Large Power Supply And Propeller Proto Board

idbruce

Hello Everyone

This may sound like a couple of dumb questions, but I am unsure, that is why I am asking


In my current project, I have (2) stepper motors, (2) stepper motor drivers, (1) Propeller Proto Board, (1) 1.0A 12VDC power supply, (1) combination 0.5A 5VDC and 4.0A 30VDC power supply, (2) 12VDC cooling fans, (1) LED, (1) power switch, and (1) momentary pushbutton switch. Due to safety concerns, I will be mounting the 30VDC power supply in a NEMA 1 type enclosure. Okay now for the questions.

1. In an attempt to save money, I would like to mount all the items onto or within the NEMA 1 type enclosure, except for the stepper motors. Will there be too much electrical noise for the Propeller to operate properly in such an environment?
2. If question number one is acceptable, is it acceptable to attach the power supply chassis grounds, Propeller VSS, and the stepper driver chasis grounds all to the enclosure or should something be isolated?
3. Considering that the stepper drivers only require a 3.3VDC signal, and the pushbutton only requires 3.3VDC, can I power up the Propeller Proto Board with the 0.5A 5VDC from the combination power supply?

Thank You In Advance
Bruce

EDIT: The NEMA 1 type enclosure will be a size of 8 X 8 X 6

Leon

If you pay careful attention to the wiring you should be able to use a single enclosure. A common ground might be all that you need.

3 won't work unless you modify the board and bypass the 5V regulator, as the regulators are in series.

idbruce

@Leon

3 won't work unless you modify the board and bypass the 5V regulator, as the regulators are in series.

I never looked at or noticed that before, but you are correct. From the schematic, it appears that feeding the 5 volt bus with the available 5 volts would be a simple bypass that should feed the 3.3 regulator.

Bruce

Leon

It might be a good idea to disconnect the output lead of the 5V regulator, it could be damaged by 5V into the output.

idbruce

@Leon
Yea I thought about that, and I am not saying you are wrong, but I wonder if that is definite damage. I have another 5 volt regulator laying around, and I think I might just test to see if it will damage a regulator by backfeeding the rated voltage. Simply because I would prefer not to modify the Proto Board unless it is absolutely necessary.

I suppose I could just get a little larger enclosure and add a 120V outlet and a wall wart, but I was trying to avoid that.

Bruce

Leon

Of course, it will have to withstand some voltage on the output when the 9V supply is removed and it is powered by the capacitor on the output until it discharges. The data sheet should have something on it.

idbruce

The datasheet shows a "Battery Backup Regulated Supply" with the output going to a 5V battery, so I am assuming it should be okay, because they don't mention or show a diode.

Cluso99

Some regulators do suffer if there is a voltage at Vo without any voltage on Vin. I would need to recheck, but I think you can supply the 5v to the Vi of the regulator and all that will happen is that the regulator will not adequately regulate the 5V. However, if you have 5V logic, this will not work.

Best to isolate the Vo by a link, preferably a 3 pin link so that the two Vin's are on the ends and the selected Vin is in the center. That way, only one supply can be used at a time. But I guess the pcb is done.

Duane Degn

I've read you can use a diode from 5V to Vin. Apparently the diode is also helpful if you have a large capacitor that could cause backward voltage across the regulator when Vin is removed.

I forget if I read this in regulator's datasheet, on the forum or in the Hydra book. I do have the impression it was a reliable source.

Duane

Cluso99

While the diode will protect the regulator, you have to be careful of what else is on the input side because now you are feeding a little less than 5V back to the input side of the regulator. There is always a caveat

idbruce

Thank guys for the replies!

Right next to the regulators in the Proto Board schematic, they show the Proto Board power indicator LED being supplied by 5V. I overlooked that little bugger. With the exception of that little discrepancy, I believe 5V to VI or VO would have worked just fine, but I got to have my pretty Proto Board LED

Another solution might be to test the voltage of the 5V secondary winding of the transformer to obtain the actual output voltage. If it is high enough, I could just change the regulatior and fuse on the power supply to get a better voltage for powering the Proto Board.

Bruce

jeff-o

Some tips:

1. Keep the AC stuff on one side of the enclosure, and DC stuff on the other. Try not to have AC power lines crossing DC or signal lines.
2. How you attach grounds/VSS/-V will depend on the outputs of the power supplies. They will probably have + and - outputs. Connect all the - outputs together, and to the driver and propeller grounds. The chassis (case) grounds on the power supplies should not be connected to the DC grounds, only to AC ground.
3. The best way to get the 3.3V you need is using a 3.3V LDO regulator connected to the 5V output. Usually all you'll need is the regulator itself and a capacitor at the input and output (check the device datasheet for exact values)

idbruce

Hey Guys

Will this work for me, if I use a large heat sink on the 7812 regulator?

Bruce

jeff-o

idbruce wrote: »

Hey Guys

Will this work for me, if I use a large heat sink on the 7812 regulator?

Bruce

Should work fine. You can save yourself some cost and board space by combining C2 and C3 into a single capacitor. 220uF should be plenty.

idbruce

@jeff-o

Thanks for your reply.

Just out of curiousity, before I make that circuit board, I am going to try and power the Proto Board from 5V on the power supply and see what the outcome is. If everything is fine, I think I will just tap a 12V regulator into the 30V power lugs of the power supply to feed the cooling fans.

Bruce

idbruce

@Everyone

For those of you who may be following this thread, here are the results of a test I just perfomed. As previously mentioned, I have a combination 0.5A 5VDC and 4.0A 30VDC power supply and I performed a test of using the 5VDC logic supply to power a Propeller Proto Board. Here are the results:

• VIN 5.028V
• 5V Logic Bus 4.061V
• VDD 3.098V
• Proto Board LED lights up

Providing that VDD does not drop below 2.7V brownout threshold, I should be okay powering the Proto Board with the 5V logic supply. I think I will be okay, but I will have to do more tests to find out for sure.

Bruce

Duane Degn

Bruce,

I hope you don't mind if I follow up about a protection diode.

The LM1086 (which the proto board uses) has section in its data sheet about protection diodes.

Here's the text:



Here's Figure 5:
This is for an adjustable regulator but I think it would also apply to a fixed 5V regulator.



I would think you could bring your 5V into the Vout side of the 5V regulator (with an added diode). You could connect the 5V source to the 5V position of the servo jumper or one of the other 5V locations on the board.

The power LED would still work since it's powered by the 5V line.

I'm not sure if the above circuit is intended for prolonged use or not. It might be intended to only offer short term protection from large capacitors.

It would be good to find out if this would work well over a long period of time. I know I've wanted to be able to use a 5V source to power a proto board before and I'm sure there are others who would like to do the same.

Duane

BTW The Propeller-ProtoBoard-v1.2 schematic doesn't have the power LED anywhere (that I can see) on the non-USB board. The USB protoboard schematic shows it is powered by 3.3V (which is incorrect). I just noticed this since I was checking to see if there was difference in the way the LED was powered on the non-USB vs. the USB versions. There isn't a difference.

idbruce

@Duane

I hope you don't mind if I follow up about a protection diode

Any helpful information is always appreciated.

However I am still not convinced that a diode is even needed. I personally think that a person could provide 5v to the output pin of the 5v regulator and get 3.3v out of the 3.3v regulator. Please refer to the attached picture for battery backup.

I have also included a cutout from the Propeller Proto Board manual which shows the power led, although I could not find a version number anywhere on the schematic.

Bruce

Duane Degn

Bruce,

I missed that circuit. Thanks. That could be very useful. I've wondered about using a battery backup with my projects before. I'll probably use the circuit you just posted.

I noticed in the text concerning diode protection, the concern was mainly about Vin being pulled to ground. So if your Vin side isn't grounded, you're probably right about not needing the diode.

Duane

idbruce

Okay I just performed another test.

5.03VDC was fed into the 5V bus on a Propeller Proto Board. No magic smoke emitted from the 5V regulator, the power LED lit up, and VDD had 3.3V. I waited ten minutes, and then turned power on and off ten times. I then disconnected the 5V feed going into the 5V bus, connected 9V to the Proto Board power plug, and received 4.98V on the 5V bus.

Summary:

• The regulator survived the test

Bruce