LT8300
applicaTions inForMaTion
In general, choose a transformer with its primary mag-
netizing inductance about 20% to 40% larger than the
minimum values calculated above. A transformer with
much larger inductance will have a bigger physical size
and may cause instability at light load.
Linear Technology has worked with several leading mag-
netic component manufacturers to produce pre-designed
flyback transformers for use with the LT8300. Table 1
shows the details of these transformers.
Turns Ratio
Selecting a Transformer
Note that when choosing the R resistor to set output
FB
Transformer specification and design is perhaps the most
criticalpartofsuccessfullyapplyingtheLT8300.Inaddition
to the usual list of guidelines dealing with high frequency
isolated power supply transformer design, the following
information should be carefully considered.
voltage, the user has relative freedom in selecting a trans-
former turns ratio to suit a given application. In contrast,
the use of simple ratios of small integers, e.g., 4:1, 2:1,
1:1, provides more freedom in settling total turns and
mutual inductance.
Table 1. Predesigned Transformers — Typical Specifications
TRANSFORMER
PART NUMBER
L
L
LEAKAGE
(µH)
PRI
(µH)
400
300
NP:NS:NB
8:1
VENDOR
TARGET APPLICATIONS
750312367
750312557
4.5
2.5
Würth Elektronik
Würth Elektronik
48V to 3.3V/0.51A, 24V to 3.3V/0.37A, 12V to 3.3V/0.24A
6:1
48V to 3.3V/0.42A, 24V to 3.3V/0.32A, 12V to 3.3V/0.22A
48V to 5V/0.38A, 24V to 5V/0.27A, 12V to 5V/0.17A
750312365
750312558
300
300
1.8
4:1
Würth Elektronik
Würth Elektronik
48V to 5V/0.29A, 24V to 5V/0.22A, 12V to 5V/0.15A
1.75
2:1:1
48V to 12V/67mA, 24V to 12V/50mA, 12V to 12V/33mA
48V to 15V/62mA, 24V to 15V/44mA, 12V to 15V/28mA
750312559
750311019
300
400
2
5
1:1
Würth Elektronik
Würth Elektronik
48V to 24V/67mA, 24V to 24V/50mA, 12V to 24V/33mA
6:1:2
48V to 3.3V/0.42A, 24V to 3.3V/0.32A, 12V to 3.3V/0.22A
48V to 5V/0.38A, 24V to 5V/0.27A, 12V to 5V/0.17A
750311558
750311660
300
350
1.5
3
4:1:1
Würth Elektronik
Würth Elektronik
48V to 5V/0.29A, 24V to 5V/0.22A, 12V to 5V/0.15A
2:1:0.33
48V to 12V/0.134A, 24V to 12V/0.1A, 12V to 12V/0.066A
48V to 15V/0.124A, 24V to 15V/0.088A, 12V to 15V/0.056A
750311838
350
3
2:1:1
Würth Elektronik
48V to 12V/67mA, 24V to 12V/50mA, 12V to 12V/33mA
48V to 15V/62mA, 24V to 15V/44mA, 12V to 15V/28mA
750311659
10396-T026
300
300
2
1:1:0.2
6:1:2
Würth Elektronik
Sumida
48V to 24V/67mA, 24V to 24V/50mA, 12V to 24V/33mA
2.5
48V to 3.3V/0.42A, 24V to 3.3V/0.32A, 12V to 3.3V/0.22A
48V to 5V/0.38A, 24V to 5V/0.27A, 12V to 5V/0.17A
10396-T024
10396-T022
300
300
2
2
4:1:1
Sumida
Sumida
48V to 5V/0.29A, 24V to 5V/0.22A, 12V to 5V/0.15A
2:1:0.33
48V to 12V/0.134A, 24V to 12V/0.1A, 12V to 12V/0.066A
48V to 15V/0.124A, 24V to 15V/0.088A, 12V to 15V/0.056A
10396-T028
L10-0116
300
500
2.5
7.3
2:1:1
6:1
Sumida
48V to 12V/67mA, 24V to 12V/50mA, 12V to 12V/33mA
48V to 15V/62mA, 24V to 15V/44mA, 12V to 15V/28mA
BH Electronics
48V to 3.3V/0.42A, 24V to 3.3V/0.32A, 12V to 3.3V/0.22A
48V to 5V/0.38A, 24V to 5V/0.27A, 12V to 5V/0.17A
L10-0112
L11-0067
230
230
3.38
2.16
4:1
4:1
BH Electronics
BH Electronics
48V to 5V/0.29A, 24V to 5V/0.22A, 12V to 5V/0.15A
48V to 5V/0.29A, 24V to 5V/0.22A, 12V to 5V/0.15A
* All the transformers are rated for 1.5kV Isolation.
8300f
12
Linear [ Linear ]
