I'm trying to trouble shoot an existing power supply. There are four separate rails feeding from a single transformer on a single PCB. Voltages range from 7 to 19. All four rails use an LM5576 buck regulator.
One of the rails puts out it's expected 19V but heats up very rapidly. (No load) Using a laser thermometer to record the temperature, I see it rise above 100 degrees (F) in a matter of seconds. (the other three remain at room temperature.)
Cutting the supply relieves this and LM5576 will immediately begin returning to room temperature.
The interesting thing, and this is where my question comes from, the output inductor will continue to rapidly rise in temperature for a short time even after power is cut to the circuit.
My basic question is, what might be going on here? Why would the inductor continue to get hotter even after the power is cut? Can I use this information to decipher what is wrong with the circuit?
My limited knowledge guess is that the energy needed to have the inductor continue to heat up is coming from the supply capacitor. Where else could it come from?
But why would the inductor continue to heat up while the regulator it's connected to is already cooling?
Thanks for any insight on this.
One of the rails puts out it's expected 19V but heats up very rapidly. (No load) Using a laser thermometer to record the temperature, I see it rise above 100 degrees (F) in a matter of seconds. (the other three remain at room temperature.)
Cutting the supply relieves this and LM5576 will immediately begin returning to room temperature.
The interesting thing, and this is where my question comes from, the output inductor will continue to rapidly rise in temperature for a short time even after power is cut to the circuit.
My basic question is, what might be going on here? Why would the inductor continue to get hotter even after the power is cut? Can I use this information to decipher what is wrong with the circuit?
My limited knowledge guess is that the energy needed to have the inductor continue to heat up is coming from the supply capacitor. Where else could it come from?
But why would the inductor continue to heat up while the regulator it's connected to is already cooling?
Thanks for any insight on this.
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I suspect there is some heat stored inside the core emanating slowly after power down. On the other hand I am convinced that power stored inside caps is way too small to heat up the inductor significantly.
The more I thought about it, the more I came to the same conclusions. No way a 470uF cap has the energy to heat even a small coil. And just like engine coolant, the temp tends to rise a bit immediately after turning off the car, on account of it's no longer circulating through the radiator and the engine block is still really hot.
Now I just need to figure out why it's heating up in the first place.
Thanks!
Now I just need to figure out why it's heating up in the first place.
Thanks!
