AN2844

Adapter features

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2

Adapter features

2.1

Main characteristics

The following is a list of the specifications and main parameters of the demonstration board.

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Minimum input voltage: 125 VDC

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Maximum input voltage: 1250 VDC

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Output voltage: 5 V - 3.0 A

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Maximum output power: 15 W

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Short-circuit protection based on auto-restart feature

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Minimum switching frequency limited to 30 kHz

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Overall converter efficiency > 60%

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Non-galvanic isolated solution used in most metering applications

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PCB type and size:

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material used for PCB: FR-4

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double-sided layout

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thickness of copper: 35 µm

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total diameter of demonstration board: 58 x 120 mm.

2.2

Circuit description

This device is a flyback converter, a very popular and well-known topology in switch-mode

power supply applications where the required output power is in the range of

5 to 200 W. The popularity of this type of converter comes from the simplicity of its design,

the small number of components and its resulting low cost compared to other topologies in

the same output power range.

The converter is based on the L6565 PWM driver that operates in quasi-resonant mode,

meaning zero voltage or valley switching during the turn-OFF phase. Current mode control

is the primary control method. An ESBT switch must be used for this application. The ESBT

is a cascade configuration of a high-voltage bipolar junction transistor (BJT) and a low-

voltage power MOSFET. STMicroelectronics™ optimizes the performance of both devices

and offers this kind of switch in one single package so as to simplify the application’s design,

reduce electromagnetic interference and price, and increase reliability and performance

(see Figure 3). The ESBT switch, compared to a high-voltage switch, offers a low ON-state

voltage drop like a BJT. The switch is very robust, easy to drive and has a relatively fast

switching speed similar to that of a MOSFET.

For more detailed information on the design of the discontinuous conduction-mode flyback

converter, refer to the application note AN1889 "ESBT STC03DE170HV in

3-phase auxiliary power supply".