Periodical restarts after maximum power reached
Hello,
we build an controllerboard for one of our products where we included an power supply of about 95 W.
For this power supply we use an TOP 271 and an transformer from Kaschke (No 067.050). You'll
find our schematic of the power supply attached.
We have produced about 500 to 600 pcb and have actually some pcb where we have a little problem
but we can't find the reason. The power supply normaly see a motor load of about 40 W and a peak
power of about 70 W. The motor drives an drawer of an cabinet and the contoller will monitor the
current of the motor. If the motorcurrent exeeds an limit, the motor should stop. The maximum motor-
current is calculated, that the power consumption is about 90 W.
At the pcb with the problem we have the following effect:
- if the motor is running and no overload is detected, everything works fine
- if the motorcurrend exeeds the adjusted limit, the motor stop (as desired) but also the power
supply runs down to about 3 V and after about 1.5 second the power supply will restart. If the
output voltage reaches about 15 V, the power supply turns off again. These restarts repeats
about every 1.5 seconds.
- If the failure occurs and we disconnect the power supply from the mains for about 1 Minute,
the power supply will work as desired till the motorcurrent exeeds the limit again.
We checked all the components at the pcb and we also replace the TOP to an new one. But all this
didn't help. Can you give us an idea what can be the reason for our problem?
Thanks for your help in advandce
kind regards
N. Holscher
评论
For an overcurrent event it doesn't matter what the input voltage is. The controller must work at all mains voltage and freuency because we sell the product worlwide,
I made some more tests and my assumption is also the transformer. At the moment i havn't a new one on hand but i ordered some for testing.
Thanks for your help.
kind regards
N. Holscher
if you run to close to max power the feedback loop will lose control of Vout reg and you will get a restart - you need to design with more power headroom.
Just for reference, here is a backwards analysis of the TOP271 using your Kaschke transformer, done using PI expert. I would perhaps want to run just a little more in continuous mode at low line to bring down the peak drain current, but the design loks workable with that transformer. I also took the liberty of dialing down the current limit.
| Attachment | 大小 |
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| TOPSwitch-JX_Flyback_Forum_Q_013020.pdf (38.03 KB) | 38.03 KB |
Sorry for my late reply.
After replace the transformer to an new one, the power supply works well. Thanks for your help.
It would be useful to test the transformer that you replaced to see if it conforms to specifications. If a transformer is accidentally dropped before installation, the shock can crack the core and reduce the inductance, forcing the power supply to run at a higher peak current for a given output power.
One diagnostic approach would be to monitor the TOPSwitch drain current and the motor current with current probes during an overcurrent event. Does it matter what the input AC voltage is during an overcurrent event?
From you description, it appears that the TOPSwitch is hitting its primary current limit and going into autorestart. You might want to try swapping transformers between a good and bad unit to see if the problem follows the transformer.