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NCP1237

Fixed Frequency Current Mode Controller for Flyback Converters

ON Semiconductor 

VDD

INTC

INTC

NCP1237

SIMPLIFIED INTERNAL BLOCK SCHEMATIC

+

+

−

VOVP

blanking

tLatch(OVP)

Brown−out

HV stop

HV sample

BO

OVM

HV dc

Latch

1 kW

Vclamp

VDD

RFB(up)

−

+

+

VOTP

FB

blanking

tLatch(OTP)

S

Q

R

Soft−start

end

Brown−out

Reset

−

+

+

V skip

TSD

Latch

Reset

UVLO

VDD

IC Start

TSD

Dual HV

start−up

current source

TSD HV current

Reset

UVLO VCC

VDD management

Start

Soft−skip ramp

Reset

tSSKIP

Skip

FB

KFB

slope

comp.

HV sample

V to I

IOPC = 0.5m x

(VHV−125)

VFB(OPC)

PWM

+

−

Soft−start

+

−

tSSTART

Soft−start Start

ramp

End

Reset

IC Start

IC Stop

Jitter

Skip

Sawtooth

Stop Foldback

Oscillator

DCMAX

DMAX

FB

Clamp

Soft−start end

S

blanking

Q

tLEB

CS

+

+

−

R

blanking

tBCS

VILIM

ILIMIT

ILIMIT

DMAX

S

Fault Flag

Q

R

PWM

R

Q

S

ITRAN

+

VCS(tran)

+

−

UVLO

ITRAN

IC stop

+

+

−

VCS(stop)

timer

tfault

Fault

ttran

Brown−out

Reset

Protection

Mode

release

Autorecovery

protection

mode only

timer

tautorec

HV stop

Latch

TSD

Figure 3. Simplified Internal Block Schematic

HV

VCC

DRV

GND

http://onsemi.com

3

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