AN1513

Schematic

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1

Schematic

The power supply topology is a discontinuous current mode flyback converter, designed with

secondary feedback, optocoupler and TL431C. The output voltage regulation is performed

on the 6.5 V, so the output voltage 10 V can change according to the load applied on both

outputs.

To keep the drain voltage at a safe level and to meet the standby power specification, the

clamper used is a Transil 1.5KE220A instead of a classic R-C-D circuit. While the R-C-D

circuit dissipates energy in any load condition, the Transil dissipates energy only when the

drain voltage spike reaches its breakdown voltage. This consideration is important in order

to keep low consumption (<1 W) during standby operation mode.

A Zener diode is also connected to pin Comp for short circuit protection. This diode clamps

the voltage on pin Comp under the maximum value (4.5 V), reducing the maximum power

delivered by the SMPS.

undervoltage lockout threshold and the VIPer starts working in hiccup mode. Even if the

peak output current is higher than the nominal one, thanks to the on/off cycles, the average

current flowing in the shorted output components is kept under control at a safe value

avoiding diodes failure and any other damage to the circuit.

The output rectifiers are Schottky diodes for better efficiency thanks to their lower forward

voltage drop and negligible switching losses.

The output capacitors are low ESR type to minimize the output ripple and to manage the

RMS output ripple current.

Table 1.

Electrical specifications

Parameter

Value

Input voltage

Output voltage 1

6,5 V±3% at 2.5 A

Output voltage 2

10 V±8% at 1.5 A

Standby consumption

<1 W

Efficiency

>80%

Max working ambient temperature

60°C