78L05 — 100mA Fixed 5.0V Positive Linear Voltage Regulator

Overview

The 78L05 (LM78L05 / MC78L05 / L78L05) is the classic 3-terminal positive fixed linear voltage regulator delivering $+5.0\text{V}$ DC at up to $100\text{ mA}$ . Housed in a through-hole TO-92 package, it is the low-current, compact companion to the ubiquitous 1.5A LM7805 (TO-220).

Operating with an input voltage range from $7.0\text{V}$ to $30.0\text{V}$ DC, the 78L05 incorporates internal thermal overload protection, internal short-circuit current limiting, and safe-area compensation. It is widely used across breadboards, consumer electronics, audio preamplifiers, and retrocomputing modules for local point-of-load 5V regulation where load currents remain below $100\text{mA}$ .

Quick reference


Regulator Type	Positive Fixed Linear Voltage Regulator
Package	TO-92 (3-pin through-hole) / SOIC-8 / SOT-89
Output Voltage ( $V_{OUT}$ )	$+5.0\text{ V}$ DC ( $\pm 4\%$ or $\pm 5\%$ )
Input Voltage Range ( $V_{IN}$ )	$7.0\text{ V}$ to $30.0\text{ V}$ DC ( $35\text{ V}$ max surge)
Dropout Voltage ( $V_{DROP}$ )	$1.7\text{ V}$ typical ( $2.0\text{ V}$ max at $100\text{mA}$ )
Maximum Output Current ( $I_{OUT}$ )	$100\text{ mA}$ continuous ( $140\text{ mA}$ peak)
Quiescent Ground Current ( $I_Q$ )	$3.5\text{ mA}$ typical ( $5.5\text{ mA}$ max)
Operating Junction Temp	$0^\circ\text{C}$ to $+125^\circ\text{C}$ (Commercial) / $-40^\circ\text{C} \dots 125^\circ\text{C}$ (Industrial)

Pinout (TO-92 Package)

Looking at the flat front face of the TO-92 package with leads pointing downward:

text

        ┌─────────┐
        │  TO-92  │
        │  78L05  │
        └─┬───┬───┬─┘
          1   2   3
        VOUT GND VIN

(Note: When viewing from the bottom lead entrance, Pin 1 is Output on the right or left depending on convention; looking at the flat face, left-to-right is Pin 1: Output, Pin 2: Ground, Pin 3: Input).

Pin	Name	Type	Description
1	`VOUT`	Power Output	Regulated $+5.0\text{ V}$ DC output (Connect $0.1\ \mu\text{F}$ bypass capacitor)
2	`GND`	Ground	Common system ground reference ( $0\text{ V}$ )
3	`VIN`	Power Input	Unregulated DC input ( $+7.0\text{ V}$ to $+30.0\text{ V}$ )

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Output Voltage ( $25^\circ\text{C}$ )	$V_{OUT}$	4.80	5.00	5.20	V	$V_{IN} = 10\text{V}, I_O = 40\text{mA}$ (4% A-grade)
Output Voltage (Full Temp)	$V_{OUT}$	4.75	5.00	5.25	V	$7.0\text{V} \le V_{IN} \le 20\text{V}, I_O = 1\text{mA} \dots 40\text{mA}$
Line Regulation	$\Delta V_{OUT}$	—	32	150	mV	$7.0\text{V} \le V_{IN} \le 20\text{V}$
Load Regulation	$\Delta V_{OUT}$	—	15	60	mV	$I_O = 1.0\text{mA} \dots 100\text{mA}$
Dropout Voltage	$V_{DROP}$	—	1.7	2.0	V	$T_J = 25^\circ\text{C}, I_O = 100\text{mA}$
Quiescent Current	$I_Q$	—	3.5	5.5	mA	$V_{IN} = 10\text{V}, I_O = 0\text{mA}$
Peak Output Current	$I_{OUT(pk)}$	110	140	—	mA	$T_J = 25^\circ\text{C}$
Ripple Rejection	$RR$	41	49	—	dB	$f = 120\text{ Hz}, V_{IN} = 8\text{V} \dots 18\text{V}$

Typical Application Circuit

text

  Unregulated DC In (7.0V - 24V)
           │
           ├───[ C_IN: 0.33µF Ceramic / Tantalum ]──┐
           │                                        │
       [Pin 3: VIN]                                 │
         78L05                                      │
       [Pin 2: GND] ────────────────────────────────┼─── Common System GND
       [Pin 1: VOUT]                                │
           │                                        │
           ├───[ C_OUT: 0.1µF Ceramic ]─────────────┘
           │
  Regulated +5.0V DC Output (Up to 100mA)

Thermal & Power Dissipation

Because the 78L05 is a linear regulator, all excess voltage is converted directly into heat:

$P_{diss} = (V_{IN} - V_{OUT}) \times I_{OUT}$

With $V_{IN} = 9\text{V}$ and $I_{OUT} = 50\text{mA}$ : $P_{diss} = (9\text{V} - 5\text{V}) \times 0.05\text{A} = 0.20\text{ Watts} \quad (\Delta T \approx 0.20\text{W} \times 160^\circ\text{C/W} = +32^\circ\text{C})$
With $V_{IN} = 24\text{V}$ and $I_{OUT} = 100\text{mA}$ : $P_{diss} = (24\text{V} - 5\text{V}) \times 0.1\text{A} = 1.9\text{ Watts} \quad (\text{Thermal shutdown will trigger in TO-92})$

Common mistakes

Assuming 78L05 is a Low-Dropout (LDO) regulator: The 78L05 requires at least $7.0\text{V}$ input ( $V_{IN} \ge V_{OUT} + 2.0\text{V}$ ) to regulate 5.0V. It will not work from a 5V USB port or 6V battery pack (use an LM2931-5.0 or LP2950-5.0 instead).
Pinout mirror confusion: The TO-92 78L05 pinout (VOUT-GND-VIN) is completely different from the TO-220 LM7805 pinout (VIN-GND-VOUT). Reversing input and output pins will cause the chip to draw excessive current and overheat.

Notes

78L05 vs LM7805: 78L05 is rated for $100\text{ mA}$ max in TO-92; LM7805 is rated for $1.5\text{ A}$ max in TO-220.

Interface	3-Terminal Passive (VOUT, GND, VIN)
Package	TO-92 (3-pin through-hole) / SOIC-8 / SOT-89