78M05 — 500mA Fixed 5.0V Positive Linear Voltage Regulator

Overview

The 78M05 (L78M05 / MC78M05 / LM78M05) is the medium-power 3-terminal positive fixed linear voltage regulator delivering $+5.0\text{V}$ DC at up to $500\text{ mA}$ ( $0.5\text{A}$ ). Housed in standard TO-220, DPAK (TO-252), and IPAK packages, it fills the design space between the low-power $100\text{mA}$ 78L05 (TO-92) and the heavy-duty $1.5\text{A}$ LM7805 (TO-220).

Operating with an input voltage range from $7.0\text{V}$ to $35.0\text{V}$ DC, the 78M05 incorporates full internal thermal overload protection, internal short-circuit current limiting, and output transistor safe-operating-area (SOA) protection. It is an ideal regulator for microcontroller boards, relay driver circuits, and sensor subsystems that require more than $100\text{mA}$ without requiring the physical board footprint or heatsink mass of a full 1.5A regulator.

Quick reference


Regulator Type	Positive Fixed Linear Voltage Regulator
Package Options	TO-220-3 / DPAK (TO-252) / SOT-82 / IPAK
Output Voltage ( $V_{OUT}$ )	$+5.0\text{ V}$ DC ( $\pm 2\%$ to $\pm 4\%$ )
Input Voltage Range ( $V_{IN}$ )	$7.0\text{ V}$ to $35.0\text{ V}$ DC
Dropout Voltage ( $V_{DROP}$ )	$2.0\text{ V}$ typical at $500\text{mA}$
Maximum Output Current ( $I_{OUT}$ )	$500\text{ mA}$ ( $0.5\text{ A}$ ) continuous
Quiescent Ground Current ( $I_Q$ )	$4.2\text{ mA}$ typical ( $6.0\text{ mA}$ 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-220 / DPAK Package)

Looking at the front labeled face of the TO-220 / DPAK package with leads pointing downward:

text

        ┌──────────────┐
        │  O  [Metal]  │ ── Tab is internally tied to Pin 2 (GND)
        ├──────────────┤
        │    78M05     │
        └─┬────┬────┬──┘
          1    2    3
         VIN  GND  VOUT

Pin	Name	Type	Description
1	`VIN`	Power Input	Unregulated DC Input voltage ( $+7.0\text{ V}$ to $+35.0\text{ V}$ )
2 (Tab)	`GND`	Ground	Common system ground reference ( $0\text{ V}$ , internally tied to tab)
3	`VOUT`	Power Output	Regulated $+5.0\text{ V}$ DC output (Requires $0.1\ \mu\text{F}$ bypass capacitor)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Output Voltage ( $25^\circ\text{C}$ )	$V_{OUT}$	4.90	5.00	5.10	V	$V_{IN} = 10\text{V}, I_O = 350\text{mA}$ (2% A-grade)
Output Voltage (Full Temp)	$V_{OUT}$	4.75	5.00	5.25	V	$7.0\text{V} \le V_{IN} \le 20\text{V}, I_O = 5\text{mA} \dots 350\text{mA}$
Line Regulation	$\Delta V_{OUT}$	—	3.0	50.0	mV	$7.0\text{V} \le V_{IN} \le 25\text{V}, I_O = 200\text{mA}$
Load Regulation	$\Delta V_{OUT}$	—	10.0	50.0	mV	$I_O = 5.0\text{mA} \dots 500\text{mA}$
Dropout Voltage	$V_{DROP}$	—	2.0	2.5	V	$T_J = 25^\circ\text{C}, I_O = 500\text{mA}$
Quiescent Current	$I_Q$	—	4.2	6.0	mA	$V_{IN} = 10\text{V}, I_O = 200\text{mA}$
Peak Output Current	$I_{OUT(pk)}$	500	700	—	mA	$T_J = 25^\circ\text{C}$
Ripple Rejection	$RR$	62	80	—	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 1: VIN]                                 │
         78M05                                      │
       [Pin 2: GND] ────────────────────────────────┼─── Common System GND
       [Pin 3: VOUT]                                │
           │                                        │
           ├───[ C_OUT: 0.1µF Ceramic ]─────────────┘
           │
  Regulated +5.0V DC Output (Up to 500mA)

Comparison: 78L05 vs 78M05 vs LM7805

Parameter	78L05	78M05	LM7805
Max Current	$100\text{ mA}$	$500\text{ mA}$	$1500\text{ mA}$ ( $1.5\text{A}$ )
Typical Package	TO-92	TO-220 / DPAK	TO-220 / TO-3
Pinout (Facing Front)	`VOUT - GND - VIN`	`VIN - GND - VOUT`	`VIN - GND - VOUT`
Thermal Resistance ( $\theta_{JA}$ )	$\approx 160^\circ\text{C/W}$	$\approx 65^\circ\text{C/W}$	$\approx 50^\circ\text{C/W}$

Common mistakes

Assuming 78M05 shares the 78L05 pinout:
- 78M05 / LM7805 (TO-220 / DPAK): Pin 1 = VIN, Pin 2 = GND, Pin 3 = VOUT
- 78L05 (TO-92): Pin 1 = VOUT, Pin 2 = GND, Pin 3 = VIN Always verify the package type when migrating a design between 78L05 and 78M05.
Neglecting thermal heatsinking at high input voltages: At $V_{IN} = 15\text{V}$ and $I_{OUT} = 400\text{mA}$ , dissipated power is $P = (15 - 5) \times 0.4 = 4.0\text{ Watts}$ . Without a heatsink, the internal thermal protection will trip within seconds.

Notes

"M" Designation: In standard semiconductor nomenclature, the "M" denotes Medium power ( $500\text{mA}$ ), "L" denotes Low power ( $100\text{mA}$ ), and no letter denotes standard power ( $1.0\text{A} \dots 1.5\text{A}$ ).

Interface	3-Terminal Passive (VIN, GND, VOUT)
Package	TO-220-3 / DPAK (TO-252) / SOT-82 / IPAK