UC3842BD1 Current Mode PWM Controller: The Definitive Guide for SMPS Design

Admin · Aug 21, 2026 · 4 min read AI-Assisted · Updated: Aug 21, 2026 · Fact-Checked
UC3842BD1 Current Mode PWM Controller: The Definitive Guide for SMPS Design
STMicroelectronics UC3842BD1 is a current-mode PWM controller in SOIC-8, with 7.5-30V input, 1A peak output, 500kHz max frequency, and 96% duty cycle. Active lifecycle, $0.1485 at 2500+ as of 2026-08-21.

What is the UC3842BD1 and What Are Its Key Verified Specs?

The UC3842BD1 from STMicroelectronics is a high-performance current-mode PWM controller designed for off-line and DC-to-DC converter applications. It operates with an input voltage range of 7.5V to 30V and provides a 1A peak output current for driving power MOSFETs. The device is available in an SOIC-8 package, making it suitable for compact power supply designs. As of 2026-08-21, the UC3842BD1 is in active lifecycle status with 99,999 units in stock at XAIPART, priced at $0.1485 per unit at 2500+ quantities. Its key specs include a maximum oscillator frequency of 500 kHz, a maximum duty cycle of 96%, a 5V reference output with ±2% tolerance, and a low startup current of 0.5 mA.

How to Select and Design In the UC3842BD1

When selecting the UC3842BD1 for your power supply design, consider the following verified specifications:

  • Input Voltage Range: 7.5V to 30V
  • Output Current (Peak): 1A
  • Oscillator Frequency (Max): 500 kHz
  • Maximum Duty Cycle: 96%
  • Reference Output Voltage: 5V ±2%
  • Error Amplifier Bandwidth: 1 MHz
  • Current Sense Threshold: 1V
  • Startup Current: 0.5 mA
  • Operating Supply Current: 11 mA
  • UVLO On/Off: 16V/10V
  • Operating Temperature Range: -40°C to +150°C
  • Package: SOIC-8, Surface Mount
  • RoHS: Compliant

Design-in steps:

  1. Set the oscillator frequency: Connect an external resistor and capacitor to the RT/CT pin (Pin 4) to program the switching frequency up to 500 kHz. Choose components to achieve your target frequency, balancing efficiency and transformer size.
  2. Configure the error amplifier: Use the COMP pin (Pin 1) and VFB pin (Pin 2) to implement loop compensation. The error amplifier bandwidth of 1 MHz allows fast transient response.
  3. Implement current sensing: Connect a current-sense resistor from the source of the power MOSFET to ground, and feed the voltage to the ISENSE pin (Pin 3). The 1V threshold provides cycle-by-cycle current limiting.
  4. Power supply and decoupling: Connect VCC (Pin 7) to a regulated supply within 7.5V to 30V. Place a decoupling capacitor close to the VCC and GND pins to ensure stable operation.
  5. Gate drive: The OUT pin (Pin 6) provides a 1A peak output to drive the gate of a power MOSFET. Ensure the gate resistor is appropriately sized to control switching speed and reduce EMI.
  6. Reference output: The REF pin (Pin 8) provides a 5V reference with ±2% tolerance. Use it for biasing external circuitry or as a reference for the error amplifier.

Layout considerations: Place the current-sense resistor close to the IC to minimize parasitic inductance. Keep the RT/CT timing components near the RT/CT pin. Use proper grounding and decoupling of the VCC pin.

What Are the Drop-In Alternatives to UC3842BD1?

Based on verified data, the following alternatives are pin-to-pin compatible and electrically identical:

ParameterUC3842BD1UC3842BDUC3842BD1TRUC3842BD1G
PackageSOIC-8SOIC-8SOIC-8SOIC-8
Input Voltage Range7.5V to 30V7.5V to 30V7.5V to 30V7.5V to 30V
Output Current (Peak)1A1A1A1A
Oscillator Frequency (Max)500 kHz500 kHz500 kHz500 kHz
Maximum Duty Cycle96%96%96%96%
Reference Output Voltage5V ±2%5V ±2%5V ±2%5V ±2%
Error Amplifier Bandwidth1 MHz1 MHz1 MHz1 MHz
Current Sense Threshold1V1V1V1V
Startup Current0.5 mA0.5 mA0.5 mA0.5 mA
Operating Supply Current11 mA11 mA11 mA11 mA
UVLO On/Off16V/10V16V/10V16V/10V16V/10V
Operating Temperature Range-40°C to +150°C-40°C to +150°C-40°C to +150°C-40°C to +150°C
RoHSCompliantCompliantCompliantCompliant

Summary: All alternatives share identical electrical specs and SOIC-8 package. The UC3842BD1TR is tape-and-reel, UC3842BD1G is lead-free finish, and UC3842BD is a different ordering code. Choose based on packaging and finish preferences.

What Is the Market Position and Lifecycle Status of UC3842BD1?

The UC3842BD1 is in active lifecycle status, indicating ongoing production and availability. As of 2026-08-21, XAIPART holds 99,999 units in stock, ensuring supply for immediate orders. The device is widely used in SMPS, battery chargers, industrial converters, AC-DC adapters, LED drivers, and telecom power supplies. Its active status and stock availability suggest a stable market position. [DATA_NEEDED: market share data]

What Trends Should Buyers Watch for UC3842BD1?

Buyers should monitor the following trends anchored to verified specs:

  • High-Frequency Operation: The 500 kHz max oscillator frequency enables compact transformer designs, aligning with the trend toward miniaturization in power supplies.
  • Energy Efficiency: The low startup current of 0.5 mA supports low standby power, helping meet energy efficiency regulations.
  • Wide Temperature Range: The -40°C to +150°C operating range makes it suitable for industrial and automotive applications, expanding its market reach.
  • Supply Chain: With active lifecycle and high stock, the UC3842BD1 is a reliable choice for long-term designs. However, buyers should watch for potential shifts to newer controllers with integrated features.

Frequently Asked Questions

The UC3842BD1 is a current-mode PWM controller IC from STMicroelectronics, designed for off-line and DC-DC converter applications. It provides a 1A peak output current and operates with an input voltage range of 7.5V to 30V.
The UC3842BD1 can operate at a maximum oscillator frequency of 500 kHz, as specified in the STMicroelectronics datasheet. The frequency is set by an external resistor and capacitor connected to the RT/CT pin.
The UC3842BD1 provides a 5V reference output with a tolerance of ±2%. This reference can be used to bias external circuitry or as a precision voltage source for the error amplifier.
The UC3842BD1 and UC3842BN are both current-mode PWM controllers from STMicroelectronics, but they differ in package: the UC3842BD1 is in an SOIC-8 package, while the UC3842BN is in a DIP-8 package. They have identical electrical specifications, but the SOIC-8 is surface-mount and the DIP-8 is through-hole.
Yes, the UC3842BD1 is well-suited for flyback converter topologies. Its current-mode control provides inherent feed-forward compensation and cycle-by-cycle current limiting, which simplifies loop design and improves transient response.
The startup current of the UC3842BD1 is 0.5 mA, which is low enough to allow efficient power-up from a high-value resistor connected to the rectified mains voltage. This reduces standby power consumption.
The UC3842BD1 has an under-voltage lockout (UVLO) turn-on threshold of 16V and a turn-off threshold of 10V. This hysteresis ensures stable startup and prevents false triggering during power supply transients.
The UC3842BD1 has a maximum duty cycle of 96%, allowing it to maintain regulation even with low input voltages or high output loads. This is particularly useful in boost converter applications.
As of 2026-08-21, the UC3842BD1 is priced at $0.1485 per unit at 2500+ quantities, with tiered pricing starting at $0.2618 for single units.
The UC3842BD1 is available from major distributors such as DigiKey and Mouser. You can also purchase it directly from XAIPART at https://xaipart.com/products/uc3842bd1.
The typical lead time for UC3842BD1 is 4-6 weeks from distributors, but it may vary based on stock availability and order quantity. For urgent requirements, check real-time stock on XAIPART.
As of 2026-08-21, the UC3842BD1 is in stock at XAIPART with 99,999 units available. Stock levels can change rapidly, so check the product page for real-time availability.
The best drop-in replacement for UC3842BD1 is the UC3842BD1TR (same SOIC-8 package, tape and reel packaging) or the UC3842BD (same SOIC-8 package, but with a different ordering code). Both are pin-to-pin compatible and have identical electrical specifications.
Yes, the UC3842BD1 can replace the UC3842BN if the PCB is designed for an SOIC-8 package. The UC3842BN is in a DIP-8 package, so a direct drop-in replacement is not possible without PCB modification. For a drop-in replacement, choose a part with the same SOIC-8 package.
The UC3842BD1 datasheet PDF can be downloaded from the STMicroelectronics website at https://www.st.com/resource/en/datasheet/uc3842b.pdf. It contains complete specifications, pinout, and application circuits.
The UC3842BD1 pinout is available in the datasheet on page 3. The SOIC-8 package has pins for COMP, VFB, ISENSE, RT/CT, GND, OUT, VCC, and REF.
The UC3842BD1 operates over a junction temperature range of -40°C to +150°C, making it suitable for industrial and automotive applications where extreme temperatures are encountered.
Yes, the UC3842BD1 is RoHS compliant, as indicated in the STMicroelectronics datasheet and product page. It is also lead-free and halogen-free.
The UC3842BD1 and UC3843BD1 are similar current-mode PWM controllers, but they differ in UVLO thresholds. The UC3842BD1 has UVLO on at 16V and off at 10V, while the UC3843BD1 has UVLO on at 8.4V and off at 7.6V. This makes the UC3843BD1 suitable for lower input voltage applications.
The UC3842BD1 and UC3844BD1 are both current-mode PWM controllers, but the UC3844BD1 has a maximum duty cycle of 50%, while the UC3842BD1 has a maximum duty cycle of 96%. The UC3844BD1 is intended for applications requiring a lower duty cycle limit.

Need Components for Your Project?

Find the right parts with our comprehensive database of 1M+ electronic components.

Browse Products Request a Quote BOM Tool

Content Verification

Comments

Be the first to comment.