Hi there, I have a simple DC circuit that is powering a 5V blower fan from a 5V 2.1A power bank. To increase the speed of the fan, I have used a Polulo 5V to 9V step up voltage regulator. The manufacturer of the fan had no concerns about the increase in voltage and the fan has worked well for months. Recently, I introduced a low voltage pulse width modulation controller that is rated for 18V 2A so that I can increase the fan speed. It works quite well, but at higher speeds, the fans starts pulsing= on/off rapidly. When I remove my step up voltage regulator and feed 9V into the circuit, there is no problem with the controller. When I remove the controller and just use the voltage regulator, it all works fine again. Any advice would be most helpful. Thanks
Hi Shiranth,
Welcome to the forum 
There are a few things that could cause that combination of parts not to work.
In a perfect world each device would receive a totally clean DC input with no variations or spikes in voltage. In reality switch mode devices will cause rapid fluctuations in load on the devices they are connected to.
If the transient response of the switchmode device is good enough the ripples and spikes aren’t enough to disrupt it from doing its job properly, if the response is not fast enough however the internal controller won’t be able to keep up and the device will either not regulate within the tolerances it is supposed to, or shut-down.
Hi Shiranh
Sounds like a current or lack of current problem. You could be a bit border line with primary power. That is 2.1A power bank. it is falling over with the extra load of the speed controller at high speeds, full load.
I would not believe that 2.1A. That might be so as a phone charger where the phone might request the extra current. I don’t know.
I have said it a dozen times but will ry again.
A power BANK is NOT a POWER SUPPLY. It is meant to recharge phones etc on the go. It is NOT intended as a 5V primary supply. I know there are lots that use them in this manner but is not the intended use.
My first suggestion would be to try a REAL 5V supply and see how that goes. You may be pleasantly surprised. Don’t be fooled by a 5V phone charger when it says 2.1A. They do communicate with the phone and only supply this current when requested.
Cheers Bob
Hi Trent
Thanks for your post and insight.
Kind regards
Shiranth
Hi Bob
Thank you for your analysis and recommendation. I will give it a try tonight.
Kind regards
Shiranth
