CCCS (Dependent Current Source) Symbol

The CCCS (Dependent Current Source) symbol (IEC 60617 / ANSI Y32.2).

Definition: The CCCS symbol represents a current-controlled current source — a dependent source whose output current equals a dimensionless current gain β (A/A) times a controlling current flowing through a designated branch elsewhere in the circuit — drawn per IEEE 315 / ANSI convention as a DIAMOND containing a current-direction arrow, with the controlling branch (Ctrl In, Ctrl Out) carrying the sensed current.

Also known as: current-controlled current source, dependent current source, controlled current source, F source, current amplifier source, current gain source, beta source.

What the CCCS (Dependent Current Source) symbol means

The CCCS symbol denotes an idealized two-port element: a controlling branch (Ctrl In to Ctrl Out) carries a current ix — sensed through ideally zero resistance — and an output port (Out+, Out−) forces a current iout = β·ix regardless of the voltage across it. The gain β (also written F, Ai, or hfe in transistor contexts) is dimensionless, amps per amp, making the CCCS the idealization of a pure current amplifier.

This element is the classic model of bipolar transistor action: in the common-emitter h-parameter model, collector current is hfe times base current — a CCCS with β of 50–500. Current mirrors, Darlington pairs (whose composite gain is roughly β1·β2), and optocoupler current-transfer ratios are all naturally described as current-controlled current sources. In SPICE the CCCS is the F element and, like the CCVS, senses its controlling current through a named voltage source: F1 out+ out− Vsense beta.

How to identify the CCCS (Dependent Current Source) symbol

The output side is a DIAMOND enclosing an ARROW: dependent source (diamond), current output (arrow showing positive current direction). The controlling side is a series branch — Ctrl In and Ctrl Out — through which the controlling current ix flows, with the gain written beside the diamond as β·ix. The combination of internal arrow plus a current in the gain expression uniquely identifies the CCCS among the four dependent sources.

Sort the siblings quickly: arrow inside = current output (F or G); ± inside = voltage output (E or H); ix in the expression = current-controlled (F or H); vx = voltage-controlled (G or E). IEC-tradition schematics may show an annotated circle instead of the diamond, in which case the β·ix annotation is the identifier. In BJT small-signal diagrams the CCCS frequently appears drawn between collector and emitter with the label β·ib.

Function in a circuit

In analysis the CCCS imposes iout = β·ix, linking two branch currents. Mesh analysis handles it naturally when ix is a mesh current; nodal analysis adds an auxiliary relation expressing ix in terms of node voltages through the element carrying it. The output is an ideal current source (infinite output impedance); the sensing branch is an ideal short (zero voltage drop).

As a device model, the CCCS is the amplifying element of the BJT hybrid model: ic = hfe·ib. It also captures current mirrors (β ≈ 1 from the programming branch to each output leg), Darlington composite gain, and the current-transfer ratio (CTR) of an optocoupler, where the output phototransistor current is CTR times the LED current — a CCCS whose β might be 0.5 to 6 (50–600%).

Standards: IEC vs ANSI

IEC 60617	IEC 60617 does not assign a diamond to dependent sources; strict IEC schematics annotate a circular current-source symbol with the controlling law (β·ix). The diamond remains the dominant convention in textbooks and simulator documentation worldwide.
ANSI/IEEE 315	IEEE 315 / ANSI practice draws the CCCS as a diamond with an internal arrow and the controlling current identified on a designated branch. SPICE implements it as the F element with the controlling current measured through a named voltage source: F<name> out+ out− Vsense gain.
Key difference	The visual split is the familiar diamond (IEEE/textbook) versus annotated circle (IEC). As with the CCVS, SPICE requires the controlling current of an F element to flow through a voltage source — a 0 V dummy source if necessary — because branch currents are only observable through voltage sources in the netlist formulation.

Terminals / pins

Pin	Name
out_pos	Out+
out_neg	Out-
ci	Ctrl In
co	Ctrl Out

Typical values

The gain β is dimensionless (A/A). Representative magnitudes: small-signal BJT hfe 50–500 (2N3904 ≈ 100–300); power transistors 20–100; Darlington pairs 1,000–30,000 composite; current mirrors approximately 1 (or a deliberate ratio set by emitter-area/resistor scaling, e.g. 1:2, 1:10); optocoupler current-transfer ratios 0.5–6 (50–600%). Ideal-element assumptions: zero volts across the sensing branch, infinite output impedance. SPICE example: Vsense b x 0 plus F1 c e Vsense 150 models a transistor with β = 150.

Where the CCCS (Dependent Current Source) symbol is used

BJT small-signal and h-parameter models, where collector current equals hfe (β) times base current
Current mirror analysis, treating each mirror output as a unity-gain (or ratio-scaled) CCCS of the programming current
Darlington pair equivalent circuits with composite current gain approximately β1·β2
Optocoupler models, where output current is the current-transfer ratio (CTR) times LED current
SPICE behavioral modeling of current amplifiers and current-mode signal processing blocks
Two-port hybrid-parameter (h-parameter) network representations, whose forward-transfer element hf is a CCCS

Example

Modeling an NPN transistor's collector circuit, the CCCS's Ctrl In and Ctrl Out pins sit in the base branch sensing ib (via a 0 V source in SPICE), while its Out+ and Out− pins connect from collector to emitter delivering iout = β·ib; with β = 150 the netlist Vsense base bint 0 and F1 col emit Vsense 150 makes 10 µA of base current produce 1.5 mA of collector current, reproducing the transistor's current amplification exactly.

Key facts

The CCCS equation is iout = β·ix; β is a dimensionless current gain in A/A — the same quantity as a BJT's hfe.
Symbol: diamond (dependent) containing an arrow (current output, direction of positive flow); the controlling current flows in a designated branch (Ctrl In / Ctrl Out).
SPICE letter F denotes the CCCS in the E/G/H/F scheme; the controlling current must be routed through a named voltage source, e.g. F1 out+ out− Vsense 150.
The BJT is the canonical CCCS: ic = β·ib is the heart of the transistor hybrid model, with β typically 50–500 for small-signal parts.
Current mirrors are CCCS elements of gain ≈ 1 (or a designed ratio); Darlington pairs multiply gains for composite β of 1,000–30,000.
Optocoupler current-transfer ratio (CTR) is a CCCS gain, commonly 50–600%, linking LED current to phototransistor current across galvanic isolation.
The ideal CCCS senses its control current with zero voltage drop and drives its output with infinite output impedance.
Dependent sources — the CCCS included — are never zeroed when computing Thevenin/Norton equivalents; only independent sources are killed.

Frequently asked questions

What is the difference between a CCCS and a VCCS?

Both output a current (diamond with an internal arrow), but the CCCS is controlled by a CURRENT flowing through a branch (iout = β·ix, gain dimensionless A/A), while the VCCS is controlled by a VOLTAGE across two nodes (iout = gm·vx, gain in siemens). The gain expression tells you which: an ix means CCCS, a vx means VCCS. Physically, the CCCS models bipolar transistor current gain; the VCCS models FET transconductance.

Why is the CCCS called the F source in SPICE?

SPICE assigns each dependent source a letter: E (VCVS), G (VCCS), H (CCVS), and F (CCCS). A netlist line beginning with F declares a current-controlled current source, with syntax F1 out+ out− Vsense gain, where Vsense is the name of the voltage source through which the controlling current flows. The letters are historical SPICE conventions rather than initials of the source names.

How does a CCCS model a bipolar transistor?

The defining action of a BJT is current amplification: collector current equals β (hfe) times base current. In the small-signal hybrid model, a CCCS labeled β·ib is drawn from collector to emitter, controlled by the base-branch current. With β = 150, every microamp into the base commands 150 µA of collector current. Adding rπ at the base and ro at the output refines the model, but the CCCS is its amplifying core.

What are the units of CCCS gain?

None — it is a pure ratio, amps out per amp in (A/A). This matches the other dimensionless dependent source, the VCVS (V/V), and contrasts with the VCCS (siemens) and CCVS (ohms). In transistor datasheets the same quantity appears as hFE or β; in optocouplers as CTR, usually quoted as a percentage.

How does SPICE sense the controlling current for an F element?

Through a voltage source. SPICE's formulation only tracks branch currents that flow through voltage sources, so the controlling branch must contain one — if none exists naturally, insert a 0 V dummy source (Vsense a b 0), which acts as a perfect ammeter without affecting the circuit. The F card then references it by name: F1 out+ out− Vsense 100.

Is a current mirror a CCCS?

Functionally, yes. A current mirror copies the current programmed in its reference branch to one or more output branches, which is exactly a CCCS with β ≈ 1 (or a designed ratio, achieved by scaling emitter areas or degeneration resistors). Analyzing a mirror as a unity-gain CCCS with finite output resistance is standard practice for hand calculation of bias networks and active loads.

Related symbols

Place the CCCS (Dependent Current Source) symbol on a wiring diagram or schematic in the free online circuit diagram maker — no download required.