bipolar voltage supply with zero crossing (+/- 100V)

Hi all,

Thanks for all for your help. I will be starting construction on these things in the coming weeks, and will report back on how it goes.

Unbeknownst to me, the department had hired an electronics technician and he arrived today.. I just met with him, and showed him the designs, and he was mightily impressed (thanks again). He will build them, and then I will report back.

Cheers

Did you tell him about this forum or are you planning to take credit for the ideas?

I also forgot to mention that the absolute maximum input voltage from the transformer is 99VAC, any higher than this and the zeners across the LM317 and LM337 will start to conduct which will cause the output voltage to rise and if it's increased further the zeners will be toast. I chose an 80V transformer as assuming regulation of 10% (the output being 10% higher than the rating when unloaded) and a high mains voltage it should be alright.

You can buy the LM317 and LM337 in higher voltage rating of 60V, this will allow you to use 60V zeners and allow the input voltage to go up to 113V, you can also connect zeners in series with the rectifiers to further reduce the output.

If you can find a suitable 80V transformer then you don't need to worry about the above but I just thought I'd add those comments just incase you find yourself restricted to transformers with ratings of say 110V.

Hero999 said:

Did you tell him about this forum or are you planning to take credit for the ideas?

Click to expand...

The conversation went something like this;

Me: "Hi there Electronics guy, the name's DrDunk."
Him: "Hi DrDunk, nice to meet you, what can I do for you."
Me: "Ahhh, don't ask yourself what can you do for me, instead ask, what can I do for you..."
Him: "What the?"
Me: "We can make a shiteload of money off these great bipolar supplies that I have thought up"
Him: "Ya what?!? Top effort! My first day, and already on a winner..."
Me: "True... Here's my design."

Apologies, that was very lame. Of course I told him straight away about this excellent forum and the wonderful gurus there waiting to help. I am a scientist, and plagiarism is a big no no...

Thanks for the extra info, I will pass this on to him.

An interesting point, this guy has had a varied life. He actually patented a revolutionary technique to safeguard VCRs from being dubbed.. Apparently they were sold in Russia?!? However then it went belly up when the DVD came out...

Cheers!

DrDunk said:

Me: "Hi there Electronics guy, the name's DrDunk."
Him: "Hi DrDunk, nice to meet you, what can I do for you."
Me: "Ahhh, don't ask yourself what can you do for me, instead ask, what can I do for you..."
Him: "What the?"
Me: "We can make a shiteload of money off these great bipolar supplies that I have thought up"
Him: "Ya what?!? Top effort! My first day, and already on a winner..."
Me: "True... Here's my design."

Click to expand...

Sounds like a cause for celebration, just open a few cans of Fosters and put another Quokka on the barbie.

JimB

JimB said:

Sounds like a cause for celebration, just open a few cans of Fosters and put another Quokka on the barbie.

Click to expand...

Fosters!?!? Only tastes good in Europe. Over here it takes like run off from a peat bog...

And as for the quokka, can't eat them. Being endangered is not the problem, they are too stringy and hard to swallow..

Anyway, apologies for going off topic, thanks again for all the help!

I would also get hints from the deflection plate drivers of an oscilloscope. Preferably an inexpensive, low bandwidth design.

Follow up on the suggested design by specie

Hi All,

I wanted to write and provide some feedback on the circuit diagram for the bipolar power supply suggested by specie. We have built the supply, and it works well. There were two modifications that were needed following testing;

1) Two capacitors were added near the output of each channel. These were needed as there was an oscillation found in the circuit following construction (15kHz). One was right at the output, 0.86 µF (to ground). The other was connected before R14, and between R12 and VR2, 0.47µF. See the schematic.

2) We also replaced R14 with a 330k resistor as the voltage regulation was not optimal when a 1 Mohm load was put on all of the outputs. Varying one output affected the others by a few volts.

Initially we tried to use four LM324's, the thinking being that if one blew up then we would still have three viable channels to work with. However, there was a problem then with R1, that it was overheating from too much current being drawn. We returned to the original schematic, were one LM324 was used for all four channels.

Finally, we added some nice lcd displays (Dick Smith Australia, PN Q-2220) , 10 turn pots, and BNC outputs on the back (From RS). It is a thing of beauty! I have attached some pictures of the unit, and also some doodling on the provided schematic.

So all in all, it is a major success! Thanks to all that helped along the way.

Best wishes,
Dr Dunk

Looks a nice job, well done!.

Glad to be of help.

Looks, good.

What about voltage stability?

Hi there,
I was thinking of hooking the supply up to a chart recorder and monitoring the output over a couple of hours. How else would you suggest to test the stability?

Cheers!
DrDunk

You could manually measure it at regular intervals.

You could leave it connected to a multimeter with a minimum amd maximum setting for a few hours.

A chart recorder will be better if the resolution is high enough to show minor variations clearly.