Figure 7. Components of a PWM switching system-based AC/DC converter and an implementation example While the components are similar to those of the transformer system described previously, in this converter the diode bridges, the primary-side electrolyte capacitor, and the switching elements(transistors) all should meet high voltage-tolerant specification.
Overview/Development Background Aluminum electrolytic capacitors are commonly used as primary side smoothing capacitors for switching power supplies. However, when used in regions where electric power conditions may fluctuate or when internal circuit components malfunction, abnormal voltage may be applied to the capacitor.
However, in a simple combination with synchronous rectification, normal control is no longer possible in continuous-mode operation, and there is the possibility that the primary-side switching elements(MOSFETs) and secondary-side rectification elements(MOSFETs) may be turned on simultaneously, so that a through-current gives rise to element destruction.
The value of R19 is set such that when the primary-side maximum current Ippk(0.66 A) flows, the CS pin overcurrent detection voltage is Vcs 1 V. 1.5Ω Moreover, the loss P_R19 of the resistor R19 is Considering pulse resistance, P_R19 is assumed to be 1 W or higher.
Other features include: Broad dimmer compatibility(meets NEMA SSL6 dimming curves) with wide selection of U.S. TRIAC-based dimmers and High dim ratio typically<1000:1 Turns-on and turn-off at almost the same dimming angle(no pop-on) Highly integrated single-stage combined PFC and accurate primary-side regulated constant current output for low solution cost Download this new design report(DER-364) now to learn more.
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