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TNY264 Datasheet(PDF) 8 Page - Power Integrations, Inc. |
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TNY264 Datasheet(HTML) 8 Page - Power Integrations, Inc. |
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8 / 20 page  8 B 7/01 TNY264/266-268 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 (85-265 VAC). The inductor (L1) forms a π-filterinconjunction 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-filterdescribedaboveincombination 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 BE of transistor Q1 to sense the voltage across the current sense resistor R4. When the drop across R4 exceeds the V BE 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 PC Standby Circuits Figures 15 and 16 show examples of circuits for PC standby applications. They both provide two outputs: an isolated 5 V and a 12V primary referenced output. The first, using TNY266P, provides 10W, and the second, using TNY267P, 15 W of output power. Both operate from an input range of 140 to 375VDC, 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 PC 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 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 4 M Ω, 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 k Ω 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 15W design an additional output capacitor, C7, is required due to the larger secondary ripple currents compared to the 10W PC 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 5V output is sensed by U2 and VR1. R5 is used to ensure that the Zener diode is biased at its test current. The Zener regulation method provides sufficient accuracy (typ. ± 3%). 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. |
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