Hi forum,
I saw that people was reporting really high temperatures on the power supply, I checked the diodes (D5) and I got 70C (with 26C ambient, after ~30mins without the back part of the enclosure)* , not as much as others have reported (>95C), but still too much.
So decided to change all the diodes on the secondary:
D4 SS310 with
STPS6M100SF | slighty better diode.
D5 SS310 with
FERD40H100SFP | way better diode.
D6 SS310 with SB1045L | way better diode.
then I install some small heatsinks but they didn't made much of a difference.
so I installed bigger ones.
Finally got this temperatures:
D4 47C*
D5-inner 48C*
D5-outter 47C*
FERD40H100SFP-top 44C*
FERD40H100SFP-heatsink 46C
U1-heatsink 60C
U4-heatsink 62C
at 24C ambient.
*I Just put the thermocouple on top of the plastic package, *probably* not the best way to do it.
Hantek had to used either a fan o better parts.
The DC-DC converter seems hopeless, it's just not good, I mean it uses transistors for the switching... I thinking into replace it with something that uses mosfets, synchronous preferable, with this change U1 may reduce it's temperature a bit.
BTW does anyone knows what type the connector is on the output?
Also, for people that want to change D5, if you're on a 220VAC country, you *probably* should use a 100V part, 60V diode seems risky to use... I always saw that on SMPS they always use high voltage diodes on the secondary and had the doubt if was really needed or another victim of "we are using the cheapest part that'll do the job" thing, so looking for an answer I found an app note from Infineon with all the equations involved on SMPS design, on page 21 (attached) the mention the equation related to the diode voltage:
Vdiode=Vout+(DCpeak*(Ns/Np))
Ns/Np it's the transformer turn-ratio, which we don't know, but the U1 datasheet mentions the ratio 12/90 that *probably* hantek used on the PS, so for the voltages I got the diode ratings:
110/120/127 VAC using infineon turn-ratio example: 38.06V
110/120/127 VAC using DK124 turn-ratio example: 34.34V
220 VAC using infineon turn-ratio example: 60.07V
220 VAC using DK124 turn-ratio example: 53.63V
In countries were we have 110/120/127 VAC we *probably* can use a 60V part I use the 100V part mostly because was the only FERD on full plastic package when made the order.
BTW, on the U1 datasheet they recommend (for a 12V out) a 300V part