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Visitor xx77abs
Visitor
6,478 Views
Registered: ‎03-07-2012

Powering Spartan-3 FPGA Starter Kit Board with batteries ?

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Hello ! I have Spartan-3 FPGA Starter Kit Board:

(http://www.xilinx.com/support/documentation/boards_and_kits/ug130.pdf)

 

Now I need to power whole board with AA batteries. I have 4 1.2V AA Ni-Mh batteries, so I thought I could try powering the board with these batteries. My main concern is about safety of the board and FPGA chip - I don't want to fry anything :)

 

I don't have spare DC connector (like the one on the end of the original AC to 5V DC adapter), so I thought about connecting batteries to A1 Expansion Connector. User manual says:

"Pin 1 on each connector is always GND. Similarly, pin 2 is always the +5V DC output from the switching power supply."

 

Does this mean that pins 1 and 2 are directly connected to the 5V power supply? In other words, is it safe to connect batteries to pins 1 and 2 on A1 connector ?

 

Thanks !

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Scholar austin
Scholar
8,401 Views
Registered: ‎02-27-2008

Re: Powering Spartan-3 FPGA Starter Kit Board with batteries ?

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xx,

 

Pin 1 of PS2 three pin jumper block, is the 5V input to the regulators.  Ground is the negative contact.  There should be some convenient ground points (look at the schematic).  Remove any jumper on PS2 (and do not use a PS2 Keyboard!).

 

The regulators appear to be very tolerant of the 5V, with the restriction being that as the voltage goes above 5V, more power is asted as heat in the LM1086 regulator.

 

So, 4 AA cells is ~ 6 volts, which is just fine, to drive the LM1086.  Should power the whole board, for awhile, depending on what the design is doing.


An AA battery capacity is nominally 2-3 AHr, so if the whole design needs 1 ampere, you might get two to three hours from your four alkaline AA batteries.

 

Alkaline batteries work longer at lower loads, by perhaps as much as 50% more, so less load is good, or using C batteries, or even D batteries, might be a better choice.

 

Watch that the LM1086 regulator isn't getting too hot, as it is running at a bit more than 10% higher voltage, which doesn't sound like much, but the regulator output is at 3.3V, so 1.7v vs. 2.7v is the drop for 5v vs 6v, so that is 58% more power wasted as heat, than with the 5v supply....if it does get too hot, it will shut down.



Austin Lesea
Principal Engineer
Xilinx San Jose

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Scholar austin
Scholar
8,402 Views
Registered: ‎02-27-2008

Re: Powering Spartan-3 FPGA Starter Kit Board with batteries ?

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xx,

 

Pin 1 of PS2 three pin jumper block, is the 5V input to the regulators.  Ground is the negative contact.  There should be some convenient ground points (look at the schematic).  Remove any jumper on PS2 (and do not use a PS2 Keyboard!).

 

The regulators appear to be very tolerant of the 5V, with the restriction being that as the voltage goes above 5V, more power is asted as heat in the LM1086 regulator.

 

So, 4 AA cells is ~ 6 volts, which is just fine, to drive the LM1086.  Should power the whole board, for awhile, depending on what the design is doing.


An AA battery capacity is nominally 2-3 AHr, so if the whole design needs 1 ampere, you might get two to three hours from your four alkaline AA batteries.

 

Alkaline batteries work longer at lower loads, by perhaps as much as 50% more, so less load is good, or using C batteries, or even D batteries, might be a better choice.

 

Watch that the LM1086 regulator isn't getting too hot, as it is running at a bit more than 10% higher voltage, which doesn't sound like much, but the regulator output is at 3.3V, so 1.7v vs. 2.7v is the drop for 5v vs 6v, so that is 58% more power wasted as heat, than with the 5v supply....if it does get too hot, it will shut down.



Austin Lesea
Principal Engineer
Xilinx San Jose

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Visitor xx77abs
Visitor
6,468 Views
Registered: ‎03-07-2012

Re: Powering Spartan-3 FPGA Starter Kit Board with batteries ?

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Hi Austin,

 

thank you for you reply. Just to confirm that I've understood you, if I connect batteries to Pin 1 of PS2 jumper block and somewhere on ground (let's say Pin 1 of A1 expansion connector), there should be no problems ?

 

Also, I've checked resistance between voltage input to the LM1086 regulator and Pin 1 of PS2 jumper, and it is as close to zero ohms as it can be. I've also checked resistance between Pin 2 of A1 expansion connector and voltage input to the LM1086 regulator and it is also as close to zero ohms as it can be. Does that mean that Pin 2 of A1 expansion connector is also 5V input to the regulators ? I'm asking because it would be much easier to use Pin1 and Pin 2 of A1 expansion connector. If I can't use them, then I'll use Pin 1 of PS2 jumber block.

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Scholar austin
Scholar
6,463 Views
Registered: ‎02-27-2008

Re: Powering Spartan-3 FPGA Starter Kit Board with batteries ?

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DON'T USE AN OHMMETER!!!

 

Depending on the compliance voltage of the ohmmeter and how it is built, it may measure anything, anything at all.


I would not connect to any other pin than I stated, as I looked at the schematic.  PS2 pin 1 is the same as the 5V connector cener pin, which is +5V then the power supply is plugged into the jack on the board (when using batteries, DO NOT CONNECT THE POWER SUPPLY!).

 

Ground is any convenient ground.  Look at the schematic.  Often all the even pins in an IO header are ground, which may be very convenient.  You check the schematic.

 

Checking the ground with an ohmmeter is probably useful, but you may need to be able to measure below 1 ohm, and please do not use an ohmmeter with more than 1 or 2 volts compliance (current source) as 9V may burn out an IO pin (will exceed the absolute maximum ratings).

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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Visitor xx77abs
Visitor
6,455 Views
Registered: ‎03-07-2012

Re: Powering Spartan-3 FPGA Starter Kit Board with batteries ?

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Ok, thanks !

 

I've checked the schematic ("Figure A-3: Voltage Regulators, JP2 Jumper Setting for PS/2 Port Voltage") and I clearly see that Pin 1 of PS2 jumper is the same as the input voltage to the LM1086. Also, Pin 1 is called VU.

 

I've also checked "Figure A-1: A1, A2, and B1 Expansion Connectors" and it states for A1, A2 and B1 expansion connectors that Pin 1 is GND and Pin 2 is VU. Does that mean that Pin 2 of A1, A2 or B1 expansion connector is actually connected to the 5V connector center pin, just like Pin 1 of the PS2 jumper?

Please understand that I don't want to be rude or stubborn, I just want to explore all the possibilities and learn something.

 

Also, if you have time, could you please tell me what would happen if I would connect batteries and power supply (adapter)? I know that I shouldn't do it, but I don't know exactly why. 

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Teacher rcingham
Teacher
6,442 Views
Registered: ‎09-09-2010

Re: Powering Spartan-3 FPGA Starter Kit Board with batteries ?

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"what would happen if I would connect batteries and power supply (adapter)?"

Not entirely predictable, but the worst-case is rapid disassociation of the batteries. Some batteries contain toxic or corrosive chemicals.
SO DON'T DO IT!

------------------------------------------
"If it don't work in simulation, it won't work on the board."
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Scholar austin
Scholar
6,434 Views
Registered: ‎02-27-2008

Re: Powering Spartan-3 FPGA Starter Kit Board with batteries ?

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xx,

 

Yes, the 5V also goes out on those expansion connectors.

 

You have your answer for the battery + power supply at the same time.

 

Generally, alkaline batteries don't like being recharged (unless they are specifically designed for recharging, and then only under controlled current conditions).  I don't expect a spectacular failure, but it is possible.  Most likely is nothing happens.  But you would never forgive me if I told you something, and it broke the board.


And, the power supply will not like being connected to 6v, a it is 5v, and you may damage the power supply (but this is not likely, just possible).

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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Visitor xx77abs
Visitor
6,432 Views
Registered: ‎03-07-2012

Re: Powering Spartan-3 FPGA Starter Kit Board with batteries ?

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Thanks, both rcingham and austin!
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