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Nextion with KA78T05

Herman Scheper #71930 I am using the Nextion 5"display. When building my Ubitx V5 I used a small step down converter to generate the 5V for the Nextion display. It all worked 100% Now the building is almost finished i want to replace the 5V stepdown converter. ( It is giving a little amountt of noise…) I ordered ( Aliex..) 5 pcs of KA78T05 TO-220 stabilisors. ( is the 3A version-? ) Then I replaced the 7805 mounted on the Arduine and replaced it for the KA78T05 version…. No working Arduino and no working display. I find input=12V output=0V. ? Checked before and after the pinning? 1=input / 2 = earth/ 3 =output ? Find a datasheet on Internet and can not find what I am doiing wrong. After that make a test print only for the KA78T05 and I can not get the 5V output. Output also on a 2nd KA78T05 is still 0Volt. ? Frustrating.? ( I used a 7809 on the same test and output was 9.00 Volt!) What I am doiing wrong...…….? ? ? ( ordered today local few 78S05 ? ( = 1.5A version? ) So who knows what I am doiing wrong...? ? ? ? ? ? ? ? ? ? ? ? Tnx.? Herman
MVS Sarma All Messages By This Member #71931 I suffered with 10pcs of? bad 78t05 from ali seller and demanded refund and got it. toggle quoted message Show quoted text On Mon, 16 Sep 2019, 9:37 pm Herman Scheper, <Hsrscheper@...> wrote: I am using the Nextion 5"display. When building my Ubitx V5 I used a small step down converter to generate the 5V for the Nextion display. It all worked 100% Now the building is almost finished i want to replace the 5V stepdown converter. ( It is giving a little amountt of noise…) I ordered ( Aliex..) 5 pcs of KA78T05 TO-220 stabilisors. ( is the 3A version-? ) Then I replaced the 7805 mounted on the Arduine and replaced it for the KA78T05 version…. No working Arduino and no working display. I find input=12V output=0V. ? Checked before and after the pinning? 1=input / 2 = earth/ 3 =output ? Find a datasheet on Internet and can not find what I am doiing wrong. After that make a test print only for the KA78T05 and I can not get the 5V output. Output also on a 2nd KA78T05 is still 0Volt. ? Frustrating.? ( I used a 7809 on the same test and output was 9.00 Volt!) What I am doiing wrong...…….? ? ? ( ordered today local few 78S05 ? ( = 1.5A version? ) So who knows what I am doiing wrong...? ? ? ? ? ? ? ? ? ? ? ? Tnx.? Herman
PA3GYV - Werner All Messages By This Member #71932 Probably a bad batch, I stopped order parts from AliExpress. Had the same with a batch of IRF510. Complete rubbish.?
Murray Wills (ZL2IQ) All Messages By This Member #71952 开云体育 Hi I did the same only the KA78T05 I got (bought 10 cause they were cheap) went red hot ? so I shut it all down and went back to the step down to power the Nextion. Luckily it didn’t seem to introduce any noise for me. Something wrong with the KA78T05’s as they should have been able to handle the current. toggle quoted message Show quoted text From: [email protected] <[email protected]> on behalf of MVS Sarma via Groups.Io <mvssarma@...> Sent: Tuesday, September 17, 2019 4:12:57 AM To: [email protected] <[email protected]> Subject: Re: [BITX20] Nextion with KA78T05 ? I suffered with 10pcs of? bad 78t05 from ali seller and demanded refund and got it. On Mon, 16 Sep 2019, 9:37 pm Herman Scheper, <Hsrscheper@...> wrote: I am using the Nextion 5"display. When building my Ubitx V5 I used a small step down converter to generate the 5V for the Nextion display. It all worked 100% Now the building is almost finished i want to replace the 5V stepdown converter. ( It is giving a little amountt of noise…) I ordered ( Aliex..) 5 pcs of KA78T05 TO-220 stabilisors. ( is the 3A version-? ) Then I replaced the 7805 mounted on the Arduine and replaced it for the KA78T05 version…. No working Arduino and no working display. I find input=12V output=0V. ? Checked before and after the pinning? 1=input / 2 = earth/ 3 =output ? Find a datasheet on Internet and can not find what I am doiing wrong. After that make a test print only for the KA78T05 and I can not get the 5V output. Output also on a 2nd KA78T05 is still 0Volt. ? Frustrating.? ( I used a 7809 on the same test and output was 9.00 Volt!) What I am doiing wrong...…….? ? ? ( ordered today local few 78S05 ? ( = 1.5A version? ) So who knows what I am doiing wrong...? ? ? ? ? ? ? ? ? ? ? ? Tnx.? Herman
Razvan (M0HZH) All Messages By This Member #71953 Why would you need another regulator ? The LM7805 is designed for 1A output and the 5" Nextion display + Raduino uses about 500mA (per specs). You only need a heatsink for the LM7805. This will be true for any other linear replacement you use (KA78T05 / 78S05 etc) as the dissipated power is the same.
Jerry Gaffke All Messages By This Member #71956 Could be that you got bad parts. Or could be that the part is getting too hot, and going into thermal shutdown. So you need a better heatsink. On page 2 of this Fairchild datasheet for the LM78T05, it says that the "thermal resistance junction to air" is 65 degrees C per Watt. The "junction" is on the silicon die, heat must travel from die to the metal TO220 tab, and from there get carried off into the air. ? ?? Thermal resistance junction to case", that is from die to?the TO220 tab? is 2.5 degrees C per Watt.? Useful to know if you have a good heatsink for it. Assume we are supplying the LM78T05 with 12 Volts and drawing 1 Amp at 5 Volts from it. The LM7805 is then dissipating? (12v-5v) * 1a = 7 Watts,? and if being used without a heatsink then the tab will be 7*65= 455 degrees C (819 F) above the ambient air temperature. If the ambient air is 23 degrees C (73 F), then the tab will be around 23+455 = 478 C (892 F). Actually, it will never get anything like that hot.? The device goes into thermal shutdown (and the output goes to zero Volts) when it gets too hot,. Not explicitly stated in the datasheet but I assume somewhere around 125 C (257 F). (It also has a separate mechanism to limit the maximum current in case you manage to short the output with a screwdriver.) So if the device seems to work for a few seconds and then quits,?touch the tab with a wet finger.? If your finger sizzles, then the LM78T05 (or LM7805) is too hot. I can believe that some devices out there sold for cheap are factory seconds that don't meet spec, or rejects that don't work at all, or some totally different device that has been painted over with an "LM78T05" logo. A test for basic function would be to put a 50 ohm resistor (able to dissipate at least 1/2 Watt) across the 5 Volt output, so it is only being asked to give? 5v/50 = 0.1 Amp. Then measure the output voltage, see if it really is 5 Volts. The Fairchild "thermal resistance junction to air" figure of 65C/Watt is much higher than TI's LM7805 figure of 19C/Watt. ?? Perhaps due to different assumptions about available air flow? The "thermal resistance junction to case" figures are fairly close, 2.5C/W for the LM78T05 vs 3.0C/W for the LM7805. Both are TO220 devices, so the additional thermal resistance from case to air should also be about the same. Jerry, KE7ER toggle quoted message Show quoted text On Tue, Sep 17, 2019 at 04:05 AM, Razvan (M0HZH) wrote: Why would you need another regulator ? The LM7805 is designed for 1A output and the 5" Nextion display + Raduino uses about 500mA (per specs). You only need a heatsink for the LM7805. This will be true for any other linear replacement you use (KA78T05 / 78S05 etc) as the dissipated power is the same.
Herman Scheper #71958 开云体育 You are 100% right!! tnx ? toggle quoted message Show quoted text Van: [email protected] <[email protected]> Namens Razvan (M0HZH) Verzonden: dinsdag 17 september 2019 13:06 Aan: [email protected] Onderwerp: Re: [BITX20] Nextion with KA78T05 ? Why would you need another regulator ? The LM7805 is designed for 1A output and the 5" Nextion display + Raduino uses about 500mA (per specs). You only need a heatsink for the LM7805. This will be true for any other linear replacement you use (KA78T05 / 78S05 etc) as the dissipated power is the same.
Herman Scheper #71960 开云体育 Hello Jerry, ? I ordered 5 pcs. of them. After it did not work-from the 1th second!! )- i tested 2 of them on a small breadboard. Without load and with a load of a few 100 Ohms. The did never work. Always output ?zero Volt.?? Some other members on this forum had the same experience with them. So never buy this parts form Aliex. ? Tnx fort he explanation. ? Rgds,? Herman? PA0BAB ? ? toggle quoted message Show quoted text Van: [email protected] <[email protected]> Namens Jerry Gaffke via Groups.Io Verzonden: dinsdag 17 september 2019 16:13 Aan: [email protected] Onderwerp: Re: [BITX20] Nextion with KA78T05 ? Could be that you got bad parts. Or could be that the part is getting too hot, and going into thermal shutdown. So you need a better heatsink. On page 2 of this Fairchild datasheet for the LM78T05, it says that the "thermal resistance junction to air" is 65 degrees C per Watt. The "junction" is on the silicon die, heat must travel from die to the metal TO220 tab, and from there get carried off into the air. ? ?? Thermal resistance junction to case", that is from die to?the TO220 tab? is 2.5 degrees C per Watt.? Useful to know if you have a good heatsink for it. Assume we are supplying the LM78T05 with 12 Volts and drawing 1 Amp at 5 Volts from it. The LM7805 is then dissipating? (12v-5v) * 1a = 7 Watts,? and if being used without a heatsink then the tab will be 7*65= 455 degrees C (819 F) above the ambient air temperature. If the ambient air is 23 degrees C (73 F), then the tab will be around 23+455 = 478 C (892 F). Actually, it will never get anything like that hot.? The device goes into thermal shutdown (and the output goes to zero Volts) when it gets too hot,. Not explicitly stated in the datasheet but I assume somewhere around 125 C (257 F). (It also has a separate mechanism to limit the maximum current in case you manage to short the output with a screwdriver.) So if the device seems to work for a few seconds and then quits,?touch the tab with a wet finger.? If your finger sizzles, then the LM78T05 (or LM7805) is too hot. I can believe that some devices out there sold for cheap are factory seconds that don't meet spec, or rejects that don't work at all, or some totally different device that has been painted over with an "LM78T05" logo. A test for basic function would be to put a 50 ohm resistor (able to dissipate at least 1/2 Watt) across the 5 Volt output, so it is only being asked to give? 5v/50 = 0.1 Amp. Then measure the output voltage, see if it really is 5 Volts. The Fairchild "thermal resistance junction to air" figure of 65C/Watt is much higher than TI's LM7805 figure of 19C/Watt. ?? Perhaps due to different assumptions about available air flow? The "thermal resistance junction to case" figures are fairly close, 2.5C/W for the LM78T05 vs 3.0C/W for the LM7805. Both are TO220 devices, so the additional thermal resistance from case to air should also be about the same. Jerry, KE7ER On Tue, Sep 17, 2019 at 04:05 AM, Razvan (M0HZH) wrote: Why would you need another regulator ? The LM7805 is designed for 1A output and the 5" Nextion display + Raduino uses about 500mA (per specs). You only need a heatsink for the LM7805. This will be true for any other linear replacement you use (KA78T05 / 78S05 etc) as the dissipated power is the same.
Mark Hatch All Messages By This Member #71961 Perhaps thermal overload, but I was having problems with the 7805 until I replaced it when I put in a 5" Nextion. I did not try the heat sink as it required more cutting to fit then I wanted to try. I also planned on additional boards (stand alone signal analyzer and JACKAL, so a higher rated 7805 mounted on the back panel (using the case as the heat sink) worked well for me.? Mark
ajparent1/kb1gmx All Messages By This Member #71963 Very simple the 7805 and kin are linear regulators and at 500ma the max voltage that? can be tolerated before the power dissipated as heat is about 1.5W which places the input voltage at not more than 8V, you need to be at more like 7.5 due to heating. Now add a decent chunk of metal, a heat sink, and that goes up depending on the size of the heat sink. How to calculate all that is trivial, the series current though the device (current into pin1) times the voltage across it (voltage from pin 1 to pin3) and that in watts of heat dissipated.? *Note the 78xx series of regulators must have about 2V minimum across it to regulate (for 5V part that's about 7V).? Even at 100-150ma a heatsink (not less than 2" square exposed air) is advised.? The maximum temperature before shutdown or damage is about 125C (hot enough to burn skin). Max wattage is dependent on quality of heatsink but the 2.5degreesC/Watt is the limit or about 40W but max current is usually reached before that and in some cases max voltage.? However to get that out of the nominal 7805 that means a heat sink of about 2x2 inches with .5" fins with some airflow. For those making up their own circuits insure there are a 1uf (or larger) at? Pin 1(input), and .1uf on pin 3 (output) to ground close to the regulator as it can oscillate and that will cause failure like behavior. I started using those regulators when the first came out in the early 70s for microcomputers (8008 and on) and?I have a bag of them from the early 80s I still use.? Good reliable part, cheap too but often abused and misused. Allison
_Dave_ AD0B All Messages By This Member #71965 Have had success with the stock 7805 mounted on the raduino. Have 4 of the critters with up to 3.5" nextions I use a stock power transistor heat sinks with an additional hole. To mount it. Have found mounting the 7805 out of the front raduino offers more room if the board is mounted properly in the case. -- 73 Dave k0mbt
MVS Sarma All Messages By This Member #71966 Check , raduino with nextion miight need 1amp odd. You cant work at 100% with input 12 or 13.5v. If the 7805 input is just 3v above what you said is understandable. Better try a genuine 78s05 it might manage.? All the best Sarma vu3zmv toggle quoted message Show quoted text On Tue, 17 Sep 2019, 4:35 pm Razvan (M0HZH), <razvanfatu@...> wrote: Why would you need another regulator ? The LM7805 is designed for 1A output and the 5" Nextion display + Raduino uses about 500mA (per specs). You only need a heatsink for the LM7805. This will be true for any other linear replacement you use (KA78T05 / 78S05 etc) as the dissipated power is the same.
Razvan (M0HZH) All Messages By This Member #71967 Maximum current draw for the 5" Nextion (backlight @ 100%) is?410mA? Arduino Nano ~20mA Si5351 (all outputs enabled) ~22mA Assuming 13.8V input, there's over 4W of thermal power to be dissipated. As Allison already explained, whatever IC you'll use it'll need a heatsink. Also, try to keep the heat away from the Si5351 oscillator crystal as it would generate frequency drift.
Lawrence Galea All Messages By This Member #71968 When dropping down voltage I always use more than one regulator in series to split the dissipation. E.g. 7809 or 7808 from the nominal 12V then to the 7805 and bolt them to the aluminium case or to a heat sink with thermal compound. They are cheap enough not to bankrupt you. Take care when buying from Ali etc Regards Lawrence toggle quoted message Show quoted text On Tue, Sep 17, 2019 at 11:50 PM Razvan (M0HZH) <razvanfatu@...> wrote: Maximum current draw for the 5" Nextion (backlight @ 100%) is?410mA? Arduino Nano ~20mA Si5351 (all outputs enabled) ~22mA Assuming 13.8V input, there's over 4W of thermal power to be dissipated. As Allison already explained, whatever IC you'll use it'll need a heatsink. Also, try to keep the heat away from the Si5351 oscillator crystal as it would generate frequency drift.

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