MC7805 PCB Design Guide: Footprint, Pinout, and Alternatives

The MC7805 is onsemi's 5 V, 1 A fixed positive linear voltage regulator in the MC7800 series. It is a monolithic integrated circuit with internal current limiting, thermal shutdown, and safe-area compensation for the output transistor. The datasheet specifies a 2.0 V typical dropout voltage at 1 A, 3.2 mA typical quiescent current, and 68 dB typical ripple rejection at 120 Hz. onsemi offers it in three packages — TO-220-3, DPAK-3, and D2PAK-3 — with four tolerance/temperature grades (C: 4% / 0 to +125 degC, B: 4% / -40 to +125 degC, AC: 2% / 0 to +125 degC, AB: 2% / -40 to +125 degC). This page is grounded in the onsemi MC7800-D datasheet and the live onsemi MC7800 product page.

The name '7805' is a multi-source jellybean designation. Texas Instruments manufactures the LM7805 (originally National Semiconductor), STMicroelectronics makes the L7805, and onsemi makes the MC7805. onsemi's own product page explicitly positions the MC7800 series as 'Application: LM7805, L7805 alternative.' The three parts share the same pinout and functional architecture — input, ground, output — and are broadly interchangeable in many circuits, but each manufacturer's datasheet guarantees different limits for line regulation, load regulation, quiescent current, and dropout voltage. When a rating is near the edge of your design, verify the exact datasheet for the manufacturer on your reel. The mistakes that cook MC7805s or the circuits around them are predictable: misunderstanding that the TO-220 tab is at ground potential, undersizing the filter capacitor and dropping below the dropout floor at the ripple trough, trusting the 0.2 A short-circuit current limit at low input voltages, assuming 1 A is a free-air rating without checking the thermal numbers, and treating the output capacitor as truly optional without reading the fine print on the 0.1 uF minimum. Each is covered below.

What breaks boards

1. 01

   The TO-220 tab is electrically connected to ground. Account for that when sharing a heatsink

   onsemi's TO-220 case drawing connects the tab to pin 2 (Ground). Direct contact with a heatsink at the same circuit ground does not short the output, but the tab is not electrically isolated. Use an insulating pad and shoulder washer when the heatsink is tied to another potential or shared with devices whose tabs are not at the same node. Verify tab connections before combining power devices on one heatsink.

2. 02

   The 2.0 V dropout is typical at 1 A and 25 degC. At cold start or high current the headroom requirement can be larger.

   The datasheet specifies 2.0 V typical dropout at IO = 1.0 A and TJ = 25 degC. The input voltage must remain at least 2.0 V above the output 'even during the low point on the input ripple voltage' per the Standard Application section. A 9 V transformer secondary with a bridge rectifier and filter capacitor can dip below 7 V at the ripple trough under full load, especially with tolerance stack-up on the transformer regulation and line voltage. If the input trough dips below roughly 7 V (5 V output plus 2 V dropout), the regulator drops out of regulation and the output follows the ripple. Size the filter capacitor for the worst-case line-low, load-high condition, not the nominal case.

3. 03

   Short-circuit current folds back to 0.2 A at Vin = 35 V. Do not rely on this as your only fault protection at lower input voltages.

   The 0.2 A short-circuit figure is typical and is specified at Vin = 35 V. It is not a guaranteed current limit for every input voltage, temperature, and package condition. Internal current limiting and thermal shutdown protect the regulator, but they do not replace upstream protection sized for the source, wiring, connector, and board traces.

4. 04

   The 1 A capability depends on keeping the junction within its thermal limit

   The datasheet says the regulator can deliver more than 1.0 A with adequate heatsinking and lists 65 degC/W junction-to-ambient for the TO-220 package. Dissipation is approximately (Vin - Vout) x Iout, so input voltage and load current determine the thermal problem. Check junction temperature using the complete thermal path for the actual package, interface material, heatsink or PCB copper, airflow, and ambient temperature. The current headline is not a free-air guarantee.

5. 05

   The output capacitor is optional for stability but values below 0.1 uF can cause instability. Not all 'optional' capacitors are truly optional.

   The datasheet states 'CO is not needed for stability; however, it does improve transient response. Values of less than 0.1 uF could cause instability.' This is a subtle warning: while the regulator is internally compensated and technically stable with no output capacitor, using a capacitor that is too small (below 0.1 uF) can actually create instability where none existed without a capacitor. This is a quirk of the 78xx architecture — the output stage has a zero in its transfer function that a very small capacitor can shift into a problematic range. If you add an output capacitor, use at least 0.1 uF. If you do not add one, the regulator remains stable but transient response suffers. The practical choice is a 0.33 uF to 1 uF ceramic close to the output pin, which provides both stability margin and transient improvement without the bulk of a large electrolytic.

Key specifications

Verified against the manufacturer datasheet on 2026-07-12. Confirm the current revision before production use.

Alternatives

• L7805CV: STMicroelectronics equivalent: 5 V, 1.5 A positive regulator in TO-220. Higher guaranteed output current (1.5 A vs 1.0 A) but different quiescent current and dropout characteristics. Check ST's L7800 series datasheet before substituting.
• LM317T: Adjustable 1.5 A positive regulator in TO-220. Not a 5 V fixed output — requires two external resistors to set the output voltage. Use when you need an adjustable rail or a non-standard voltage, not a drop-in 5 V replacement.
• AMS1117-3.3: Low-dropout alternative: 3.3 V fixed output at 1 A with 1.1 V typical dropout. Not a 5 V part, but if your design can run at 3.3 V, the LDO cuts headroom from 2.0 V to 1.1 V. Available in SOT-223, no heatsink required for moderate loads.
• TLV1117: TI's adjustable LDO in SOT-223 and TO-252. Set to 5 V with two resistors. 1.2 V max dropout at 800 mA — tighter headroom than the MC7805 at the cost of two external resistors. Use when the input rail is only 6-7 V and the 2.0 V dropout of the 7805 would eat your margin.

Common questions

Is the MC7805 the same as an LM7805?

Electrically and functionally they are both 5 V, 1 A fixed positive linear regulators with the same TO-220 pinout (input, ground, output). But LM7805 is a Texas Instruments part number — originally a National Semiconductor design acquired by TI in 2011. MC7805 is onsemi's part number for the same class of device. onsemi's own product page explicitly positions MC7800 as an 'LM7805, L7805 alternative.' The core architecture is shared, but the datasheet guarantees — line regulation, load regulation, quiescent current limits, dropout voltage — differ between manufacturers. When the design operates near a limit, check the exact datasheet for the manufacturer on your reel.

How much heatsinking does an MC7805 need?

It depends on input voltage, output current, ambient temperature, package, and the complete thermal path. Estimate dissipation as (Vin - Vout) x Iout, then calculate junction temperature with the applicable junction-to-case, interface, heatsink, or junction-to-ambient resistance. The datasheet lists 65 degC/W junction-to-ambient and 5 degC/W junction-to-case for the TO-220 package, but the finished assembly determines the usable current.

Can I use the MC7805 with a 12 V input?

Yes — the maximum input voltage is 35 Vdc for the 5 V output variant. But every volt above the output is turned into heat. At 12 V input and 1 A output, the regulator dissipates 7 W (12 V - 5 V = 7 V drop across the pass transistor x 1 A). That requires a substantial heatsink — 7 W through 65 degC/W without a heatsink would produce a 455 degC junction rise, tripping thermal shutdown almost instantly. At 12 V input, you either need a large heatsink or you should consider a switching regulator if efficiency matters. For low-current applications (under 100 mA), the dissipation is manageable and a small heatsink or the board copper of a DPAK variant may suffice.

What are the MC7805 tolerance grades (C, B, AC, AB) and which should I buy?

onsemi offers four grades: C (4% tolerance, 0 to +125 degC), B (4% tolerance, -40 to +125 degC), AC (2% tolerance, 0 to +125 degC), and AB (2% tolerance, -40 to +125 degC). Choose the tolerance and temperature grade from the circuit limits and environment, then select an active package/orderable from onsemi's current table. Automotive programs should use the appropriately qualified NCV7805 orderable rather than assuming every MC7805 carries the same qualification.

MC7805 vs L7805CV vs LM7805: which one goes on my BOM?

All three are 5 V, 1 A (or 1.5 A for L7805) fixed positive regulators with the same TO-220 pinout. The choice is largely about manufacturer preference and availability. The MC7805 (onsemi) is the lowest-cost active TO-220 variant commonly stocked at $0.22 in volume. The L7805CV (STMicroelectronics) is rated for 1.5 A output — useful if the load occasionally exceeds 1 A. The LM7805 (Texas Instruments) is the original National Semiconductor part. All three require the same 2 V headroom and the same heatsinking math. If your BOM says '7805' without a prefix, the assembly house may substitute any manufacturer; if a specific limit matters, specify the full manufacturer part number.

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