Re: Viewsonic VA800 with rolling lines
You could connect the +12V outputs of two old AT power supplies in series, with the 240V/120V output of one connected to the mains input the other. That way one AC on/off switch can operate both PSUs. Make sure that the secondary grounds of each supply are isolated from the case.
A more sophisticated way would be to modify one PSU by removing the +5V, +3.3V, -12V and -5V rectifiers. Disconnect the grounded centre tap of the +12V transformer secondary winding. Then add an additional common anode dual Schottky diode pair (in the spot vacated by the +5V dual rectifier) to create a 24V Schottky bridge rectifier. Modify the values of the feedback resistors for the error amp in the PWM regulator so that it senses +24V rather than +5V/+12V.
Make appropriate changes or deletions to the PowerGood circuitry, if required. Also replace the capacitor(s) on the original +12V rail (now +24V) with 35V or 50V types.
You could connect the +12V outputs of two old AT power supplies in series, with the 240V/120V output of one connected to the mains input the other. That way one AC on/off switch can operate both PSUs. Make sure that the secondary grounds of each supply are isolated from the case.
A more sophisticated way would be to modify one PSU by removing the +5V, +3.3V, -12V and -5V rectifiers. Disconnect the grounded centre tap of the +12V transformer secondary winding. Then add an additional common anode dual Schottky diode pair (in the spot vacated by the +5V dual rectifier) to create a 24V Schottky bridge rectifier. Modify the values of the feedback resistors for the error amp in the PWM regulator so that it senses +24V rather than +5V/+12V.
Make appropriate changes or deletions to the PowerGood circuitry, if required. Also replace the capacitor(s) on the original +12V rail (now +24V) with 35V or 50V types.
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