Contents
- 1Introducing the Linkworld Stability Power LPJ9-25 420 W
- 1.1Packaging and accessories
- 2Connectors & cabling
- 2.1Casing & cooling
- 3Input filtering
- 4Primary side
- 4.1+5 V stand-by rail
- 5Secondary side
- 5.1Build quality
- 6Load testing
- 6.1Loading +5 V SB
- 6.2Hold-up time
- 6.3Combined loading
- 6.4Combined loading ripple
- 6.5Crossloading, overloading
- 6.6Crossloading, overloading ripple
- 6.7Fan speed, temperatures and noise
- 7Conclusion and evaluation
- 7.1Thanks
- 7.2Discussion
Primary side
The primary side of the LPJ9-25 starts with input bridge rectifier made of four discrete diodes, 1N5406. These handle current of 3 A continuous at 75 °C or 200 A peak surge (for 8.3 ms) at 600 V. The voltage drop is 1.2 V at 3 A. Using these is OK here as the unit should not draw more than 3 amps at 200 V. The Fuhjyyu MK input capacitors seem quite small for their rating of 470 µF/200 V. But the real capacity is actually about 455 µF, or 227 µF effective. I would not have expected such a result especially when Fuhjyyu is such a garbage brand. But they are also for just 85 °C so who knows.
The switchers are D304X (12/24 A at 400 V, ICEO 50 μA at 400 V, tf 0.7 μs at IC 5 A, IB 1 A ) NPN transistors in TO-220 package. They are in the ordinary half-bridge configuration. As you can see their heatsink is not so tiny, as it is tall it has some reasonable area and it is also quite thick. But such size would be OK for low-efficiency modern two-transistor-forward topology, not this ancient half bridge with even lower efficiency. Their base capacitors are 2.2/50 from Fuhjyyu, more garbage.
There is different controller than we are used to: Weltrend WT7514L. This DIP-16 microchips combines PWM controller with secondary monitor. It is physically located on the secondary side but it can only monitor UVP/OVP, plus provide Power Good signal and monitor PWR On. That is all. The unit may be slightly more efficient because of it, on the other hand the main transformer is only EE-33 and it is very short. My estimate from this unit is maybe 330 W, it won’t do even close to 400 W ever.
+5 V stand-by rail
Surprisingly there is no garbage stand-by circuit in the LPJ9-25, but SanKen STR-6069H PWM IC with integrated transistor. The FET has resistance of 6 ohm and can provide 10 W continuously. The transformer is tiny though with 18mm core.
The Schottky diode for one-way rectification is SR340 (3/80 A at 30 V and 25 °C, drop of 0.6 V at 3 A) in DO-27 package. The filtering capacitors, or, more precisely, crapacitors, are garbage from Canicon, LOWESR series, 1000/10 before the coil and just 220/16 after it.
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