audioguru Posted July 6, 2006 Report Share Posted July 6, 2006 If you have a perfect heatsink for a 2N2219 so that its case is held at 25 degrees C, then its max dissipation is only 3W when its internal temperature is at its max of 200 degrees C. A perfect heatsink is impossible so its max dissipation is only about 2W.A 2N3055 output transistor has a minimum current gain of 25 with a collector current of 3A. So its max base current is 3A/25= 120mA. Its driver transistor will have 32V across it (24VAC transformer) when the project's output voltage is low, and 120mA through it which results in a dissipation of 3.84W. The 2N2219 will melt. A TIP31A can dissipate a max of 40W and will be fine with a little finned heatsink.You might be able to use a 2N2219 if it has a very good heatsink with a fan, and select a 2N3055 for very high current gain. Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted July 7, 2006 Report Share Posted July 7, 2006 ok you have a valid point , i will send some pics of my heat sink , so you can judge on that Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 7, 2006 Report Share Posted July 7, 2006 A picture of a heatsink won't say much.The heatsink's datasheet will say exactly how well it will cool. Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted July 7, 2006 Report Share Posted July 7, 2006 see there is no heatsink here available with respect to datasheet. i have heatsink of a processor and one of some other device , by the way LM301 plastic or LM101A metal op amp can also be used instead of LM741. Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 7, 2006 Report Share Posted July 7, 2006 see there is no heatsink here available with respect to datasheet.Here, nearly everything has a detailed datasheet. We can select a heatsink that will cool perfectly.LM301 plastic Quote Link to comment Share on other sites More sharing options...
cynicmonster Posted July 7, 2006 Report Share Posted July 7, 2006 Geez Guru...you are a Theorist...lol. My knowledge from this site has improved 10-fold+. Keep it up! Quote Link to comment Share on other sites More sharing options...
argeelektronik Posted July 8, 2006 Report Share Posted July 8, 2006 L4970A 5-30 VOLT 10 AMPER 40 volt input, 5-30 out, smps Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 8, 2006 Report Share Posted July 8, 2006 Hi Arge,Sure, a Switching Mode Power Supply (SMPS) can provide a high 10A output current and a variable voltage, but it has ripple at its switching frequency.This project is a linear power supply that gets hot and when when working properly doesn't have ripple. Quote Link to comment Share on other sites More sharing options...
ante Posted July 8, 2006 Report Share Posted July 8, 2006 Hi AG,What makes the ripple (100 – 500 kHz) incurable here? Quote Link to comment Share on other sites More sharing options...
MonSSter Posted July 8, 2006 Report Share Posted July 8, 2006 Hi!exams are over, so i can finish the power supply now ... i think i located the problem and that is the voltage on q1, collector is 0.8~0.9V so i'm asking if that could be the problem( i have no output ) Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 8, 2006 Report Share Posted July 8, 2006 i think i located the problem and that is the voltage on q1, collector is 0.8~0.9V so i'm asking if that could be the problem( i have no output )If Q1 is connected wrong, shorted, doesn't have R13 and R14 the correct values or doesn't have a negative supply (-5.6V) for R14 then U2 will get hot.Q1 is supposed to turn on and short the output of U2 to 0V when the negative supply disappears quickly when the AC power is turned off so that the output voltage doesn't rise. Quote Link to comment Share on other sites More sharing options...
MonSSter Posted July 8, 2006 Report Share Posted July 8, 2006 r13 has ~34V ... and r14 has 0.8-0.9V ... Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 8, 2006 Report Share Posted July 8, 2006 Hi MonSSter,I don't think its negative supply is working.One end of R14 connects to the base of Q1. The other end connects to the -5.6V supply. Check the parts that are supposed to make the negative voltage.Without the negative voltage then Q1 conducts all the time and shorts the output of U2 to ground. Quote Link to comment Share on other sites More sharing options...
MonSSter Posted July 8, 2006 Report Share Posted July 8, 2006 ..and what are the parts for negative voltage? Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 8, 2006 Report Share Posted July 8, 2006 These are the parts and how it works: Quote Link to comment Share on other sites More sharing options...
MonSSter Posted July 9, 2006 Report Share Posted July 9, 2006 ok i belive that diodes are dead or something, because on d7, theres 0.7V .. so i will replace them during the weak and then report again .. tnx! Quote Link to comment Share on other sites More sharing options...
Thomas Posted July 9, 2006 Report Share Posted July 9, 2006 I think the terminals of D7 are connected in the wrong way. Just try to rotate the thing by 180 Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted July 14, 2006 Report Share Posted July 14, 2006 Can i use 2n3055 in place of 2n2219 , it is also a power transistor Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted July 14, 2006 Report Share Posted July 14, 2006 how ever 2n3055 will be placed on the heatsink Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 14, 2006 Report Share Posted July 14, 2006 Can i use 2n3055 in place of 2n2219 , it is also a power transistorQ2 doesn't need a rating of 15A and 115W, but a 2N3055 transistor will work fine.I can buy a TIP31A power transistor for $.68US and a 2N3055 power transistor for $1.68US.There are many power transistors with ratings and prices like a TIP31A. Quote Link to comment Share on other sites More sharing options...
jiangrm Posted July 17, 2006 Report Share Posted July 17, 2006 hi AG,1. How to decide the value of R9? Why don't we use 10K or 470R?2. What's the purpose of C5? How to calculate the value?3. Is C9 used to improve the stability of U2?4. Can I connect output(pin6) of U2 to base of Q2 (bypass R15)? If not, why?5. If the system should be grounded, which part of the circuit should connect to ground as well? Quote Link to comment Share on other sites More sharing options...
MonSSter Posted July 17, 2006 Report Share Posted July 17, 2006 well replacing D7 did nothing new ... so i measure the voltage on r2 where there is 17.7V, and on D5 there's 0V(?!) ... any ideas? Quote Link to comment Share on other sites More sharing options...
Thomas Posted July 17, 2006 Report Share Posted July 17, 2006 Did you make sure that every diode in the negative 5,6V supply is soldered in the right way round? Quote Link to comment Share on other sites More sharing options...
MonSSter Posted July 17, 2006 Report Share Posted July 17, 2006 yep ... many many times :D Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 17, 2006 Report Share Posted July 17, 2006 1. How to decide the value of R9? Why don't we use 10K or 470R?R9 feeds the adjusted reference voltage to U2 and limits the loading effect of C4 on the output of U3. If its value is higher then U2 might pickup interference. If its value is lower then U3 might oscillate due to C4 being at its output or R9 won't discharge C4 quick enough during current limiting.2. What's the purpose of C5? How to calculate the value?It is a supply bypass capacitor for high frequencies, because C1 is so big it has high inductance. Analog electronic circuits oscillate without it or if its value is too low. C5 could be 0.1uF to about 1uF and a ceramic disc is best at high frequencies.3. Is C9 used to improve the stability of U2?Yes, because Q2 and Q4 are in its negative feedback loop and are much slower than U2 and cause delay, the combination could oscillate without C9.4. Can I connect output(pin6) of U2 to base of Q2 (bypass R15)? If not, why?U2 oscillates if its load is capacitive and is directly at its output. R15 isolates the capacitance of Q2 and I recommend reducing its value to 100 ohms.5. If the system should be grounded, which part of the circuit should connect to ground as well?Connect the 0V output to ground and the project supplies variable positive voltages above ground.Connect the Positive output to ground and the 0V connection supplies variable negative voltages below ground.Don't ground any part of the output and the project can be connected in series with another supply that might be grounded. Quote Link to comment Share on other sites More sharing options...
login
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.