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Free Power Supply schematic suitable for a single 3.5" hard drive

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Updated April 6th 2016

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FREE SINGLE HARD DRIVE POWER CIRCUIT - For the " Do-It-Yourself "

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 Please bare in mind that the start-up current or "inrush-current" can be as high as 1.5 Amps initially,
 settling down to a low current of around 800mA,    depending on drive manufacturers specifications.

 The circuit above can be made using phenolic  VeroBoard  (TM)  or on a printed circuit board of the layout as shown below.
 The circuit PCB layout ( below ) can be modified ( if you so wish ) larger caps? however works fine as it is layed out (below).
 It would however,be advisable to spend the time and do it correctly , using a small  "self etched"  circuit board and using a
 adequately large heat sink to dissipate the heat ( as a by-product ) of the voltage reduction through the voltage regulators.
 Below, a 15.0 V AC (center tapped dual 7.5 VAC @ 1.amp) 7.5 + 7.5 = 15.0 x 1.414 = 21.21 V DC. Careful with 240 Volts. 
 Alternatively, a 12.6 VAC (center tapped dual 6.3 VAC @ 1.amp) 6.3 + 6.3 =12.6 x 1.414 = 17.816 V DC or thereabouts.
 below, a 15.0 VAC (center tapped dual 7.5 VAC @ 1.amp) 7.5 + 7.5 = 15.0 x 1.414 = 21.21 V DC. Care with 240 Volts. 
 Try to keep the secondary Output voltages to, say 5.0 Volts AC at 1.5 amps, 5V + 5V = 10V x 1.414 = 14.14 V DC or
 thus resulting in less power wasted (dissipated as heat) into a substancial heat sink. Vin must be 2V above Vout.


For calculating the possible amps available from any of the above transformer calculations,
simply multiply DC amps by 0.62 .    eg:   As in the below bridge rectifier circuit, multiply 
Amps DC = 1.5 A x 0.62 = 0.93 Amps or 930 milli Amps.     For a 2 amp calculation, multiply 
Amps DC = 2.0 A x 0.62 = 1.24 Amps or 1240 milli Amps. Note: always use a 4700uF capacitor.

Free PSU Layout1

Free PSU Layout3

Free PSU Layout4

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Free PSU Layout5

LOW POWER +12V & +5V plug Pin-outs

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rights to use this page are assigned for use by   Educational Institution Use  or for  private  individuals only.

Permission ( only in writing ) can be given for commercial links
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Disclaimer:   Whilst every effort is made to ensure the accuracy of these circuits,   there will be some out there
who will make it and do it wrong, thus destroying their hard drive or in some cases their motherboard and Hard 
drive. We do not make any warranties regarding these web site circuits, these are to be used as a "guide only".
You alone must determine if it is suitable for "your expertise" to build or assemble any project, here or elsewhere.
If you think you cannot do it, then play safe and don't. Please, save yourself the agony and find someone qualified 
who can ! We cannot, nor will not be responsible for any errors or omissions or accidents made in using this circuit.

These circuits were devised here at Unitech and kept as simple and yet as functionally possible for all folks to use.
The circuits contained on the Unitech Electronics web site are "as is" and no warranty what-so-ever regarding accuracy, 
functionability or suitability for your purpose or your personal application is made what so ever. Use at your own risk.

We draw your attention to the fact that some circuits are connected to the domestic  240 V AC mains.     If you are not
fully conversant with mains wiring safety procedures, then please consult someone who is. Death is very permanent.


Why am I getting small shocks from my Electronic equipment and it is biting me with electrical sparks ?

Why am I getting small shocks from my Electronic equipment & it is biting me with nasty electrical sparks ?


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