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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > PFC (Power Factor Correction)

Texas Instruments UC3855BN

Name: UC3855BN
Brand: Texas Instruments
SKU: UC3855BN
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: UC3855BN

Manufacturer:: Texas Instruments

Category:: PFC (Power Factor Correction)

Package:: 20-DIP (0.300", 7.62mm)

Datasheet:: UC3855BN.pdf

Description:: IC PFC CTR AV CURR 500KHZ 20DIP

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Product details

Overview

UC3855BN from Texas Instruments is a high-frequency average current-mode PFC controller IC designed for boost-type power factor correction preregulators. It integrates ZVT (Zero Voltage Transition) active snubbing, inductor current synthesizer, analog multiplier with line compensation, 7.5V ±1% reference, and dual gate drivers (GTOUT/ZVTOUT) - enabling stable near-unity power factor operation up to 500kHz in AC/DC front-end supplies for industrial SMPS and server PSUs.

For engineers reviewing the UC3855BN datasheet, UC3855BN pinout, UC3855BN application, or UC3855BN equivalent, this page delivers verified technical context, validated pin functions, real-world application mappings, and confirmed alternative options for high-efficiency PFC design validation and BOM optimization.

Technical Context

The UC3855BN implements fixed-frequency average current mode control using an internal current synthesizer that reconstructs inductor current from a single current sense transformer signal - eliminating slope compensation and reducing sensing losses. Its integrated ZVT circuitry senses zero-voltage switching via the ZVS pin and drives a dedicated auxiliary MOSFET through ZVTOUT to minimize diode recovery and MOSFET turn-on losses.

It features a single-quadrant analog multiplier with line voltage feedforward (VRMS input), enabling universal input operation (90–264VAC) and fast transient response. The voltage amplifier (5MHz GBW, 80dB open-loop gain) and current amplifier (2.5–5MHz gain-bandwidth product, <4mV offset) jointly support tight output regulation and low THD line current programming.

Key Specifications

Parameter	Value and Actual Design Meaning
Operating Temp Range	0°C to +70°C - suitable for commercial-grade industrial power supplies, not extended temp automotive or military use.
Max Switching Frequency	500kHz - enabled by ZVT architecture and high-speed gate drivers; reduces magnetics size without sacrificing efficiency.
Reference Voltage	7.5V ±1% - precision internal reference enables accurate voltage loop setpoint and stable soft-start ramp generation.
Gate Driver Output	±1.5A peak GTOUT / ±0.75A peak ZVTOUT - sufficient to drive main and auxiliary MOSFETs directly without external buffers.
Current Amplifier GBW	2.5–5MHz - supports fast current loop response for low-distortion line current shaping at high frequencies.
Oscillator Accuracy	160–240kHz total variation (line + temp) - ensures predictable timing across operating conditions for reliable PFC loop stability.
Startup Supply Current	150µA typical - enables low-power auxiliary supply design and reduces standby losses in offline converters.

Pinout & Package

UC3855BN is housed in a 20-pin Plastic Dual In-line Package (PDIP-N), 0.300" wide, with standard DIL-20 pinout compatible with JEDEC MS-001. Pin 1 is located at the left end of the top row when viewed from the top with notch or dot orientation.

Pin/Terminal	Circuit Role	Design Meaning
CA	Inverting input of current amplifier	Connects to compensation network; common-mode range −0.3V to 5V enables robust noise immunity in high-dv/dt PFC environments.
CAO	Current amplifier output	Drives PWM comparator; rail-to-rail swing (0.1–7.5V) provides full duty-cycle control authority over GTOUT.
CI	Current synthesizer capacitor node	Integrates buffered ION signal during switch-on and discharges proportionally to di/dt during off-time - reconstructs continuous inductor current waveform.
CS	Level-shifted current synthesizer output	Feeds CA input and peak limit comparator; voltage >1.5V disables GTOUT - provides cycle-by-cycle overcurrent protection.
CT	Oscillator timing capacitor	Frequency set by f ≈ 1/(11200·CT); min 200pF ceramic required for accuracy and layout immunity up to 500kHz.
GND	Signal and power ground reference	All voltages referenced here; bypass capacitors must connect with shortest possible leads to minimize ground bounce in high-di/dt switching.
GTOUT	Main MOSFET gate driver output	1.5A peak totem-pole output; requires ≥10Ω series gate resistor and Schottky clamp to GND to suppress ringing and undershoot.
IAC	Multiplier line voltage current input	Accepts rectified AC line current proportional signal; nominal 650mV level eliminates zero-crossing compensation resistors.
IMO	Multiplier output current	Current-mode output feeding CA amplifier; requires external resistor to GND matching CA input impedance for proper gain scaling.
ION	Current sense transformer secondary input	Buffered, diode-level-shifted input to CI; termination resistor sized for 1V peak signal at max switch current.
OVP	Overvoltage protection input	Hysteretic comparator (7.5V trip, 400mV hysteresis) disables both GTOUT and ZVTOUT on boost OV fault - prevents capacitor overvoltage failure.
REF	7.5V precision reference output	Supplies 25mA; disabled below UVLO threshold or during OVP fault; requires ≥0.1µF ceramic bypass for stability.
RVS	Output voltage sense buffer	Provides 3V nominal buffered signal; forms second input to current synthesizer - enables output voltage feedforward for improved dynamic response.
SS	Soft-start control voltage	Charged by internal current source during startup; ramps VAO reference to limit inrush current and prevent output overshoot.
VCC	Positive supply input	UVLO thresholds: UC3855BN-A = 15.5V ON / 9V OFF; UC3855BN-B = 10.5V ON / 9V OFF; internally clamped to 20V.
VAO	Voltage amplifier output	100mV–6V swing; controls multiplier gain; levels <1.5V inhibit multiplier output - prevents instability at light load.
VSENSE	Voltage amplifier inverting input	Feedback node for boost output; nominal 3V from divider; must exceed 1.5V at 25°C for current synthesizer to function.
VRMS	Line RMS voltage feedforward input	0–5.5V range; 1.5V = low line, 4.7V = high line; enables constant power operation and fast line transient response.
VZVS	ZVT zero-voltage sense input	Detects ~0V drain voltage via blocking diode; comparator threshold 2.6V; initiates ZVTOUT pulse to enable resonant turn-on.
ZVTOUT	ZVT auxiliary MOSFET driver	750mA peak totem-pole output; drives smaller auxiliary switch; also usable as sync output for multi-phase systems.

Key Features

Feature	Design Value
ZVT (Zero Voltage Transition) circuitry	Reduces MOSFET turn-on loss and diode reverse recovery stress - enables 500kHz operation with lower EMI and higher efficiency than hard-switched PFC.
Inductor current synthesizer	Reconstructs continuous inductor current from single current transformer - eliminates need for shunt resistor, improves SNR, and avoids sensing losses in high-power designs.
Analog multiplier with VRMS feedforward	Enables universal input (90–264VAC) operation and maintains constant power delivery across line variations - critical for global AC/DC compliance.
High-bandwidth current amplifier	5MHz gain-bandwidth product and <4mV input offset - ensures fast, accurate current loop response for low THD (<5%) line current shaping.
Dual independent gate drivers	GTOUT (±1.5A peak) and ZVTOUT (±0.75A peak) support separate main and auxiliary switch control - simplifies ZVT implementation without external drivers.
Integrated OVP with hysteresis	7.66V trip with 400mV hysteresis disables both outputs - protects bulk capacitor from overvoltage failure during load dump or regulation fault.

Applications

Server Power Supplies	Industrial AC/DC Converters
Use Scenario: 1kW+ ATX or redundant PSUs requiring >98% efficiency and EN61000-3-2 Class A compliance. IC Role / Device Role / Timing Role: Primary PFC controller managing boost stage; sets 200–300kHz switching frequency and regulates input current waveform in real time. Use Value: ZVT architecture reduces conduction and switching losses, enabling higher power density and lower thermal stress on boost diode and MOSFET.	Use Scenario: Programmable logic controller (PLC) power modules with wide-input (85–264VAC) and high-reliability requirements. IC Role / Device Role / Timing Role: Fixed-frequency average current-mode PFC controller; provides stable line current regulation across temperature and line variations. Use Value: 1% 7.5V reference and low-offset amplifiers ensure consistent regulation accuracy over 0–70°C, supporting long-term field reliability.
Medical Equipment PSUs	Telecom Rectifiers
Use Scenario: UL60601-1 certified diagnostic imaging or patient-monitoring power supplies needing ultra-low EMI and high safety margin. IC Role / Device Role / Timing Role: Core PFC controller implementing active snubbing to suppress high-frequency noise generated during diode recovery. Use Value: Built-in ZVT reduces broadband EMI emissions - lowers filter component count and eases CISPR 11/EN55011 certification effort.	Use Scenario: -48V telecom rectifiers operating from 90–264VAC input with strict hold-up time and efficiency targets. IC Role / Device Role / Timing Role: High-bandwidth PFC controller using VRMS feedforward to maintain constant output power during rapid AC line sags/swells. Use Value: Line-compensated multiplier ensures stable output power down to 90VAC - preserves hold-up time and prevents brownout shutdown.

Server Power Supplies

Industrial AC/DC Converters

Use Scenario: 1kW+ ATX or redundant PSUs requiring >98% efficiency and EN61000-3-2 Class A compliance.

IC Role / Device Role / Timing Role: Primary PFC controller managing boost stage; sets 200–300kHz switching frequency and regulates input current waveform in real time.

Use Value: ZVT architecture reduces conduction and switching losses, enabling higher power density and lower thermal stress on boost diode and MOSFET.

Use Scenario: Programmable logic controller (PLC) power modules with wide-input (85–264VAC) and high-reliability requirements.

IC Role / Device Role / Timing Role: Fixed-frequency average current-mode PFC controller; provides stable line current regulation across temperature and line variations.

Use Value: 1% 7.5V reference and low-offset amplifiers ensure consistent regulation accuracy over 0–70°C, supporting long-term field reliability.

Medical Equipment PSUs

Telecom Rectifiers

Use Scenario: UL60601-1 certified diagnostic imaging or patient-monitoring power supplies needing ultra-low EMI and high safety margin.

IC Role / Device Role / Timing Role: Core PFC controller implementing active snubbing to suppress high-frequency noise generated during diode recovery.

Use Value: Built-in ZVT reduces broadband EMI emissions - lowers filter component count and eases CISPR 11/EN55011 certification effort.

Use Scenario: -48V telecom rectifiers operating from 90–264VAC input with strict hold-up time and efficiency targets.

IC Role / Device Role / Timing Role: High-bandwidth PFC controller using VRMS feedforward to maintain constant output power during rapid AC line sags/swells.

Use Value: Line-compensated multiplier ensures stable output power down to 90VAC - preserves hold-up time and prevents brownout shutdown.

Equivalent & Alternatives

The following parts are listed as comparable options for similar PFC controller applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
UC3855ADW	SOIC-20 package; same electrical specs but rated for −40°C to +85°C industrial temp range vs. UC3855BN's 0°C to +70°C.	Suitable for wider ambient environments (e.g., outdoor telecom cabinets); requires PCB rework due to surface-mount vs. through-hole PDIP.	Select UC3855ADW when extended temperature operation or automated assembly is required; UC3855BN remains optimal for cost-sensitive through-hole prototyping or legacy board reuse.
L6562A	Fixed-frequency average current-mode PFC controller with integrated 600V startup circuit; no ZVT; max 250kHz switching; different pinout and compensation structure.	Lower complexity, no auxiliary ZVT components needed; less efficient above 200kHz; lacks current synthesizer - requires shunt or transformer + op-amp.	Choose L6562A for simpler, lower-cost 100–200W designs where 500kHz operation and ultra-low EMI are not required; UC3855BN preferred for >300W, high-density, or EMI-critical applications.

Compared with UC3855ADW, UC3855BN offers identical core functionality in a through-hole PDIP package ideal for lab validation and low-volume builds, while L6562A provides a lower-complexity alternative without ZVT - trading peak efficiency and EMI performance for reduced bill-of-materials and layout simplicity.

Availability

UC3855BN is available at Aetrix Electronics and suitable for industrial AC/DC converters, server power supplies, and telecom rectifiers requiring stable component supply with long-lifecycle support and traceable sourcing.

Supply support for UC3855BN includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and power management technologies, with decades of expertise in power conversion ICs.

The UC3855BN belongs to TI's high-performance PFC controller family, engineered specifically for high-efficiency, high-frequency boost preregulators in industrial and computing power supplies - emphasizing ZVT-enabled efficiency, line-interactive regulation, and system-level EMI reduction.

FAQ

What is the operating temperature range of the UC3855BN?

The UC3855BN is specified for operation from 0°C to +70°C - a commercial-grade temperature range suitable for indoor industrial equipment, server PSUs, and telecom rectifiers. Unlike the UC2855B variant (−40°C to +85°C), it is not rated for extended temperature environments. Designers should verify ambient thermal margins and derate accordingly for sustained high-load operation.

Does UC3855BN support ZVT (Zero Voltage Transition) operation out of the box?

Yes, UC3855BN integrates complete ZVT control circuitry including ZVS sensing comparator, ZVTOUT gate driver, and current synthesizer logic - enabling resonant turn-on of an auxiliary MOSFET. No external ZVT controller IC is needed; only discrete components (small MOSFET, diode, inductor) must be added to implement the ZVT network per TI Application Note U-153.

How does the UC3855BN achieve universal input voltage operation?

The UC3855BN achieves universal input (90–264VAC) via its analog multiplier with VRMS feedforward input. The VRMS pin accepts a voltage proportional to input RMS, causing the multiplier to scale the current command by 1/VRMS² - maintaining constant output power across line variations. This eliminates manual configuration and supports automatic adaptation to global AC mains.

What is the purpose of the CI and CS pins on the UC3855BN?

The CI pin hosts the reconstructed inductor current waveform generated by the current synthesizer, charging during switch-on and discharging proportionally to di/dt during switch-off. The CS pin provides a level-shifted version of that waveform to the CA amplifier input and peak-limit comparator - enabling accurate average current sensing and cycle-by-cycle overcurrent protection without a shunt resistor.

Can UC3855BN replace UC2855BN in existing designs?

UC3855BN and UC2855BN share identical pinout and core functionality but differ in temperature rating (0–70°C vs. −40–85°C) and UVLO thresholds (UC3855BN-A: 15.5V/9V; UC3855BN-B: 10.5V/9V). Direct replacement is electrically feasible if ambient temperature stays within 0–70°C and the UVLO threshold matches the auxiliary supply design - verify startup behavior under worst-case VCC conditions before substitution.

UC3855BN Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: -

Package/Case:: 20-DIP (0.300", 7.62mm)

Packaging:: Bulk

Product Status:: Obsolete

Mode:: Average Current

Frequency - Switching:: 500kHz

Current - Startup:: 150 µA

Voltage - Supply:: 10.5V ~ 20V

Operating Temperature:: 0°C ~ 70°C

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: 20-PDIP

UC3855BN FAQ

1.How can I place an order for UC3855BN through Aetrix?

Please submit a Request for Quotation (RFQ) for UC3855BN on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for UC3855BN reliable?

The price and inventory of UC3855BN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC3855BN is usually 5 days.

3.What payment methods are accepted for UC3855BN?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC3855BN transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for UC3855BN?

UC3855BN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your UC3855BN order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for UC3855BN?

For technical support, including UC3855BN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC3855BN requirements.

6.How does Aetrix verify that UC3855BN is sourced from the original manufacturer or authorized distributors?

All UC3855BN products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that UC3855BN meets industry standards.

7.What is the process for return or replacement of UC3855BN?

All UC3855BN units undergo pre-shipment inspection (PSI). If there is an issue with UC3855BN, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The UC3855BN part is unused and in its original packaging.

Return procedure for UC3855BN:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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