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I currently have a dual power supply, that supplies +/-15V. One -output of the PS is connected to the other channel's +output (GND). Now, the problem is that I need +/-50V. I bought two step-up boost converters (cheap ones from Amazon), but now I realise that I may have the wrong idea. The converters have +/- input and +/- output, and I connected the +15V from the PS into the +input of one, and -15V into the -input of the other. The unconnected inputs are grounded. Now, my idea was that one of them would give +50V (which it does), and the other -50V. Note that my +converter has its -input and -output grounded, my -converter has its +input and +output grounded.

However, the -50V is not working, and the PS keeps getting current locked. Am I connecting things wrong, or is my idea wrong?

EDIT: Sorry for the confusing explanation. Here is a rough sketch of what I'm trying to do:

connection diagram

(Source)

I am using this to power a high voltage op-amp, specifically OPA454.

I'm not sure what "isolated" boost converter, but I have two of these from Amazon:

DROK Micro DC Converter Power Transformer 120W 12V/24V/48V 10-32V to 35-60V Volt Regulator Module Boost Step-up Inverter Board DIY for Car Auto Vehicle Motor

Thanks for all the help.

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  • \$\begingroup\$ I followed this for a while, then got lost in all the hand waving. Show a diagram. Starting the process to close as unclear, so hurry. The clock is ticking. A link to the datasheet of these 50 V modules would help. It is important to know whether they are isolated or not. \$\endgroup\$ – Olin Lathrop Aug 31 '18 at 0:14
  • \$\begingroup\$ they must be isolated for V- use. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 31 '18 at 0:20
  • \$\begingroup\$ Looks like it is not isolated so the in- = out- \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 31 '18 at 3:17
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    \$\begingroup\$ No. Look into the schematic of the boost converter or a gerneric boost converter. Ground wire runs from input to output so you have no galvanic isolation. \$\endgroup\$ – winny Aug 31 '18 at 7:01
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I disagree. I think your circuit can work with one minor modification...remove the connection between the +/-15V supply.

You don't mention where you're getting +/-15 from, but if it's a bench supply, the outputs are usually isolated unless you connect or ground them externally. Your -50V supply is probably trying to generate 50V over a common ground between its negative input and its negative output.

If you're using a dual supply with a common ground, you may need an additional one--and they have to be isolated from each other, which means isolated from any common inputs as well. Compared to your output ground, the -15 supply will be providing -50V on its negative terminal, and -35V on the positive.

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Your circuit cannot ever work. The modules provide a regulated voltage between the output terminal and -ve lead of the power convertor.

schematic

simulate this circuit – Schematic created using CircuitLab

You would need to have the lower DC-DC convertor be an isolated module (no connection from input to output) to make this work.

One other way to do this is to get a Boost convertor that supplies 100V output and use an electronic ground (rail splitter circuit). I've used a bunch of these to provide 75V for stepper motors ...but they extend to 120V. You could use 30V input to reduce the input current requirement.

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  • \$\begingroup\$ Another solution is to replace the lower boost converter with a non-isolated buck converter and disconnect it from the -15V input. This configuration makes the buck converter an inverting boost converter. In the OP's case it does require a converter with an input range of 15-65V and an output range that includes 50V at 65Vin, and it will require a substantial amount of current to start up, but it does work. \$\endgroup\$ – ajb Aug 31 '18 at 14:42
  • \$\begingroup\$ Actually, neither needs to be isolated. But the task does require one converter which passes the negative input through unswitched, and another which passed the positive rail through unswitched. Both varieties do exist (found a single-cell phone charger booster than connected the high side through...). But of course one single unisolated design cannot fulfill both roles. \$\endgroup\$ – Chris Stratton Sep 3 '18 at 1:49
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Note that after clicking on Product Details you get a bullet list of features. Near the top, it clearly says "non-isolated". That means the negative of the power input is internally connected to the negative of the power output.

For your circuit to work, the modules would have to be isolated. That means there is no direct connection between input and output. The output can float (within some range, usually a few 100 V at least) with respect to the input. With such modules, you could power two of them from the same 15 V supply, but connect their outputs to make a ±50 V supply with ground.

In your case, you say that your ±15 V supplies are really separate (apparently isolated) supplies, and you connected them together to make a ±15 V supply with ground. Don't do that. Leave them unconnected, and have each power one converter.

However, the real answer is probably to get two isolated 50 V supplies that can run directly off of whatever is powering the 15 V supplies. It seems silly to use 15 V supplies only to power 50 V supplies. Make 50 V directly, if that's what you ultimately want.

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  • \$\begingroup\$ "Non-isolated" means that something is connected through, but not necessarily the negative rail. I recall trying to use a single-cell phone charge booster in a dual-voltage project, only to discover that what was common was its positive rail. \$\endgroup\$ – Chris Stratton Sep 3 '18 at 1:51
  • \$\begingroup\$ @Chris: Yes, but in the case of the OP's 50 V modules, the documentation is rather slim. If it's not explicitly stated, it would be very very unusual to have anything other than the two grounds connected. \$\endgroup\$ – Olin Lathrop Sep 3 '18 at 13:29

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