Replace 5V regulator

[jhsa]

A while ago I bought 2 little switched regulators/BECs.. they are good for 2A I think.
My question is, would it be possible to replace the 9x voltage regulator with one of these?
Would there be a problem with the noise generated by the regulator? would a ferrite ring be needed?

Thanks,
João

[MikeB]

It might be OK The switching will create some noise on the supply, and this might cause the analog supply to the sticks/pots to become noisy leading to increased jitter on the sticks.

Mike.

[jhsa]

And how could we overcome that?
I'm interested in this for 2 rasons.
1. more efficiency out of the batteries.
2. the original V. Reg is working on it's limit really..

João

[Flaps 30]

Replace the regulator with the 78M05 or the 7805 as I have done, so that I have a bit more headroom for hall effect sticks and other things. You could replace the M128 with a less power hungry and cheaper M128A or wait a while to see how the M2561 progresses and leave the existing regulator in place. Personally I prefer replacing what is there with something better, but not too good, so that tracks burn out or connectors become stressed before the current limit is reached on the regulator.

Below is the image of one TX that is modified to take a 7805. Track cut between the red lines. On the other TX I fitted an SMD 78M05. The 7808 installation IMO looks neater.

[ReSt]

Some time ago I replaced both, the mainboard and the beeper regulator with one stepdown converter.
That made the servos run that noisy, that I removed the step down converter and used the normal regulators again.

Reinhard

[jhsa]

ok.. that is what i wanted to know.. thanks all.
7805 will be then..
João

[mbanzi]

I have a few of these lying around from another project that I'm thinking of using:

AP1115A 5V 600mA

I believe they are pin compatible with the 78L05:

[Flaps 30]

Looked at the datasheets for the AP1115A and the 78L05 and it does look like it will drop into the same place as the 78L05. The only concern I would have with it, would be the power dissipation/temperature rise if you decided to draw anything like its maximum from it with a 3S pack. I have an inbuilt fear (through experience) of hot semiconductor devices and how they love to fail as they heat up above to anything like 60°C or more.

[MikeB]

Max junction temp 125C.
Thermal resistance 164C/W.
If you assume an ambient temp. of 50C (Tx left in the sun!), you should only allow about 0.45W of power dissipation.
If the battery voltage is 10V, then the current should be limited to around 90mA, so although it is rated at a higher current then the 78L05, you won't be able to use the extra current without it overheating.
This is why a physically bigger regulator is better.

Mike.

[jhsa]

A switched regulator would be better.. doesn't the taranis have one? what measures could be taken to avoid the possible jittering of the servos?

João

[Flaps 30]

Thanks Mike.. You are faster than me at the calculations. I agree with what you say.

The 7805 can dissipate up to 2 Watts with an ambient temperature of 25°C which would limit the current you could draw from it to around 400mA with an 8 cell NiMh pack. Running the 7805 at 100mA brings that power dissipation with the same pack, to around 500mW. Our current draw from the 5 volt regulator is under half that figure which is safe under normal operating conditions. I haven't checked the temperature of the stock 78L05 on the TX. Maybe someone could do a check on that if they have one of those infra red thingies. Failing that a calibrated finger might just do.

Don't forget to keep your transmitters out of the Sun and ideally in a cool area.

[ShowMaster]

A switched regulator would be better.. doesn't the taranis have one? what measures could be taken to avoid the possible jittering of the servos?

João

Hang a scope on the output and main busses with the switcher running and see if it's dirty. Look for spikes and hash at the switching freq and higher.

A 7805 can deteriorate over time from excessive heat and not shut down but instead go into oscillation.
In the old analog TV days (7 years ago) I've seen 30 KC ripple on a 5v buss in Sony pro analog monitors. Hit them with freeze spray and it stops but comes back right away. Noticeable in the video but subtle usually. Replace it and it'll all good again, just 5v DC.
Heat sink area is very important in a hot case in the sun I'm guessing. SM

[jhsa]

tomorrow I will scope the output of the 5V switched regulators I have.. I'm curious now

João

[ShowMaster]

My switching 30 amp 12 v ps I use on my ham gear has a very interesting knob. It's purpose is to change the switching frequency to eliminate "birdies" from the frequency I'm listening to.
I simply turn it until I only hear the weak signals and not a loud tone.
Point being, switchers output RF harmonics and if not super clean, hash and trash on their outputs.
SkyNorth uses them on his boards so he's a good one to ask about it as well as proper filtering.
SM

[jhsa]

so, when i scope it, what kind of frequencies should I be looking for?

[MikeB]

What Skynorth does is use a 5V switching pre-regulator, then s 3.3V linear regulator for the ARM processor. Depending on the battery you are using, you could try a 7V switching pre-regulator then a 5V linear one.

Mike.

[Flaps 30]

A 7805 can deteriorate over time from excessive heat and not shut down but instead go into oscillation.

This isn't something that I have seen while running the device within its ratings. Oscillations concerning this (and most other 3 pin regulators) is well known, hence why most circuits will show a fair amount of decoupling of the input and output to counter this problem. Sometimes when I am using a regulator feeding into a system that has a fair amount of capacitance I will add a diode in parallel with the input and output connections, so that the regulator doesn't suffer reverse voltage across it on switch off.

My switching 30 amp 12 v ps I use on my ham gear has a very interesting knob. It's purpose is to change the switching frequency to eliminate "birdies" from the frequency I'm listening to.

Yes I have an Alinco DM-330MW here with that very knob. I can hear the RF junk from it from around 1Mhz all the way up to around 20Mhz. It isn't a high level compared to some of the junk switch mode PSU's that are around, much of the junk has been removed by the addition of a ferrite ring that has the ground and plus volts wound around it a few times.

I like Mike's idea, but why bother when a 7805 will do the job. IMO it's far better to keep things simple, rather than add complexity for the hell of it. It just adds more stuff to go wrong.

If you insist on trying a switch mode. This may be small enough (20 * 20 * 5mm) to fit into the TX ----> http://www.ebay.co.uk/itm/370835990155? ... 1438.l2649

[jhsa]

I only thought about the switched regulator because of the efficiency.. No heat dissipated so, longer battery life. Also in warm days there is less chance of the reg shutting down.. Not that it will happen where I live at the moment

By the way did you glue your 7805 to the board? If so what did you use?

João

[Flaps 30]

Hmm... Personally I don't feel that there is much to gain as to battery life. The DJT module eats most of the juice from the battery.

No the 7805 isn't glued down. The centre pin (0 Volts) is the only thing holding it to the board. The solder mask (as per photo) was removed to give a solder point for the centre connection to the regulator. If you are doing this change and you have a Smartieparts board fitted, make sure that the 7805 is flat on the board, as there isn't much in the way of height spare between the regulator and the bottom of the Smartieparts board.

You may recall that the reason for the modification initially was to see if the spikes could be removed when the horizontal trims were used, which it didn't. But it did ring a few alarm bells as to the current/power dissipation in the 78L05 which was pretty high due to the change to the M128. So IMO it was a good move regardless, and it also pushed me to change the regulator in the spare (modified) transmitter.

[jhsa]

didn't you remove the old regulator? Is that not a problem? to parallel them? I know that we shouldn't parallel switched regs..

João

[Flaps 30]

If you look at the first picture with the 7805 in place, you will see that I made reference to cutting the track between the red lines, which disconnects the output of the original 78L05.

Take a closer look at the second image that is showing how the board was prepared to accept the 7805, you will see the track cut between the left hand leg of the 78l05 and the small chip capacitor.

You could remove the 78L05 if you so wish. Personally I try not to create too much work or destroy something for the hell of it. You never know. Maybe in a few years time we will have a very low current draw super duper chip that makes the M128 and M2561 look like playthings, which would allow you to use the original regulator.

[LTMNO]

Hello all, i was curious to the verdict of the discussion... is a Switched Regulator okay to put in there.. the one that was mentioned above?
I just sold my other radio and now I am building a new one. I haven't had a chance to start on this.. and I figure now is the time to start piecing together the items that I require.
Thanks for your time.

[Flaps 30]

I have used the small switch mode as an additional BEC to drive some servo's in one model. No checks made on how much (if any) noise or other Gremlins that it might be producing. It works fine where I am using it.. As for use in the TX. Nothing has changed my view on the use of a switch mode in the TX. I would avoid it if possible, but that is a personal preference.

LTMO - Any reason why you are thinking of taking that path, rather than say a 7805?

[sokolum]

Is any 5V switched volt regulator giving issues to the transmitter? Because recently I have replaced my standard volt regulator of my er9sky board. Last thing I want is that it gives more internal distortions.

http://openrcforums.com/forum/viewtopic ... tor#p67472

Sent from Tapatalk

[MikeB]

On the SKY board, this acts as a pre-regulator. It is followed by a linear 3.3V regulator for the processor so you should have no problems. My own SKY board I'm using includes a switch mode 5V regulator.

Mike.

[LTMNO]

I have used the small switch mode as an additional BEC to drive some servo's in one model. No checks made on how much (if any) noise or other Gremlins that it might be producing. It works fine where I am using it.. As for use in the TX. Nothing has changed my view on the use of a switch mode in the TX. I would avoid it if possible, but that is a personal preference.

LTMO - Any reason why you are thinking of taking that path, rather than say a 7805?

Hi FLAPS
No decision made. Was just trying to her what the consensus was. At a minimum the 7805 is the path. . But if switching reg is not an issue then I would go that route. From my understanding it the more efficient way. This is from what I read here...

[Flaps 30]

The decision is yours. The switch mode that I linked to earlier seems to work fine feeding two servo's in one of my models. I just have a thing about trying to avoid switch modes wherever I can. The actual gain by using a switch mode in this case I feel is not enough to warrant its use.

If you go the switch mode route it would be great if you could post something about it here.

[LTMNO]

Will do.

[bob195558]

Hi Flaps 30,

I think I am almost ready to do your version of 5V Regulator Upgrade Mod, but I have a question about the Yellow wire in your Photo.

Is this Yellow wire a connection between the two outside Grounds of the 5V regulators?
Or is it for something different and/or do I need to have the two outside Grounds connected?

The Photo is cut of, on the bottom which would shows where the Yellow wire is connected.
I just want to be sure before I start doing your version of the 5V Regulator Mod.
What looks like hot glue, is not clear to where the Yellow wire is connected.

Thank You!

Track Cut and Solder surface Cleaned for regulator Ground connection for 7805 5V Regulator.

5V Regulator Prep Track Cut GND Solder.jpg (94.4 KiB) Viewed 18447 times

This is the 7805 5V Regulator that I purchased from Radio Shack and looks like it may be the same one that you used with your 5V Regulator Mod.
Data Info for this Radio Shack 7805 5V Regulator: LM7805C, 1C51AS, Internal thermal overload protection, Stable fixed output voltage, Up to 1.0 amp output current,
Output transistor safe area protection, Internal short-circuit current limit and the cost was: $1.99.
Input voltage: 35V, Operating Temperature: 0 degrees C to +70 degrees C, Max. Junction temperature: 150 degrees C.

Bob

7805 5V Regulator from Radio Shack

[Salty]

Hey what does this mod actually do?