2

2

Re sistors

Vdc

325

P

10.56mW

Rstart

up

10M

=

=

=

-

W

Rstart

up

10M

-

=

W

Vdc max

230Vac

2

325Vdc

=

·

=

LM5023

OUT

QR

CS

VCC

GND

90-264 VAC

High

Voltage

Start-up

VSD

Depletion

Mode

FET

CVCC

LM5023

SNVS961C – APRIL 2013 – REVISED AUGUST 2013

www.ti.com

Figure 8. Start-Up With a Depletion Mode FET

An alternative start-up circuit employs an Enhancement Mode FET with resistors connected from the rectified dc

bus to the Gate of the FET, Figure 9. After the input AC power is applied the Enhancement Mode FET supplies

Drain output, which is pulled up to VCC during start-up, goes low. This grounds the Gate of the start-up MOSFET

turning it off. The start-up resistors are always in the circuit, therefore the standby power consumed will be higher

than if a Depletion Mode FET were used.

•

Vin = 230 Vac

•

VCC = 10 V

•

•

•

10

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