Datasheet LT8300 (Analog Devices) - 17
| Fabricante | Analog Devices |
| Descripción | 100VIN Micropower Isolated Flyback Converter with 150V/260mA Switch |
| Páginas / Página | 24 / 17 — APPLICATIONS INFORMATION Step 4: Choose the Output Capacitor. Step 6: … |
| Revisión | A |
| Formato / tamaño de archivo | PDF / 1.4 Mb |
| Idioma del documento | Inglés |
APPLICATIONS INFORMATION Step 4: Choose the Output Capacitor. Step 6: Select the RFB Resistor
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LT8300
APPLICATIONS INFORMATION Step 4: Choose the Output Capacitor.
A 68V Zener with a maximum of 72V will provide optimal The output capacitor should be chosen to minimize the protection and minimize power loss. So a 68V, 0.5W Zener output voltage ripple while considering the increase in size from On Semiconductor (MMSZ5266BT1G) is chosen. and cost of a larger capacitor. Use the equation below to Choose a diode that is fast and has sufficient reverse volt- calculate the output capacitance: age breakdown: L 2 VREVERSE > VSW(MAX) C PRI •ISW OUT = V 2 • VOUT • ΔVOUT SW(MAX) = VIN(MAX) + VZENER(MAX) Example: Example: V Design for output voltage ripple less than 1% of V REVERSE > 144V OUT, i.e., 120mV. A 150V, 0.6A diode from Diodes Inc. (BAV20W) is chosen. 300µH •(0.21A)2
Step 6: Select the RFB Resistor.
COUT = = 4.6µF 2 • 12V • 0.12V Use the following equation to calculate the starting value for RFB: Remember ceramic capacitors lose capacitance with applied voltage. The capacitance can drop to 40% of N R PS • (VOUT + VF ) quoted capacitance at the maximum voltage rating. So a FB = 100µA 10uF, 16V rating ceramic capacitor is chosen. Example:
Step 5: Design Snubber Circuit.
2 •(12V + 0.3V) The snubber circuit protects the power switch from leak- RFB = = 246k age inductance voltage spike. A DZ snubber is recom- 100µA mended for this application because of lower leakage Depending on the tolerance of standard resistor values, inductance and larger voltage margin. The Zener and the the precise resistor value may not exist. For 1% standard diode need to be selected. values, a 243k resistor in series with a 3.01k resistor The maximum Zener breakdown voltage is set according should be close enough. As discussed in the Application to the maximum VIN: Information section, the final RFB value should be adjusted V on the measured output voltage. ZENER(MAX) ≤ 150V – VIN(MAX) Example: VZENER(MAX) ≤ 150V – 72V = 78V Rev. A For more information www.analog.com 17 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Operation Applications Information Typical Applications Package Description Typical Application Related Parts
APPLICATIONS INFORMATION Step 4: Choose the Output Capacitor.
A 68V Zener with a maximum of 72V will provide optimal The output capacitor should be chosen to minimize the protection and minimize power loss. So a 68V, 0.5W Zener output voltage ripple while considering the increase in size from On Semiconductor (MMSZ5266BT1G) is chosen. and cost of a larger capacitor. Use the equation below to Choose a diode that is fast and has sufficient reverse volt- calculate the output capacitance: age breakdown: L 2 VREVERSE > VSW(MAX) C PRI •ISW OUT = V 2 • VOUT • ΔVOUT SW(MAX) = VIN(MAX) + VZENER(MAX) Example: Example: V Design for output voltage ripple less than 1% of V REVERSE > 144V OUT, i.e., 120mV. A 150V, 0.6A diode from Diodes Inc. (BAV20W) is chosen. 300µH •(0.21A)2
Step 6: Select the RFB Resistor.
COUT = = 4.6µF 2 • 12V • 0.12V Use the following equation to calculate the starting value for RFB: Remember ceramic capacitors lose capacitance with applied voltage. The capacitance can drop to 40% of N R PS • (VOUT + VF ) quoted capacitance at the maximum voltage rating. So a FB = 100µA 10uF, 16V rating ceramic capacitor is chosen. Example:
Step 5: Design Snubber Circuit.
2 •(12V + 0.3V) The snubber circuit protects the power switch from leak- RFB = = 246k age inductance voltage spike. A DZ snubber is recom- 100µA mended for this application because of lower leakage Depending on the tolerance of standard resistor values, inductance and larger voltage margin. The Zener and the the precise resistor value may not exist. For 1% standard diode need to be selected. values, a 243k resistor in series with a 3.01k resistor The maximum Zener breakdown voltage is set according should be close enough. As discussed in the Application to the maximum VIN: Information section, the final RFB value should be adjusted V on the measured output voltage. ZENER(MAX) ≤ 150V – VIN(MAX) Example: VZENER(MAX) ≤ 150V – 72V = 78V Rev. A For more information www.analog.com 17 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Operation Applications Information Typical Applications Package Description Typical Application Related Parts