# Get -50V to 50V range from battery output

I have the following problem: on the system which is battery-powered(4S1P Li-ion battery, 14.8V) I need to create outputs from -50V to 50V. The system has microcontroller on-board.

I am baffled on how to do it. Initially, I planned on using bipolar DAC which would give output of +/- 5V or so and then amplify it with gain of 10 to get total +/- 50V.

The problem is, how to get power supply with range from -50V to +50V from the 4S Li-ion battery? I am familiar with concept of having two 50V sources, then connecting the + of one source to the - of another and using that point as common ground. Total current needed at +/-50V is 300mA. Loads are resistive.

Am I allowed to connect in this topology using two boost converters(switchers)? Would it work?

Thanks; D. Petric

• How much current do you need at the +/-50V? Commented Jul 22, 2016 at 6:39
• "Voltage direction flow" isn't correct. Voltage doesn't flow - current does. "... and then amplify it with gain of 10 to get total +/- 50V." The amplifier would require power > 50 V and < -50 V to do that so that idea won't work. Explain what the power is for and how much current you need. Put the details in your original question. Commented Jul 22, 2016 at 7:05
• What do you want to do after the DAC? Keep in mind there are very few opamps which can withstand 100 V. Commented Jul 22, 2016 at 7:08
• If DAC gives out 5V, I need to amplify to 50V. If it gives -50V, I need to amplify to -50V. That's what needs to be done after the DAC. Commented Jul 22, 2016 at 8:01
• @D.Petric An amplifier would not work, because an amplifier that can output 50 V needs a power supply with 50 V or more. You need a switching regulator. Commented Jul 25, 2016 at 7:54

If you want to do this with a single SMPS circuit, you need some kind of transformer or capacitive coupling. You can do this with SEPIC topology http://www.linear.com/solutions/7345

TI has app note with transformer and capacitive coupling options for boost topology http://www.ti.com.cn/cn/lit/an/slua288/slua288.pdf

Buck can also be used for this but obviously it does not apply here.

If you want a straightforward solution, use boost for +50V and buck-boost for -50V. You can often use buck converter as buck-boost, texas has app notes for a few different solutions. As a bonus this way both outputs are well regulated, dual output can have problems with cross-regulation.TI appnote shows you the efficiency and regulation suffers when you start draining more than 100mA.

• It occurs to me that since the output voltage is rather high (+/- 50V), capacitive coupling is probably not practical. That latter boost design can be implemented with a transformer that should handle it fine presuming parts have required tolerances. Commented Jul 28, 2016 at 10:24

A switch-mode power supply (SMPS) is typically the most efficient and straightforward way of converting a battery source into bipolar supply rails.

Am I allowed to connect in this topology using two boost converters(switchers)? Would it work?

No, not if you are talking about the classic boost converter in this picture:

The problem is that the negative terminal of the boosted voltage is the same as the negative terminal of the power supply (battery pack). If connect a second one of these to the same battery and then connect its positive terminal to the negative terminal of the first one, you short-circuit the second one. It's not going to like that.

You can use a normal boost converter for the +50V, but for the -50V you will need what is called an inverting switching regulator.

• Thanks; can you give me an example for inverting switching regulator which can work up to -50V? Commented Jul 22, 2016 at 7:59
• To recommend a specific part I would have to know more about your application, as requested in the comments below your question. Another answer already recommends some parts, maybe those can help you get started. But in the end you need to search the manufacturer pages or the store pages yourself for a part which fits your requirements. There are hundreds of different regulators with wildly different characteristics like maximum voltage, maximum ripple, maximum current, etc. Commented Jul 22, 2016 at 13:52
• Given two batteries like in OP's diagram, you can make a positive boost regulator and a negative boost regulator. But I think if very tight regulation is not needed I would prefer the dual output solution in order to drain the two batteries equally. Commented Jul 22, 2016 at 14:48
• Yes, you could do that, but the OP's question sounded like there is only a monolithic battery pack with a single output. The two battery image was just to clarify how to put two power supplies in series. Commented Jul 25, 2016 at 7:51