• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 686 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM3406HV efficiency

Marcello Simonetta
Prodigy 30 points
Other Parts Discussed in Thread: LM3406
I am investigating the efficiency of the driver LM3406HV.

I am working with a demo board (http://www.ti.com/lit/ug/snva407b/snva407b.pdf).

I am feeding 4 red LED with 0.356 A DC and 25 V. Each LED exhibits 2V voltage drop.

I calculated the driver efficiency dividing the overall LEDs strip voltage drop multiplied by the driver output current by the power supply voltage multiplied by the overall current that it supplies to the circuit, i.e. I divided the electrical power fed by the driver to the LEDs by the total electrical power supplied to the circuit.

By doing so I get a power efficiency equal to 40%.

It does not seem to agree nor with what is declaired in the datashet neither with the result of the simulation (http://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=44C17AF323A05425).

Since I can not get rid of this, I would like to ask you a couple of questions:

1) Is the mentioned efficiency really a power efficinecy?
2) Am I doing something conceptually wrong, like comparing something different from what is compared in the datasheet?
3) Is it possible that the evaluation board so strongly affects the efficiency measurement?

Just to resume:

- DRIVER: LM3406HV
- LEDs N.: 4
- LED COLOR: RED
- LED VOLTAGE DROP: 2 V
- LED RESISTANCE: 5.5 Ohm
- CURRENT: 0.356 A
- DUTY CYCLE: 100% (DC)
- SUPPLIED VOLTAGE: 25 V

Experimental result:

- P_OUT/P_IN = (V_OUT*I_OUT)/(V_IN*I_IN) = 0.4


Simulation result (http://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=44C17AF323A05425):

- Efficiency = 0.8

PWM and output voltage
 


This is, instead, the setup used

  • 0
    TI__Mastermind 25500 points

    40% efficiency is unlikely so it could be measurement setup, it's hard to tell from that picture. But follow these rules when measuring and you should get better results:

    1. Use an ammeter in series with the input supply. Never trust the reading on a power supply for input current.

    2. Measure the input voltage with a DMM directly at the input connectors of the PCB. Do not measure before the ammeter and again, do not trust the voltage reading on the supply.

    3. Use an ammeter in series with the LED load to measure LED current.

    4. Use a DMM to measure the voltage across the LED string including the ammeter as it is now part of the real output power.

    The LM3406 should be running close to the simulation results.