AP1601 datasheet(11/22 Pages) AKM

11 / 22 page

［AP1601］

MS 1454-E-01

2012/08

NS、NB are respectively the number of the secondary winding and the auxiliary winding of transformer T1 .

The VVFC voltage is reflected in the OSC pin voltage and is in the range from 0.2V(typ) to 2V(typ); if it is less than

0.2V , the OSC voltage will be 0.2V, and if it is more than 2V(typ), the OSC pin voltage will be 2V(typ). (refer to

Figure 6.)

As the graph in Figure 6 shows, VVFC which is the center of VF variation should be 1V to compensate LED VF

variation. When the voltage is 1V, the ratio of R11 and R12 is approximately given by the following formula.













R11’s selectable range is from 5kΩ to 100kΩ. The number of transformer auxiliary winding is determined by the

VDD voltage.

The VDD pin voltage, VDD in stable operation, is approximately given by the following formula,















When the LED VF variation is expected to be ±30%, the VDD voltage, which is the center of the variation, should

be set approximately to 15V to be operating within the VDD operating voltage range.

Bottom voltage detection (VTHZC)

Figure 8 shows the schematic of bottom voltage detection on the VFC pin.

As the figure is shown, the rising edge of the internal CKL is the regular interval (=Ts)

However, by the bottom voltage detection function, CLK is kept on high level until VFC becomes less than VTHZC

as shown in the dashed line box A in the figure.

If the VFC pin is already less than VTHZC at the internal CLK rising edge, the OUT pin should be VOUTH level.

However, there are the following exceptions in order to prevent malfunction.

①

If internal CLK rises while the OUT pin is VOUTH level, the CLK will not be maintained.

②

TBLANK period (700ns, design value) immediately after the OUT pin becomes VOUTL level, ZCD(Internal) shown in

Figure 8 is held as low level and VTHZC detection on the VFC pin is disabled.

OUT

VDS

VFC

CLK(Internal)

VTHZC

ZCD(Internal)

Figure 8. Bottom voltage detection (VTHZC)

By this bottom voltage detection function, the external MOSFET is able to turn on in low voltage and current

level, and a noise-reduction effect can be expected. Furthermore, switching-loss can be reduced and power

efficiency will be improved.

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