ITTSB.EU Blog Forum
ITTSB Blog Specific => ITTSB General Discussion => PC computing hardware - software => Topic started by: Kiriakos GR on September 04, 2025, 03:00:32 PM
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I am not a micro-controller programing enthusiast, but in the past year I did engage and use USB to TTL converter.
Mainly for communication of a test and measurement instrument with my Desktop PC.
My industrial version of USB to TTL / RS232/ RS485 converter, this has electrical isolation from mains, this including a resettable fuse at the ratting of 200mA.
The concept is mainly the protection of converter electronics, rather the protection of USB port of a computer.
This USB to TTL converter, it does not supply power to connected devices.
I did started this topic, after exploring the new trend at USB to TTL converter these delivering and power at 5V.
In other words, they connect directly at USB 2.0 or USB 3.0 computer port, they may consume approximately 20 ~ 60mA for them self.
Therefore any externally powered device (electronic circuit), this has an available supply to use of 450mA as Max.
So what are the actual specifications of these Surface Mountable PTC Resettable Fuse's?
For USB port protection there is only one part number, and this is FSMD050-0805R
Operating voltage 6V
Trigger current:
1A 23C
900mA 30C
850 mA 40C
760 mA 50C
Constant current operation 500mA
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My new application ahead, this requires an USB to TTL converter this able to deliver constant output of 240–300mA.
Should I get one with resettable fuse protection?
Well the answer this has to do with the age of the hardware = PC motherboard.
Back in time (2002 ~ 2012) all INTEL based motherboards they had poor over-current protection at the USB 2.0 ports.
The INTEL South bridge chip, this was having inside and the USB controller, four ports.
Any accident of USB Ports over-current, this was driving the entire INTEL South bridge chip in permanent damage.
If you were lucky? only the USB controller circuit this were killed, and you had to switch at using Add-On (USB 2.0 ports) PCI card.
And for BIOS setup you were forced to use PS2 port keyboard.
Newer motherboards, especially the ones supporting USB 3.0, they have much more robust hardware, some designed to function even as mobile phone (FAST) chargers (1.5A).
I own PC computers of newer and older era, the older is a DELL with windows XP.
I will be in tears no matter which one will get damaged, and therefore I am going to sellect the modernized electronic design, of USB to TTL converter with a resettable fuse. :)