MP4031GS datasheet(18/19 Pages) MPS

18 / 19 page

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

EV4031-S-00A Rev.1.01

www.MonolithicPower.com

11/25/2014

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

APPENDIX

RIPPLE SUPPRESSOR

(Innovative Proprietary)

For Triac dimming LED lighting application, a

single stage PFC converter needs large output

capacitor to reduce the ripple whose frequency is

double of the Grid. And in deep dimming situation,

the LED would shimmer caused by the dimming

on duty which is not all the same in every line

cycle. What’s more, the Grid has noise or inrush

which would bring out shimmer even flicker.

Figure 6 shows a ripple suppressor, which can

shrink the LED current ripple obviously.

Figure 6: Ripple Suppressor

Principle:

Shown in Figure 6, Resister R, capacitor C, and

MOSFET M compose the ripple suppressor.

Through the RC filter, C gets the mean value of

the output voltage VCo to drive the MOSFET M. M

works in variable resistance area. C’s voltage VC

is steady makes the LEDs voltage is steady, so

the LEDs current will be smooth. MOSFET M

holds the ripple voltage vCo of the output.

Diode D and Zener diode DZ are used to restrain

the overshoot at start-up. In the start-up process,

through D and DZ, C is charged up quickly to turn

on M, so the LED current can be built quickly.

When VC rising up to about the steady value, D

and DZ turn off, and C combines R as the filter to

get the mean voltage drop of VCo.

The most important parameter of MOSFET M is

the threshold voltage Vth which decides the

power loss of the ripple suppressor. Lower Vth is

better if the MOSFET can work in variable

resistance area. The BV of the MOSFET can be

selected as double as VCo and the Continues

Drain current level can be selected as decuple as

the LEDs’ current at least.

About the RC filter, it can be selected

LineCycle

50 / f

 

. Diode D can select 1N4148,

and the Zener voltage of DZ is as small as

possible when guarantee

DDZ

C _PP

0.5 V





Optional Protection Circuit

In large output voltage or large LEDs current

application, MOSFET M may be destroyed by

over-voltage or over-current when LED+ shorted

to LED- at working.

Gate-Source (GS) Over-voltage Protection:

Figure 7: Gate-Source OVP Circuit

Figure 7 shows GS over-voltage protection circuit.

Zener diode DG and resistor RG are used to

protect MOSFET M from GS over-voltage

damaged. When LED+ shorted to LED- at normal

operation, the voltage drop on capacitor C is high,

and the voltage drop on Gate-Source is the same

as capacitor C. The Zener diode DG limits the

voltage VGS and RG limits the charging current to

protect DG. RG also can limit the current of DZ at

the moment when LED+ shorted to LED-. VDG

should bigger than Vth.

Drain-Source Over-voltage and Over-current

Protection

As Figure 8 shows, NPN transistor T, resistor RC

and RE are set up to protect MOSFET M from

over-current damaged when output short occurs

at normal operation. When LED+ shorted to LED-,

the voltage vDS of MOSFET is equal to the vCo

which has a high surge caused by the parasitic

parameter. Zener Dioder DDS protects MOSFET

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