Datasheet LNK3202, LNK3204-7, LNK3294, LNK3296 (Power Integrations) - 5

LinkSwitch-TN2 Applications Example
R5 26.7 kΩ R1 11.8 kΩ 1% C3 RF1 R3 D2 10 µF 8.2 Ω 2.49 kΩ L2 C1 1N4005GP 25 V
12 V,
2 W 1 mH
FB BP/M
1% 100 nF
120 mA D S
L1 D3 1 mH 1N4007
LinkSwitch-TN2 85-265
C4 C5 D1 280 mA C2 R4
VAC
4.7 µF 4.7 µF LNK3204 100 µF 3.3 kΩ 400 V UF4005 D4 400 V 16 V 1% 1N4007
RTN
PI-7857-092616

Figure 8. Universal Input, 12 V, 120 mA Constant Voltage Power Supply using LinkSwitch-TN2.
A 1.44 W Universal Input Buck Converter
Regulation is maintained by skipping switching cycles. As the output The circuit shown in Figure 8 is a typical implementation of a 12 V, voltage rises, the current into the FEEDBACK pin will rise. If this 120 mA non-isolated power supply used in appliance control such as exceeds I then subsequent cycles will be skipped until the current FB rice cookers, dishwashers or other white goods. This circuit may also reduces below I . Thus, as the output load is reduced, more cycles FB be applicable to other applications such as night-lights, LED drivers, will be skipped and if the load increases, fewer cycles are skipped. electricity meters, and residential heating control ers, where a To provide overload protection if no cycles are skipped during a non-isolated supply is acceptable. 50 ms period, LinkSwitch-TN2 will enter auto-restart, limiting the average output power to approximately 3% of the maximum overload The input stage comprises fusible resistor RF1, diodes D3 and D4, power. Due to tracking errors between the output voltage and the capacitors C4 and C5, and inductor L2. Resistor RF1 is a flame proof, voltage across C3 at light load or no-load, a small pre-load may be fusible, wire wound resistor. It accomplishes several functions: required (R4). For the design in Figure 8, if regulation to zero load is A. Inrush current limitation to safe levels for rectifiers D3 and D4; required, then this value should be reduced to 2.4 kΩ. B. Differential mode noise attenuation;
Key Application Considerations
C. Acts as an input fuse in the event any other component fails short-circuit (component fails safely open-circuit without emitting
LinkSwitch-TN2 Design Considerations
smoke, fire or incandescent material).
Output Current Table
The power processing stage is formed by the LinkSwitch-TN2, Data sheet maximum output current table (Table 1) represents the freewheeling diode D1, output choke L1, and the output capacitor C2. typical practical continuous output current for both mostly discontinu- The LNK3204 was selected such that the power supply operates in ous conduction mode (MDCM) and continuous conduction mode (CCM) the mostly discontinuous-mode (MDCM). Diode D1 is an ultrafast of operation that can be delivered from a given LinkSwitch-TN2 diode with a reverse recovery time (t ) of approximately 75 ns, device under the fol owing assumed conditions: RR acceptable for MDCM operation. For continuous conduction mode (CCM) designs, a diode with a t of ≤35 ns is recommended. 1. Buck converter topology. RR Inductor L1 is a standard off-the-shelf inductor with appropriate RMS 2. The minimum DC input voltage is ≥70 V. The value of input current rating (and acceptable temperature rise). Capacitor C2 is the capacitance should be large enough to meet this criterion. output filter capacitor; its primary function is to limit the output 3. For CCM operation a KRP* of 0.4. voltage ripple. The output voltage ripple is a stronger function of the 4. Output voltage of 12 VDC. ESR of the output capacitor than the value of the capacitor itself. 5. Efficiency of 75%. Optional resistor R5 supplies the BYPASS pin external y for signifi- 6. A catch/freewheeling diode with t ≤75 ns is used for MDCM RR cantly lower no-load input power and increased efficiency over all operation and for CCM operation, a diode with t ≤35 ns is used. RR load conditions. 7. The part is board mounted with SOURCE pins soldered to a sufficient area of copper to keep the SOURCE pin temperature at To a first order, the forward voltage drops of D1 and D2 are identical. or below 100 °C. Therefore, the voltage across C3 tracks the output voltage. The voltage developed across C3 is sensed and regulated via the resistor *KRP is the ratio of ripple to peak inductor current. divider R1 and R3 connected to U1’s FEEDBACK pin. The values of R1 and R3 are selected such that, at the desired output voltage, the voltage at the FEEDBACK pin is 2.00 V.
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Rev. M 10/20 www.power.com Document Outline Product Highlights Description Output Current Table Pin Functional Description LinkSwitch-TN2 Functional Description Applications Example Key Application Considerations Quick Design Checklist Absolute Maximum Ratings Thermal Resistance Key Electrical Characteristics Typical Performance Characteristics PDIP-8C (P Package) SMD-8C (G Package) SO-8C (D Package) PDIP-8C (P) and SMD-8C Package Marking SO-8C (D) Package Marking MSL Table ESD and Latch-Up Part Ordering Information