VK05CFL-E STMicroelectronics, VK05CFL-E Datasheet - Page 4

• Manufacturer Part Number: VK05CFL-E
• Description: MOSFET & Power Driver ICs Electronic Driver CDF Application
• Manufacturer: STMicroelectronics

Specifications of VK05CFL-E

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

VK05CFL
APPLICATION DESCRIPTION
Technology Overview
The VK05CFL is made by using STMicroelectronics proprietary VIPower M3-3 technology. This
technology allows the integration in the same chip both of the control part and the power stage. The power
stage is the “Emitter Switching”. It is made by putting in cascode configuration a bipolar high voltage
darlington with a low voltage MOSFET. This configuration provides a good trade-off between the bipolars
low ON drop with high breakdown voltage in OFF state, and the MOSFETS high switching speed. The
maximum theoretical working frequency is in the range of 300KHz.
Circuit description
The electrical scheme of the VK05CFL used as a self-oscillating converter to drive fluorescent tubes is
shown in Fig. 1.
Figure 1: Application schematic
This topology does not require the saturable transformer to set the working frequency. Two secondary
windings are wound on the main ballast choke Lp. These windings have two functions:1) to trigger the ON
state and 2) to provide the power supply to the device. A good trade-off for the ratio between the primary
winding Lp and the two secondary windings is 10:1; in order to minimize the power dissipated on the
resistors R4 - R5 and to guarantee sufficient voltage to supply the device.
The steady-state working frequency is set by the two capacitor C5 and C6. They are charged by a current
I
OFF. By choosing the same value for C5 and C6 the circuit will work with a duty-cycle of 50%. During the
start-up, as the resonance frequency is higher than the steady-state frequency, the secondary voltage
falls lower than the device sustain voltage before the capacitor C5-6 is charged, switching OFF the device.
For this reason the circuit can work at different frequencies during the start-up and steady-state phases.
The resistor R2 and the capacitor C8 are needed to bias the internal diac in the low side device in order
to start-up the system. In the high side device the diac pin must be connected to the midpoint. R1 is the
pull-up resistor and C7 is the snubber capacitor.
Input filtering is realized by R4-C10 and R5-C11. It is necessary to have a proper supply voltage on the
input pin.
4/14
cap
300 A. When the voltage on the capacitor reaches an internal fixed value the power stage is turned
Bridge
Input Filter
+
C8
L2s
R2
L1s
C11
R5
C10
R4
C5
C6
sec
osc
sec
osc
diac
diac
VK05CFL
VK05CFL
Collector
Collector
Source
Source
R1
C7
Lp
C4
Tube
PTC
C13
C2
C3
1