8/1/2023 0 Comments Ac power converter![]() ![]() In a few specific field applications, it is necessary to be able to use either an AC or a DC battery supply, whichever is available. 7: Typical output stage of an AC/DC converter. Hack #3: External DC supply on the AC/DC outputįig. So far, we have only considered hacking the output of an AC/DC module, but what if we wanted to use alternative power sources? This is about Hack #3. ![]() For example, in Figure 4, +12V 0.1A, +3.3V 1A and -3.3V -0.15A would be possible with all of the output voltages tightly regulated. It is useful because the majority of multi-rail applications need significantly more power on the one rail than on the others (main load + auxiliary loads), but this is not a problem when switching regulators are used. This is much higher than the AC/DC’s nominal 416mA output current. If, in the example of Figure 4, the regulated outputs were adjusted to ☓.3V, then, as long as the overall load was less than 5W, the maximum output current per rail that could be drawn would be up to 1.5A. Lower the output voltage, the higher the output current. There is an additional advantage to using switching regulators on the outputs: They also deliver constant power. However, if switching regulators are used to post-regulate the outputs as shown in Figure 4, both the output voltages remain stable over all load combinations, even down to no load/full load conditions. The advantage of regulating the combined output voltage is that the sum of the negative and positive rails remains fixed, but only regulating the positive or just the negative output offers less variation on that particular rail. However, there are differences among them if unbalanced loads are used. Regulated output shown in blue.Īll of these regulation methods offer the same output voltages with balanced loads. Table 1: Comparison of bipolar regulation methods (typical values for ☑2V nominal output). Therefore, the entire multi-output rail power supply could be built into a 1” x 1” board space by mounting the SMD components on the underside of the PCB next to the output pins (Figure 5). Although it can deliver an impressive 1A output current, the case size is only 5mm x 3mm with a low profile 1.6mm height. The RPX-1.0 is a complete DC/DC power supply with integrated inductor. Two RPX-1.0 non-isolated SMD switching regulator modules are used to generate the adjustable output rails, one of which is used in the positive-to-negative configuration. This is because the fuse and Class B EMI filter are all built in. The RAC05-12SK is a universal AC input (85VAC to 264VAC) 5W board-mount power supply, which despite having an only 1”x1” footprint, needs no external components. Hence, three in series will drop 2.1V (Figure 2):įig.4: Adjustable bipolar (±) output rails from a single output AC/DC converter.įigure 4 shows a multiple output power supply (+12V, adjustable +1 to +10V and adjustable -1 to +-10V), which only uses three low-cost main components. Silicon diodes have a typical 0.6V-0.7V forward voltage drop across them. If the output voltage was also made adjustable, the worst case input/output voltage combination combined with the high turns ratio could easily facilitate the converter operation to become unstable.Įvidently, it is possible to place positive and negative voltage LDO linear regulators on an AC/DC with ☑2V outputs to regulate the voltages down to ☑0V, but is there a cheaper and simpler hack? The control loop in an AC/DC converter is optimised to compensate for a wide range of input voltages (typically 85-264VAC) and a fixed output voltage. This is because the rectified AC voltage is significantly higher than the output voltage. The reason is simple: Unlike, say, an isolated 24-to-5V DC/DC converter, which might have a transformer with a 5:1 turns ratio, an equivalent AC/DC converter with 230VAC RMS input to 5V output will need a transformer with a 65:1 turns ratio. Low power AC/DC converters do not normally offer adjustable output voltages. What can you do? You need to start hacking your AC/DC! You check the manufacturer’s datasheets and find that a power supply with all of these particular input and output voltage combinations does not exist as a standard product. 1: EV charging system with universal AC or DC supply. ![]()
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