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VK05CFL
Secondary Filter Design
The design of RC network applied on the sec pin of both devices has to be done taking into account the
following considerations:
1) The sec filtered voltage must reach the device ON threshold at the end of the negative dV/dt and before
the end of the freewheeling diode conduction in order to avoid hard switching or switching ON delay.
2) The filtered voltage must be high enough (greater than 5V) at the end of T
on
in order to guarantee the
device supply voltage.
A good choice for time constant (τ=RC) is in the range:1.5 µs ÷ 3.3 µs.
The resistor value has chosen in relation to the power dissipated on it during the start-up phase, the worst
condition is verified when the preheating is used.
Tube pre-heating
By using the VK05CFL, the tube pre-heating can be done with the classical solution with PTC (see
application schematic in figure 1) or with a more reliable low voltage network (see figure 5b). The pre-
heating low voltage network allows to obtain an optimum pre-heating avoiding the overstress on the PTC
thus improving the ballast reliability and the lamp life-time.
Figure 5a: Pre-heating phase with PTC
APPLICATION BOARD
Please note that this demo can be used for Europe (230Vrms) market as well as for USA (110Vrms)
market.
In order to use the demoboard for Europe market the following modification must be done: electrolytic
capacitors C1 and C12 must be replaced with only one electrolytic capacitor Cx = 3,3µF/400V connected
with the positive pin on the D1 catode and the negative pin on the D3 anode. Also different power range
CFL can be driven by using this demoboard; on the left side of the component list reported below you find
component values able to drive CFL in the power range 5W to 15W, the component values written in
brackets in the table on the right are referred to the power range 15W to 23W.
sec
VK05CFL
Low side
osc
VK05CFL
High side
+
10µ
39K
1.2n
I
osc
1M
+
10µ
39K
1.2n
Iosc
1M
sec
osc
I
lamp
Figure 5b: Pre-heating low voltage network
Obsolete Product(s) - Obsolete Product(s)
