DocID024821 Rev 2

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AN4314

Main characteristics and circuit

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1

Main characteristics and circuit

The main characteristics of this single-stage LED driver demonstration board are given in

the table below.

The main feature of the converter is that the input current is almost in phase with the mains

voltage; therefore the power factor is close to unity. This is achieved by the L6564H

controller, which shapes the input current as a sine wave in phase with the mains voltage.

An external high-voltage startup circuitry is not needed because it is already embedded in

the IC.

The power supply utilizes a typical non-isolated buck-boost converter topology with a simple

inductor to transfer energy to the LED load.

The converter is connected after the mains rectifier and the capacitor filter, which in this

case is quite small, to avoid damage to the shape of the input current. The buck-boost

switch is represented by the power MOSFET Q3 and driven by the L6564H.

At startup, a 0.85 mA internal current source of the L6564H charges the V

CC

capacitor (C8),

until the voltage on the V

cc

pin reaches the startup threshold, then it is shut down.

The T1 auxiliary winding (pins 6-7), the charge pump (C14, R16, D4) and the BJT voltage

regulator (Q2, DZ2, R3) generate a constant V

CC

voltage that powers the L6564H during

normal TM operation.

R37 is also connected to the auxiliary winding to provide the transformer demagnetization

signal to the L6564H ZCD pin, turning on the MOSFET at any switching cycle. The

MOSFET used is the STI8N65M5, a new MDmesh™ V, low-cost, low on-resistance, 710 V

device housed in an I

2

The multilayer inductor, using a standard ferrite size EF-25, is manufactured by Magnetica.

Table 1. Main characteristics and circuit

Parameter

Value

Line voltage range

85 to 265 V

AC

Line frequency (fL)

47-63 Hz

LED string voltage drop

70 V ±10 % (23-LED p.n. X42182) [

6]

LED nominal current

350 mA ±3 %

LED current ripple pk-pk

100 mA

Rated output power

25 W

Power factor

> 0.9

Efficiency

> 89 @ 230 V

Maximum ambient temperature

50 °C

Conducted EMI

In accordance with EN55022 Class-B

Protections

Preventing overvoltage, load disconnection and short-circuit