Why PC Switchers?
• Ex PC switchers are readily available for almost
nothing
• Potentially useful as high current 12 V
supplies.supplies.
Other design Issues in SMPS
• Power Factor control (PFC)
• RFI/ EMI
• Regulator of low voltages (3.3V)
Sinusoidal Input current (PFC)
• Power electronics Make up a considerable
proportion of the electricity load.
• Current drawn by these devices is very peaky.
• Legislation drawn up in ~2002 to control this.• Legislation drawn up in ~2002 to control this.
Radiated Noise
• Radiated noise is stopped with screening
• Usually the case is quite sufficient.
• Conducted noise is more of an issue
• Input and output filters.• Input and output filters.
Good Candidates for conversion
• PFC – Big iron choke on input!
• +12 V rail > 12 Amps
• Total output power > 250 W
• “Noise-Killer” = Quiet fan• “Noise-Killer” = Quiet fan
• Check for presence of input EMI filter
• Is it heavy ?
Pins of interest
• Yellow +12 V
• Black 0 V
• Red +5 V
• Green PS-ON• Green PS-ON
• Get rid of the rest!
• Grounding PS-ON (Green) should start PSU
• At this stage you will be left with a lot of useful hook-up wire.
Modifications
• Add load Resistor to 5 V rail
• Adjust output voltage
• Modify for 13.6 V on “12 V rail”
• Add screw terminals• Add screw terminals
• Add more output filtering
• Rewind transformer ???
• Depends how adventurous you are !
Improving Output Voltage Regulation
• Normally the regulation is done from the 5 V
• Sometimes combined with feedback from 12V
• Change the feedback to the 12 V rail only
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