UC1103

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

6 of 9

www.unisonic.com.tw

QW-R502-961.d



OPERATION DESCRIPTION

The UTC UC1103 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 UC1103 is connected to the line input through a resistor (100K is recommended). During

startup, the internal startup circuit in UTC UC1103 is enabled. Meanwhile, line input supplies a constant current to

disabled and the IC turns on.

Operating Current

The operating current of UTC UC1103 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

UC1103

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

∆

+

V

×

N

N

=

V

O

S

A

AUX

(1)

Where △V indicates the drop voltage of the output diode.

Figure2. Auxiliary voltage waveform

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 UC1103 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.