AC-DC｜FAQ

AC-DC FAQ

2020.01.01

AC-DC

What is the difference between isolated type and non-isolated type devices?
In an isolated type device, the primary side (AC line) and the secondary side (DC output) are separated, so that the risk of electrical shocks is reduced. In a non-isolated device, the primary side and the secondary side are connected, and so there is the concern that electrical shocks may occur. Depending on the application, an isolated type device may be necessary.
Can the NC pin of an IC be connected to something else without problem?
The NC pin is as a rule an open pin not connected to the internal chip, and so there is no problem. As exceptions, however, there are cases in which conditions forbidding connection to other devices are imposed, and so cautionary notes should be checked in each case. Moreover, depending on the IC manufacturer, the pin may be “Not Connected” or it may be labeled “Do Not Connect”; when there is uncertainty, the manufacturer should be consulted.
What is the configuration of the self‐excited chopper type switching regulator?
An example of constituent blocks is shown. The configuration may differ somewhat depending on the device, but in essence, a chopper type switching regulator configuration is used. For separate cases, please refer to block diagrams and the like.
What is the flammability grade of the outer (package) resin?
The flammability grade is UL 94 V-0.
What is the isolation voltage of the outer (package) resin?
20 kV/mm or higher.
A double-protection fuse is inserted into the AV 100 V line, but is a separate fuse needed?
Yes, it is needed, and must always be used.
Can a jumper chip be used instead of a fuse?
A jumper chip cannot be substituted for a fuse.
What is the reason for requiring a fast-acting fuse?
The fuse is necessary in order to prevent further damage to the equipment, including in some cases such dangerous states as smoking and flames, when an overcurrent flows due to overloading or a short-circuit.
Can an external coil other than the recommended product be used?
The external coil greatly affects the AC-DC converter characteristics and performance. A coil equivalent to the recommended product can be used, but thorough evaluations are essential.
A sound occurs depending on the direction of mounting of the coil.
In self-excited oscillation type devices, the switching frequency may change depending on the coil mounting direction. If the switching frequency is within the audible range, it is possible that coil vibrations might be an audible sound. Also, depending on the position, resonance with the mounting board is another possibility. The mounting direction and location must be studied, including any sounds that occur.
What is the reason for a change in oscillation frequency with the coil direction?
In the case of self-excited oscillation, magnetic flux generated by the coil affects the driving circuit of the AC-DC converter itself, so that the oscillation frequency changes.
I want to reduce the capacitance of the input smoothing capacitor; would this be a problem?
When the output current is small, there is no problem with reducing the capacitance. However, the input capacitor must be able to allow input ripple currents, and so when changing the capacitance, the capacitor must be examined to confirm that the allowed ripple current for the capacitor is appropriate.
The recommended withstanding voltage for the output capacitor is 25 V. Is there a problem with using a 16 V capacitor?
At a minimum, there must be a margin with respect to the preset output voltage. Moreover, the output capacitor affects the output ripple voltage. In general, there is a tendency for the ESR (equivalent series resistance) to be larger for smaller capacitor withstanding voltages, and so consequently the output ripple voltage is increased. It should be confirmed that the output ripple voltage that occurs is within the allowed range. In addition, the allowed ripple current is smaller, and so a capacitor with an allowed ripple current equal to that of the recommended capacitor should be used.
Can you provide the results of open/short tests for components and pins?
Basically, these can be provided; please inquire for specific models.

【Download Documents】 Basics of AC-DC Converter and Design Procedures

A hand book for beginners to AC-DC converter design, covering the basics of AC-DC conversion and various conversion methods, as well as the procedures and issues involved in designing an AC-DC converter.

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