LM7805 (5V Regulator) Symbol
Definition: The LM7805 symbol represents a three-terminal fixed positive 5 V linear voltage regulator IC that delivers a regulated 5.0 V DC output from an input voltage of 7–35 V at up to 1 A continuous current, with pins IN (input), GND (ground), and OUT (output), drawn in schematics as a labelled three-pin rectangular block or TO-220 outline following general IC conventions, designated U or VR followed by a number.
Also known as: 7805, 78L05, 78M05, µA7805, MC7805, positive 5V regulator, 5 volt linear regulator, 78xx 5V.
What the LM7805 (5V Regulator) symbol means
The LM7805 symbol identifies the classic 78xx-series fixed 5 V positive linear voltage regulator, one of the most ubiquitous three-terminal regulator ICs ever produced. The device requires no external components beyond input and output decoupling capacitors to deliver a stable, regulated 5 V supply from any unregulated DC source between 7 V and 35 V. In schematic diagrams the LM7805 symbol communicates that the node is the regulated 5 V power-supply output and that the downstream circuit operates exclusively from this rail.
The LM7805 is manufactured by numerous companies under various part numbers (LM7805, µA7805, MC7805, KA7805) but all are pin-compatible and functionally equivalent to the original Fairchild/National Semiconductor specification. The symbol in a circuit diagram marks the voltage-domain boundary between the unregulated input (typically from a bridge rectifier, a 9 V battery, or a 12 V supply) and the fixed 5 V output rail that powers TTL logic, microcontrollers, and digital peripherals.
How to identify the LM7805 (5V Regulator) symbol
The LM7805 symbol is a three-pin rectangular block or TO-220 transistor outline with three labelled leads: IN on the left, GND at the bottom, and OUT on the right. The label 'LM7805', '7805', or '5V REG' appears inside or beside the block. When drawn as a TO-220 package in a component outline symbol, the three leads from left to right (with the metal tab facing away) are IN, GND, OUT — the standard 78xx pin order. Schematic tools may show the output voltage (5 V) as an annotation beside the OUT pin. Filter capacitors (typically 0.1–0.33 µF on IN and OUT) are almost always shown adjacent to the device in the schematic.
Function in a circuit
The LM7805 contains an internal band-gap voltage reference, an error amplifier, and an NPN series-pass transistor. The error amplifier compares the output voltage to the internal reference (5.0 V ± 4%) and drives the pass transistor to correct any deviation. The device provides built-in overload protection (current limiting at ~1.5–2.3 A), short-circuit protection, and thermal shutdown (junction temperature limit 150 °C). Input voltage must exceed the output by the dropout voltage (2–3 V minimum) for regulation to be maintained; below this margin the output follows the input. A 0.33 µF ceramic capacitor on IN and a 0.1 µF on OUT, placed as close as possible to the device pins, are required to prevent high-frequency oscillation.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617 does not define a dedicated schematic symbol for the LM7805 or the 78xx regulator family. In IEC-style schematics the device is drawn as a general rectangular function block with three pins labelled IN, GND, and OUT, carrying the designation 'LM7805' or '7805'. |
|---|---|
| ANSI/IEEE 315 | IEEE 315-1975 (ANSI Y32.2) defines no specific symbol for the LM7805. The device follows the standard three-terminal IC block convention in ANSI schematics: IN and GND on the left, OUT on the right (or labelled as a grounded three-terminal device). Reference designator U or VR followed by a number. |
| Key difference | IEC and ANSI/IEEE representations are identical for the LM7805 block; no standard-specific glyph differentiates them. The TO-220 package outline symbol is drawn identically in both IEC-style and ANSI-style schematics. |
Terminals / pins
| Pin | Name |
|---|---|
| in | IN |
| out | OUT |
| gnd | GND |
Typical values
Input voltage: 7–35 V (minimum 7 V for regulation, absolute maximum 35 V); Output voltage: 5.0 V ± 4% (4.80–5.25 V over all conditions); Output current: 1 A continuous (TO-220), 500 mA (TO-220 limited by heat), 100 mA (TO-92 / 78L05), 500 mA (D-PAK / 78M05); Dropout voltage: 2 V minimum (typically 2–3 V); Quiescent current: ~8 mA; Line regulation: ± 100 mV; Load regulation: ± 100 mV (0–1 A); Thermal shutdown: 150 °C junction temperature; Junction-to-ambient θJA: ~50 °C/W (TO-220, no heat sink).
Where the LM7805 (5V Regulator) symbol is used
- Microcontroller and digital logic supply: regulating 9 V or 12 V batteries or wall adapters to 5 V for TTL logic, Arduino Uno, Raspberry Pi peripheral interfaces, and 5 V sensors
- Embedded system PCBs: providing a stable 5 V rail as the primary supply rail from a higher-voltage DC bus in industrial and consumer electronics products
- USB device power supply backup: supplementing or replacing 5 V USB power when the supply current exceeds USB port limits, using a 7–12 V external adapter through an LM7805
- Prototype and hobby circuits: the LM7805 in TO-220 package is the default choice for regulated 5 V breadboard supplies due to its availability, low cost, and self-contained operation
- Sensor module supply: providing a clean 5 V reference supply for 5 V-tolerant sensors, ADC reference inputs, and legacy 5 V analogue circuitry
- Educational and teaching laboratories: the LM7805 is the canonical fixed linear regulator taught in introductory electronics courses worldwide
Example
In a 9 V battery-powered Arduino Uno project schematic, an LM7805 (U1) receives the 9 V battery supply at its IN pin through a 1 A fuse (F1) and a 0.33 µF ceramic input capacitor (C1) to ground; the GND pin connects to the circuit ground; the OUT pin delivers regulated 5 V through a 0.1 µF bypass capacitor (C2) to the VCC rail powering all TTL-level logic ICs and the Arduino's 5 V pin. The LM7805 block symbol is labelled 'U1 / LM7805 / 5 V' with input 9 V and output 5 V annotated on the respective pins.
Key facts
- The LM7805 is a three-terminal fixed positive 5 V linear voltage regulator: it accepts 7–35 V at IN and delivers a regulated 5.0 V at OUT with no external components beyond input/output decoupling capacitors.
- The TO-220 package pin order left-to-right (tab facing away) is: IN, GND, OUT — the standard 78xx lead order, different from the LM317 adjustable regulator order of ADJ, OUT, IN.
- Maximum continuous output current is 1 A (TO-220 with heat sink); without a heat sink the maximum safe current is limited by thermal resistance to approximately 200–300 mA at 25 °C ambient with a 9 V input.
- The LM7805 requires a minimum 2 V input-to-output differential (dropout voltage); at VIN < 7 V the output voltage drops below the 5 V regulation point.
- Built-in protections include: output current limiting (~1.5 A), thermal shutdown at 150 °C junction temperature, and safe-area protection — the device is self-protecting under most overload conditions.
- The reference designator for the LM7805 in schematics is U followed by a number (e.g. U1) or VR followed by a number (e.g. VR1); IEC and IEEE 315 both use U as the standard IC designator.
- The LM7805 belongs to the 78xx fixed regulator series; other members provide 6 V (7806), 8 V (7808), 9 V (7809), 12 V (7812), 15 V (7815), and 24 V (7824) outputs; the complementary 79xx series provides equivalent negative voltages.
Frequently asked questions
What does the LM7805 symbol look like in a schematic?
The LM7805 symbol is a three-pin rectangular block with pins labelled IN (left), GND (bottom), and OUT (right), carrying the label 'LM7805' or '7805'. When drawn as a TO-220 package outline, the three leads left-to-right are IN, GND, OUT. Filter capacitors (0.33 µF on IN, 0.1 µF on OUT) are almost always drawn adjacent to the device in the schematic.
What does the LM7805 do in a circuit?
The LM7805 takes an unregulated DC input voltage between 7 V and 35 V and delivers a stable, regulated 5.0 V output at up to 1 A. It requires no external components beyond decoupling capacitors to operate. The output remains at 5 V ± 4% despite variations in input voltage or load current, within its rated operating range.
What input voltage does the LM7805 need?
The LM7805 requires a minimum input voltage of approximately 7 V (5 V output + 2 V dropout) to maintain regulation. The absolute maximum input voltage is 35 V. Common input sources are 9 V batteries, 12 V wall adapters, or 7.5–9 V unregulated bridge rectifier outputs.
What is the pin order of the LM7805 in a TO-220 package?
In the TO-220 package the three leads from left to right (with the metal heatsink tab facing away from you) are: IN (pin 1), GND (pin 2), OUT (pin 3). This is the standard 78xx series pin order. Note that the LM317 adjustable regulator has a different pin order (ADJ, OUT, IN), so the two types are not directly pin-compatible.
Does the LM7805 need a heat sink?
A heat sink is needed when the power dissipated — (VIN - 5) × IOUT — causes the junction temperature to approach 150 °C. Without a heat sink the TO-220 junction-to-ambient thermal resistance is ~50 °C/W; at 500 mA from a 12 V source the dissipation is (12 - 5) × 0.5 = 3.5 W, causing a 175 °C temperature rise above ambient. A heat sink reducing thermal resistance to 5–10 °C/W is required for currents above 200–300 mA with large input-output differentials.
What is the difference between LM7805, 78M05, and 78L05?
LM7805 (TO-220) supplies up to 1 A output current. 78M05 (TO-220 or D-PAK) is rated for 500 mA. 78L05 (TO-92 small package) is rated for 100 mA. All three deliver the same 5 V regulated output voltage from the same input voltage range; the suffix letter (L, M, blank) indicates the current capacity, and the package is selected accordingly for the load requirements.
Can I use the LM7805 to supply 3.3 V devices?
No. The LM7805 produces a fixed 5 V output; it cannot be adjusted to 3.3 V. To supply 3.3 V devices from a higher voltage, use a dedicated 3.3 V fixed regulator such as the LM1117-3.3, AMS1117-3.3 (LDO), or LM7833 (78xx-series 3.3 V member). Alternatively, use the adjustable LM317 with appropriate external resistors to set 3.3 V output.
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