IX9915

8

www.ixysic.com

R01

always into pin FB). This error causes the regulated

output voltage to increase which increases the current

current to less than 1% is accomplished by setting the

Where:

2.2 Compensation

The dominate pole of the error amplifier is around

13kHz. In a typical system with a low-bandwidth

requirement, it doesn't need any external

compensation. Frequency response of the system can

be optimized for the specific application by placing a

compensation network between the OC and FB pins

of the IX9915. For designs with more critical

bandwidth requirements, measurement of the loop

response must be made and compensation adjusted

as necessary.

2.3 Design Example

A design example for the bleeder circuitry in LED lamp

exhibits the detailed steps. In this example, it will target

through the Darlington transistor:

In fact, the components in the dashed rectangle

function as a comparator, its gain:

around 82dB. That is to say, once the error amplifier

starts to regulate, the Darlington transistor will be shut

affecting the predetermined voltage:

Substituting:

into formula (2):

R

1

V

REG

50

A

-------------



50

A

100

I

IB MAX





=

V

REG

I

HMAX

–

R

E



V

BE

+

=

(1)

V

REG

I

HMAX

–

R

E

V

BE

+



=

25mA

100

 1.5V

+



=

4V

=

A

R

0

R

2



g

m



R

1

R

2

+

------------------------------

=

R

2

R

1

R

2

+

------------------

V

REF

V

REG

-------------

1.299V

4V

-----------------

0.325

==

=

g

m

1S (typical)

=

V

LINE-TH

V

REG

I

1

I

Q

+

 R

3



+



(2)

P

V

rms



2

100k



-------------------

=

R

2

9.6k





R

1

R

2

V

REG

V

REF

-------------

1

–







=

R

1

20k



