there is enough posts already on the power supply,
and I know it is 19.6 V maximum.
Anyhow, I carry enough AC/DC Adapters already,
so I want to drive the TX1 developer board with my laptop adapter.
I was thinking to cut the wire from the original adapter
and make a connector to my laptop power supply (65W, 20V).
It would be 0.4 Volts too high, but I could built in a resistor
to take that off.
(0.4 Volts * 3.25 I max from the Adapter = 1.3 Watts to burn in the resistor)
It will be 3 years until everything is driven by USB C which can carry 20 Volts too
and we will need less adapters in this World. But until then, would the above work?
Instead of a resistor use a hefty diode/rectifier…then the voltage drop won’t be relative to how much power is draw, it’ll be the rectifier’s forward voltage drop. Be careful though…you should check if that 20V supply is well regulated at 20V, and be certain the 20V rating is just some nominal/average unregulated rating.
Thanks for the quick answer. Yes any diode should let it drop by .7 volts, correct!
I think a 1N4004 would do?
The voltage is unregulated I would say - as is the voltage from the original 19 V AC adapter if i am not mistaken (symbol made up from dash sign with interrupted dash sign below):
I’m not sure if a 1N4004 has enough current capacity at peaks, although it probably would work at lower power…even so, you’d need a heat sink on something that small, which wouldn’t be easy (and you’d have to expect to not use port powered USB or PCIe). You don’t actually need a lot of current carrying ability, but there is a tendency to have a higher voltage drop on beefier diodes…plus something capable of higher current would not need any special cooling. Here’s something which is overkill and would do the job quite well (forward voltage drop exceeds 1V so it gives you some safety margin):
Thanks a lot for the advice.
I am thinking I might as well connect it directly to the 20V power supply,
I have read somewhere in the forum that it would ‘tolerate’ up to 24 volts.
I searched in the datasheets and found that some DC/DC converter used on the dev board can carry more than that, but I am not sure about the FET that comes right after the plug and the TX1 module later.
i might just give it a try…