Twosky2000 Posted January 30, 2017 Posted January 30, 2017 hi there, I'm trying to power my NanoPI over a Loudspeaker cable with 12V. At the end I have a 7805 voltage regulator with 100nF at input and output. At the Powersupply i meassure 12V and 200-300mA current. The 7805 gets extremely hot! Anyone seen similar behavior or got me a tip? Sincerely, Twosky2000
zador.blood.stained Posted January 30, 2017 Posted January 30, 2017 Well, 7805 is a linear regulator, so it will generate a lot of heat at this voltage difference and current. Tips? Use a switching (buck) converter. 1
pzw Posted January 30, 2017 Posted January 30, 2017 Agree with zador. What you can try to do (if possible) is lower the voltage to 8-9V, instead of 12V. That will remove 1W of heat from the 7805. Also install a heatsink on the regulator, and do not forget to add a electrolytic capacitor of 220uF - 1000uF at the output of the regulator to take care of the current surges a SBC produces at times. Depending on the exact type of the 7805 you might run into the max. current handling capacity. The most common TO220 version is standard 1A max... There are 78M05 units, but those will require a heatsink for the much higher current. All in all is a 7805 a poor choice for your application. I would recommend looking at a switching regulator of i.e. Recom. Do not forget the additional capacitance on the output though... 1
zador.blood.stained Posted January 30, 2017 Posted January 30, 2017 For the 78xx electrolytic cap should be on input and ceramic cap should be on output (as close to the regulator as possible). For all types of regulators looking at the datasheet is recommended before trying to apply a common sense - some require a ceramic cap on the output while others require electrolytic one for the stability. In any case 78xx or any kind of linear regulator should not be used here - it will consume more power than the board itself at this voltage difference. 2
pzw Posted January 30, 2017 Posted January 30, 2017 Zador; In my years designing / building all sorts of electronic circuits I have always used the datasheets as a reference starting point. I have also found out that in a lot of cases there can be improvements made, especially looking at voltage stability and noise suppression from voltage regulators. Yes, the datasheet recommends a electrolytic capacitor on the input and just a ceramic capacitor on the output.. However when you are looking at a load on a 7805 which will have a lot of higher frequency load changes, it is recommendable to use (preferably and low ESR) electrolytic cap on the output of the regulator.. It can prevent / solve strange issues.
Igor Posted January 30, 2017 Posted January 30, 2017 LM2596 should be right for the job - it can cope with such loads and they are dirt cheap. https://www.aliexpress.com/wholesale?SearchText=LM2596 2
Twosky2000 Posted January 30, 2017 Author Posted January 30, 2017 I tested a L7805cv and a L78s05cv in TO-220. School was to many years ago. I will try to get a smaller power-supply (6V) or use an other converter. Thank you very much, this is a genius community
zador.blood.stained Posted January 30, 2017 Posted January 30, 2017 Zador; In my years designing / building all sorts of electronic circuits I have always used the datasheets as a reference starting point. I have also found out that in a lot of cases there can be improvements made, especially looking at voltage stability and noise suppression from voltage regulators. Yes, the datasheet recommends a electrolytic capacitor on the input and just a ceramic capacitor on the output.. However when you are looking at a load on a 7805 which will have a lot of higher frequency load changes, it is recommendable to use (preferably and low ESR) electrolytic cap on the output of the regulator.. It can prevent / solve strange issues. Agree - for 7805 an electrolytic cap at the output can improve things, but it should be noted that it should be used together with the ceramic one and not instead of it. Also it should not be too big or it may cause an overcurrent at the start.
zador.blood.stained Posted January 30, 2017 Posted January 30, 2017 I will try to get a smaller power-supply (6V) or use an other converter. For the 7805 dropout voltage lower than 3V is not recommended and lower than 2V may not work reliably, so the input voltage should be at least 8V. 1
Magnets Posted January 30, 2017 Posted January 30, 2017 The LM2596 modules on aliexpress all use counterfeit ICs but do work This is probably a better bet: https://www.aliexpress.com/item/DC-6-24V-12V-24v-to-5V-USB-Output-charger-step-down-Power-Module-Mini-DC/32679427711.html This guy on youtube tests the cheap buck modules, go back 6+ months https://www.youtube.com/channel/UCKs_u8kcQBQsERZhpZHU_7Q/videos beware: the really small ones with the tiny adjust potentiometers are very difficult to adjust to 5.00v and if you press on the pot it changes the voltage. Or you could get a 12v car USB adapter
westyd1982 Posted January 30, 2017 Posted January 30, 2017 I've been using Murata 78SR DC/DC converters for this. They are high efficiency and put out 1.5 A. I've been buying them from Mouser: http://www.mouser.com/ProductDetail/Murata-Power-Solutions/OKI-78SR-5-15-W36-C/?qs=sGAEpiMZZMslBFvnKnOhcsAPP%252bIEe4SP
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