RC India

Hello Sai,

See pics what i was talking about...



Changed the title as per request.

Check out pics of two new transmitters

Changed the title of the thread from "Ckt" to "circuit" so that the thread is searchable.  It is sad to see people do not have about 1.5 seconds extra to put in 4 extra keystrokes.

More importantly, what is this thread about ?  Put some description in the original post so that the rest of the audience can also understand what is going on.  If it is the continuation of some discussion, it should have been posted in that thread.

 :headscratch: :headscratch: :headscratch:

this is just because we cannot send Pictures through Private Messages...
Or there is a way which i am not aware !!!

The PM system does not support images, and has been kept that way to encourage public discussion as much as possible.  But if you really want to do it, host the image else where, and use the "img" tags to embed the link.  When the recipient sees the message, he will see the image itself, not the link.

Ok ....Thank you.... can you please suggest some URL of this "else where" .... can face book be a good idea!!!

But i think i will have to add the person as friend..

"Else where" are things like Photobucket, Imgur etc.

Admin: could you please change the topic name to --> Regulator IC heating issue in FlySky 6ch TX

Hello Kalyan,

I saw you helping Gbisht to repair his charger on this forum. I am facing a problem with my FLYSKY 6CH TX. Issue is it works for 3-4 min ok but then behaves erratic, I lost 2 self made models due to this, initially since i did not know how to fly so though its my mistake but when it was repetitive I opened the TX and saw SMD 78L05 IC when Tx is ON this IC is getting hot and my assumption is that the thermal cutoff might be working which may be the reason for erratic behaviour.

What do you suggest ? can changing this IC resolve the issue? Or can something else is faulty...

The TX works well for initial 2-3 mins.

DO I go ahead and replace it with 0.5Amp 78M05 IC.PLease advice.

See the pics here: http://www.rcindia.org/radios-and-receivers/ckt-pics/msg115794/#new

Reply from Kalyan.......

Look,
7805 is a regulator ic. and opening the cabinet, make power on and run for 5 minute. sense the heat. if it looks wrong, it is not the fault of 7805, but it's overload. Overload caused by leaky Capacitors (Filter capacitors, large one). If you trace the capacitor, connected with two lead of 7805, just replace that first and observe the heat. If still excess heat occurs, check the link fails or not in receiver by powering it. (Link LED will indicate). If LED goes off, your RF circuit shuts down; needs opening of RF Module. Measure current. If LED stands, your microcontroller portion takes excess currents and shuts off.

First of all replace large can capacitors. Then sense heat.

Thanks Kalyan..... it will take a while (weekend) for me to replace the 47mfd caps ... will update once done.

HI Kalyan,
I replaced all the can capacitors to eliminate any issue.. all were 47mfd.... but still the regulator Ic Both 100mAmp & 500mAmp are getting heated !!!!! I tried to do table test but could not notice the erratic behavior i.e TX RX were in Sync.
Checked the voltage of both regulators it was 5V (+/- 0.05 Volt) what else can be the issue???

Can we put a robust 5V ckt inside the TX ? 

In my opinion, you should not put a high power 5V inside the device. The 7805 is getting hot only because there is some short somewhere in the circuit. If you supply more current you may end up frying your radio.. Measure the resistance between the output leads of the 7805 and check to see if there are any shorts.

Heating will be always if it regulates. but ceck if the link fails or not!

what is the input voltage being supplied to the Tx?

Input is 1.5x8 alkaline cells = 12Volts, however when i measured it was 11.5 volts ( cells have been used)

It could be you're dissipating off quite some watts (6.5 volts * current consumed) as heat. Try lowering the input voltage (but not lower than 7v). Lin Regs need about 2 v of dropout voltage to provide adequate regulation.

Lowering voltage???? There must be some other use of 12 volt...anyway just having a. Diode before 5 volt regulator will help???
Kalyan I can understand device getting warm because of regulation but these are hot you cant touch them for long. And I checked for 4 min link did not fail
Still needing advice

A diode in front will dissipate part of the heat but you're still only dissipating heat, not efficient.

There is no other use of 12v in your tx.

The problem as I see is that the linear regulator is being asked to drop 11.5v supply to 5v. 11.5 - 5 = 6.5 volts. If your Tx consumes about 0.2A of current, the energy dissipated is 1.3W. LM7805 has a thermal resistance of about 65C/W.You're probably running at much higher than the ambient (which *is* hot to touch). Now that was for 0.2A, take it any higher and temperature will rise.

In any case, it is not going to harm your Tx, so you might want to try and reduce the voltage and check for the heat.

Just  a query if there is no requirement of 12Volts ( I have not traced) in the TX then why we have 12volt supply?
The manufacturer should have put 6 cells (9 volts ) instead of 8 cells (12 volts).... did not get it ??

Lastrite - if there were shorts TX wouldnt have worked .... its working only thing i am worried is heating of regulator + at times loss of control while flying.

That perhaps the manufacturer should answer.

They did the same with the 9x, requires 5v, the battery holder is for 8 cells. I think they did it so if someone uses rechargeable NiCd, they'd be running it a 1.2v *8 = 9.6 v

Rightly Pointed. :hatsoff:

And good to here that Tx link is stable now.

All Tx rechargable cells work at near 9 -11 volt. and Tx malfunctions sometime > 11.2 Volt. I have experienced this when I inserted new DuraCell 8 cells in Turnigy 9x, it started malfunction. But when after using/checking, the voltage reduced to 11 volt, it started working correctly.

The excess voltage is used for faithful operation of regulator. The uC stage often designed with 7809 and 7805 in series.

In your case, as the regulator IC is inside, please add some heatsink and watch range with time test. I think the problem should vanish. And surely, if you use LiPO, change it to LiFePo or add a single diode (1N4007) in battery line.

In case of simulator use there should be some switch which should isolate Tx Mdule to save power which is not available regular Cheap versatile Txs.

I Think any one of the power line solution will solve your problem. But please add heatsink MUST to regulator.

Good Luck

Another reason for excess heating in design view.
It demoisturise Leaky Electrolyte Capacitors and brings life sometimes, or you can say increase module life. Good Idea but innovative reverse engineering. Ha. Ha.

If the Tx was like this from purchase we could have put down the heating issue to bad design. As this is not the case, I think, we can safely rule out the possibility of overheating due to regulation. Now this points to some circuit component that is drawing more power than it was designed to, thus overloading the regulator. Some times solder flakes fall on the pcb shorting out paths. The circuit may still work as these are not 0 resistance paths.

Another option would be to use a regulated power supply at 9V (IC7809 or LM317) and feed it through the battery terminals without modifying the internal circuitry. You can supply this external regulator with a LiPo. Now test the radio. Since it is now supplied by a stable 9V you can figure out if there is some heat related issues with the internal regulators.

Is the problem solved? :P

NO .... i am yet to fly again but afraid that i will break my plane... any way trying to get heat sink for regulator so that heat dissipates.... what to do for the SMD 78L05 ????

If space provide, replace with regular large 7805 with heatsink i. e. TO220 package.
Costs is Rs. 5/- at Kolkata.

Thanks Kalyan & lastrites for all the support....
Cost of IC is not of much matter...... Point is investing time..... rather than flying i am stuck in this !!!!

Will do as suggested for a to220 package 7805.

But Still i wonder the heat .. I have used 7805, 09, 12 ICs at lot many applications but they were not so hot??

http://www.electro-tech-online.com/general-electronics-chat/18861-heat-sink-7805-a.html
http://www.dutchforce.com/~eforum/index.php?s=e10e05c80419782fedb0c7f8a9209ec1&showtopic=21384
http://www.electronicspoint.com/l7805cv-too-hot-t23923.html

Reduce the input voltage, you'll be a happy man! You need a heatsink badly if you're dissipating over 1.5w

Your 7805 might be oscillating crazy, what caps do you have connected?

lastRites, your point makes sense that if it wasn't there earlier, why now? rastsaurabh, did you ever check the heat before replacing these, they might have been overheating all the time.

In the end, there are only two choices, either generate lesser heat or get rid of the extra generated.

The excess heat in RF Amplifier transistor may be so hot so as to burn the transistor instantly if not antenna properly matched and reflected wave generated. But the regulator have no such issue except loading current and potertial difference between input and output voltage.

However, I am waiting for some study materials for clearing some issue simply. God knows how long I have to wait. ;D

Kalyan Da, would not the circuitry get effected if he replaces 78L05 with regular one, in case there is some faulty bridging after the output. ???
The actual cause of heat generation has not been found yet.
I think this(any bridging) can also be a reason for excess heat generation. :-\
the provided IC provides 500ma of current, while the regular is designed for many times more(2a i guess,dont know exactly).
So there are chances of frying the post circuitry i guess.

 :iagree:

As this regulator feeds power to entire ckt, it should be hot. And it was earlier soldered with PCB foil as heatsink. Moreover, Now signal stable means, some leaky capacitor replacement improves some load behavior.
And,
troubeshooting needs step-by-step approach.

The TX is new and rarely used ...... why i suspected TX was that the model plane flew well initially but all of a sudden became uncontrolable and crashed. When i could not find any reason, I opened the TX and felt the 7805 to be hot so there is no pre post study. I used new alkaline batteries with were 12Volts but now are used up to 11Volts so i can expect some improvement when i fly.

@ girish - the cap i used are 47Mfd 25Volt Philips make. Replaced all 6 of them all were same value old ones are some unknown company.

Now insted of plane, use BEC and servos and test for at least 15 minutes at a long distance.
your tx should be stable now. All the txs are designed and optimized for NiMH and NiCD battery. So when new alkaline/dry cell is used (EMF=1.56volt), heat generation become so hot, it malfunctions. E-Sky are better in this case as they use 4 cell insted of 8 cell.

However, if final stage RF power is to be maximized, it's supply voltage should be as high as possible in addition of highly selective matched antenna using some network (PI or ladder). So a good regulator with high voltage battery (of-course within designed limit) can give higher range if not any other section malfunction. But if entire RF stage use 5 volt, then it is better to supply reduced voltage. in this case you can try to use a dummy cell (shorted one) and can get good result. If entire section works on 5 volt, you can save even 2 cell. But always test range while doing this experiment.

Good Luck.

If I want to use a normal lipo to power my tx(at full charge gives 12.6v) should we use an external step down regulator? What should be stepped down voltage, 10v?

LiFePO are better than LiPO.
In LiPO Use 2 nos 1N4007 in series to drop out voltage.

approximately causing a drop of 1.4 Volts ??