#Styles of cases for a 2n3055 transistor full
As you nave a full wave rectifier T becomes 0.01 seconds because the reservoir capacitor gets charged twice for every cycle of the mains. As you are in the UK your mains frequency will be 50Hz, giving a period of 1/50 sec = 0.02 seconds. In your case, with a 10,000uF (0.01F) reservoir capacitor and a current drain of say 1A, the ripple voltage can be calculated by V= IT/C, where V is in Volts peak to peak, I is in Amps and T is in seconds. You can get pretty close to the peak to peak ripple voltage as described When you are designing a power supply, like yours, you needed to know the ripple voltage on the reservoir capacitor. I expect that you know that the normal scam is to put a small capacitor, say 1000uF capacitor n a big can marked 10, 000uf say. You mention about possible problems with the quality of your reservoir capacitor. Maybe I should but a 100K resistor across it, sound a good idea. I'll wear safety glasses and a flak jacket for a while. As I said above I have a 10,000uF 63V cap - mind you it's from China so who knows. I made a right cods explaining that transformer - sorry. The transformer is tapped for 110V and 230V input and 2 x18V or 36V at 4.44A output. As I thought I was building a 36V power supply (I had forgotten 1.4141 - it's 50 years since I last dabbled in electronics) I don't mind loosing a few volts. I have a 10,000uF cap after the bridge rect so about 51V. The transformer is for 36V 4.44A output at 230V. I have bough a few 'spare' 2N3055's and LM317AHVT's. The case temperature is always 30% odd lower than the junction. During all the tests the heat sink was about 20C cooler than the 2N3055 case. From the video's it plain that metal to metal with heat compound is the best. I have noticed a 0.47Ohm resistor used in may circuits and wondered why - I know now - thanks. I should have omitted the LM338 and the LM317 should read LM317AHVT which can handle 60V. The person closest to the time when the solder melted and the 2N3055 self protected won the prize. We used to solder leads to them and turn them upside down with some current flowing thru them. Have fun: I have destroyed many 2N3055s along the way. You can also calculate the resistor power dissipation from, W = I * I * R where, I is current in Amps, R is resistance in Ohms and W is power in Watts. But you have the best approach of not using an insulating washer at all. On the other hand, mica is better and alumina is excellent. If you ever use insulating washers, rubber, kapton etc are pretty high thermal resistance. And, as a general rule of thumb with a decent heatsink, you will be limited to around 25W dissipation for a 2N3055 they have a high thermal resistance, junction to case, of 1.5DCW, whereas a good figure would be 0.5 DCW. This is in fact limited by the dissipation rather than the SOAR but you should always check the SOAR, even for MOSFETs which, contrary to what you read on the net, do suffer from secondary breakdown.īy the way, the thermal resistance of a TO3 case to heatsink without a washer but with thermal paste is taken as 0.5DCW. In practice the junction temperature would be much higher than this so a practical maximum current at 40VCE would be around 1.5A. See figure 2 of the 2N3055/MJ2955 data sheet: From this you can see that at 40VCE the 15A, 2N3055 can only handle 3A at temp case = 25 degC. In addition to the maximum junction temperature of a transistor, you need to keep an eye on the safe operating area (SOA). I should be running around 60 C (or not ?) The thermal resistance junction to case is 1.5 C/W. Extrapolating his results I should be able to draw 39W per 2N3055 at about 40C case temperature or less. Metal to metal with compound was by far the best. Quite a down to earth approach but unfortunately nothing with metal to metal with heat compound - AND fan. I may fit a 150mm 0.4A fan if the 125mm doesn't cover the heat sinks. 1 heat sink per 2N3055 in an x pattern under a 125mm 0.5A fan blowing from outside the case down the heat sink fins with a 30mm gap at the bottom. I thought 3A from the transformer a safe limit. I was considering using 4 x 2N3055's each at about 0.75A at 52V (39W each). On her page is a link to the circuit that states she removed the 0.1 Ohm 10W resistors as it limited her current output.
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