UPSR100

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

4 of 6

www.unisonic.com.tw

QW-R502-946.c

OPERATION DESCRIPTION

The UTC UPSR100 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. It uses Pulse Frequency Modulation (PFM) method to build

discontinuous conduction mode (DCM) flyback power supplies.

Startup control

The current biasing of UTC UPSR100 is adjustable by an external resistor. Internal time constants, thresholds and

the output current depend from the value of this resistor. The startup circuit activates the IC after startup and

deactivates the IC in case of UVLO.

Operating Current

The Operating current of UTC UPSR100 is as low as 500µA. 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

UPSR100

captures the auxiliary winding feedback voltage at FB pin and operates in constant-voltage (CV) mode to

regulate the output voltage. The auxiliary voltage reflects the output voltage is given by:

）

（

V

Δ

+

V

×

N

N

=

V

O

S

A

AUX

(1)

Where

V

△

indicates the drop voltage of the output diode.

Figure 2. Auxiliary voltage waveform

and it is hold until the next sampling. The sampled voltage is compared with 4V reference voltage and the error is

amplified. The error amplifier output reflects the load condition and controls the Toff time to regulate the output

voltage, thus constant output voltage can be achieved.

Constant Current Operation

When the sampled voltage is below 4V reference voltage and the error amplifier output reaches its maximum, thus

UTC UPSR100 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.