TNY263(2016) Ver la hoja de datos (PDF) - Power Integrations, Inc

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TNY263
(Rev.:2016)

TinySwitch-II Family Enhanced, Energy Efficient, Low Power Off-line Switcher

Power Integrations, Inc 

TNY263-268

A simple constant current circuit is implemented using the VBE

of transistor Q1 to sense the voltage across the current sense

resistor R4. When the drop across R4 exceeds the VBE of

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

undervoltage 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.

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

undervoltage. When the AC is turned off, the undervoltage

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 undervoltage threshold, when the AC is turned on again.

With R2 and R3, giving a combined value of 2 MΩ, the power

up undervoltage 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 TinySwitch-II based designs. During turn-on the

rectified DC input voltage needs to exceed 200 V undervoltage

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.

8

Rev. J 08/16

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