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UC3844BN

STMicroelectronics

STMicroelectronics UC3844BN, current-mode PWM controller, 8-DIP (0.300", 7.62 mm), 48% max duty cycle, switching frequency up to 500 kHz, 0°C to 70°C operation.

STMicroelectronics UC3844BN
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[IN STOCK] In Stock: 3,217 pcs
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MOQ 5 · Tube · RoHS · EIA-481 · DAP/DDP · T/T

[ORIGINAL SEALED] [PRE-SHIP HD PHOTOS] [30D WARRANTY · COC] [TRACKED DAP/DDP]

Technical specifications

UC3844BN specifications
Parameter / AttributeSpecification / Value
Output typeTransistor Driver
MountingThrough Hole
Voltage - supply (Vcc (Vdd))10V ~ 30V
Frequency - switchingUp to 500kHz
I/O channels1
Output phases1
Duty cycle48%
Operating temperature0°C ~ 70°C (TJ)
PackageTube
FunctionStep-Up, Step-Up/Step-Down
TopologyBoost, Flyback
Clock syncNo
Case8-DIP (0.300\", 7.62mm)
Control featuresFrequency Control
Output configurationPositive, Isolation Capable
Synchronous rectifierNo
100% Footprint Match · Solder-Ready (No PCB Redesign Needed)

Need Stock or a Drop-in Second-Source for UC3844BN?

Package: DIP-8 / SOIC-8 · Pin-compatible replacements with immediate Shenzhen spot stock

Footprint Match 98%
Supply Chain & Allocation Reality:

The UC384x family is the current-mode PWM controller inside a generation of offline switching supplies, adapters, chargers and ATX standby rails - an 8-pin part that appears in repair in every country, and the most-fitting-wrong-part in power-supply benches. The four suffixes are not interchangeable decorations: the start-up threshold is either 16V (3842/3844, offline rails) or 8.4V (3843/3845, low-voltage rails), and the maximum duty cycle is either full (3842/3843) or 50 percent (3844/3845, for half-bridge and push-pull topologies). The wrong suffix shows up as a supply that will not start, or a transformer that saturates.

Verified Pin-Compatible Replacements (4 verified alternatives)

UC3843 TI / onsemi / STMicroelectronics DIP-8 / SOIC-8
Pin-to-Pin (Minor Clock/Init Tuning)
Availability & Target Pricing:

The Low-Voltage Start Sibling

Shenzhen Spot Stock (24-48h Dispatch)

Electrical & Core Specs:

Identical current-mode PWM engine with the UVLO window shifted down: 8.4V turn-on / 7.6V turn-off against 16V / 10V for the UC3842. Full duty cycle, 500kHz class oscillator, 5V reference, totem-pole output.

Works from lower VCC rails - the part for DC-DC converters running from 12V and 24V buses.

Compatibility & Drop-In Notes: In an offline supply fitted as a substitute for a 3842, the supply can attempt to start at a lower rail voltage - usually it simply works off the aux winding, but brown-out behavior and start-up resistor design were sized around 16V. Do not swap in this direction as routine repair policy; match the original suffix.
Package & Solder Footprint: DIP-8 / SOIC-8, pin-identical across the family.
Shenzhen Warehouse Stock & MOQ: Deep multi-fab stock; the DC-DC builders part.
Request Volume Quote for UC3843 Compare UC3844BN vs UC3843 Spec Matrix
UC3844 TI / onsemi / STMicroelectronics DIP-8 / SOIC-8
Pin-to-Pin (Minor Clock/Init Tuning)
Availability & Target Pricing:

The 50% Duty Offline Sibling

Shenzhen Spot Stock (24-48h Dispatch)

Electrical & Core Specs:

Same 16V UVLO as the 3842 with the output limited to 50 percent maximum duty by an internal toggle flip-flop - the part for half-bridge and push-pull offline converters.

16V turn-on / 10V turn-off; the offline start-up window.

Compatibility & Drop-In Notes: Fitting a 3844 where a 3842 belongs halves the maximum duty and the converter underperforms or drops out; fitting a 3842 where a 3844 belongs lets a push-pull transformer see full duty - saturation and blown switches. The suffix is functional, not cosmetic.
Package & Solder Footprint: Same 8-pin body and pin assignment.
Shenzhen Warehouse Stock & MOQ: Stocked as the half-bridge part; keep the four suffixes separated in the drawer.
Request Volume Quote for UC3844 Compare UC3844BN vs UC3844 Spec Matrix
UC3845 TI / onsemi / STMicroelectronics DIP-8 / SOIC-8
Pin-to-Pin (Minor Clock/Init Tuning)
Availability & Target Pricing:

Low Start and 50% Duty Combined

Shenzhen Spot Stock (24-48h Dispatch)

Electrical & Core Specs:

The fourth quadrant of the matrix: 8.4V UVLO with the 50 percent duty flip-flop - low-voltage push-pull and half-bridge converters.

8.4V turn-on / 7.6V turn-off.

Compatibility & Drop-In Notes: Listed to complete the ladder; substitutions across the family must carry both numbers - threshold AND duty - or the repair reintroduces the failure.
Package & Solder Footprint: Same DIP-8 / SOIC-8 pinout.
Shenzhen Warehouse Stock & MOQ: Stocked as part of the four-suffix kit for supply repair benches.
Request Volume Quote for UC3845 Compare UC3844BN vs UC3845 Spec Matrix
UC2842 TI / onsemi DIP-8 / SOIC-8
100% Drop-in (Zero Code Change)
Availability & Target Pricing:

The Industrial-Temperature Grade

Shenzhen Spot Stock (24-48h Dispatch)

Electrical & Core Specs:

Electrically the same controller in the UC284x (industrial temperature) grade against the UC384x (commercial) - same thresholds and duty per suffix digit.

Same UVLO scheme; the 2 in the prefix is temperature range, not function.

Compatibility & Drop-In Notes: When a supply runs hot or outdoors, the industrial grade is the honest replacement. Reading the prefix as function misleads - only the last digit sets threshold and duty.
Package & Solder Footprint: Same body and pinout across all temperature grades.
Shenzhen Warehouse Stock & MOQ: Stocked for industrial service work; verify the prefix on the marking.
Request Volume Quote for UC2842 Compare UC3844BN vs UC2842 Spec Matrix
Buyer & Quality Checklist for Sourcing Alternatives
  • Read two numbers before any substitution: UVLO start threshold (3842/3844 = 16V, 3843/3845 = 8.4V) and maximum duty (3842/3843 = full, 3844/3845 = 50 percent). Wrong threshold = will not start or starts on brown-out; wrong duty = underperformance or transformer saturation.
  • On the 50-percent parts (3844/3845) the oscillator runs at twice the switching frequency by design - when repairing, set RT/CT for the doubled value or everything downstream shifts.
  • The start-up network is part of the chip choice: offline designs charge VCC through a resistor from the high rail, and the aux winding must take over before the 10V turn-off. Fitting a lower-threshold suffix changes when that handover happens.
  • Current-sense input tolerances and leading-edge blanking are fixed in silicon - if a repair needed a snubber change to behave, suspect the wrong suffix or a clone die before redesigning the sense network.
  • The clone market here is deep: relabeled no-name dies pass DC tests and drift on frequency. For fleet repairs, keep verified lots and photograph the markings.
  • UC184x / UC284x / UC384x are temperature grades of the same function - use the industrial grade for hot enclosures rather than substituting down.
Frequently Asked Technical Questions

Q: What is the difference between UC3842 and UC3843?

A: The start-up threshold: UC3842 turns on at 16V (offline supplies), UC3843 at 8.4V (low-voltage DC-DC). Everything else - including full duty capability - is the same. Match the original suffix so the start-up network behaves as designed.

Q: Can I use a UC3842 where a UC3844 was fitted?

A: No - the 3844 is the 50-percent-duty part used in push-pull and half-bridge designs. A full-duty part in that socket can saturate the transformer and destroy the switching devices. The last digit encodes the duty limit; respect it.

Q: Why does my supply not start after a PWM chip replacement?

A: Check the suffix first: a 3843/3845 fitted into an offline design starts at 8.4V and the bias winding handover may misbehave, and a 16V part in a low-voltage design never reaches its threshold. Wrong-threshold swaps are the most common self-inflicted repair failure on this family.

Technical details

What the UC3844BN does in a flyback supply

It drives a single external transistor with a maximum duty cycle of 48%, which sets the practical step-up ratio in a flyback converter. Switching frequency reaches up to 500 kHz, allowing the use of smaller magnetics at the cost of tighter layout and higher switching losses.

STMicroelectronics lists the UC3844BN as Obsolete. We can source and quote to order against your quantity — confirm the BOM position count and we will search available inventory across our supplier network.

Duty-cycle ceiling and flyback design fit

The 48% max duty cycle is the key parametric difference from the UC3842 family (which allows up to 96%). In a flyback, this limits the maximum output voltage for a given input and turns ratio — a designer moving from a UC3842-based design to the UC3844BN must recalculate the transformer. The UC3844BN is pin-compatible with the UC3842/3/5 series in the same 8-DIP package, but the duty-cycle clamp is hard-wired at 48% — it is not adjustable.

Package and mounting — through-hole DIP

Supplied in a Tube, the 8-DIP (0.300", 7.62 mm) package with 2.54 mm pitch is a standard through-hole footprint. No MSL concern — the DIP body is robust against reflow and hand-soldering.

UC3844BN
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