Product Overview
A 3A Step-Up Switcher That Leaves the Output Voltage Up to You
Condition
Listed Used and sold with no test result on file. Stock is five pieces, and the part in the photos is representative of that stock rather than the exact piece that will be picked for your order. On the photographed piece the case marking is crisp and fully legible: the National Semiconductor script N logo, a 63XX code, LM2577T-ADJ, and P+. All five leads are straight and uncut, with no solder on them. The mounting tab is bare metal with fine surface scratches around the mounting hole, and the back of the tab shows light mottling and a few small dark specks. The photos are the spec for the piece shown.
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Product Overview
The LM2577 is National Semiconductor's Simple Switcher step-up regulator: a current-mode PWM converter that puts the oscillator, error amplifier, soft start, cycle-by-cycle current limit, thermal shutdown, and a 3A NPN power switch on one five-lead TO-220 chip. The family runs from a 3.5V to 40V input at a fixed 52 kHz switching frequency, which is what keeps the inductor and output capacitor small enough to live on an ordinary board instead of a separate power module. The -ADJ suffix marked on this piece is the adjustable member of the family, so instead of the factory-fixed 12V and 15V versions the output is set by an external resistor divider working against the internal 1.23V feedback reference, and the same device covers boost, flyback, and forward converter topologies. The 63XX line above the part number is a factory date and lot code, not part of the ordering number. Pin assignments, the divider math, and the external inductor and capacitor values for your rail are not confirmed here - verify against the LM2577 datasheet before use.
Key Features
- Marked LM2577T-ADJ with the National Semiconductor script N logo, a 63XX code, and P+ on the photographed piece
- Five-lead TO-220 case with a drilled mounting tab for a heatsink or chassis
- Adjustable output version, set by an external divider rather than a fixed factory voltage
- 3.5V to 40V input range with a 3A internal switch, per the LM2577 family datasheet
- Fixed 52 kHz switching frequency, current-mode PWM control
- On-chip soft start, cycle-by-cycle current limit, and thermal shutdown
- Sold each, condition Used, no electrical test result on file
Applications
- Bench builder lifting a 5V or 12V supply to a higher rail for a bias circuit, EL panel driver, or display board, with the divider set to whatever that design asks for
- Repair tech rebuilding a failed boost stage on an older instrument board that was laid out around the 52 kHz Simple Switcher family
- Battery project running from a 6V or 9V pack that has to hold a steady higher output as the cells sag toward the 3.5V input floor
- Prototype shop keeping a few adjustable pieces on the shelf so one part number covers several output voltages instead of stocking the fixed -12 and -15 variants
Frequently Asked Questions
What does the -ADJ suffix mean on this part?
It marks the adjustable version. The fixed members of the family set the output at the factory, while the -ADJ device feeds an external resistor divider back to the 1.23V reference so you choose the output voltage in your own design. Confirm the divider values and the usable output range against the LM2577 datasheet before you commit a board layout.
How does the five-lead TO-220 case mount?
It is the standard TO-220 outline with five leads instead of three and a metal tab drilled for a single screw, so it bolts to a heatsink or a chassis wall the same way a TO-220 regulator does. Whether that tab is electrically tied to one of the pins is not confirmed here - verify against the datasheet before bolting it to a grounded surface without an insulator.
Can this stand in for an LM2577T-12 or LM2577T-15?
Same case, same pin count, but not a drop-in. A board built for a fixed version usually runs feedback straight from the output, and the adjustable part needs a divider on that node to see 1.23V. You can set an -ADJ device to 12V or 15V, but you have to change the feedback network to do it.
It says Used and untested - what am I actually taking on?
Straight answer: one LM2577T-ADJ regulator, condition Used, with no electrical test result on file, so plan on it as untested. Nothing here claims this piece switches, regulates, or holds its current limit under load. What we can show you is what the camera shows on the representative piece: original marking still crisp, five straight uncut leads with no solder on them, and a tab with light surface scratches. If your build can absorb a device that has not been proven on a bench, this is a straightforward way to get an adjustable boost stage in your hands without chasing a full reel. Shipping is $8 flat rate, free once your order passes $28, and orders leave our Idaho warehouse the same or next business day.
The script N on this case puts it in National's own Simple Switcher years, before the catalog moved to Texas Instruments and the little 52 kHz boost chip quietly kept doing its job. Pick your two resistors, and the output voltage is your decision now.
