Isolated Flyback Converter with 18V-28V Input and 12V Output
- Rajkumar Sharma
- 5 Views
- moderate
- Tested
- SKU: EL154029
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The project presented here is a micropower no-opto isolated flyback converter featuring the LT8304 chip from Analog Devices. This circuit outputs 12V and maintains tight regulation with a load current from 10mA up to 1A and over an input voltage from 18V to 28V. The project needs less than 0.5% of its full output power as a minimum load to maintain good output voltage regulation. The transformer leakage inductance causes a voltage spike on the primary side after the power switch turns off. To limit this leakage inductance spike within the MOSFET voltage rating of 150V, an RC snubber, and a TVS clamp are installed to dampen the ringing and clamp the MOSFET drain voltage to a safe level.
Features
- Supply Input 18V to 28V DC
- Output 12V 10mA-1A
- Low Ripple Burst Mode Operation at Light Load
- Minimum Load < 0.5% (Typ) of Full Output
- Accurate EN/UVLO Threshold and Hysteresis
- Undervoltage Lockout Accurate 1.214V Threshold
- Internal Compensation and Soft-Start
- Temperature Compensation for Output Diode
- Output Short-Circuit Protection
- PCB Dimensions 56.36 x 17.46 mm
The LT8304 is a monolithic micropower isolated flyback converter. By sampling the isolated output voltage directly from the primary-side flyback waveform, the parts require no third winding or optoisolator for regulation. The output voltage is programmed with two external resistors and a third optional temperature compensation resistor. Boundary mode operation provides a small magnetic solution with excellent load regulation. Low ripple Burst Mode operation maintains high efficiency at light load while minimizing the output voltage ripple. A 2A, 150V DMOS power switch is integrated along with all the high voltage circuitry and control logic into a thermally enhanced 8-lead SO package.
The LT8304 operates from an input voltage range of 3V to 100V and delivers up to 24W of isolated output power. The high level of integration and the use of boundary and low ripple Burst Mode operation result in a simple to use, low component count, and high efficiency application solution for isolated power delivery.
Connections
- CN1: Pin 1,2 = +DC Input, Pin 2,3=GND
- CN1: Pin 1,2 = +DC Output, Pin 2,3=GND
- D1: Output LED
Schematic
Parts List
NO. | QNTY. | REF. | DESC | MANUFACTURER | SUPPLIER | SUPPLIER PART NO |
---|---|---|---|---|---|---|
1 | 1 | CN1 | 4 PIN MALE HEADER PITCH 2.54MM | WURTH | DIGIKEY | 732-5317-ND |
2 | 1 | CN2 | 4 PIN MALE HEADER PITCH 2.54MM | WURTH | DIGIKEY | 732-5317-ND |
3 | 2 | C1,C2 | 4.7uF/50V X7S CERAMIC SMD SIZE 1206 | YAGEO/MURATA | DIGIKEY | |
4 | 1 | C3 | 220PF/50V CERAMIC SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
5 | 1 | C4 | 47uF/35V ELEKTROLYTIC CAPACITOR | WURTH | DIGIKEY | 732-8508-1-ND |
6 | 2 | C5,C8 | 47uF/25V X5R CERAMIC SMD SIZE 1210 | YAGEO/MURATA | DIGIKEY | |
7 | 1 | C6 | 1uF/50V CERAMIC SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
8 | 1 | C7 | 4.7K/1KV CAPACITOR THT | TDK | DIGIKEY | 445-CK45-B3AD472KYVNACT-ND |
9 | 1 | D1 | DFLS1150 | DIODE INC | DIGIKEY | DFLS1150DICT-ND |
10 | 1 | D2 | PMEG6030EP/MBRS360 | ONSEMI | DIGIKEY | MBRS360T3GOSCT-ND |
11 | 1 | D3 | LED RED SMD SIZE 0805 | OSRAM | DIGIKEY | 475-1278-1-ND |
12 | 1 | R1 | 1M 5% SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
13 | 1 | R2 | 100E 5% SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
14 | 1 | R3 | 88.7K 1% SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
15 | 1 | R4 | 237K 1% SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
16 | 1 | R5 | DNP | |||
17 | 1 | R6 | 10K 5% SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
18 | 1 | R7 | 100K 5% SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
19 | 1 | R8 | 2.2K 5% SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
20 | 1 | T1 | 750315126 TRANSFORMER | WURTH | DIGIKEY | 1297-1194-1-ND |
21 | 1 | U1 | LT8304 SOIC8 | ANALOG DEVICE | DIGIKEY | 505-LT8304IS8E#PBF-ND |
22 | 1 | ZD1 | CMZ5944B | CENTRAL SEMI | DIGIKEY | 1514-CMZ5944BTR13PBFREECT-ND |
LT8304 Block Diagram
Connections