| 摘要 |
The welder has inverters (14), (16), (Fig 1), powered respectively by smoothing capacitors (6), (9) which are normally connected in series across a rectifier (2) when the A.C. supply thereto is at a higher voltage (eg. 400 volts) but are switched to parallel connection by a relay 10 if a control circuit 12 senses that the A.C. supply is at a lower voltage (eg. 200 volts). The control circuit 12 senses the A.C. voltage by means of a zener diode 38 responsive to the rectified output of a control transformer 25, the lower A.C. voltage causing energisation of a relay 34 which in turn energises relay 10 and switches primary windings 25a, 25b of transformer 25 from series to parallel. A latch circuit 45 holds relay 34 energised regardless of the increase in the output of transformer 25 caused by this switching. The control circuit thus far described functions adequately for A.C. supplies of substantially constant voltage. However, the gradually rising output produced on starting of an engine-driven generator (60) would result in the inverter (14), (16) being maintained in the parallel connection on a generator output which has risen through the lower voltage to the higher voltage. A zener diode 64 is therefore provided which responds to the A.G. supply being above the lower voltage by energising a relay 62 to open contacts (61) at the output of the generator (60) thereby momentarily de-energizing the control circuit 12 causing circuit 45 to unlatch resulting in the series connection of inverters (14), (16) on reclosing of contacts (61). <IMAGE>
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