UC3845BN

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UC3845BN

SWITCHING CONTROLLER

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Specifications

Supplier Rochester Electronics, LLC
Package Bulk
ProductStatus Active
OutputType Transistor Driver
Function Step-Up, Step-Up/Step-Down
OutputConfiguration Positive, Isolation Capable
Topology Boost, Flyback
NumberofOutputs 1
OutputPhases 1
Voltage-Supply(Vcc/Vdd) 7.6V ~ 30V
Frequency-Switching Up to 500kHz
DutyCycle(Max) 48%
SynchronousRectifier No
ClockSync No
ControlFeatures Frequency Control
OperatingTemperature 0°C ~ 70°C (TA)
MountingType Through Hole
Package/Case 8-DIP (0.300, 7.62mm)

Overview

Description

UC3845BN is a popular 8-pin current‑mode PWM controller from TI (Unitrode) for switch‑mode power supplies. It combines a 5V reference, an error‑amplifier input for regulation, a current‑sense input, and a PWM comparator with an output stage that drives a power MOSFET or transistor gate. An external resistor (RT) sets the switching frequency, and the device includes undervoltage lockout and a duty‑cycle limit to protect the transformer and switch. It is widely used in offline and DC‑DC converters (flyback, buck, boost) in universal or wide‑input power supplies. The BN suffix indicates a specific package variant (8‑pin).

Features

UC3845BN features (concise):
- 5V reference and error amplifier for closed-loop, opto-coupler feedback in isolated SMPS
- Current-mode PWM control with peak current sense input for stable regulation
- External RT/CT oscillator to set switching frequency (typical tens of kHz; adjustable)
- Cycle-by-cycle current limiting with leading-edge blanking
- UVLO with hysteresis to ensure proper startup/shutdown
- Overvoltage protection and thermal shutdown for protection
- Output drive capable of switching power MOSFET/BJT gates (TTL-compatible)
- Optional soft-start and external compensation for stable control loop
- Suitable for flyback, buck, boost, and other SMPS topologies
Note: All timing/voltages depend on external components and application.

Package

UC3845BN comes in an 8-pin DIP (PDIP) package, through-hole.

Pinout

Pin count: 8 pins (DIP-8/SO-8; package variant “N” indicates the 8‑pin package).
Pin functions (UC3845BN, pin 1–8):
- 1 COMP – Error amplifier output (used with the compensation network).
- 2 VFB (VFB/FB) – Inverting input of the error amplifier (feedback signal).
- 3 IS – Current-sense input (sense resistor for current-mode control).
- 4 GND – Ground.
- 5 VCC – Supply voltage input.
- 6 RT/CT – Timing resistor/capacitor input for oscillator frequency.
- 7 OUTPUT – PWM output to drive the power switch (MOSFET gate).
- 8 VREF – 5V reference output.

Manufacturer

Manufacturer: Texas Instruments (TI). TI is a US-based multinational semiconductor company that designs and manufactures analog and mixed-signal integrated circuits, microcontrollers, and embedded processors.

Application

- Purpose: UC3845BN is a high-performance current-mode PWM controller for switch-mode power supplies (SMPS).
- Topologies: used in off-line and DC-DC SMPS for isolated and non-isolated designs (flyback, forward, flyback-forward, push-pull, half-bridge, buck/boost).
- Applications: AC/DC adapters, telecom/industrial and computer/consumer SMPS, LED constant-current drivers, battery chargers, and other low-to-medium power supplies.

Equivalent

Equivalents to UC3845BN include the KA3842/KA3843/KA3844/KA3845 family (drop-in cross with UC384x devices from various vendors). Other cross-refs: TI UC3842/UC3843/UC3844/UC3845 and TI UCC38xx variants. Note: verify pinout, reference voltage, slope compensation, and UVLO, as there can be small differences between revisions.

Shipping

Shipping MethodsWe

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Shipping Fee Reference (DHL/FedEx):

DHL: Shipping cost ranges from $25-$45 (0.5kg), with an estimated delivery time of 2-5 business days.

FedEx: Shipping cost ranges from $25-$40 (0.5kg), with an estimated delivery time of 3-7 business days.

UPS: Shipping cost ranges from $25-$45 (0.5kg), with an estimated delivery time of 3-7 business days.

TNT: Shipping cost ranges from $25-$65 (0.5kg), with an estimated delivery time of 3-7 business days.

EMS: Shipping cost ranges from $30-$50 (0.5kg), with an estimated delivery time of 7-15 business days.

Registered Air Mail: Shipping cost is $2-$4 (0.1kg), with an estimated delivery time of 5-20 business days.

Payments

Payment Methods

The Payment term is 100% Prepaid.

Currently, we only accept the below payment methods:

1. PayPal

2. Credit/ Debit Card

3. Wire Transfer

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