Flyback convertor for driving vacuum fluorescent displays

The new device, which supports a wide range of power requirements via appropriate selection of an external MOSFET and magnetic components, is designed to work over the automotive battery voltage range of 7-40 V and over the temperature range of -40°C to +125°C ambient.



While targeted primarily for use in VFD power supplies, which require multiple voltage rails to drive the anode, grid, and filament, the A4401 is also suited to any other automotive applications that require several regulated voltage rails.



The A4401 includes an integrated transconductance amplifier, which can be used to monitor and regulate the voltage on either one or several outputs where good cross-regulation is required. It also includes many other valuable features such as soft-start circuitry, a low quiescent 'sleep' mode

and a high-voltage enable pin.



The quasi-resonant, discontinuous flyback convertor operates near the critical conduction boundary. A novel adaptive turn-on control scheme is used to optimise the turn-on and turn-off phase of the MOSFET to reduce EMI emissions while minimising switching losses.



The converter is self-oscillating, operating at switching frequencies dependent on the input voltage, load and external components. An onboard linear regulator that is powered directly from the battery provides the housekeeping supply, avoiding the need for complex bias supplies.



Internal diagnostics provide comprehensive protection against overloads, input undervoltage, and over-temperature conditions. The A4401 is supplied in an 8-pin narrow SOIC package (suffix L), which is

lead (Pb) free, with 100% matt tin lead-frame plating.