UC3842TN STMicroelectronics Integrated Circuit (Dual-In-Line Packages) In Stock
The UC3842TN is a current-mode PWM controller IC for flyback, forward, and boost switch-mode power supplies from STMicroelectronics. It operates from 12 V to 30 V supply, supports up to 500 kHz switching frequency, and delivers 1 A peak gate drive current. Packaged in an 8-pin PDIP for through-hole SMPS designs.
- Manufacturer
- STMicroelectronics
- Package
- Dual-In-Line Packages
- Pin Count
- 8
- Lifecycle
- OBSOLETE
- Datasheet
- UC3842TN Datasheet PDF
- Category
- Integrated Circuit
- Temp Range
- ?°C to 105.0°C
- RoHS
- Compliant
- Lead Time
- 3–7 business days
- Shipping
- DHL Express · Worldwide
Key Features
- Current-mode PWM control with cycle-by-cycle current limiting for fast overload and short-circuit protection
- 1 A peak gate-drive output for direct MOSFET switching without external buffer transistors
- Operating supply range 12 V to 30 V with undervoltage lockout for reliable startup in off-line supplies
- Switching frequency programmable up to 500 kHz via external RC network for compact transformer designs
- 8-pin PDIP package simplifying prototyping and repair of industrial and consumer power supplies
Applications
The UC3842TN is a foundational current-mode PWM controller for offline flyback power supplies in adapters, chargers, industrial equipment, and motor drives requiring regulated outputs from AC mains inputs. Its cycle-by-cycle current limiting and internally fixed oscillator make it straightforward to implement stable buck, boost, and flyback topologies with MOSFET switches up to 500 kHz. The device is also widely used in retrofit and repair applications because its 8-pin PDIP pinout is industry-standard and interchangeable with numerous second-source equivalents from multiple manufacturers.
Specifications
| YTEOL | 0 |
| Analog IC - Other Type | SWITCHING CONTROLLER |
| Control Mode | CURRENT-MODE |
| Control Technique | PULSE WIDTH MODULATION |
| Input Voltage-Max | 30V |
| Input Voltage-Min | 12V |
| Input Voltage-Nom | 15V |
| JESD-30 Code | R-PDIP-T8 |
| Number of Functions | 1 |
| Output Current-Max | 1A |
| Package Body Material | PLASTIC/EPOXY |
| Package Shape | RECTANGULAR |
| Package Style | IN-LINE |
| Qualification Status | Not Qualified |
| Surface Mount | NO |
| Switcher Configuration | SINGLE |
| Switching Frequency-Max | 500kHz |
| Terminal Form | THROUGH-HOLE |
| Terminal Pitch | 2.54mm |
| Terminal Position | DUAL |
| ## UC3842TN Alternates Showing results | Image |
| Package | Dual-In-Line Packages |
Compliance & Regulatory
| RoHS Status | Compliant |
| Lead-Free | Yes (Pb-Free) |
| ECCN | EAR99 |
| HTS Code | 8542.39.00.60 |
Alternate & Equivalent Parts
Compatible alternatives and drop-in replacements for UC3842TN:
Rochester Electronics LLC 1A SWITCHING CONTROLLER, 500kHz SWITCHING FREQ-MAX, PDIP8, HALOGEN AND LEAD FREE, PLASTIC, DIP-8
Switching Controller, Current-mode, 1A, 500kHz Switching Freq-Max, BIPolar, PDIP8
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Frequently Asked Questions
What switching frequency range does the UC3842TN support and how is it programmed?
The UC3842TN supports switching frequencies from a few kHz up to approximately 500 kHz, set by an external resistor and capacitor connected to the RT/CT pins. Increasing frequency reduces transformer and filter component size but increases switching losses, so most off-line flyback designs using the UC3842TN operate at 50 kHz to 200 kHz as a practical trade-off between efficiency and magnetics volume.
How does current-mode control in the UC3842TN improve power supply loop stability compared to voltage-mode control?
In current-mode control, the UC3842TN senses the peak inductor current each switching cycle and uses it as an inner feedback loop, which effectively converts the power stage into a voltage-controlled current source. This reduces the control-to-output transfer function to a single pole below half the switching frequency, making the outer voltage loop easier to compensate with a simple type-2 error amplifier and eliminating the right-half-plane zero complications that challenge voltage-mode flyback designs.
What is the undervoltage lockout threshold of the UC3842TN and why is it important for offline power supply startup?
The UC3842TN has an undervoltage lockout with a turn-on threshold of approximately 16 V and a turn-off threshold of 10 V, providing 6 V of hysteresis. This hysteresis prevents chattering during startup from a bootstrap resistor, allowing the supply voltage to ramp from mains rectification to 16 V before the controller begins switching, and keeping it running until the VCC drops below 10 V during a mains dip, improving startup reliability in offline flyback converters.
Can the UC3842TN drive a power MOSFET directly, or is an external gate-driver buffer required?
The UC3842TN's output stage delivers up to 1 A peak source and sink current, which is sufficient to switch most common 600 V N-channel MOSFETs with gate charges up to about 100 nC at 100 kHz without an external buffer. For larger die MOSFETs with gate charges above 150 nC or at switching frequencies above 200 kHz, adding a discrete totem-pole gate driver reduces switching transition times and lowers MOSFET conduction and switching losses.
How does the UC3842TN differ from the UC3843 and which flyback topologies suit each device?
The UC3842TN and UC3843 share the same current-mode PWM architecture, but the UC3842 has a maximum duty cycle clamped to 50%, making it suitable for forward converters and two-switch flyback designs that require this limit for volt-second balance. The UC3843 allows duty cycles up to 100%, giving it more flexibility for single-ended flyback and boost designs where duty cycles exceeding 50% are needed to regulate over a wide input voltage range.
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About STMicroelectronics
STMicroelectronics is a global semiconductor leader serving customers across the spectrum of electronics applications. ST's products are found in a wide range of applications including automotive, industrial, personal electronics, and communications.
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