There should be 5V DC input to DC output voltage difference for better operation. Problem is not to lose voltage over Rf but mainly across M1. Measure DC at C1 to determine DC in.
If DCin-DCout is high, it adds 0.8W per 1V on M1 in your case, so better drop it at the transformer. If low, adjust the transformer choice again.
Iload 0.8A and -for example- at this load spare current on shunt device is 0.1A, so M1 overall current is 900mA.
R1: 600/900 = 0.6666R 0.56R .. 0.62R minimum 3-5W.
5V (DC_out - DC_in) voltage on M1 and 0.9A produces 4.5W dissipation.
Shunt dissipation is 5V*0.1A= 0.5W.
Overall dissipation on the heatsink is 5W.
This heatsink IMHO is insufficient (poorly designed, not anodized, the lamellas are horizontals, no enough air flow -convection-).
It has about 5-8 K/W thermal resistance(without forced convection), so 5W produces 25-40 Celsius grade OVER the base -ambient- temperature (25 C ), so heatsink temperature would reach even 50-65C grade.
R1: 600/900 = 0.6666R 0.56R .. 0.62R minimum 3-5W.
5V (DC_out - DC_in) voltage on M1 and 0.9A produces 4.5W dissipation.
Shunt dissipation is 5V*0.1A= 0.5W.
Overall dissipation on the heatsink is 5W.
This heatsink IMHO is insufficient (poorly designed, not anodized, the lamellas are horizontals, no enough air flow -convection-).
It has about 5-8 K/W thermal resistance(without forced convection), so 5W produces 25-40 Celsius grade OVER the base -ambient- temperature (25 C ), so heatsink temperature would reach even 50-65C grade.
Yep those are correct calcs and cautions. On necessary assumptions nonetheless. He didn't give us full data yet.
Hi @Salas ,
I am newbie, I will use this ubib (photos) to power a new Dac with 5v and 500ma Power requirements.
Is it compatible??
Thanks
Antônio
I am newbie, I will use this ubib (photos) to power a new Dac with 5v and 500ma Power requirements.
Is it compatible??
Thanks
Antônio
It is compatible if the setting resistor value and the Mosfets sinking are correct for the job. 1 Ohm will run about 600mA for instance. 3.3 Ohm I see is good just for 180mA. Everything is in the PDF guide on first post. Read it carefully.
Thank you @Salas,
I am newbie. So I have to replace de green resistor for 1ohm.
Am I right?
Thanks again
Antônio
I am newbie. So I have to replace de green resistor for 1ohm.
Am I right?
Thanks again
Antônio
Last edited:
Fins should be positioned sidewards, verticaly placed to ensure airflow. You surely need to do so especially so for the 600mA.
Ed
Hi,
I attached one more heatsink. I think now would be ok. I can add a fan in necessary.
Any help is welcome.
Thanks
I attached one more heatsink. I think now would be ok. I can add a fan in necessary.
Any help is welcome.
Thanks
I think only the bigger heatsink will do already.. But the way it is posisioned now(fins downward) will close off the airflow. So no cooling down of the sink.
If you bring it in standing position (vertical fins), small side down a few centimeters from from the groundplane, you will have flow. Just try it and mesure the temp on the metal, just above the fets. I think it will reach 45/50 Celcius. Will be oke.
Last edited:
Thanks.
I will try and measure the temperature.
I will get back
Thanks again
Antônio
Hello,
I tested a 8 port switch as a dummy load to test the 600ma ubib. The temperature of the heatsink is cool.
I do not think the 8 port switch consumes that much.
Can you recommend a dummy load unit for this test. I have hear about auto lamps.
Any help is welcome.
Thanks
Antônio
I tested a 8 port switch as a dummy load to test the 600ma ubib. The temperature of the heatsink is cool.
I do not think the 8 port switch consumes that much.
Can you recommend a dummy load unit for this test. I have hear about auto lamps.
Any help is welcome.
Thanks
Antônio
In shunt regulator you want the load to consume near to the constant current setting. The less the load consumes the difference is burned off in the shunt itself. Just 100mA diff would be thermally optimum. Dummy load value is easy, calculate a power resistor by Ohm's law. Rdum=Vout/ILoad.
Read the instructions.
Read the instructions.
Hi @Salas
So to test the heatsink capability for 600ma load I will need a 8ohms resistor as a dummy load?
Resistor of how many watts?
Thanks
Antônio
So to test the heatsink capability for 600ma load I will need a 8ohms resistor as a dummy load?
Resistor of how many watts?
Thanks
Antônio
Last edited:
8-10 Ohm heavy power resistor will do to simulate 400-500mA load at 5V. You always leave a spare for the shunt to burn in itself.