6. Frequently Asked Questions
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It’s ideal for non-isolated AC LED lighting (e.g. LED bulbs or tube lamps) where high power factor and simple circuitry are needed. Designers use it in retrofit LED lamps (E27/E14/GU10) and tube lights (T8/T10) to replace traditional inductors and discrete PFC stages.
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The MT7855BD itself has no built-in digital dimming interface. Brightness is controlled by setting the LED current via external resistors on the ADJ/CS pins. In practice, analog dimming (changing the ADJ pin voltage) can adjust current, but there is no integrated PWM or trailing-edge dimming support. For dimmable applications, an external dimming circuit is needed.
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The IC includes over-voltage protection (OVP), over-current protection (OCP), and over-temperature compensation. These protect against faults like output shorts or overheating, improving reliability.
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The MT7855BD is only available in a DIP-7 package. A related device, the MT7855BS, uses an SOP-7 (surface-mount) package. The SOP-7 version (MT7855BS) has a slightly lower output current (300 mA), while the DIP-7 MT7855BD provides ~350 mA. Engineers should choose the package best suited to their assembly process.
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APFC means Active Power Factor Correction. The MT7855BD integrates a boost-like PFC stage so the lamp draws current with high PF (typically >0.90) straight from AC mains. This avoids the need for a separate PFC converter, simplifying design and meeting regulations for low current harmonics.
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The direct alternative is its SOP-7 counterpart (MT7855BS) or other Maxic APFC buck drivers (e.g. MT7854BD/SOP-7, MT7840 series). Global distributors also offer similar non-isolated buck LED drivers from other vendors. EstiSource can assist in finding equivalent parts or stocking brokers if the MT7855BD is hard to source.