UPSR1103 Datasheet, PDF (5/8 Pages) Unisonic Technologies – HIGH PRECISION CC/CV PRIMARY SIDE SWITCHING REGULATOR

UPSR1103
Advance
CMOS IC
 OPERATION DESCRIPTION
The UTC UPSR1103 is a primary control unit for switch mode charger and adapter applications. It operates in
primary-side sensing and regulation. Opto-coupler and TL431 could be eliminated. Proprietary built-in CV and CC
control can achieve high precision CV/CC performance. The device integrates PWM controller to enhance the
performance of discontinuous conduction mode (DCM) flyback converters.
High-Voltage Startup control
The HV pin of UTC UPSR1103 is connected to the line input through a resistor (100K is recommended). During
startup, the internal startup circuit in UTC UPSR1103 is enabled. Meanwhile, line input supplies a constant current to
charge the hold-up capacitor through the resistor. When the VDD voltage reaches V_TH(ON), the internal startup circuit
is disabled and the IC turns on.
Operating Current
The operating current of UTC UPSR1103 is as low as 1.6mA. Good efficiency and very low standby power can be
achieved.
Constant Voltage Operation
The output voltage is defined by the transmission ratio between the secondary and auxiliary winding. The UTC
UPSR1103 captures the auxiliary winding feedback voltage at VS pin and operates in constant-voltage (CV) mode to
regulate the output voltage. The auxiliary voltage reflects the output voltage is given by:
V_AUX
=
N_A
N_S
×（V_O
+
∆V）
(1)
Where △V indicates the drop voltage of the output diode.
Figure2. Auxiliary voltage waveform
Via a resistor divider connected between the auxiliary winding and VS, the V_AUX is sampled at the Tsampling end
and it is hold until the next sampling. The sampled voltage is compared with 2.5V reference voltage and the error is
amplified. The error amplifier output reflects the load condition and controls the Toff time and the Ipk to regulate the
output voltage, thus constant output voltage can be achieved.
Constant Current Operation
When the sampled voltage is below 2.5V reference voltage and the error amplifier output reaches its maximum,
thus UTC UPSR1103 operates in constant-current (CC) mode. The CC point and maximum output power can be
externally adjusted by external current sense resistor Rcs. The larger Rcs, the smaller CC point is, and the smaller
output power becomes.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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