UPSR100_15 Datasheet, PDF (5/7 Pages) Unisonic Technologies – HIGH PRECISION CC/CV PRIMARY-SIDE PWM POWER SWITCH

UPSR100
Preliminary
CMOS IC
 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 voltage regulator provides the internal power supply V_DD. For V_CC and V_DD external capacitors are required.
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_AUX
=
N_A
N_S
×（V_O
+
∆V）
(1)
Where △V indicates the drop voltage of the output diode.
Figure 2. Auxiliary voltage waveform
Via a resistor divider connected between the auxiliary winding and FB, the V_AUX is sampled at the Tsampling end
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.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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QW-R502-946.d