Is this circuit idea crazy?

Probably a firewall issue. Active mode FTP requires accepting connections from outside, which many firewalls prohibit by default.

If you run your own firewall, there will be a predefined rule available to allow outbound FTP.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

Hi,

I know for sure, I had the same problems approx. half a year ago with John's ftp (checked on several days). Neither Firefox or FTP programs did work. I put that down to my location here in Europe, and have not tried again since then.

Today I tried the above approach with Firefox and it worked miraculously. (I had also tried copying the address that last the time, because directly clicking on the link in Thunderbird, mangles it obviously.)

Regards,

Marcel

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=A0 =A0 =A0 =A0 =A0 =A0 =A0.-. | | =A0 =A0 =A0 =A0 | |

| | | Rin =A0 =A0 | | Rbias =A0 =A0 =A0 =A0 =A0 =A0

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0'-'

=A0 =A0 =A0 =A0Rfb =A0 =A0 |

=A0 =A0 =A0 =A0___ =A0 =A0 |

-|___|----o

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

| =A0 =A0 =A0 =A0 =A0 =A0 |

---. =A0 =A0 =A0|

| =A0 =A0 =A0| =A0 =A0 =A0|

=A0 =A0C1 =A0 | =A0 =A0 =A0|

=A0 =A0 =A0 | =A0 =A0 =A0|

=A0 =A0|<

=A0| =A0>-----o----| =A0 Q1

=A0 =A0 =A0 =A0 =A0 |\ =A0MMBT3906

=A0 |/ =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |

=A0 =A0U1 =A0 =A0 =A0 =A0 =A0 =A0 |

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 o-----> current V >

=A0 =A0 =A0 =A0 =A0 ___ =A0 =A0 |

---|___|----o

=A0 =A0 =A0 =A0 =A0Rshift =A0 |

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0.-.

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| |

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| | Rset

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0'-'

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=3D=3D=3D

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0GND

=A0 =A0...Jim Thompson

A,

w

With eg a half ohm sense R your accuracy problems would vanish. 50mA across 0.5ohms is 25mV. So if you had max offset of 5mV you could use less R, shrink the power loss and still be well within error budget. Which begs the question, why have you been trying to use 15 milliohms?

NT

One day there arrived in the mail a box from TI containing 9000 pieces of superb selected house-numbered (SK3093?) high-beta PNPs. They were intended for Burr-Brown and got mis-shipped. We did all sorts of cool products with them. A few years later, we ran out and ordered more from TI. No problem.

John

I have no problem seeing the image - but FYI:

That sad old FTP thing:

Quote: "... The short list of real life TCP ports we looked at a few moments back contained, among other things, FTP. FTP is a sad old thing and a problem child, emphatically so for anyone trying to combine FTP and firewalls. FTP is an old and weird protocol, with a lot to not like. The most common points against it, are

• Passwords are transferred in the clear * The protocol demands the use of at least two TCP connections (control and data) on separate ports * When a session is established, data is communicated via ports selected at random

All of these points make for challenges security-wise, even before considering any potential weaknesses in client or server software which may lead to security issues. These things have *tended* to happen.

Under any circumstances, other more modern and more secure options for file transfer exist, such as sftp or scp, which feature both authentication and data transfer via encrypted connections. Competent IT professionals should have a preference for some other form of file transfer than FTP. ..."

CERT=AE Coordination Center:

Quote: "... The site uses good security practice by separating the machines that provide these external services from those that perform internal services. It is important to have strong network boundaries (preferably using firewalls) ... Sites using dynamic packet filtering firewalls may need to take additional steps to ensure that third-party PORT commands are blocked by the firewall. If you need to address this problem, we encourage you to check with your vendor to determine the steps you should take. ..."

-

Active FTP vs. Passive FTP, a Definitive Explanation:

Some way down: What is the difference between Active and Passive FTP?:

Quote: "...That's the specific problem that passive FTP is designed to solve, however it does I believe complicate the firewall issues on the server end..."

-

Problems with the FTP protocol:

Quote: "... Currently vsftpd (Very Secure FTPD) is the only ftp server I know of specifically designed with security as it's main goal. ... Kurt: What do you think of FTP in general? H D Moore: To be plain, FTP sucks ... For a secure transfer protocol, I recommend scp, part of the OpenSSH package. There are FREE windows clients available, as well as Full-Featured GUI applications by companies like F-Secure. SCP does incur an encryption overhead, but for most cases it is fast enough. ..."

It's not only Kurt that have this opinion:

Firewall Configuration Prerequisites. By Jay Beale, Lead Developer, Bastille Linux Project ( snipped-for-privacy@bastille-linux.org), Principal Consultant JJB Security Consulting and Training (C) 2000, Jay Beale:

ll-prereqs.html Quote: "... Well, there's a partial solution to this, in that you can force everyone's clients to use "passive" mode FTP, which works like this: ... So, this is more normal. The client is opening that second connection, albeit to an arbitrary high (1024-65535) port on the server. *This is better, though it now opens the server up to greater risk. See, now the firewall on the server end has to allow all connections to high ports on the FTP server machines*. Now, a knowledgeable admin can reduce this port range, from 1024-65535, to something more manageable like

40,000-45,000, but this still leaves a wide port range that has to be allowed in the server-side firewall. So, is there any hope?

Well, barring killing off FTP, there is. Stateful firewalls can watch the data stream and understand the port negotiation. Unlike non- stateful firewalls, which have to allow every potential port, stateful firewalls can allow through packets destined for the specific additional data port, at the specific "right time" in the connection. ..."

-

Quote: "... Protocol: TCP Direction: Inbound Local Port(s): 1024-65535 Action: Allow It

Protocol: TCP Direction:Outbound Remote Port(s): 1024-65535 Action: Allow It ... But wait a minute! Doesn't this cause all kinds of problems [

*Security problems* ! ] for the server side firewall? [The in front of the FTP-server] Yes it does, but servers have away round this. Most FTP servers allow a server administrator to specify a range of local ports [it's a bad but half-good solution] the FTP server is allowed to open and use. ..."

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=A0 =A0 =A0 =A0 =A0 =A0 =A0.-. | | =A0 =A0 =A0 =A0 | |

| | | | Rin =A0 =A0 | | Rbias =A0 =A0 =A0 =A0 =A0 =A0

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0'-'

=A0 =A0 =A0 =A0 =A0Rfb =A0 =A0 |

=A0 =A0 =A0 =A0 =A0___ =A0 =A0 |

---|___|----o

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

|| =A0 =A0 =A0 =A0 =A0 =A0 |

-----. =A0 =A0 =A0|

|| =A0 =A0 =A0| =A0 =A0 =A0|

=A0 =A0C1 =A0 | =A0 =A0 =A0|

|\ =A0 =A0 =A0 | =A0 =A0 =A0|

=A0| =A0 =A0|<

=A0| =A0>-----o----| =A0 Q1

/ =A0 =A0 =A0 =A0 =A0 |\ =A0MMBT3906

=A0 |/ =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |

=A0 =A0U1 =A0 =A0 =A0 =A0 =A0 =A0 |

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 o-----> current V >

=A0 =A0 =A0 =A0 =A0 ___ =A0 =A0 |

-----|___|----o

=A0 =A0 =A0 =A0 =A0Rshift =A0 |

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0.-.

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| |

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| | Rset

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0'-'

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=3D=3D=3D

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0GND

=A0 =A0 =A0...Jim Thompson

0mA,

Now

At 2A, 0.5 ohms gives 2W dissipation and 1v drop. Hot.

A 1206 1/2w 0.05 ohm sense resistor dissipates 200mW. That's easier in SMD.

e.g. Susumu RL1632S-R051-F. $0.12 @ 5k, DigiKey.

-- Cheers, James Arthur

you don't really need a website just a webserver, copy the files to the webservers homedir and you can access the files like now

-Lasse

With, eg., a half ohm sense R, and a 2A, 12V input, my accuracy problems would vanish. And, I'd burn up 2W out of the 48W going in just to measure the current! Since I'm aiming at 90% conversion efficiency, that's almost half of my total loss budget all going up in smoke in one resistor. That's more power than I'm burning up in any other single component. And I'd be doing it just to make the current sense easier.

--
www.wescottdesign.com

A general sense of stinginess with power loss, mostly. I'll go higher if I need to, but that resistor value calculates out to 1/4W at 4A (I misquoted earlier -- it's 2A _out_, after step-up, but around 4A in).

Every 1/2W is a loss of another percent of overall efficiency, and I'm trying to be able to count the lost points without needing to take off my shoes.

--
www.wescottdesign.com

Hmm. Their Input Offset Voltage is "Extrapolated", and they only list 1mV typical with no maximum. Since software is absolutely free* I think I'm still with my chopped-current idea.

• :)

--
www.wescottdesign.com

Thank you for posting that. I'll toy with the idea.

--
www.wescottdesign.com

Yes, you should. Everyone should have a website. And be otherwise exactly like me*. Actually, while it's a total misuse of intent, Facebook would probably work pretty well for this.

Interesting. It doesn't work for me.

• Shudder. That's a joke. Really.

--
www.wescottdesign.com

I didn't mention the fact that it's a step-up converter, the output of which is available at all times (it's a battery charger that's destined to be built into the battery pack; if the battery voltage is less than the input voltage then the thing needs to say "she's dead, Jim" and move on).

So I can use a cheapo common op-amp powered from the output side. Even if it wasn't charging batteries, I could afford for it not to be terribly accurate at startup, as long as nothing got burnt up.

--
www.wescottdesign.com

my=20

That's one of the drawbacks of digital math. Positional, symbolic number systems have an advantage in that respect.

mike

I'm going to suggest a PMOS to the customer (they're an all-digital group who's contracting with me to do the messy analog stuff). They're already using a PNP elsewhere; I'll let him know the tradeoffs, and let him decide if he wants the burden of another part on his BOM.

--
www.wescottdesign.com

I'm putting up files for public access, so I don't have security problems.

John

Tim Wescott a écrit :

Not crazy, but that one is simpler and handles all offset polarities.

___ Load

Fred Bartoli a écrit :

Note that load and source have been swapped...

--
Thanks,
Fred.

I'm only seeing that work if Rtop is very small, to set the correct current through the transistor -- is that what you were thinking? So at

2A, I'll get a 30mV drop across the sense resistor; if I set Rtop equal to 10 ohms then I'll get 3mA through the transistor. Then if Rset = 1k I'll get 3V at my current sense output.

If that's the case, then setting "1K or such" equal to Rfb should cancel out the input bias currents, leaving one with all relevant offsets.

Hmm. It does save a resistor, and I don't see your "Ioffset" being necessary (which is a good thing -- I can't count on the supply voltage to be constant, and I don't have anything that's regulated from it).

--
www.wescottdesign.com