KA7541 查看數據表（PDF） - Fairchild Semiconductor

零件编号

产品描述 (功能)

生产厂家

KA7541

Simple Ballast Controller

Fairchild Semiconductor 

tss = C-----s-----×-----V--

i

=

0----.--2----×-----1---0----–---6----×-----2-

313 × 10–9

=

1.28s

For example, the soft start capacitor of 0.2µF makes the soft start time (tss) to be 1.28sec.

KA7541

fsw, VCS

fsw (pre)

fsw (nor)

2V

tss

Figure 3. Frequency & Soft start capacitor voltage variation during soft start

No Lamp Protection

When the voltage at pin #4 is lower than 2V, the gate drive output is off state, so the external power MOSFET stops switching.

In no lamp protection circuit the dc link voltage is divided by a couple of resistors including both lamp filaments, and The

divided voltage is applied to the pin #4 before the MOSFETs start switching.

VR4 = Vdd × R-----1----+-----R----------2--------+----------R--------R-3---2------4+---------2---------×----------R--------f----+----R-----4-

≅

400

×

---------------------------------------1----5---K-----Ω-----------------------------------------

180KΩ + 3----3---0----K----Ω------+-----6----8---0----K----Ω--- + 15KΩ

2

V3

=

V2

×

-------R-----3--------

R2 + R3

≅

200V

When in normal mode the average voltage of the V3 is the half of the dc link voltage (Vdd). So, in order to make stable start

condition, the resistors are designed to make the voltage of V3 to be the half of the dc link voltage.

7

Share Link: