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LNK6774E Datasheet(PDF) 8 Page - Power Integrations, Inc. |
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LNK6774E Datasheet(HTML) 8 Page - Power Integrations, Inc. |
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8 / 24 page  Rev. C 03/14 8 LinkSwitch-HP www.powerint.com www.powerint.com Applications Example 30 W, 12 V Universal Adapter The circuit shown in Figure 11 is a high efficiency universal input 30 W, 12 V output adapter using the LNK6766E. The supply uses primary winding coupled sensing for the following features: output regulation, line undervoltage lockout, input and output OVP. With primary winding sense there is no need for an external secondary referenced error amplifier such as a TL431 and optocoupler. The winding sense of bus voltage also eliminates the need for direct input voltage sensing which requires more components and is more dissipative than winding sense method. Output regulation is ±5%, active-on efficiency is 86% and no-load input power is less than 30 mW. The rectified and filtered input voltage is applied to the primary winding of T1. The other side of the primary is driven by the integrated power MOSFET in U1. Diode D1, C3, R2, R3 and VR1 comprise the clamp circuit, limiting the leakage inductance turn-off voltage spike to safe value. Zener diode VR1 also helps to reduce input power consumption during no-load conditions. Start-up of the power supply is initiated by sensing the forward negative pulse current from feedback winding through R19 into Figure 11. Schematic of a Universal Input 30 W, 12 V, 2.5 A Adapter. the FEEDBACK pin. This sensing is accomplished by periodically turning on the power MOSFET to sense input voltage condition with very short low frequency sampling pulses. During the forward pulse sampling time the FEEDBACK pin is held to zero volts by an internal clamp. When negative forward pulse current exceeds 250 mA, LinkSwitch-HP for two consecutive switching cycles will initiate start-up with a soft-start sequence that reduces component stress and allows the output to rise in a smooth monotonic manner. The desired input voltage for start-up is determined by the turns ratio of primary winding to feedback winding and the value of R19. Regulation is accomplished by sampling the feedback winding during flyback period through the resistor divider R19 and R20 through FEEDBACK pin. This sampled voltage is compared to an internal error amplifier threshold of 2 V. The value of R19 is already determined by the line undervoltage function so the output regulation point is determined by setting the proper value for R20. The loop compensation is provided by the network from COMPENSATION pin to ground. In the case above, a low frequency to mid frequency gain of 20 dB for the error amplifier is established by R7 and C7. Capacitor C8 functions essentially as a noise filter and is typically 100 pF. There is also an internal 16 kHz filter within the device. It is advised to limit R7 to no greater than 260 k W to avoid stability and noise sensitivity. PI-6844-120312 C18 2.2 nF 250 VAC VR1 BZG03C130 130 V L4 10 mH BR2 DF206ST-G 600 V C2 68 µF 400 V D2 BAV21WS- 7-F T1 RM8 D1 DL4937 C6 22 µF 16 V C8 100 pF 50 V C23 10 pF 50 V C20 4.7 nF 50 V C3 10 nF 630 V C12 1000 µF 16 V C13 680 pF 100 V D8 STPS30100ST C5 470 nF 50 V 7 FL2 FL1 9 6 8 C14 150 nF 275 VAC R29 3.3 M Ω R30 3.3 M Ω F1 2 A 90 - 265 VAC 12 V, 2.5 A J3 RTN J4 J1 J2 LinkSwitch-HP D S FB BP CP PD CONTROL U1 LNK6766E C22 10 µF 16 V L5 100 µH R19 41.2 k Ω 1% R8 23.2 k Ω 1% 1/8 W R7 100 k Ω 1/8 W R9 4.3 k Ω 1% 1/8 W R13 20 Ω 1/8 W R2 100 Ω 1/2 W R3 3 k Ω R28 27 k Ω R20 10.2 k Ω 1% C7 100 nF 25 V |
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Similar Description - LNK6774E |
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