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STMicroelectronics UC3843BN
- Part No.:
- UC3843BN
- Manufacturer:
- STMicroelectronics
- Category:
- DC DC Switching Controllers
- Package:
- 8-DIP (0.300", 7.62mm)
- Datasheet:
-
UC3843BN.pdf
- Description:
- IC REG CTRLR BST/FLYBK 8-MINIDIP
- Quantity:
- Payment:
- Shipping:
Inventory:1,286
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Product details
Overview
UC3843BN from STMicroelectronics is a high-performance current-mode PWM controller IC designed for fixed-frequency DC-DC and off-line power supplies. It features a trimmed oscillator guaranteed at 250 kHz, under-voltage lockout with 8.4 V turn-on/7.6 V turn-off thresholds, latching PWM for cycle-by-cycle current limiting, and a totem-pole output capable of ±1 A peak drive - enabling direct N-channel MOSFET gate control in flyback, forward, and boost converters.
For engineers reviewing the UC3843BN datasheet, UC3843BN pinout, UC3843BN application, or UC3843BN equivalent, key selection considerations include its 8-pin DIP package, 5 V ±1% internal reference, 0.5 mA start-up current, and duty cycle capability up to 96% - critical for optimizing efficiency and transient response in isolated AC-DC adapters and industrial SMPS designs.
Technical Context
The UC3843BN implements current-mode control via a high-gain error amplifier (90 dB open-loop gain, 1 MHz bandwidth), a precision 1 V current-sense comparator with 3 V/V gain, and an internally trimmed oscillator whose frequency is set by external RT/CT components. Its latch-based PWM logic ensures single-pulse per cycle current limiting, while automatic feed-forward compensation improves line regulation.
Under-voltage lockout (UVLO) incorporates hysteresis (0.8 V) and enables reliable start-up from low-input rails; the 5 V reference (±20 mV load/line regulation) powers timing components and provides stable biasing for feedback networks. The totem-pole output stage operates with 0.4 V low-level saturation at 20 mA and supports fast rise/fall times (≤150 ns into 1 nF).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Oscillator Frequency | 250 kHz guaranteed at 25°C; programmable up to 500 kHz via RT/CT - sets switching frequency and defines minimum dead time in hard-switched topologies. |
| UVLO Thresholds | 8.4 V (on), 7.6 V (off) - enables reliable operation from low-voltage DC inputs (e.g., 12 V bus) without false triggering during brownout. |
| Max Duty Cycle | 96% - supports high step-up ratios in boost converters and wide input range in flyback designs without external duty cycle clamping. |
| Start-up Current | <0.5 mA - reduces auxiliary winding losses and enables high-impedance bias networks in energy-efficient offline supplies. |
| Output Drive | ±1 A peak sink/source - directly drives medium-power MOSFET gates (e.g., 10–50 nC Qg) without external buffers in sub-100 W applications. |
| Reference Voltage | 5.00 V ±100 mV (0–20 mA load) - provides stable timing and feedback reference, reducing component count in voltage-mode derived circuits. |
| Error Amp Gain | 90 dB open-loop gain, 1 MHz unity-gain bandwidth - ensures robust loop stability with standard Type II/III compensation in current-mode control. |
Pinout & Package
UC3843BN is housed in an 8-pin plastic dual in-line package (Minidip), with lead spacing of 2.54 mm and body dimensions 10.92 × 7.95 mm. Pin 5 serves as the common ground for both analog and power sections, requiring star grounding for noise immunity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - COMP | Error amplifier output | Provides access to EA output for external Type II/III compensation; must be decoupled to ground to prevent oscillation. |
| 2 - VFB | Inverting input of error amplifier | Receives feedback voltage from output divider; sets regulation point when referenced to 2.5 V internal threshold. |
| 3 - ISENSE | Current sense comparator input | Accepts voltage proportional to primary-side current; trips PWM latch when ≥1.0 V - enabling precise peak current limiting. |
| 4 - RT/CT | Oscillator timing node | Connects external resistor (to VREF) and capacitor (to GND) to set fOSC and maximum duty cycle; CT also filters oscillator ramp. |
| 5 - GROUND | Analog + power ground | Single-point return for all internal circuits; must be routed separately from power ground traces to avoid noise coupling. |
| 6 - OUTPUT | Totem-pole gate driver | Sources/sinks up to 1 A; low-state saturation ≤0.4 V at 20 mA - suitable for driving MOSFETs with RDS(on) < 1 Ω in <100 W designs. |
| 7 - VCC | Supply input | Operates from 7.6–30 V; internal zener clamp limits max voltage to 36 V - allows direct connection to rectified AC or bulk DC rails. |
| 8 - VREF | 5 V reference output | Supplies 5 V ±2% at up to 20 mA; powers RT/CT network and optional optocoupler bias - eliminates need for external reference. |
Key Features
| Feature | Design Value |
|---|---|
| Latching PWM architecture | Ensures one pulse per clock cycle during overcurrent events - prevents transformer saturation and enables predictable fault recovery in flyback converters. |
| Internally trimmed 5 V reference | ±100 mV accuracy over temperature and load - eliminates external reference IC and reduces BOM cost in cost-sensitive AC-DC adapters. |
| Low start-up current (<0.5 mA) | Enables high-impedance startup networks using large-value resistors - reduces standby power and simplifies auxiliary supply design. |
| Automatic feed-forward compensation | Compensates for input voltage variations in real time - improves line regulation to <0.5% without additional circuitry. |
| High-current totem-pole output | ±1 A peak drive with fast edge rates (≤150 ns) - supports direct gate drive of MOSFETs with gate charge up to 40 nC at 250 kHz. |
Applications
| AC-DC Adapter | Flyback SMPS |
|---|---|
|
Use Scenario: 5–24 V output, 10–65 W universal-input (85–265 VAC) wall adapters for consumer electronics. IC Role / Device Role / Timing Role: Primary-side PWM controller providing current-mode regulation, cycle-by-cycle current limiting, and 250 kHz switching timing. Use Value: Enables compact transformer design and tight output regulation (±3%) across line/load variations without optocoupler compensation. |
Use Scenario: Isolated 12 V/1 A output for industrial sensors powered from 24 VDC input. IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller managing MOSFET switching, feedback via TL431/shunt regulator, and UVLO for brownout protection. Use Value: Delivers consistent 96% max duty cycle and 0.5 mA start-up current - ensuring reliable cold-start and stable operation under variable load. |
| Boost Converter | DC-DC Industrial Supply |
|
Use Scenario: 12 V to 24 V boost converter for battery-powered test equipment requiring low-noise 2 A output. IC Role / Device Role / Timing Role: Current-mode controller implementing slope compensation, error amplification, and gate drive with integrated 5 V reference. Use Value: Leverages 3 V/V current-sense gain and 1 V trip threshold to achieve accurate peak current control - minimizing output ripple and improving efficiency. |
Use Scenario: 48 V to 5 V/3 A isolated DC-DC module for factory automation controllers. IC Role / Device Role / Timing Role: Primary-side PWM controller handling input undervoltage detection, soft-start via external RC, and latch-based fault shutdown. Use Value: UVLO hysteresis (0.8 V) and 150°C junction rating ensure robust operation in high-ambient industrial environments with fluctuating input rails. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar current-mode PWM controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UC3842BN | Higher UVLO (16 V on / 10 V off); same oscillator, reference, and output specs. | Better suited for universal AC input (>100 VDC after bridge) rather than low-voltage DC-DC. | Select UC3842BN when input exceeds 14 V; use UC3843BN for 12 V bus or battery-derived supplies. |
| TL494CN | Fixed-frequency voltage-mode controller; dual output; no integrated current sense comparator or 5 V reference. | Requires external current sensing and reference; supports push-pull and half-bridge topologies. | Choose TL494CN only when dual-output or voltage-mode control is required; UC3843BN offers simpler current-mode implementation. |
Compared with UC3842BN and TL494CN, the UC3843BN delivers optimized low-threshold UVLO and integrated current sensing for single-ended topologies - reducing external component count and improving reliability in space-constrained, low-input-voltage SMPS designs.
Availability
UC3843BN is available at Aetrix Electronics and suitable for AC-DC adapters, flyback SMPS, boost converters, and industrial DC-DC supplies requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for UC3843BN 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
STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, delivering innovative analog, power, and microcontroller solutions for industrial, automotive, and consumer markets.
The UC384xB family was developed specifically for cost-effective, high-reliability current-mode PWM control in off-line and DC-DC power conversion - emphasizing minimal external parts count, robust fault handling, and production-ready thermal performance.
FAQ
What is the maximum operating junction temperature for UC3843BN?
The UC3843BN has a specified junction operating temperature range of –40°C to +150°C. Its thermal resistance (Rth j-amb) is 100°C/W in the Minidip package, meaning it can dissipate up to 1.25 W at 25°C ambient before reaching thermal limit - sufficient for most 30–65 W designs with basic heatsinking or PCB copper area.
Can UC3843BN drive a MOSFET directly without a gate driver IC?
Yes - the UC3843BN's totem-pole output sources and sinks up to 1 A peak current with ≤0.4 V saturation at 20 mA, enabling direct drive of N-channel MOSFETs with gate charge ≤40 nC at 250 kHz. For higher Qg devices or faster switching, an external buffer is recommended to maintain edge integrity.
How does the UC3843BN implement cycle-by-cycle current limiting?
It uses a dedicated current-sense comparator that monitors voltage at Pin 3 (ISENSE). When this voltage reaches 1.0 V (±100 mV), the comparator resets the PWM latch, immediately terminating the output pulse - enforcing precise peak current control independent of duty cycle or input voltage.
Is the 5 V reference on Pin 8 regulated under varying load conditions?
Yes - the internal 5 V reference maintains ±2% accuracy (4.90–5.10 V) across 1–20 mA load and full temperature range, with load regulation of ≤25 mV. It supplies timing components and can bias optocouplers or shunt regulators, eliminating need for external references in most designs.
UC3843BN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 8-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Up, Step-Up/Step-Down
- Output Configuration:
- Positive, Isolation Capable
- Topology:
- Boost, Flyback
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- 7.6V ~ 30V
- Frequency - Switching:
- Up to 500kHz
- Duty Cycle (Max):
- 96%
- Synchronous Rectifier:
- No
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Frequency Control
- Operating Temperature:
- 0°C ~ 70°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 8-Mini DIP
UC3843BN FAQ
1.How can I place an order for UC3843BN through Aetrix?
Please submit a Request for Quotation (RFQ) for UC3843BN 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 UC3843BN reliable?
The price and inventory of UC3843BN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC3843BN is usually 5 days.
3.What payment methods are accepted for UC3843BN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC3843BN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for UC3843BN?
UC3843BN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your UC3843BN 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 UC3843BN?
For technical support, including UC3843BN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC3843BN requirements.
6.How does Aetrix verify that UC3843BN is sourced from the original manufacturer or authorized distributors?
All UC3843BN 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 UC3843BN meets industry standards.
7.What is the process for return or replacement of UC3843BN?
All UC3843BN units undergo pre-shipment inspection (PSI). If there is an issue with UC3843BN, 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 UC3843BN part is unused and in its original packaging.
Return procedure for UC3843BN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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