Started by Cwiiis, 17:44, 20 August 21
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Quote from: RetroCPC on 23:15, 18 September 212.4XV is fine Try the Audio
Quote from: RetroCPC on 04:17, 19 September 21Chris,You (hopfully should) have 5V PSU rail so even worst case 5V / 100 (ohms) = 50mA50mA *5V = 250mW (This is worst case as you will not see the full 5V swing on the transistor Emitters).Just confirm you have 5V PSU input NOT higher (such as 12V).
Quote from: Bryce on 16:22, 25 September 21Great little project, but I still think there is a problem or mistake somewhere, those resistors definitely shouldn't be getting hot.Bryce.
Quote from: Bryce on 19:21, 25 September 21The problem is, as long as you haven't found the issue, the device is using a lot more current than it should.Bryce.
Quote from: Cwiiis on 19:32, 25 September 21Indeed. My best guess is that R5-R12 are actually too low in value. Looking at the datasheet for the transistors, their suggested circuits have both lower voltage and considerably higher resistance, so presumably much lower current. I don't know what the relationship with the current at this point in the circuit is with what is necessary for the output though, so I'm loathe to just swap them out without better knowledge of the effects.
Quote from: Bryce on 20:11, 25 September 21Actually, that's one of the most fundamental calculations in electronics - Ohms Law: V=IxR, so the voltage drop across the component divided by the resistance determines the current that will flow. The watts dissipated is calculated with P=IxV. So if it's getting too hot (too many watts) you need to lower the voltage (not possible in this case) or increase the resistance which will lower the current.Bryce.
Quote from: Cwiiis on 01:43, 26 September 21I understand that, but I wonder why the original VGA splitter circuit, which seems to be replicated all over the web, chooses 100 ohms at this point... Does the current just need to be that high, or could I substitute them all with 250ohm resistors (or more) and expect everything to work ok? I would just try it out, but I'm a little wary to modify something that works and has things attached that I really don't want to break
Quote from: Bryce on 10:11, 28 September 21Because it was designed for the inputs of a VGA Monitor, not a CTM. Increasing the value to 220R or 270R (250 is not a standard resistor value) will not damage anything because it's lowering the current, not increasing it. I would definitely increase the value to 270 if they are getting warm.Bryce.
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