IW1816 Datasheet, PDF (12/18 Pages) Dialog Semiconductor – Off-Line Digital Green-Mode PWM Controller Integrated

iW1816
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
The auxiliary voltage is given by:
( ) = V_AUX
N _AUX
N_S
V_O + ∆V
(10.5)
and reflects the output voltage as shown in Figure 10.3.
The voltage at the load differs from the secondary voltage by a diode drop and IR losses. Therefore, if the secondary
voltage is always read at a constant secondary current, the difference between the output voltage and the secondary
voltage is a fixed ΔV. Furthermore, if the voltage can be read when the secondary current is small, ΔV is also small.
With the iW1816, ΔV can be ignored.
The real-time waveform analyzer in the iW1816 reads this information cycle by cycle. The part then generates a
feedback voltage V_FB. The V_FB signal accurately represents the output voltage under most circumstances and is used
to regulate the output voltage.
10.4 Constant Voltage Operation
After soft-start is completed, the digital control block measures the output conditions. It determines the output power
levels and adjusts the control system according to either a light or a heavy load. If this is in the normal range, the
device operates in the Constant Voltage (CV) mode, and changes the pulse width (T_ON) and off-time (T_OFF) in order to
meet the output voltage regulation requirements.
If no voltage is detected on V_SENSE, it is assumed that the auxiliary winding of the transformer is either open or shorted
and the iW1816 shuts down.
10.5 Constant Current Operation
At overload condition, the iW1816 enters constant current (CC) mode to limit the output current on cycle-by-cycle
basis. During this mode of operation the output current is limited to a constant level regardless of the output voltage,
while avoiding continuous conduction mode operation. In case of very heavy loading, when the output voltage is low
enough, the iW1816 shuts down.
To achieve this regulation the iW1816 senses the load current indirectly through the primary current. The primary
current is detected by the I_SENSE pin through a resistor from the BJT emitter to ground.
V_NOM
CV mode
Datasheet
www.dialog-semiconductor.com
Output Current
I_OUT(CC)
Figure 10.4 : Power Envelope
Rev. 1.0
12 of 18
30-Jun-2016
© 2016 Dialog Semiconductor