PSU Setup

[napierzaza]

I have a 5V PSU that works up to 2 amps. I'm trying to hook it up to my core but I'm not sure I'm doing it correctly. Basically I'm just putting the power to the power pins (right before the rectifier). For some reason the measured 5v suddenly goes down to <2v when it's plugged in. I just setup a core module where I just took out the 7805 and ouf pins for connecting power into where the IC was. Is this okay? I suppose it's a regulated supply as it's 5v consistantly (I can't find a 7805 on the board, maybe a similar chip is present?).

[lylehaze]

For the 7805 on the core to work properly, it needs a supply that never falls below about 7 or 7.5 volts (depending on brand).

The rectifier can take AC or DC in, but it will drop about

2 volts as well (diode forward voltage drop).

If you take out the rectifier and regulator, it MAY work, but now you are depending on the quality of regulation of your "mystery power supply". If it has problems, they might very well NOT show up on a meter. A meter is not fast enough to show spikes and transients.

I'd suggest sticking with the rectifier and regulator that came with your core, and using a supply of about 9 Volts ac or DC to drive it. It's the most reliable choice you have.

Good Luck,

LyleHaze

[EDIT] You might want to read "Core Supply theory of Operation", near the beginning of this forum list. It can answer some of your questions.

[Lall]

If you have already 5V stabilized power supply, you can connect it directly to J2 instead of J1 on the core.

To be safer, you should un-solder the 7805 regulator but you can leave C3 and C4 for correct decoupling.

Please note that you should be absolutely sure of what you're doing as from J2 there's NO protection at all agains overvoltage, ... When you connect a power supply to J1, the regulator is playing the role of the protection which is safer. In other words, you run the risk of burning PICs, optocouplers, whatever connected to your core if somethings goes wrong when you use the J2 option.

As Lyle proposes, the best is to keep the Core rectifier and regulator and find out another PSU with higher output voltage. If you really feel safe with using J2 then that's a second option...

Best regards,

Lall

[napierzaza]

Argh, well I found a really god PSU that has 12+, -12, and 5v (2amps). It would be really hard to have two PSUs in the case that I'm working on, this one fits perfectly and seems to give good voltages. Anyhow I can't really power it using J2 can I? I have my FM on there. Is it any different to hook it up via the holes left by the 7805 once I remove it? My limited experience in electronics says no, because it's still pretty close to that capacitor... but...

[Lall]

Yes, you can solder it in the empty holes left from the 7805.

Just watch out to choose the two right ones and much more important the right polarity. That would be a pity to burn the FM chip because of an inversed polarity. Remember, there's no protection at all when you power the core+fm from J2.

Best regards,

Lall

[napierzaza]

How senstive is the FM? will a .1 volt difference make or break it? I appears as if my PSU is slightly above 5v.

[TK.]

Thats ok, according to the datasheets the PIC can be supplied with up to 5.5V, and for the OPL3/YAC I think it's similar

Best Regards, Thorsten.