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PDF KA7541 Data sheet ( Hoja de datos )
| Número de pieza | KA7541 | |
| Descripción | Simple Ballast Controller | |
| Fabricantes | Fairchild | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de KA7541 (archivo pdf) en la parte inferior de esta página. Total 14 Páginas | ||
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KA7541
Simple Ballast Controller
www.fairchildsemi.com
Features
• Internal soft start
• Flexible soft start frequency
• No lamp protection
• Trimmed 1.5% internal bandgap reference
• Under voltage lock out with 1.8V of hysteresis
• Totem pole output with high state clamp
• Low start up and operating current
Descriptions
The KA7541 provides simple and high performance
electronic ballast control functions. KA7541 is optimized for
electronic ballast requiring a minimum board area, reduced
component count and low power dissipation. Internal soft
start circuitry eliminates the need for an external soft start
PTC resistor. The initial soft start switching frequency and
soft start time can be adjusted depending on the types of
lamps. Protection circuitry has also been added to prevent
burning out of switches in no lamp condition. output gate
drive circuit clamps power MOSFET gate voltage
irrespective of supply voltage
8-DIP
1
8-SOP
1
©2001 Fairchild Semiconductor Corporation
Rev. 1.0.3
1 page  
KA7541
Start-up Circuit
Start up current is supplied to the IC through the start up resistor (Rst). In order to reduce the power dissipation in Rst, the Rst
is connected to the full wave rectified output voltage.
The following equation can be used to calculate the size of Rst
Rst
<
-V----i-n----(---a---c----)---×---------2-----–-----V----t--h----(--s----t--)--,--m-----a----x-
Ist,max
PRSt=
(---V----i--n----(--a----c---_---m-----a----x---)----⋅-------2-----–----V-----c---c---)---2-
RSt
≤
0.5
W
= 8----5-----×---------2-----–----1---0----.-5-- = 440kΩ
0.25 × 10–3
RSt ≥ 2 × (Vin(ac_max) ⋅ 2 – Vcc)2
RSt ≥ 260K
∴260K ≤ RSt ≤ 440K
The size of start up capacitor (Cst) is normally decided in terms of the start up time and operating current build up time with
auxiliary operating current source.
The turn off snubber capacitor (Cq2) and two diodes (D1, D2) constitute the auxiliary operating current source for the IC. The
charging current through the Cq2 flows into the IC and also charges the start-up capacitor. If the size of Cq2 is increased, the
VCC voltage of the Cst is also increased.
Rectifier
Output
Q1
Q2
To VCC
(Pin 8)
Rst
+
− Cst
D2
Cq2
D1
Figure 1. Start up circuit
Oscillator
The gate drive output frequency is as half as that of the triangular waveform in timing capacitor (Ct) at pin #2. In normal
operating mode, the timing capacitor charging current is 50µA. The discharging current is seven times of the charging current
(7× 50µA). The charging period of the timing capacitor is the on duty of the gate drive. The discharging period is the off duty
of the gate drive.
The rising slope and falling slope of the triangular waveform are as following.
Rising slope: dv / dt = i / C = 50µA / Ct
Falling slope: dv / dt = i / C = 7 × 50µA / Ct
For example, when the timing capacitor is 180pF,
∆Tch = 6.69µ
∆Tdis = 0.956µ
5
5 Page 
Mechanical Dimensions
Package
KA7541
Dimensions in millimeters
8-SOP
1.55 ±0.20
0.061 ±0.008
MIN
0.1~0.25
0.004~0.001
#1 #8
#4 #5
6.00 ±0.30
0.236 ±0.012
3.95 ±0.20
0.156 ±0.008
1.80
0.071
MAX
0.50 ±0.20
0.020 ±0.008
5.72
0.225
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet KA7541.PDF ] | |
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