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Compact Transformers for No-opto Flyback Topology

The "no-opto" flyback topology enables primary‑side regulation by deriving the isolated output voltage directly from the primary-side flyback waveform. This provides an isolated flyback without the need for an extra transformer winding—or opto coupler—to provide feedback across the isolation barrier from secondary side to primary side.

no-opto.png

Without the feedback winding, transformers may be designed for optimal coupling, best efficiency, smallest size and lowest cost. Coilcraft offers a variety of off-the-shelf transformers that have been optimized for these converters and designed for the most common output voltages and output power up to 24 Watts.

No-opto Isolated Flyback Converters

Controllers for no-opto flyback topology isolated converters are offered by several major IC manufacturers and are becoming increasingly popular for wide-range input-voltage, low-power, isolated converters across a variety of applications.

IC Manufacturer IC VIN Range (V) Max Pout  (W)
Maxim Integrated
(External Switch)
MAX17690 4.5 – 60 80 – 100
Analog Devices
Power by Linear
(Internal Switch)
LT8301 2.7 – 42 6/18/24
LT8302 2.8 – 42 6/18/24
LT8304 3 – 100 6/18/24
Analog Devices
(External Switch)
LT3748 5 – 100 80 – 100
LT3798 20 – 400 80 – 100
Texas Instruments
(Internal Switch)
LM5180 4.5 – 70 7
 
Features:
  • Small size
  • Low leakage inductance
  • Low DCR
  • High efficiency
  • Low cost
Selecting the proper off-the-shelf transformer can be completed in three easy steps:
  • Determine turns ratio
  • Calculate minimum primary inductance
  • Calculate primary peak current

Simply identify the target Lp, Np/Ns, and Isat, and request a sample from the individual product page links below.

Output Power Input Voltage Output Part Number
3.5 W 4.5 – 70 V 20 V, 0.1 A (sec1)
5 V, 0.3 A (sec2)
YA8864-BL
4.6 W 4.5 – 70 V 15 V, 0.20 A (sec1)
8 V, 0.2 A (sec2)
YA8916-BL
6 W 4.5 – 70 V 5 V, 1.2 A YA8779-BL
7.5 W 17 – 36 V 5 V, 1.5 A YA9280-AL
 
Output Power Input Voltage Vout
5 V 12 V 24 V
6 W (EPQ7) 8 – 28 V YA9123-BE YA9124-BE YA9125-BE
18 – 60 V YA9126-BE YA9127-BE YA9128-BE
12 W (EPQ10) 8 – 28 V YA9165-BE YA9166-BE YA9167-BE
18 – 60 V YA9168-BE YA9169-BE YA9170-BE
24 W (EP13) 8 – 28 V YA9171-CE YA9172-CE YA9173-CE
18 – 60 V YA9174-CE YA9175-CE YA9176-CE

Learn more about our Compact Transformers for No-opto Flyback Topology