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Thanks for the question. We assume that you envisage a circuit like the following:
The simple answer to your question is yes, such a transformer can be readily built. We only have to build it large enough to handle 420 W, and adjust the turns ratio so that with 6,6 A in the primary, the secondary will provide 240 V into the load as shown.
But there are limitations to this simple transformer solution.
First, if the CCR is going to operate at lower steps some of the time (common practice), then the secondary voltage will also be reduced at lower steps, and as a result there will be less illumination. This is not always considered desirable, which is why devices that provide constant output irrespective of the input current are sometimes used. There are various solutions available - Amerace does not currently offer one. One possibility is the Siemens Power Adapters.
If the first limitation can be accepted, there is another limitation which concerns operation with one or more bulbs burned out. When a bulb burns out, the total resistive load on the transformer increases. Because the primary of the transformer is fed by a forced current (CCR), the secondary current remains approximately the same, but the current in each remaining bulb goes up dramatically (because the current is now divided between 4 legs, not 5). As a result, the life of each remaining bulb will be shortened, leading to a cascading failure. If all bulbs burn out before they are replaced, a very high open circuit voltage will result. In this particular case we estimate it at more than 900 V RMS, and if a CCR with a distorted waveform is used, voltage spikes may be many thousands of volts. Unless there is some provision made to eliminate the possibility of an open circuit, we cannot recommend the use of a simple transformer in this case.
There are some situations where this simple transformer approach can be used, but they need to be carefully scrutinized in advance. Please contact us if you believe you have an application where this approach might be useful.
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