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Part Number: LM3481
I have the LM3481SEPICEVAL board and I was doing some measurements and have a few questions/concerns.
1) The datasheet for the eval board has a graph on page 5 for "Efficiency at Vout = 12V. With an input of 12V it says it has almost 90% efficiency. When I powered it up, I have 12V in the input and it reads 12.11 volts on the output. I have an electronic load with a constant current set for 1Amp. But the input current from my power supply is 1.48Amps.Vin = 12V
Iin = 1.48Amps
Vout = 12.11V
Iout = 1Amp
Power in = 17.76W
Power out = 12.11W
Efficiency = 12.11/17.76 = 0.68 or 68% efficiency. I must be missing something. Could you help me out?
2) Eval board datasheet also says on page 1 that the 12V output option can have a input voltage range of 4.5-18V. With an output current of 0-1.25 Amps
Even with no load, and 4.5V on the input, it does not output 12V. It is not able to do it. The only way I can get it to output 12V is to start with a higher input, wait for it to get to 12V then lower it to 4.5V.
3) With a 5V input on power up, it is able to see the full 12V output. But this won't work with any load. I put a 100mA load on there and the voltage drops down to almost 2V.I need reliable operation at 5. I need to boost it to 12V with 600mA. Which will be an input current of about 2Amps. Also this is a battery application, so this low efficiency is no good.Please let me know your thoughts on this.
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In reply to Youhao Xi:
In reply to Matt Lang:
The Vin and Iin where measured by the digital display on the power supply. The positive and negative cables are about 1.5 Feet in length each. I will put a meter on the input terminals and see if I get anything different.
The issues with the 5V input are still there. I even tried a different power supply.
The efficiency issue was indeed the cable from my power supply. I swapped them out for some short and thick alligator clip jumpers and the efficiency is about 89%
Vin = 12.00 V
Iin = 1.22 A
Vout = 12.03 V
Iout = 1 A
Turns out it solves the low voltage issue as well!
Vin = 4.98V
Iin = 2.766 A
It still can not start up at 4.5V with a 1.2A load. But that is perfectly fine in my application.
Thank you for your help. Without your question about my measurement, I would not have swapped my cables. They are going in the trash.
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