Any electrical engineers here?
- Thread starter Grayfox
- 11 comments
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- 9,256
- United Kingdom
- neema_t
I'm studying electronic engineering, it's not quite electrical but it might be more suited to your question... I remember you posted this before and I said I'd look at it but then totally forgot to do so! Can you post your schematic as well as the PCB design?
- 12,131
- Australia
- I_Grayson_Fox_I
The is the PCB design above.
The old DC-DC one i had, had issues.
This is the schematic I used as a template, but I have added more things to it, like fuses after the transformer, the diodes, the DC-DC jack after the rectifier for use away from mains source, the LM7812 for powering the Panel meter, fan relay and fan.
The old DC-DC one i had, had issues.
This is the schematic I used as a template, but I have added more things to it, like fuses after the transformer, the diodes, the DC-DC jack after the rectifier for use away from mains source, the LM7812 for powering the Panel meter, fan relay and fan.
- 9,256
- United Kingdom
- neema_t
Ok, well, from what I can tell it's pretty much ok but unless you know otherwise, those diodes either side of the rectifier are unnecessary. You might've put them there for a reason though, I don't know. I don't know what P. Meter, PW+ or In+ are, your DC - is technically just 0V (DC - suggests you're using a split power supply), your relay could possibly use a back emf protection diode like this:
But it may not be necessary. P LED doesn't have a pad for its cathode... And... I don't know, I think that's it. Oh, and yeah, you might experience some negative side-effects from the fan; I was going to incorporate one into my TDA2030 audio amp I'm working on but the ripple my fan caused was unacceptable, so for now I've got it running off a separate 9V battery... Kind of a rushed hack job, but it works. If I were you I'd look in to replacing the relay with a transistor circuit instead, kind of like this:
Except obviously that's the most useless diagram I could've possibly found.
That's all I can think of or see for now though.
But it may not be necessary. P LED doesn't have a pad for its cathode... And... I don't know, I think that's it. Oh, and yeah, you might experience some negative side-effects from the fan; I was going to incorporate one into my TDA2030 audio amp I'm working on but the ripple my fan caused was unacceptable, so for now I've got it running off a separate 9V battery... Kind of a rushed hack job, but it works. If I were you I'd look in to replacing the relay with a transistor circuit instead, kind of like this:
Except obviously that's the most useless diagram I could've possibly found.
That's all I can think of or see for now though.
- 12,131
- Australia
- I_Grayson_Fox_I
The diodes near the rectifier are so if i want to use a DC power source power does not flow back into it and into the transformer.
P meter + is +12v for the panel meter which will show voltage
P meter - ground for the panel meter
PW+ is voltage detection for the panel meter
IN+ is current detection for the panel meter
COM is ground for the meter
The pads labled DC are for a DC power source(car battery or something like this) that i may want to use.
P meter + is +12v for the panel meter which will show voltage
P meter - ground for the panel meter
PW+ is voltage detection for the panel meter
IN+ is current detection for the panel meter
COM is ground for the meter
The pads labled DC are for a DC power source(car battery or something like this) that i may want to use.
- 9,256
- United Kingdom
- neema_t
Yeah, you won't need those diodes. First of all, bridge rectifiers are just four diodes in one package as you can see in your schematic. Secondly, even if DC did get 'into' the transformer, it wouldn't really do anything; transformers can only transform AC. I don't think there's any harm in leaving the diodes there though, beyond a slight voltage drop anyway.
I'm assuming this is a digital panel meter, then? How come it has two grounds? I suppose one is the power supply ground and the other is the signal ground, like the common on a multimeter or oscilloscope.
Ohh, hold on a minute, you're using a 15V transformer (assuming you're using the one you posted in the other thread) and you want up to 14V out of it? I'm not sure how the LM317 works but every voltage regulator I've used has had a drop-out voltage of a couple of volts, but I suppose if it's an LDO you might be ok as their drop-out is just under a volt. Are you sure the LM317 can give you 14V from 15V? I know the 7812's drop-out is 2.5V... Oh, and the forward bias voltage drop of a typical silicon diode (a 1N4001) is 600mV, so your 15V from the transformer will already be 13.8V with those diodes in place. I'd recommend you get a different transformer, I think you'll have drop-out problems with 15V. Assuming you're using that one, anyway.
- 9,256
- United Kingdom
- neema_t
Well that's even worse, then, the 7812 needs 14.5V to have a guaranteed 12V output. You're saying you've got a 15V transformer, -1V for the bridge, -1.2V from those two diodes... That's already down to 12.8V. Assuming the drop-out voltage of the LM317 is only 0.7V (as an LDO would be) the most you're going to get is 12.1V, and that's even without considering voltage drops across other components.
Have you prototyped it? And if you have, have you tested that prototype with a full load?
