TNY263_04 POWERINT [Power Integrations, Inc.], TNY263_04 Datasheet - Page 8

• Manufacturer Part Number: TNY263_04
• Description: Enhanced, Energy Efficient, Low Power Off-line Switcher
• Manufacturer: POWERINT [Power Integrations, Inc.]

is always powered from the input high voltage, it therefore
does not rely on bias winding voltage. Consequently this greatly
simplifies designing chargers that must work down to zero volts
on the output.
2.5 W CV/CC Cell-Phone Charger
As an example, Figure 14 shows a TNY264 based 5 V, 0.5 A,
cellular phone charger operating over a universal input range
(85 VAC to 265 VAC). The inductor (L1) forms a π-filter in
conjunction with C1 and C2. The resistor R1 damps resonances
in the inductor L1. Frequency jittering operation of TinySwitch-
II allows the use of a simple π-filter described above in
combination with a single low value Y1-capacitor (C8) to meet
worldwide conducted EMI standards. The addition of a shield
winding in the transformer allows conducted EMI to be met
even with the output capacitively earthed (which is the worst
case condition for EMI). The diode D6, capacitor C3 and
resistor R2 comprise the clamp circuit, limiting the leakage
inductance turn-off voltage spike on the TinySwitch-II DRAIN
pin to a safe value. The output voltage is determined by the sum
of the optocoupler U2 LED forward drop (~1 V), and Zener
diode VR1 voltage. Resistor R8 maintains a bias current
through the Zener diode to ensure it is operated close to the
Zener test current.
A simple constant current circuit is implemented using the V
of transistor Q1 to sense the voltage across the current sense
resistor R4. When the drop across R4 exceeds the V
transistor Q1, it turns on and takes over control of the loop by
driving the optocoupler LED. Resistor R6 assures sufficient
voltage to keep the control loop in operation down to zero volts
at the output. With the output shorted, the drop across R4 and
R6 (~1.2 V) is sufficient to keep the Q1 and LED circuit active.
Resistors R7 and R9 limit the forward current that could be
drawn through VR1 by Q1 under output short circuit conditions,
due to the voltage drop across R4 and R6.
10 and 15 W Standby Circuits
Figures 15 and 16 show examples of circuits for standby
applications. They both provide two outputs: an isolated 5 V
and a 12 V primary referenced output. The first, using TNY266P,
provides 10 W, and the second, using TNY267P, 15 W of
output power. Both operate from an input range of 140 VDC to
375 VDC, corresponding to a 230 VAC or 100/115 VAC with
doubler input. The designs take advantage of the line under-
voltage detect, auto-restart and higher switching frequency of
TinySwitch-II. Operation at 132 kHz allows the use of a smaller
and lower cost transformer core, EE16 for 10 W and EE22 for
15 W. The removal of pin 6 from the 8 pin DIP TinySwitch-II
packages provides a large creepage distance which improves
reliability in high pollution environments such as fan cooled
power supplies.
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Capacitor C1 provides high frequency decoupling of the high
voltage DC supply, only necessary if there is a long trace length
from the DC bulk capacitors of the main supply. The line sense
resistors R2 and R3 sense the DC input voltage for line under-
voltage. When the AC is turned off, the under-voltage detect
feature of the TinySwitch-II prevents auto-restart glitches at the
output caused by the slow discharge of large storage capacitance
in the main converter. This is achieved by preventing the
TinySwitch-II from switching when the input voltage goes
below a level needed to maintain output regulation, and keeping
it off until the input voltage goes above the under-voltage
threshold, when the AC is turned on again. With R2 and R3,
giving a combined value of 2 MΩ, the power up under-voltage
threshold is set at 200 VDC, slightly below the lowest required
operating DC input voltage, for start-up at 170 VAC, with
doubler. This feature saves several components needed to
implement the glitch-free turn-off compared with discrete or
TOPSwitch-II based designs. During turn-on the rectified DC
input voltage needs to exceed 200 V under-voltage threshold
for the power supply to start operation. But, once the power
supply is on it will continue to operate down to 140 V rectified
DC input voltage to provide the required hold up time for the
standby output.
The auxiliary primary side winding is rectified and filtered by
D2 and C2 to create a 12 V primary bias output voltage for the
main power supply primary controller. In addition, this voltage
is used to power the TinySwitch-II via R4. Although not
necessary for operation, supplying the TinySwitch-II externally
reduces the device quiescent dissipation by disabling the internal
drain derived current source normally used to keep the BYPASS
pin capacitor (C3) charged. An R4 value of 10 kΩ provides
600 µA into the BYPASS pin, which is slightly in excess of the
current consumption of TinySwitch-II. The excess current is
safely clamped by an on-chip active Zener diode to 6.3 V.
The secondary winding is rectified and filtered by D3 and C6.
For a 15 W design an additional output capacitor, C7, is
required due to the larger secondary ripple currents compared
to the 10 W standby design. The auto-restart function limits
output current during short circuit conditions, removing the
need to over rate D3. Switching noise filtering is provided by L1
and C8. The 5 V output is sensed by U2 and VR1. R5 is used to
ensure that the Zener diode is biased at its test current and R6
centers the output voltage at 5 V.
In many cases the Zener regulation method provides sufficient
accuracy (typically ± 6% over a 0 °C to 50 °C temperature
range). This is possible because TinySwitch-II limits the dynamic
range of the optocoupler LED current, allowing the Zener diode
to operate at near constant bias current. However, if higher
accuracy is required, a TL431 precision reference IC may be
used to replace VR1.