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I am trying to build a circuit to drive different loads with different ratings. The block diagram below outlines what I am intending to do. Briefly,

  • Block A: a circuit splitting power into +/-15V DC to supply op-amps.
  • Block B: a circuit the supplies 1A DC to a 3ohms load.
  • Block C: a circuit supplying 9V DC to a micro-controller

For the input supply, I am thinking about an adapter: 120VAC in, 48VDC, 1.5A out. Current rating could be different, e.g. 2A.

Any hints on what might be the best implementation of each block, is greatly appreciated. I do not think a voltage divider is a good one for blocks B and C.

enter image description here

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  • \$\begingroup\$ One more comment. The whole circuit is driven only by the adapter, i.e. no benchtop voltage supplies \$\endgroup\$
    – Frank
    Commented May 18, 2017 at 12:35
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    \$\begingroup\$ You are spec'ing a 75W supply for a perhaps 5-6W design? You will need to add the load currents for each power branch for a good answer. \$\endgroup\$
    – sstobbe
    Commented May 18, 2017 at 12:44
  • \$\begingroup\$ What's stopping you from using 4 power adapters and a power bar? \$\endgroup\$
    – scorpdaddy
    Commented May 18, 2017 at 12:58

2 Answers 2

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If you could manage with slightly different voltages, then a reasonable choice might be a standard ATX computer power supply, which has:

  • ±12 V for your opamps. (Note: current capacity of −12 V may be small; I can't find a reference for the required minimum capacity, though.)
  • +3.3 V, which is a little bit high for your 1 A through 3 Ω, but you could add series resistance.
  • +5 V for your microcontroller, unless it's 3.3V logic. 9 volts is not a standard logic voltage, so it is likely the input to a voltage regulator on your controller board which you can just skip.

The advantage of this is that it is a single commodity part, rather than a collection of multiple converters or a custom design. (You'll still have to make a breakout board/cable for the output that would ordinarily plug into a PC motherboard. I did this by starting with a short extension cable as a readily available pre-wired connector, and cutting out the wires I wanted to use.)

The disadvantage is that you do not get the best-fitting outputs for your application — ±15 V for 'A', constant current instead of constant voltage for 'B'.

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  • \$\begingroup\$ ATX is a one thing i thought about. For my op-amps, i can operate them at +/-12V. For the MCU, I am using Arduino, and it is recommended to feed it with a voltage between 6 and 12V, one suggested 9V and tried it. For Block B, the current drawn has to be adjustable, not exceeding 1A, so do you think a power transistor controlled thru a PWM will do the job with ATX as a supply unit? \$\endgroup\$
    – Frank
    Commented May 18, 2017 at 20:07
  • \$\begingroup\$ @Sam That 6-12V figure is for the input to the regulator. You can just not use the regulator, though that bypasses some protection on Arduino boards IIRC, or you can just use 12V. I can't give good advice on the adjustable current. \$\endgroup\$
    – Kevin Reid
    Commented May 18, 2017 at 22:46
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Since the load current is quite low (opamps need less than 1mA), +15VDC from 48VDC can be obtained with a L78L15. But a series resistor before L78L15 is needed due to the maximum input voltage limitation of L78L15. Then -15VDC can be obtained from +15VDC with an ICL7660.

For 3-ohm load, it can be either a switching constant current driver or a 48V-to-3V Buck Converter. It needs to be a switching regulator, otherwise the wasted power will be too much.

For 9VDC to MCU circuit (I would expect it to be 5V or 3.3V, by the way), it can be obtained from +15VDC with a L7809. Note that the current consumption is not given, so I assumed it to be 20mA max. If higher current is needed then a switching regulator is essential for this section as well.

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    \$\begingroup\$ 48 VDC is outside the input range of 78xx series regulators, the OP really should start with a more sensible adapter like 24 VDC. \$\endgroup\$
    – sstobbe
    Commented May 18, 2017 at 12:35
  • \$\begingroup\$ @sstobbe That's why I said "But a series resistor before L78L15 is needed due to the maximum input voltage limitation of L78L15." in the 1st paragraph. But yes, 24VDC would be a more appropriate input voltage. \$\endgroup\$ Commented May 18, 2017 at 18:02

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