I have a function generator IC XR2206 from EXAR. It's application circuits uses dual power supply +/-9 volts. How can I make such a 9-0-9 dual supply from a single voltage source like a battery or an adapter?
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3\$\begingroup\$ It sounds like it won't affect you if you already have the device(s) but be aware the XR2206 was discontinued a few years back so you might have trouble getting them in the future. \$\endgroup\$– PeterJCommented Aug 18, 2013 at 6:56
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3\$\begingroup\$ For anyone interested, XR2206 (or a clone that passes every test I could throw at it) is available on various sites including Tayda and eBay for $3 and up. In multiples of 10 units, it's $1.75 each. Exar discontinued the product in 2011 citing lack of demand, but it continues to sell (and be manufactured by someone) in crazy volumes. \$\endgroup\$– Anindo GhoshCommented Aug 20, 2013 at 17:11
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1\$\begingroup\$ See my answer to How to power a circuit that needs +9VDC, GND, -9VDC?. \$\endgroup\$– TransistorCommented Jan 1, 2016 at 0:35
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3 Answers
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A relatively painless approach, assuming you have just the requisite positive supply, say +9 Volts, would be the use of a switched-capacitor voltage converter such as the MAX1044 or ICL7660 in voltage inverting mode. The first typical operating circuit schematic in the linked datasheet shows how.
This will provide an inverted voltage supply of up to 10mA, matching the positive voltage supply, up to 10 Volts: Sufficient for XR2206 operation with a high impedance load.
For higher current requirements, other negative voltage generation modules exist from various manufacturers, typically switch mode converters.
If a supply of twice the required minimum voltage is available, another option is to simply split the supply and create a virtual ground, either using an op-amp fed from a pair of matched resistors as voltage divider, or using a dedicated rail splitter part such as the Texas Instruments TLE2426.
This article provides some ideas on virtual ground / rail splitter circuits.
answered Aug 17, 2013 at 17:22
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The XR2206 works just fine off a single supply without any kind of rail splitting, you just need to read the datasheet. Figure 2 shows a single supply example.
If you go this route, be mindful of the minimum single supply voltage.
Also, a word of caution: the XR2206 is several years obsolete. Do not use it for anything that you may want to put into production.
answered Aug 17, 2013 at 19:22
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4\$\begingroup\$ While the XR2206 is officially discontinued, it is a truly brilliant piece of analog wizardry. That might be why it is available in bulk in no-name clone form even today. It remains a very popular part for various designs, and the waveforms are creamy smooth. I have a few XIC2206 parts that I picked up for under $0.80 each, and they work great. \$\endgroup\$ Commented Aug 18, 2013 at 3:11
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1\$\begingroup\$ @AnindoGhosh I am perfectly aware. The first PCB I designed was a function generator based around the 2206. Just because a discontinued part is good doesn't mean it should be used for new designs. \$\endgroup\$ Commented Aug 18, 2013 at 3:44
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\$\begingroup\$ @MattYoung +1 for this info. I was unaware of the fact that I can drive XR2206 with a single voltage source. Just for the sake of the question, I'm accepting Ghosh's answer. \$\endgroup\$– C--Commented Aug 18, 2013 at 15:07
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For a quick and simple dual power supply, use two resistors in series connected in parallel with two capacitors. Connect the two ends to the battery or power source and BAM! You have a dual power supply. Typical values for bipolar converters like this are 100k-1M for the resistors and 47uf to 4700uf depending on the current draw of your circuit.
simulate this circuit – Schematic created using CircuitLab
Note:!!! Make sure the negative rail of your power supply is not connected to ground! Use the continuity setting on your DMM to check !!!
answered Aug 17, 2013 at 18:31
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4\$\begingroup\$ That's fine for biasing an op amp, but not for powering a part. \$\endgroup\$ Commented Aug 17, 2013 at 19:23
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4\$\begingroup\$ Add a voltage follower opamp / unity gain to your circuit and you'll probably turn it in an upvoted answer. \$\endgroup\$– jippieCommented Aug 17, 2013 at 19:48
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1\$\begingroup\$ @jippie The buffered voltage divider is already covered in my answer. \$\endgroup\$ Commented Aug 18, 2013 at 3:13
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6\$\begingroup\$ This actually works really well to power a part. I've used these to power (approx) +-15V rails at 30W with less than 100mv voltage droop in the past. I was using something like 47mF caps. Is it a good design? - Nope! But it does the job if you are in a pinch and it's all you have on hand. \$\endgroup\$ Commented Aug 20, 2013 at 22:28
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1\$\begingroup\$ @OhmArchitect No. I can't work well to power a part. Indeed, you may be able to draw some power for a few ms without the rails dropping too much, if you have enough capacitance. But if you draw significant power constantly and if the power drawn from both rails is not symmetrical, you'll see your mid-rail quickly moving away from the middle. Especially with resistors as high as 100k. \$\endgroup\$– dimCommented Jul 22, 2016 at 12:27