forward conduction in the stated test.

Reverse bias, below the 0.7 V offset. The applied anode-side potential is less than 0.7 V above the cathode-side potential. It is below the offset-model comparison boundary, so this model does not permit forward conduction in the stated test.

Forward bias, above the 0.7 V offset. The applied anode-side potential exceeds the cathode-side potential by more than 0.7 V. It is above the offset-model comparison boundary; the connected circuit would determine the current.

Forward bias, above the 0.7 V offset. The applied anode-side potential exceeds the cathode-side potential by more than 0.7 V. It is above the offset-model comparison boundary; the connected circuit would determine the current.

Zero bias, below the 0.7 V offset. The applied anode-side potential is less than 0.7 V above the cathode-side potential. It is below the offset-model comparison boundary, so this model does not permit forward conduction in the stated test.

Reverse bias, below the 0.7 V offset. The applied anode-side potential is less than 0.7 V above the cathode-side potential. It is below the offset-model comparison boundary, so this model does not permit forward conduction in the stated test.

Forward bias, above the 0.7 V offset. The applied anode-side potential exceeds the cathode-side potential by more than 0.7 V. It is above the offset-model comparison boundary; the connected circuit would determine the current.

Forward bias, above the 0.7 V offset. The applied anode-side potential exceeds the cathode-side potential by more than 0.7 V. It is above the offset-model comparison boundary; the connected circuit would determine the current.

Forward bias, above the 0.7 V offset. The applied anode-side potential exceeds the cathode-side potential by more than 0.7 V. It is above the offset-model comparison boundary; the connected circuit would determine the current.

The cathode is a terminal name, not a permanently negative terminal. During forward conduction conventional current leaves it. A cathode can be at +5 V while the anode is more positive.

Zero bias, below the 0.7 V offset. The applied anode-side potential is less than 0.7 V above the cathode-side potential. It is below the offset-model comparison boundary, so this model does not permit forward conduction in the stated test.

Forward bias, above the 0.7 V offset. The applied anode-side potential exceeds the cathode-side potential by more than 0.7 V. It is above the offset-model comparison boundary; the connected circuit would determine the current.

Reverse bias, below the 0.7 V offset. The applied anode-side potential is less than 0.7 V above the cathode-side potential. It is below the offset-model comparison boundary, so this model does not permit forward conduction in the stated test.

Reverse bias, below the 0.7 V offset. The applied anode-side potential is less than 0.7 V above the cathode-side potential. It is below the offset-model comparison boundary, so this model does not permit forward conduction in the stated test.

Reverse bias, below the 0.7 V offset. The applied anode-side potential is less than 0.7 V above the cathode-side potential. It is below the offset-model comparison boundary, so this model does not permit forward conduction in the stated test.

Zero bias, below the 0.7 V offset. The applied anode-side potential is less than 0.7 V above the cathode-side potential. It is below the offset-model comparison boundary, so this model does not permit forward conduction in the stated test.

The 0.7 V offset model uses a fixed 0.7 V drop during forward conduction and no forward conduction below that boundary. Here the controls compare applied source potentials, not solved diode terminal voltages.

Terminals

⁠Source 1Source 2
A
The anode (A) is the terminal opposite the bar. During forward conduction, conventional current enters the diode at the anode.
K
The cathode (K) is the terminal at the bar. During forward conduction, conventional current leaves the diode at the cathode.

Parts of the drawing

  • Diode symbol, with numbered leaders to the triangle and the bar
1 Triangle
The diode's triangle points the way conventional current flows through it during forward conduction, from anode to cathode. The triangle does not say whether the diode is conducting: that depends on the anode's potential relative to the cathode.⁠Source 2Source 3Source 5
2 Bar
In the diode symbol shown here, the bar marks the cathode and the opposite terminal is the anode. During forward conduction, conventional current enters the anode and leaves the cathode.⁠Source 1Source 2
Fig. 2 — Diode symbol, its marks numbered
  • Diode symbol, turned 0°, with its terminal names attached

    0°

  • Diode symbol, turned 90°, with its terminal names attached

    90°

  • Diode symbol, turned 180°, with its terminal names attached

    180°

  • Diode symbol, turned 270°, with its terminal names attached

    270°

  • Diode symbol, mirrored, with its terminal names attached

    Mirrored

Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing.⁠Source 6

Fig. 3 — Diode symbol at 0°, 90°, 180° and 270°, and mirrored

Variants

Every diode variant here keeps the triangle and bar and adds one mark: arrows leaving the body for an LED, arrows arriving for a photodiode, bent bar ends for a Zener and hooked bar ends for a Schottky. With no added mark it is a generic diode.⁠Source 1Source 3

  • AK

    LED (light-emitting diode)

    Two arrows leaving the diode body mark a light-emitting diode.⁠Source 1

  • AK

    Zener diode

    Bent ends on the cathode bar mark a Zener diode, a diode meant to be used in reverse breakdown.⁠Source 1Source 3

  • AK

    Schottky diode

    Hooked ends on the cathode bar mark a Schottky diode.⁠Source 1Source 3

  • AK

    Photodiode

    Two arrows arriving at the diode body mark a photodiode.⁠Source 1

Often confused with

    • Light-dependent resistor symbol in US style; ringed: A resistor body

      Light-dependent resistor

      A resistor body

    • Photodiode symbol; ringed: A diode's triangle and bar

      Photodiode

      A diode's triangle and bar

    An LDR and a photodiode both have arrows arriving at the body, so the body decides: a resistor body for an LDR, a diode's triangle and bar for a photodiode.⁠Source 1Source 7

    • Light-dependent resistor symbol in IEC style; ringed: A resistor body

      Light-dependent resistor

      A resistor body

    • Photodiode symbol; ringed: A diode's triangle and bar

      Photodiode

      A diode's triangle and bar

    An LDR and a photodiode both have arrows arriving at the body, so the body decides: a resistor body for an LDR, a diode's triangle and bar for a photodiode.⁠Source 1Source 7

    Fig. 4 — Light-dependent resistor and photodiode, the mark that tells them apart ringedLight-dependent resistor and photodiode, the mark that tells them apart ringed

On the part

  • A diode package outline, a cylinder with leads at both ends, with a hatched band toward one end; a package marking, not part of the schematic symbol
1 Band
Many diode packages have a coloured band or stripe toward one end, and that end is the cathode lead. The band is a marking on the part: the schematic's bar names the cathode terminal but does not show where that lead sits on a package.⁠Source 3Source 8
Fig. 5 — A diode package outline, drawn apart from the symbol, with its printed band

Where you meet it

  • A diode in a loop with a battery and a resistor, drawn with no values
  • A diode in a loop with a battery and a resistor, drawn in IEC style with no values
Fig. 6 — A diode in a loop with a battery and a resistor; values left offA diode in a loop with a battery and a resistor; values left off ⁠Source 4

Notes

A diode passes current far more easily one way

A diode conducts much more readily in its forward direction than in its reverse direction. Real devices also have leakage and reverse breakdown, which this page's simplified models omit.⁠Source 2Source 3 Its two ends are the anode and the cathode, and the overlay on this sheet compares their potentials under two named models. The transistor sheet sets the diode’s triangle beside the transistor and MOSFET arrows.

An LED may carry DS rather than D

In the IPC reference-designator list cited here, BT is a battery, CB a circuit breaker, DS a lamp, display or light-emitting diode, and RT a thermistor. Other naming systems use other letters.⁠Source 4 So the letter beside an LED depends on the reference-designator list the drawing follows; its drawing is a diode’s triangle and bar either way.

Check your reading

More questions on the practice page

Pick an answer to see the reason.

  1. Question 1

    The labels on this diode are hidden. Which end is the cathode?

    A triangle pointing down with a short bar across its tip. One lead goes up from the triangle's flat base and another goes down from the bar.

    Not this one Right Answer

    The answer is “The bar end”. A schematic symbol shows how terminals connect, not where they are on a real part. Terminal letters such as E, B and C or A and K do not give lead order or package layout; the part's own documentation does.Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing.The anode (A) is the terminal opposite the bar. During forward conduction, conventional current enters the diode at the anode. The cathode (K) is the terminal at the bar. During forward conduction, conventional current leaves the diode at the cathode.

  2. Question 2

    Read the voltage applied to each end. Under the ideal model, is this diode forward or reverse biased?

    AKapplied+12 Vapplied+5 V

    A triangle pointing right with a short bar across its tip. The left-hand lead is labelled A, applied +12 V; the right-hand lead, at the bar, is labelled K, applied +5 V.

    Not this one Right Answer

    The answer is “Forward biased: the anode is more positive than the cathode”. The cathode is a terminal name, not a permanently negative terminal. During forward conduction conventional current leaves it. A cathode can be at +5 V while the anode is more positive.A diode is forward biased when its anode potential is higher than its cathode potential, and reverse biased when the cathode is higher. Page orientation does not decide bias; the current also depends on the model and connected circuit. The applied anode-side potential is higher: this is a forward-bias comparison. The ideal model permits anode-to-cathode current in the stated current-limited test; the applied values are not loaded diode voltages.

  3. Question 3

    This diode is drawn pointing left. What decides whether it is forward or reverse biased?

    AK

    A triangle pointing left with a short bar across its tip. The lead at the bar, on the left, is labelled K; the lead on the right is labelled A.

    Not this one Right Answer

    The answer is “The anode's voltage compared with the cathode's”. The diode's triangle points the way conventional current flows through it during forward conduction, from anode to cathode. The triangle does not say whether the diode is conducting: that depends on the anode's potential relative to the cathode.Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing. A diode is forward biased when its anode potential is higher than its cathode potential, and reverse biased when the cathode is higher. Page orientation does not decide bias; the current also depends on the model and connected circuit.

  4. Question 4

    Which kind of diode is this?

    AK

    A triangle pointing right with a short bar across its tip, leads labelled A on the left and K on the right, and two small arrows pointing away from the triangle.

    Not this one Right Answer

    The answer is “A light-emitting diode (LED)”. An LED and a photodiode differ only in the direction of their two arrows: an LED's point away from the body, for light given out, and a photodiode's point toward it, for light received.Every diode variant here keeps the triangle and bar and adds one mark: arrows leaving the body for an LED, arrows arriving for a photodiode, bent bar ends for a Zener and hooked bar ends for a Schottky. With no added mark it is a generic diode.Zener and Schottky symbols differ only at the cathode bar: a Zener bar has bent ends and a Schottky bar has hooked ends. Two arrows leaving the diode body mark a light-emitting diode.

  5. Question 5

    Compare the two applied voltages. Under the ideal model, what is the diode doing?

    AKapplied0 Vapplied+5 V

    A triangle pointing right with a short bar across its tip. The left-hand lead is labelled A, applied 0 V; the right-hand lead, at the bar, is labelled K, applied +5 V.

    Not this one Right Answer

    The answer is “Reverse biased, so it blocks”. A diode is forward biased when its anode potential is higher than its cathode potential, and reverse biased when the cathode is higher. Page orientation does not decide bias; the current also depends on the model and connected circuit.The diode's triangle points the way conventional current flows through it during forward conduction, from anode to cathode. The triangle does not say whether the diode is conducting: that depends on the anode's potential relative to the cathode. The applied anode-side potential is lower: this is a reverse-bias comparison. The ideal diode model blocks reverse current.

Answer key

  1. 1

    The bar end

  2. 2

    Forward biased: the anode is more positive than the cathode

    AKapplied+12 Vapplied+5 V
  3. 3

    The anode's voltage compared with the cathode's

  4. 4

    A light-emitting diode (LED)

  5. 5

    Reverse biased, so it blocks

    AKapplied0 Vapplied+5 V

Questions

Which side of a diode is positive?
Neither end is always positive. Compare the two ends with each other, not with 0 V: a cathode at +5 V is still the lower end when the anode is at +12 V, so the diode is forward biased.⁠Source 2Source 3
Is an LED symbol read the same way as a diode?
Yes. An LED keeps the triangle and bar, so the bar end is still the cathode. The two arrows leaving the body only add that it gives out light.⁠Source 1Source 2
Why do some diagrams use 0.7 V for a diode?
It comes from the offset model, a teaching approximation that treats a conducting diode as dropping a fixed 0.7 V. A real diode's forward voltage depends on its current and temperature.⁠Source 2Source 9

Print and files

Printable symbol sheetPrintable symbol sheet More worksheets

Variants as SVG line art: LED (light-emitting diode), Zener diode, Schottky diode, Photodiode

Free to reuse under CC BY 4.0. Credit: Circuit Symbols (circuitsymbols.com). Licence and credit

Sources

12 sources, numbered as cited
  1. Lessons In Electric Circuits, Vol. V — §9, Circuit Schematic Symbols (pp. 130–139)

    Tony R. Kuphaldt, retrieved 2026-09-22.

  2. Diodes — terminal polarity, ideal and offset models (pp. 1–2, 7–10)

    MIT OpenCourseWare — Chaniotakis and Cory, retrieved 2026-09-22.

  3. ModEL — PN Junctions and Diodes, §§2.3–2.7 (bias and diode variants)

    Tony R. Kuphaldt, retrieved 2026-09-22.

  4. Design to Manufacturing Standards — Reference Designators (slide 33)

    Dieter Bergman, IPC, retrieved 2026-09-22. BT battery … CB circuit breaker … DS display, lamp, light emitting diode … RT thermistor

  5. ModEL — Components and Symbols, §3.16 (diodes, p. 29)

    Tony R. Kuphaldt, retrieved 2026-09-23. Current (pointed in “conventional flow” notation) can only pass through the diode in the direction of the diode’s arrowhead symbol.

  6. Electrical Schematics, §§1.3.1–1.3.5 — nodes, crossings, references and congruent drawings

    Tufts University, retrieved 2026-09-22.

  7. DC Electrical Circuit Analysis — resistive devices and schematic ground symbols (pp. 53, 59–64)

    James M. Fiore, Mohawk Valley Community College, retrieved 2026-09-22.

  8. Lessons In Electric Circuits, Vol. III — §3.1, diode representations (Figure 3.5, p. 100)

    Tony R. Kuphaldt, retrieved 2026-09-23. Also note that the cathode stripe on the physical part (c) corresponds to the cathode on the symbol.

  9. Small-signal diode datasheet — forward-voltage graphs (p. 2)

    Vishay, retrieved 2026-09-22.

  10. ModEL — Semiconductor Logic Gates, §2.1 (schematic versus package pinout, p. 8)

    Tony R. Kuphaldt, retrieved 2026-09-23. Research a manufacturer’s datasheet for this logic gate IC to see the “pinout” diagram showing which pins on the IC package connect to which inverter gate terminals inside.

  11. ModEL — Electromechanical Relays, §§3.2–3.3 and §5.1 (normal and present contact status)

    Tony R. Kuphaldt, retrieved 2026-09-22.

  12. ModEL — Components and Symbols, §3.17 (LED symbol, p. 31)

    Tony R. Kuphaldt, retrieved 2026-09-23. The symbol for an LED is a standard rectifying diode symbol with two small arrows pointing away from it symbolizing the emitted light.