Sometimes the transformer inbuilt temperature fuse (120°C) burned. And the whole transformer had to be replaced. Prefer using tansformers with ambient temperature range TE40 and not TE60. Or not to use a transformer to 100% of its capability. Some more reserve seems to be prevent overheating especially on summertime.
By the way: Most of the DC-stages do not strictly follow the datasheet recommendations for mounting rectifier diodes at least 9.5 mm lead length to prevent overheating. You may see the result of such mounting to tough to the printed board in changing the color to "charcoale like". That is why the rectifier in my very oldschool and a little bit oversized PSU is a category 25 Amps one and of course mounted on metal case for cooling.
And a transformer can reach 115 to 120° Centigrade inside the coil, quoting Category E. Even if it is a class T40 one. In such most cases a temperature fuse has been fitted inside the primary coil set for 120°C, which cannot be replaced so easily.
In my linear supplies, I had to swap conventional silicon rectifiers for Schottky types, as the 1.6 voltage drop and 3A + forward current was producing about 5 w of heat.
The downside of Schottky types, is that they have faster switching times, and as a result, they can produce additional RF interference, unless extra R & C snubbing components are added.
As you know, not all kind of so called "Schottky"-diodes are best for that mentioned rectifier purposes. Some developments have had took place in the meantime. SiC (Silicium Carbid) Schottky seeming to be suitable, despite a look on diagrams show dependency of forward and backward current in correlation to current and temperature, and that look on might not be totally overwhelming. And those diodes got package for heatsink mountig, already. Needing a kind of heatsink anyway.
As G8JNJ mentioned above, here a very remarkable experiene, what could happen, if snubber has not been calculated out properly. Approximately half a tenthousand (or more - I do not know) of powersupplies of very recommended popular manufacturer were called back due to possible risk of fire. The schottky diode probably in use was SR3100 and needed a resistor of 10 Ohms in series to a condensor of 3.3 nF. Mainly the resistor overheated. That snubber was no more necessary, when using centere tapped secondary and a double diode such as SF163A (common anode) or SF163C (for common catode) mounted on a small heatsink.
Comments
The spectrum display is much more useful in measuring RFI than the waterfall
I built a nice linear power supply.
Some parts were new, some old.
It died this morning. :-(
It will have to wait until the weekend.
Back to the Apple wall warts.
Well, finally had time to fix it. Turns out it was a fuse inline with the AC input. :-D
Sometimes the transformer inbuilt temperature fuse (120°C) burned. And the whole transformer had to be replaced. Prefer using tansformers with ambient temperature range TE40 and not TE60. Or not to use a transformer to 100% of its capability. Some more reserve seems to be prevent overheating especially on summertime.
The output is 13.8V 1.5A, and the DC output is 5V 2.5A.
The transformer does run warm, however its a comfortable temp.
The DC stage is one of these.
For the price, I couldn't buy the parts locally cheaper.
By the way: Most of the DC-stages do not strictly follow the datasheet recommendations for mounting rectifier diodes at least 9.5 mm lead length to prevent overheating. You may see the result of such mounting to tough to the printed board in changing the color to "charcoale like". That is why the rectifier in my very oldschool and a little bit oversized PSU is a category 25 Amps one and of course mounted on metal case for cooling.
And a transformer can reach 115 to 120° Centigrade inside the coil, quoting Category E. Even if it is a class T40 one. In such most cases a temperature fuse has been fitted inside the primary coil set for 120°C, which cannot be replaced so easily.
In my linear supplies, I had to swap conventional silicon rectifiers for Schottky types, as the 1.6 voltage drop and 3A + forward current was producing about 5 w of heat.
The downside of Schottky types, is that they have faster switching times, and as a result, they can produce additional RF interference, unless extra R & C snubbing components are added.
Regards,
Martin
As you know, not all kind of so called "Schottky"-diodes are best for that mentioned rectifier purposes. Some developments have had took place in the meantime. SiC (Silicium Carbid) Schottky seeming to be suitable, despite a look on diagrams show dependency of forward and backward current in correlation to current and temperature, and that look on might not be totally overwhelming. And those diodes got package for heatsink mountig, already. Needing a kind of heatsink anyway.
As G8JNJ mentioned above, here a very remarkable experiene, what could happen, if snubber has not been calculated out properly. Approximately half a tenthousand (or more - I do not know) of powersupplies of very recommended popular manufacturer were called back due to possible risk of fire. The schottky diode probably in use was SR3100 and needed a resistor of 10 Ohms in series to a condensor of 3.3 nF. Mainly the resistor overheated. That snubber was no more necessary, when using centere tapped secondary and a double diode such as SF163A (common anode) or SF163C (for common catode) mounted on a small heatsink.
SIC_SF163A_C_w/o_snubber.jpg first picture below
SIC_diode_snubber_.jpg