Powering the floppy drive

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DrCoolZic
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Powering the floppy drive

Post by DrCoolZic » Tue Feb 18, 2014 4:57 pm

Stupid questions :)

until now I have always used an external power supply for the floppy drive and the KryoFlux board was powered by the USB cable.
I want to try a new setting where everything is powered by the USB

I have tried to connect the drive to PWR FDD1 and to PWR FDD2 without success until I have found the power rail select jumper (5v_vr / 5v_fdd).
After changing this switch to 5v_fdd2 it seems that the drive is now getting power ... but probably not enough ? The drive seems to take the command but terminate with error.

- My questions:
- is there a way to make this works? (Note that if I take a second USB to power the drive it works)
- does the board + a drive exceed the 500 mA of the USB ?
- Any rough idea of current needed by the board?

Thanks
Last edited by DrCoolZic on Tue Feb 18, 2014 5:18 pm, edited 1 time in total.

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DrCoolZic
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Re: Powering the floppy drive

Post by DrCoolZic » Tue Feb 18, 2014 5:12 pm

Looking again at Rosalie rev C schematic

seems like the +12V is connected through Zener Diode(?) to the voltage regulator ??? 1N4730 has a zener V of 3.9V if I am correct

does this means that the KryoFlux board can be powered through the 12V on PWR_FDD1 or PWR_FDD2 as 12 - 3.9 = 8.1V perfect :shock: ???

in that case the second V regulator should be connected by 5V_VR jumper

Is it not documented on purpose ???? Much easier to find 12V power supply than 7-9V PS :geek:

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mr.vince
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Re: Powering the floppy drive

Post by mr.vince » Tue Feb 18, 2014 5:21 pm

Read the QuickStart. You might be killing your board/USB interface. USB has only 500mA!!! A vintage FDD draws more.

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DrCoolZic
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Re: Powering the floppy drive

Post by DrCoolZic » Tue Feb 18, 2014 6:15 pm

The drive I am using is http://www.datasheetarchive.com/dl/Data ... 050111.pdf
It draw 1.6W in operating mode that is 320mA :)
This leave about 180 mA to KF board but does not seems enough.

Do not worry not having enough power will not kill anything :mrgreen:
There is no danger but unfortunately it is not working :ugeek:

The interesting question is the last one: is it possible to power the KF board + floppy drive with a 12V power supply connected to PWR_FDD2 going through the 1N4730 (in other word can the zener and LM117 VR handle 350 mA + KF board consumption)

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DrCoolZic
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Re: Powering the floppy drive

Post by DrCoolZic » Tue Feb 18, 2014 6:23 pm

ok ok looking at datasheet http://www.nxp.com/documents/data_sheet/1N4728A_SER.pdf
the diode as a max direct current of 217 mA therefore the answer to my question is NO for KF board + drive
However if the board has been carefully designed (and I am sure it has been) this seems to indicate that the board draw less than 200 mA (which seems reasonable) ???

Any idea of the current drawn by the board?

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DrCoolZic
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Re: Powering the floppy drive

Post by DrCoolZic » Tue Feb 18, 2014 6:35 pm

Humm I wanted to measure current on DC power connector but unfortunately wont give reliable results as USB pin 1 is always connected to +5v through a schottky diode so current will probably be split?

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mr.vince
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Re: Powering the floppy drive

Post by mr.vince » Wed Feb 19, 2014 3:16 pm

DrCoolZic wrote:Do not worry not having enough power will not kill anything :mrgreen:
Believe me, you will. I'll just take a note that if you would send in your board because of a power trail issue, I know where it comes from. The board needs power for the CPU + pull-ups, peaks can go up to 400mA.

Really, there's no reason to do what you do; unless you want to damage something. I really don't get it, you ask something, you get a reply, and then tell me (one of the guys involved in the dev process) that I am wrong. I was just trying to avoid to damage to your KF and/or your mainboard's USB power rail. So go ahead, at your own risk.

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DrCoolZic
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Re: Powering the floppy drive

Post by DrCoolZic » Wed Feb 19, 2014 3:54 pm

mr.vince wrote:
DrCoolZic wrote:Do not worry not having enough power will not kill anything :mrgreen:
Believe me, you will. I'll just take a note that if you would send in your board because of a power trail issue, I know where it comes from. The board needs power for the CPU + pull-ups, peaks can go up to 400mA.

Really, there's no reason to do what you do; unless you want to damage something. I really don't get it, you ask something, you get a reply, and then tell me (one of the guys involved in the dev process) that I am wrong. I was just trying to avoid to damage to your KF and/or your mainboard's USB power rail. So go ahead, at your own risk.
No worry I would never return a board that I have fried ;)

Adding an external 5v power supply just for the drive is a pain but unfortunately it seems to be the only way to go (this is what I have done in my final setup).
As most floppy drives sold today are only powered by USB I thought I would be possible :shock:

I never said you were wrong I just said not to worry ;)
I have developed electronic devices for over 10 years, so I believe I still have some reminiscence :roll:

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IFW
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Re: Powering the floppy drive

Post by IFW » Wed Feb 19, 2014 3:56 pm

The drain changes according to power up state of the drive for example and even on which part of controller is active... so even if you don't fry the board stability will be quite questionable...

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mr.vince
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Re: Powering the floppy drive

Post by mr.vince » Wed Feb 19, 2014 5:08 pm

Modern USB drives have been designed for low power motor spin up. Constantly overpowering a USB port can burn the power rail. In fact, many cheap USB host controllers do not care. And users risk their ports by e.g. using USB coffe cup heaters.

We have scenarios, where eg 8" drives work more reliably when drive and board are both powered via one PSU with common ground. But this is only true for the 12V rail.

Due to protection diodes the 5V rail of KF is usually at 4.7V when powered via USB. A PSU can correct this, but again, this is not a standard scenario.

All these special use cases use an additional PSU so this is not something that would resolve your problem.

We are very strict about this as inexperienced users might draw the conclusion that it's good or meaningful to power the drive via USB when it is not.

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