How to Read Voltage Regulator Part Numbers — 7805 · LM317 · AMS1117-3.3, LDO Voltage Codes and Package Letters

Illustration: At the counter of an electronic parts shop, a customer holds up a black TO-220 chip printed with 7805 and asks, “What does the 05 in 7805 mean?” A female staff member in a red apron smiles and answers, “That's the output voltage. It gives you 5V!”

A voltage regulator is a component that takes an incoming voltage and lowers it to a fixed voltage (5V · 3.3V …). Names like 7805 · LM317 · AMS1117 are short, but the part number carries the polarity (+ · −), output voltage, grade (accuracy · temperature) and package, and each manufacturer writes them differently. In particular, even if they all look the same with three legs, the pin order differs by series, so in many cases you cannot simply swap one for another.

All values were checked against the datasheets of ST · TI · onsemi · AMS · Diodes · Microchip · Torex. Click a part number to search for stock in eGuro Part Search.

1. Breaking down one part number (L7805CV)

78-series part numbers follow the order [manufacturer prefix] + 78 + two-digit voltage + grade + package (+ packing). L7805CV is ST · positive voltage · 5V · C grade · TO-220. In the ST datasheet, the C-grade 5V part is 4.8~5.2V at 25℃, while the AB · AC grades with an A are 4.9~5.1V. LDOs such as the AMS1117 use a different part number format, so they are covered separately in sections 7 and 8.

2. 78 · 79 and the last two digits — polarity and voltage

78 is a fixed type that makes a positive voltage, and 79 one that makes a negative voltage. The last two digits are the output voltage, so 7805 = 5V, 7812 = 12V, 7905 = −5V. As an exception, the 85 in ST L7885CV means 8.5V, not 85V. In TI UA78L, too, the datasheet lists 06 as 6.2V rather than 6V, and 02 as 2.6V — the two digits may not be the exact voltage, so check the datasheet.

3. 78L · 78M · 78 — current rating

L78L05ACZ is a small 100mA TO-92, and L78M05CDT-TR is a 0.5A DPAK. TI's 100mA series is named UA78L (UA78L05ACLPR). Even for the same 7805, manufacturers state the rated current differently — ST L78 · TI LM340 list 1.5A, while onsemi MC7800 lists 1.0A.

4. Grade letters — C · AC · AB · B

With an A, the output voltage is more accurate (mostly ±2%), and −40℃ grades such as B or AB · AI can be used in cold environments. However, the meaning of the letters differs by manufacturer. The B in onsemi MC7805BTG is not a more accurate grade but one with only a wider temperature range; its voltage range at 25℃ is 4.8~5.2V, the same as C. Even for the same C, ST L78 is 0~125℃, while ST L78M · L79 are 0~150℃. Temperatures refer to the temperature inside the chip (junction temperature).

5. Package letters — different for each manufacturer

For ST, V is TO-220, D2T is D²PAK, DT is DPAK and P is TO-220FP. The -DG at the end of an ST part number (L7812CV-DG) does not mean lead-free; it means TO-220 dual gauge (a metal frame of a different thickness). Conversely, the G at the end of an onsemi part number (MC7805CTG) indicates Pb-free (lead-free). onsemi's R4 · RK mean reel packing (MC7805ABD2TR4G = D²PAK 800-piece reel, MC7805BDTRKG = DPAK 2,500-piece reel). Package dimensions are in the post Component Package Names: A Complete Guide.
https://eguro.kr/en/board/view.html?b=library&id=59

6. LM317 — the adjustable type where you set the voltage

The LM317 has no fixed voltage; it is an adjustable type where two resistors set the output voltage anywhere between 1.25~37V (TI datasheet, up to 1.5A). That is why the part number has no voltage digits, and one of the three legs is an ADJ (adjust) pin instead of GND. The reference voltage is 1.25V at 25℃.

For the LM317, TI puts package codes such as KCS · KTT · DCY into the part number. The TO-220 (KCS) is marked NRND (not recommended for new designs) in the datasheet appendix. The 1117 series in the next section also has this kind of adjustable type.

7. LDOs and the 1117 series — AMS1117 · LM1117 · LD1117

An LDO (Low Dropout) is a regulator that works even with a small difference between input and output voltage. The 7805 needs a difference (dropout) of about 2V at 1A, so you must feed it around 7V to get 5V, whereas the 1117 series needs only about 1.1~1.2V at 800mA, and the AP2112-3.3 in section 8 only about 0.25V at 600mA (all typ values from the datasheets).

• AMS1117 — no package letter means SOT-223, CD = TO-252, CS = SOIC-8 (AMS1117CD-5.0). No voltage means adjustable. −40~125℃
• TI LM1117 — MP = SOT-223, DT = TO-252, S = TO-263, T = TO-220. A leading I means −40~125℃ (without it, 0~125℃). A trailing X means a larger reel (MP 1,000 pcs → MPX 2,000 pcs). The adjustable type is written -ADJ (LM1117IDTX-ADJ)
• ST LD1117 — S = SOT-223, DT = DPAK, V = TO-220, D = SO-8. The C after the two-digit voltage (33 = 3.3V) means −40~125℃ (without it, 0~125℃), and TR means reel. No voltage digits means adjustable (LD1117STR)

All three manufacturers call it 1117, but the maximum current (1A · 800mA) and maximum input voltage (AMS1117 15V, LM1117 recommended 15V · absolute maximum 20V) differ. The same name does not mean the same specifications.

8. How 3.3V is written — different for each manufacturer (incl. small LDOs)

• AP2112K-3.3TRG1 (Diodes) — K = SOT-25 (SOT-23 5-pin), 3.3V, TR = reel (3,000 pcs), G1 = Green. 600mA
• XC6206P332MR-G (Torex) — 33 = 3.3V, 2 = ±2% (1 means ±1%), MR = SOT-23 reel of 3,000 pcs, -G = halogen- and antimony-free. 200mA for the 3.0V type
• MCP1700T-3302E/TT (Microchip) — T = reel, 330 = 3.3V, 2 = 2% tolerance, E = −40~125℃, /TT = SOT-23. 250mA

Small LDOs have low input voltages — the AP2112 · MCP1700 operate up to 6.0V (absolute maximum 6.5V) and the XC6206 up to 6.0V, so you must not feed them 12V directly. The 2 in the MCP1700 part number means 2%, but the datasheet accuracy over the full −40~125℃ range is ±3%.

9. Pinouts — the most dangerous trap

Even with three legs, the pin order differs by series. If you plug an LM317 or AMS1117 straight into a 7805 socket, input and output are swapped. The tab (the metal on the heatsink side) is also connected to GND on the 7805, IN on the 7905 and OUT on the LM317 · 1117, so insulation may be needed when mounting several on one heatsink. Even within the 78 series, the 78L05 TO-92 is OUT · GND · IN, the reverse of the 7805 TO-220, and even for LDOs from the same manufacturer, SOT-23 and SOT-89 swap the IN · OUT positions. For the Diodes AP2112 SOT-89-5, even in the same package, R5 and R5A have the EN pin in different positions.

Illustration: A customer tries to plug an AMS1117 into the spot on the board where a 7805 was removed, asking, “They both have three legs, so I can just plug it in, right?” The female staff member holds out her palm to stop him and answers, “The pin order is different! The 7805 is IN·GND·OUT, and the 1117 is GND·OUT·IN.”

10. Top markings on the chip

Large TO-220s are printed with something similar to the part number, but even if you buy an LM7805CT from TI, the body is marked LM340T5 7805 (Part marking in TI's appendix). Small chips such as SOT-223 · SOT-23 carry only short codes like N05A · G3P · L3, so you have to look them up in the marking code table of that manufacturer's datasheet. On the Microchip MCP1700 SOT-23, the first two characters CS mean 3.3V, and on the Torex XC6206 SOT-23, 6 · 6 · 2 + lot characters mean 3.3V.

11. Common part numbers decoded

All decoded from the ordering information in each manufacturer's datasheet. Current is the rated (maximum) value stated in the datasheet; the current you can actually draw decreases depending on heat dissipation and the input-output voltage difference.

12. What to check when substituting

• Polarity and voltage — 78 (+) · 79 (−), fixed voltage or adjustable (ADJ)
• Pin order and tab — the table in section 9. Even with the same three legs, the IN · OUT positions differ
• Current — 78L (100mA) · 78M (0.5A) · 78 (1.5A); the 1117 also comes in 1A and 800mA
• Dropout and maximum input — how much higher the input must be than the output, and the maximum input voltage (around 6V for small LDOs)
• Grade and temperature — the meaning of the letters C · A · B · I · E differs by manufacturer, so check the datasheet
• Package and packing — compare by package name (TO-220 · SOT-223 …) rather than letters; reel · tube quantities

Sources: ST L78 (DS0422) · L78L (DS0424) · L78M (DS0425) · L79 (DS0428) · LD1117, TI LM340 (SNOSBT0L) · UA78L (SLVS010X) · LM317 (SLVS044Z) · LM1117 (SNOS412Q), onsemi MC7800/D, Advanced Monolithic Systems AMS1117, Diodes AP2112 (DS39724), Microchip MCP1700 (DS20001826E), Torex XC6206 (ETR03005) datasheets. Grades · packages · markings may differ by manufacturer and product, so check the relevant datasheet before placing an actual order.