Datasheet LT1425 (Analog Devices) - 7
| Manufacturer | Analog Devices |
| Description | Isolated Flyback Switching Regulators |
| Pages / Page | 20 / 7 — W U. TI I G DIAGRA. OPERATION |
| File Format / Size | PDF / 302 Kb |
| Document Language | English |
W U. TI I G DIAGRA. OPERATION
Model Line for this Datasheet
Text Version of Document
LT1425
W U W TI I G DIAGRA
VSW VOLTAGE COLLAPSE DETECT VFLBK 0.80× VFLBK VIN GND SWITCH OFF ON OFF ON STATE MINIMUM tON ENABLE DELAY FLYBACK AMP DISABLED ENABLED DISABLED STATE MINIMUM ENABLE TIME 1425 TD
U OPERATION
The LT1425 is a current mode switching regulator IC that The LT1425 derives its information about the isolated has been designed specifically for the isolated flyback output voltage by examining the primary side flyback topology. The special problem normally encountered in pulse waveform. In this manner no optoisolator nor extra such circuits is that information relating to the output transformer winding is required. This IC is a quantum voltage on the isolated secondary side of the transformer improvement over previous approaches because: target must be communicated to the primary side in order to output voltage is directly resistor-programmable, regu- maintain regulation. Historically, this has been done with lation is maintained well into discontinuous mode and optoisolators or extra transformer windings. Optoisolator optional load compensation is available. circuits waste output power and the extra components The Block Diagram shows an overall view of the system. they require increase the cost and physical volume of the Many of the blocks are similar to those found in tradi- power supply. Optoisolators can also exhibit trouble due tional designs including: internal bias regulator, oscilla- to limited dynamic response (temporal), nonlinearity, tor, logic, current amplifier and comparator, driver and unit-to-unit variation and aging over life. Circuits output switch. The novel sections include a special employing extra transformer windings also exhibit defi- flyback error amplifier and a load compensation mecha- ciencies. The extra winding adds to the transformer’s nism. Also, due to the special dynamic requirements of physical size and cost. Dynamic response is often flyback control, the logic system contains additional mediocre. There is usually no method for maintaining functionality not found in conventional designs. load regulation versus load. 7
W U W TI I G DIAGRA
VSW VOLTAGE COLLAPSE DETECT VFLBK 0.80× VFLBK VIN GND SWITCH OFF ON OFF ON STATE MINIMUM tON ENABLE DELAY FLYBACK AMP DISABLED ENABLED DISABLED STATE MINIMUM ENABLE TIME 1425 TD
U OPERATION
The LT1425 is a current mode switching regulator IC that The LT1425 derives its information about the isolated has been designed specifically for the isolated flyback output voltage by examining the primary side flyback topology. The special problem normally encountered in pulse waveform. In this manner no optoisolator nor extra such circuits is that information relating to the output transformer winding is required. This IC is a quantum voltage on the isolated secondary side of the transformer improvement over previous approaches because: target must be communicated to the primary side in order to output voltage is directly resistor-programmable, regu- maintain regulation. Historically, this has been done with lation is maintained well into discontinuous mode and optoisolators or extra transformer windings. Optoisolator optional load compensation is available. circuits waste output power and the extra components The Block Diagram shows an overall view of the system. they require increase the cost and physical volume of the Many of the blocks are similar to those found in tradi- power supply. Optoisolators can also exhibit trouble due tional designs including: internal bias regulator, oscilla- to limited dynamic response (temporal), nonlinearity, tor, logic, current amplifier and comparator, driver and unit-to-unit variation and aging over life. Circuits output switch. The novel sections include a special employing extra transformer windings also exhibit defi- flyback error amplifier and a load compensation mecha- ciencies. The extra winding adds to the transformer’s nism. Also, due to the special dynamic requirements of physical size and cost. Dynamic response is often flyback control, the logic system contains additional mediocre. There is usually no method for maintaining functionality not found in conventional designs. load regulation versus load. 7
