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.

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	V_IN Range (V)	Max P_out (W)
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)	LM5181	4.5 – 65	3.5
	LM5180	4.5 – 65	7
	LM25180	4.5 – 42	7
	LM25183	4.5 – 42	12
	LM25184	4.5 – 42	18
Maxim (External Switch)	MAX17690	4.5 – 60	80 – 100

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 (EP7)	4.5 – 70 V	20 V, 0.1 A (sec1) 5 V, 0.3 A (sec2)	YA8864-BL
4.6 W (EP7)	4.5 – 70 V	15 V, 0.20 A (sec1) 8 V, 0.2 A (sec2)	YA8916-BL
6 W (EP7)	4.5 – 70 V	5 V, 1.2 A	YA8779-BL
7.5 W (ER11/5)	17 – 36 V	5 V, 1.5 A	YA9280-AL
16 W (ER14)	18 – 38 V	24 V, 0.7 A	ZB1313-CL

Output Power	Input Voltage	V_out
Output Power	Input Voltage	3.3 V	5 V	8 V	12 V	15 V	24 V	48 V
5 – 9 W (ER9.5, ER11.5)	10 – 28 V		ZC1493-AE ZC1570-AE		ZC1495-AE ZC1642-AE		ZC1610-AE ZC1645-AE
5 – 9 W (ER9.5, ER11.5)	20 – 56 V		ZC1494-AE ZC1641-AE		ZC1496-AE ZC1644-AE		ZC1658-AE ZC1649-AE
6 W (EPQ7)	8 – 28 V		YA9123-BE		YA9124-BE		YA9125-BE
6 W (EPQ7)	18 – 60 V		YA9126-BE		YA9127-BE		YA9128-BE
6 W (EP7)	4 – 65 V			YA9033-AL	YA9034-AL	YA9035-AL	YA9036-AL	YA9037-AL
8 – 10 W (EPQ7)	4 – 42 V	ZB1050-AE	ZB1051-AE	ZB1052-AE		ZB1053-AE	ZB1054-AE	ZB1055-AE
12 W (EPQ7	4 – 42 V	ZA9670-BE	ZA9671-BE		ZA9672-BE		ZA9673-BE	ZA9674-BE
12 W (EPQ10)	8 – 28 V		YA9165-BE		YA9166-BE		YA9167-BE
12 W (EPQ10)	18 – 60 V		YA9168-BE		YA9169-BE		YA9170-BE
24 W (EP13)	8 – 28 V		YA9171-CE		YA9172-CE		YA9173-CE
24 W (EP13)	18 – 60 V		YA9174-CE		YA9175-CE		YA9176-CE

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Compact Transformers for No-opto Flyback Topology

No-opto Isolated Flyback Converters

Features:

Selecting the proper off-the-shelf transformer can be completed in three easy steps:

Question?

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