How to get steady 6V DC from battery?

You may be able to find a commercial DC-DC converter that fits your needs. Here is a whole raft of datasheets for various tyco converters:

One "cheap and dirty" method would be to use an inexpensive automotive type inverter to get 120 VAC, and then add a 60 watt 6 VDC switching power supply to its output. I don't know if the inverter will work over the entire 5-20 volt range, but it should certainly work from 10-16 VDC. It will probably be hard to find a wide range DC-DC converter for that range of voltage. Much depends on your budget and how many units you will need.

Paul E. Schoen, President P S Technology, Inc.

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Hello Michael,

It's not that tricky. Look at SEPIC converters. The data sheet of the National LM3478 has an example in there. 10 amps may be a stretch for that chip since it can only drive so much gate capacitance but if you can use a cap for the 10A peaks and just supply a few amps it should be fine. Else they have other chips. SEPIC can go up and down in output.

Put on the glasses when you solder one of these controllers. They only come in TSSOP.

Regards, Joerg

I have never used them, but check out what is called a BUCK/BOOST regulator. National, Linear, and Analog Devices chip data sheets would be a good place to start.

Tam

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It sounds like you need a 60watt DC to DC converter which you can make or buy ready to go. It's not particularly difficult to do this in a buck-boost device but like any thing else there are are many design considerations to get in the way of your original goal. Unless you want to become an expert on converters, I'd just buy one.

Another idea is to ask why do you want to control the voltage this way? In a servo, the motor(s) are already driven by amplifiers or PWM drivers. The rail voltage is, in reality, just a gain coefficient in the servo design. If that needs to be adjusted for stability or other reasons, do it at signal levels before the driver circuitry and don't screw around with additional power managment before the servo(s). Your just loosing efficiency to regulate power twice; once in the converter and again in the servo. If it were me, I'd think about the overall design, not just how do I get six volts. Bob

I was going to say much the same thing, except I would have said something like, "Just use separate batteries for the motors and electronics, and control the motor current, so you don't have to bother with what the voltage is."

And, why such a wide range of voltages? Don't you get to tell your production department which battery to use? ;-)

Good Luck! Rich

"Bob Eldred" wrote in news:c1d5e$42d5876d$42a7d082$ snipped-for-privacy@msgid.meganewsservers.com:

Can you suggest one? I've looked at all the manufacturers of such devices and have not been able to find one that can do 6V.

Well - the problem is that the particular servos being used have a good deal more torque at higher voltages (I think about 30% more), so ideally I'd like to supply them with a nice steady 6V supply to keep them operating at max torque. Also - I'm doing some fairly basic torque measurement/collision detection by monitoring the current powering each servo. Supply current fluctuates with voltage - so current measurements will be easier to make sense of with a steady supply.

-Michael

Rich Grise wrote in news: snipped-for-privacy@example.net:

Hi Rich - the reason for such a wide range of voltages is because a battery hasn't been chosen yet! I'd like to keep as many doors open as possible, and not constrain myself to one specific battery voltage.

The reason for wanting a constant 6V power supply is that the servos have more torque at 6V than they do at lower voltages.

-Michael

Bob Monsen wrote in news: snipped-for-privacy@comcast.com:

Unfortunately - I don't see any that are designed for my input or output voltage range.

-Michael

"Paul E. Schoen" wrote in news: snipped-for-privacy@corp.supernews.com:

Ah - well that would be much too large and heavy for my needs I would think. I'm hoping to keep this on a board 5x5cm at most.

-Michael

Joerg wrote in news:39YAe.1754$ snipped-for-privacy@newssvr13.news.prodigy.com:

Small surface mount packages are the least of my worries. In fact I'd prefer small packages as I have some fairly major constaints in regards to the board size. I'll do some more exact measurements today and see if I can figure out what my real current requirements will be, but from preliminary measurements I think 2A will be cutting it pretty tight, even with some large capacitors to smooth it out. If I could get a steady 5A supply I think that would be more than enough, though.

-Michael

Hello Michael,

You might want to go to National's power community and when you know the exact requirements and space ask the folks there. One of the applications engineers will usually answer within 24hrs. I never had any luck with their WebBench calculator since it always kicked my designs back as "impossible". But the app engineers there know their stuff well. They even let me talk to their chips designers once when a chip exhibited a rather unorthodox phenomenon.

Regards, Joerg

Well, that's just silly. Tell them it's a lot cheaper to pick a battery than to design a universal buck/boost converter! Especially if it's for a robot - just spec wheelchair batteries.

Or, you could control the current. Are there 6V wheelchair batteries?

Thanks, Rich