Powering led monitor with battery pack

Thread Starter

chubbspet

Joined Jul 26, 2018
17
Hey guys

I am trying to power a 19inch dell monitor by bypassing the psp. I use lithium ion batteries via a step up voltage converter (aka booster regulater) module. I have determined that the main driver board receives 5v from the supply. So i set the output of the regulator to 5v, then nothing happens. However, if i briefly crank it up to about 9v, the monitor actually swithes on, then i can bring the voltage back down to about 7v and it works. Can someone shed some light why this might be and how i could make it work without boosting the voltage(current) for startup?

Btw, the led gets it power completely seperately...

Thanks for any advice!
 

ebp

Joined Feb 8, 2018
2,332
Unless the monitor uses an external power supply that provides a regulated DC voltage, all of the power supplies required will be produced by switch mode power conversion. There may be need for some small current for something provided by one or more linear regulators. 2 or 3 different voltages may be required.

Switch mode power converters (hereafter "switchers") invariably have distinct start-up and shut-down voltage thresholds where the former is always higher than the latter. This is frequently necessary for a variety of reasons. One reason is that the control circuit for the switcher requires power which may originally come from the input source in an inefficient manner, but once the switcher is up and running, it provides power to itself (also from the input source) in a much more efficient manner. Between startup and "running" a capacitor may have to keep the circuit going, so it is necessary to prevent startup until the cap is charged enough to be sure it can keep it going until it self-sustains.

Without knowing the details of the circuity it is hard to know the "best" method of dealing with this. If it needs 9 V to start up, chances are that there is no reason not to just let it run at 9 V. The input power will likely be very close to the same at 9 V as it is a 7 V. The efficiency of the boost converter with 9 V output and x watts may be the same, better or worse than with 7 V output and x watts.
 

Thread Starter

chubbspet

Joined Jul 26, 2018
17
Thanks for the explanation EBP. I will digest that info and see if I can maybe test the output on a scope. So am I correct in saying that the initaial boost is an extra supply of current rather than an actuall boost in the output voltage?
 
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