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LNK304GN Datasheet(PDF) 4 Page - Power Integrations, Inc. |
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LNK304GN Datasheet(HTML) 4 Page - Power Integrations, Inc. |
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4 / 20 page  2-4 Rev. I 11/08 4 LNK302/304-306 Figure 5. Universal Input, 12 V, 120 mA Constant Voltage Power Supply Using LinkSwitch-TN. power MOSFET is turned off for the remainder of that cycle. The leading edge blanking circuit inhibits the current limit comparator for a short time (t LEB) after the power MOSFET is turned on. This leading edge blanking time has been set so that current spikes caused by capacitance and rectifier reverse recovery time will not cause premature termination of the switching pulse. Auto-Restart (LNK304-306 only) In the event of a fault condition such as output overload, output short, or an open loop condition, LinkSwitch-TN enters into auto- restart operation. An internal counter clocked by the oscillator gets reset every time the FB pin is pulled high. If the FB pin is not pulled high for 50 ms, the power MOSFET switching is disabled for 800 ms. The auto-restart alternately enables and disables the switching of the power MOSFET until the fault condition is removed. Applications Example A 1.44 W Universal Input Buck Converter The circuit shown in Figure 5 is a typical implementation of a Figure 4. Frequency Jitter. RTN 12 V, 120 mA 85-265 VAC PI-3757-112103 FB BP S D LinkSwitch-TN C4 4.7 μF 400 V C1 100 nF D4 1N4007 D3 1N4007 D1 UF4005 LNK304 D2 1N4005GP C2 100 μF 16 V RF1 8.2 Ω 2 W R1 13.0 k Ω 1% R3 2.05 k Ω 1% L2 1 mH L1 1 mH 280 mA C5 4.7 μF 400 V C3 10 μF 35 V R4 3.3 k Ω 12 V, 120 mA non-isolated power supply used in appliance control such as rice cookers, dishwashers or other white goods. This circuit may also be applicable to other applications such as night-lights, LED drivers, electricity meters, and residential heating controllers, where a non-isolated supply is acceptable. The input stage comprises fusible resistor RF1, diodes D3 and D4, capacitors C4 and C5, and inductor L2. Resistor RF1 is a flame proof, fusible, wire wound resistor. It accomplishes several functions: a) Inrush current limitation to safe levels for rectifiers D3 and D4; b) Differential mode noise attenuation; c) Input fuse should any other component fail short-circuit (component fails safely open-circuit without emitting smoke, fire or incandescent material). The power processing stage is formed by the LinkSwitch-TN, freewheeling diode D1, output choke L1, and the output capacitor C2. The LNK304 was selected such that the power supply operates in the mostly discontinuous-mode (MDCM). Diode D1 is an ultra-fast diode with a reverse recovery time (t rr) of approximately 75 ns, acceptable for MDCM operation. For continuous conduction mode (CCM) designs, a diode with a t rr of ≤35 ns is recommended. Inductor L1 is a standard off-the- shelf inductor with appropriate RMS current rating (and acceptable temperature rise). Capacitor C2 is the output filter capacitor; its primary function is to limit the output voltage ripple. The output voltage ripple is a stronger function of the ESR of the output capacitor than the value of the capacitor itself. To a first order, the forward voltage drops of D1 and D2 are identical. Therefore, the voltage across C3 tracks the output voltage.The voltage developed across C3 is sensed and regulated via the resistor divider R1 and R3 connected to U1’s FB pin. The values of R1 and R3 are selected such that, at the desired output voltage, the voltage at the FB pin is 1.65 V. Regulation is maintained by skipping switching cycles. As the output voltage rises, the current into the FB pin will rise. If this exceeds I FB then subsequent cycles will be skipped until the current reduces below I FB. Thus, as the output load is reduced, more cycles will be skipped and if the load increases, fewer 600 020 68 kHz 64 kHz V DRAIN Time ( μs) 500 400 300 200 100 0 |
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