LINEAR TECHNOLOGY LT1425 Data Sheet
Summary
This datasheet describes the Linear Technology LT1425 monolithic isolated flyback switching regulator that senses the output voltage directly from the primary-side flyback waveform, eliminating the need for a transformer third winding or optoisolator. Operating from 3V to 20V input with only 7mA quiescent current, the device integrates a high-current, high-efficiency switch capable of delivering up to 6W output power. Current mode control provides excellent AC and DC line regulation, with unique
Page 1 Text Content
LT1425
Isolated Flyback Switching Regulator
FEATURES DESCRIPTION No Transformer “Third Winding” or Optoisolator The LT®1425 is a monolithic high power switching regu- Required lator specifically designed for the isolated flyback topol- ±5% Accurate Output Voltage Without User Trims ogy. No “third winding” or optoisolator is required; the (See Circuit Below) integrated circuit senses the isolated output voltage Resistor Programmable Output Voltage directly from the primary side flyback waveform. A high Regulation Maintained Well Into Discontinuous current, high efficiency switch is included on the die along Mode (Light Load) with all oscillator, control and protection circuitry. Optional Load Compensation
The LT1425 operates with input supply voltages from 3V
Operating Frequency: 285k Hz
to 20V and draws only 7m A quiescent current. It can
Easily Synchronized to External Clock
deliver output power up to 6W with no external power
Available in 16-Pin Narrow SO Package
devices. By utilizing current mode switching techniques, it provides excellent AC and DC line regulation.
APPLICATIONS
OU TP UT OL TA GE (V The LT1425 has a number of features not found on other
Isolated Flyback Switching Regulators switching regulator ICs. Its unique control circuitry can Ethernet Isolated 5V to –9V Converters maintain regulation well into discontinuous mode in most Medical Instruments applications. Optional load compensation circuitry allows Isolated Telecom Supplies for improved load regulation. An externally activated shut-
down mode reduces total supply current to 15µA for
, LTC and LT are registered trademarks of Linear Technology Corporation. standby operation.
TYPICAL APPLICATION
Load Regulation5V to Isolated –9VOUT
ISOLATION BARRIER
ISOLATED
–9V ±5% AT 9.2
20m A TO 200m A
VIN 9.1
R1 9.0 LT1425 22.6k
1% *DALE LPE 4841-330MB
SHDN RFB
R2 SYNC 3.01k 8.7 1%
VC RREF 8.6
ROCOMP 8.5
RCCOMP R3 15k C4 OUTPUT CURRENT (m A)
SGND PGND
1425 TA02
1425 TA01
Page Summary Contents For LINEAR TECHNOLOGY LT1425 Data Sheet
Manual Details
| Brand | Linear |
|---|---|
| Pages | 20 |
| File Size | 290.29 KB |
| Published | June 18, 2026 |
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Frequently Asked Questions
What is the operating frequency range?
The switching frequency can be adjusted between 285kHz and 300kHz (typically).
Does it require a third winding or optoisolator for isolation?
No, it is designed without requiring a “third winding” or optoisolator.
What current does the chip draw in standby mode?
When activated and placed in external shutdown mode, the quiescent supply current is reduced to 15μA.
How well does it maintain regulation during light load conditions?
The device maintains regulation well into discontinuous conduction mode (light load).
What are the voltage limits for the input supply?
It operates with input supply voltages ranging from 3V up to 20V.