LMR62014 Simple Switcher

Colin R.

Hello,

First of all, thanks for taking the time to address my question/problem.

I'm using the LMR62014XMF Demo Board in my test setup to step-up 5v to 12.6v. The 12.6v load is a heater filament, which draws about 165mA in my configuration. When the heater is first turned on, it can draw as much as 225mA.

I have successfully been able to use this Demo Board board to power the heaters from 5v, but at the cost of considerably more current draw than powering them straight from 12.6v. 5v step-up to 12.6v is drawing ~400mA from the 5v supply.

Iq doesn't contribute that much and from looking at the data-sheet and the recommended web bench circuit, I don't think I should be pulling that much current.

What am I missing?

Thanks,

Colin

over 12 years ago

0 Denislav Petkov over 12 years ago

TI__Mastermind 19891 points

Hello Colin,

If I understood you correctly, you have 5V input with 12.6V output and 165mA steady load (225mA peak) and you are wondering why the current draw from the 5V power supply is around 400mA. This is expected.Here is why. Think about it in terms of input and output power. On the output you have 12.6V x 0.165A = 2.08W.

Assuming 100% efficiency from the boost converter, input power must equal output power. To provide this 2.08W of power from 5V input, you would need 2.08W / 5V = 0.416A of current from the 5V supply, again assuming 100% efficiency.

In reality, the conversion efficiency in this case is probably about 85%, which would mean about 490mA of input current from 5V.

Let me know if this makes sense or if I misunderstood your question.

Regards,

Denislav

0 Colin R. over 12 years ago in reply to Denislav Petkov

Intellectual 495 points

That's exactly what I needed. Thanks!

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LMR62014 Simple Switcher