Saturday, April 16, 2011

LA-2A board 5

At last, the final board for the LA-2A is completed. This one has only five components - four diodes in a bridge rectifier for the 6.3V regulated DC, and a big-ass 10,000 uF / 50V reservoir cap for initial smoothing of the DC before it is sent to the voltage regulator.  Note that in the original drawings I was showing a Fairchild integrated bridge rectifier rated 2A.  However, I decided that 2A was an insufficient rating for this circuit. While the heaters themselves only draw 1.3A of current, the power factor of low voltage power supplies is inherently pretty poor.  While average current should be under 2A, the RMS current will be above that.  Probably the integrated part would have worked -- these integrated parts seemed to be rated for average current -- but why cut things close?  The discrete parts I ended up using, and shown in the picture are 1N5408s -- these are 3A/1000V diodes, which should be plenty and then some.  Besides, they look cool.


 Finished board:

Note the criss-cross arrangement for the bridge, rather than the traditional diamond.  It turns out to be quite convenient for many layouts.

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