MDRC Mark 4 20 Amp Power Supply

Posted on Feb 5, 2014

I was asked by the MDRC committee of the day if I would like to take on the role as Electronic components and project officer, I didn`t see any problem with this and agreed. After being elected into the position I soon found out that a little more time would be required than I expected, most of which was spent answering m

MDRC Mark 4 20 Amp Power Supply
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ail. One item that kept popping up was a couple of small problems with a project released prior to my association with the club, being the 1988 Mark 4 Power Supply Project. The following is the upgrade notes to rid the problems without a total rehash. For over 20 years now the Moorabbin and District Radio Club has supplied kits to the amateur fraternity. Our current mark 4 has been quite popular since its introduction in 1988. However, recent constructor feedback has necessitated the need for an upgrade. The regulator circuit of the mark 4 employs a linear design based on the long standing industry standard "723" regulator from Fairchild (tm). Current trends obviously lean towards Switch Mode designs as they are inherently more efficient, physically smaller and cheaper to produce. However many switch mode designs are often noisy, even when displaying good regulation characteristics and it is for this reason that we have maintained a linear design. The Mark 4 as with earlier MDRC supplies is equipped with over Volts protection. This prevents the unregulated 24 to 28 Volts DC from causing damage to your equipment in the event of a regulator failure. It is with this part of the power supply circuit that constructors are experiencing problems, the symptoms are as follows. The over volts protection circuit is a simple resistor, zener diode arrangement with transistor switching. In the event of a output of more than 15 volts the...

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