EV4031-S-00A – TRIAC AND ANALOG DIMMABLE 16W PSR WITH PFC LED DRIVER

EV4031-S-00A Rev.1.01

www.MonolithicPower.com

4

11/25/2014

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CIRCUIT DESCRIPTION

The EV4031-S-00A is configured in a single-

stage Flyback topology, it uses primary-side-

control which can mostly simplify the schematic

and get a cost effective BOM. It can also achieve

high power factor and accurate LED current.

F1, L1, L2, L3, R1, R14, R13 CX1, DB1, and C1

compose the input stage. F1 fuses the AC input

to protect for the component failure or some

excessive short events. L1, L2, L3, R1, R14, CX1,

R13 and C1 associated with CY1 form the EMI

filter which can meet the standard EN55015. The

diode rectifier DB1 rectifies the input line voltage.

Small bulk CBB capacitor C1 is used as a low

impedance path for the primary switching current,

to maintain high power factor, the capacitance of

C1 should be selected with low value.

RV1 D10, R25, R26, R27, C12 are used for

surge test. RV1 can make sure the circuit pass

500V surge test, for higher level test, a RCD

snubber composed of D10, R25, R26, R27 and

C12 is needed.

R3, R8, R5, R23, C4, C11, D1, D4, Q1, Q3 with

R12 compose the damping circuit for reducing

the inrush current at the dimmer turning on time.

The circuit let the inrush current flow through R12

at first when triac dimmer turns on. Then Q1

turns on and shorts R12, this can save power

from R12. Q3 is used to discharge C4 when the

triac is off. D4 is used to clamp the gate voltage

of Q1 to 15V.

R4, R7, C3 are used as a bleeder circuit which

keeping the triac current above the minimum

holding current after triac turns on.

R10, R17, C9 provide sine wave reference for

the primary peak current to get an active PFC

function. R28 and Q4 parallels R29 with R17,

when the input voltage is high, which make sure

the MULT pin voltage lower than the max voltage

rating, and improves the line regulation in wide

input voltage range application.

D12, R24, R31 are used to improve the THD

performance at high side input, which is useful in

wide input voltage range application.

R11, D7, C10, D11 are used to supply power for

MP4031. A 47μF bulk capacitor C10 is selected

to maintain the supply voltage. At start-up, C10 is

first charged up through the external MOSFET

Q2 and internal charging circuit, when the VCC

voltage reaches 10V, the internal charging circuit

stops charging and the control logic works. Then

the power supply is taken over by the auxiliary

winding through R11, D7.

R6, C7, D6 and D5 are used for the gate drive of

the external MOSFET Q2.

R15, R16, C13, D9 are used to detect the

auxiliary

winding

to

get

the

transformer

magnetizing current zero crossing signal for

realizing the boundary conduction operation, and

also monitor the output OVP condition. The OVP

voltage is set by the divider ratio of R15, R16.

R21 and D8 are used to restrain the oscillation

between the leakage inductor and the parasitical

capacitor when OVP happens. If the oscillation

happens, the external MOSFET will be turned

on/off abnormally and the part can’t work in auto

restart mode.

U2 is an Optocoupler which optically couples the

PWM dimming signal from the secondary side to

the primary side. R36, R37, R38, and C17

convert the PWM signal into an analog signal,

which is divided by R30 and R19, then put into

CS pin.

D13, R32, C14, Q5, R33, C15, U3, R34, R35,

C16 compose a LDO, which is the power supply

for Optocoupler.

R18, R20 are primary sensing resistors for

primary side current control. The value of R18,

R20 set the output LED current. C2, R2, R22, D3

are used to damp the leakage inductance energy

so the drain voltage can be suppressed at a safe

level.

Diode D2 rectifies the secondary winding voltage

and the capacitor C5, C6 are the output filter.

The resistor R9 is placed as pre-load to limit the

output voltage rise too high in open load

condition.