Hello all, and thank you for taking the time to read my post. I have been experimenting with a cheap psu kit and I have observed that Q4 (2SD1047) is overheating even with a heatsink on it. I have used a 1 ohm 5W resistor as a load, at a voltage of 2 volts and 2 amps, (2 amps is what I aim for, despite the PSU saying 3 in its documentation).
I am aware that Q4 has to dissipate 26 Volts X 2 Amps = 52W of heat (28 volts being my transformer's secondary voltage), but with a thermocouple between the transistor's body and the heatsink, the reading reached 148 celsius rather quickly (sub 30 seconds) which is not good, in my opinion. I even had a fan blowing over it , which managed to keep it at a sort of constant 145 celsius.
Since the kit is some cheap Chinese stuff I wondered if the 2SD1047 could be fake, and I replaced it with a 2N6307 (8 amps collector current) to no avail, it overheating just like before. Now, I have to admit that this is my first time working with a linear PSU. I have devised two scenarios:
1. It's my lack of experience and the lack of a heatsink with good thermal mass and a fan. I believe that the temperature should not be more than 60-80 on the heatsink.
2. I should substitute the transistor with two similar power transistors, in parallel, with ballast resistors to prevent thermal runaway, which would make it easier for the PSU to handle the load.
Now, the questions that I have are:
1. Should I substitute Q4 with two transistors in parallel, a beefier single one or should I just keep everything like it is and get a proper heatsink and fan?
2. What would be the normal operating case temperature for the transistor ? ( The datasheet says 150 degrees Celsius maximum temperature)
I have attached the PSU's documentation, with the schematic being on the last page.
Thank you.
I am aware that Q4 has to dissipate 26 Volts X 2 Amps = 52W of heat (28 volts being my transformer's secondary voltage), but with a thermocouple between the transistor's body and the heatsink, the reading reached 148 celsius rather quickly (sub 30 seconds) which is not good, in my opinion. I even had a fan blowing over it , which managed to keep it at a sort of constant 145 celsius.
Since the kit is some cheap Chinese stuff I wondered if the 2SD1047 could be fake, and I replaced it with a 2N6307 (8 amps collector current) to no avail, it overheating just like before. Now, I have to admit that this is my first time working with a linear PSU. I have devised two scenarios:
1. It's my lack of experience and the lack of a heatsink with good thermal mass and a fan. I believe that the temperature should not be more than 60-80 on the heatsink.
2. I should substitute the transistor with two similar power transistors, in parallel, with ballast resistors to prevent thermal runaway, which would make it easier for the PSU to handle the load.
Now, the questions that I have are:
1. Should I substitute Q4 with two transistors in parallel, a beefier single one or should I just keep everything like it is and get a proper heatsink and fan?
2. What would be the normal operating case temperature for the transistor ? ( The datasheet says 150 degrees Celsius maximum temperature)
I have attached the PSU's documentation, with the schematic being on the last page.
Thank you.
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