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#AC-to-USB_Power_Modules_for_test_equipment

#ac-to-usb_power_modules_for_test_equipment

Arv Evans All Messages By This Member #245 Building small test equipment modules usually involves some sort of power system.? Batteries are a good start but for equipment that is only used on the workbench it seems that an AC supply is a better idea.? Problem is that many of our newer design homebrew test equipment does not require high voltages or high current, and does not need physically large mains based power supplies.? This situation prompted me to take a deeper look at AC-to-USB phone chargers and how they might be adapted for use in homebrew test equipment.? This AC mains to USB charger for cell phones was purchased at the local Dollar Store for US$1.07,? including sales tax.? One end has plug-in prongs for a mains outlet.? The opposite end has a standard USB jack for the cell phone charging cord. Specification printed on the case indicate output is 5.0V at up to 1A.? That should be adequate for small homebrew test equipment needs.??? When I plugged this charger into AC mains and measured the 5V output with no load it was exactly 5.00 volts. After hammering around the end to break the glue loose I found that the AC prongs are only spring-contacted to actual PCB input.? Assumption is that this arrangement allows other country style plug prongs to be installed.? Top view of the charger PCB.? USB jack is on the left and AC input is on the right. PCB bottom view shows full-wave rectifier at top-left corner.? A CP5212 control IC is below and to the right of that.? Another rectifier is in the lower right corner.? I could not find a schematic for this particular unit but most of what I did find on-line looks approximately like the design shown above.? This appears to be a switching circuit with feedback control from the right side of the circuit.? Typical specification on various sites indicate that isolation between AC input side and DC output side is in the area of 2000 volts.? Next effort will be to measure and document the amount of AC and DC leakage between AC side and DC side.? Then I can start working on using one of these tiny power supplies inside a piece of homebrew test equipment. This picture shows a work-in-progress AD9850 DDS VFO / Signal Generator, with the AC-to-USB power unit sitting bottom-center in the clear plastic chassis.? This power unit will have to supply 5V for the LCD & backlight, Arduino Pro-Mini, and the DDS board.? More info will be provided as work progresses.? Arv _._
ajparent1/kb1gmx #246 Arv, as an actve ham on MW, HF and VHF? II can say those things and may other not USB are Banned in teh hose till verified RF non interfering.? Can't control the neighbors but I try to not do it to myself.? For bench use USB power I have a box with six 7805 analog regulators, some with USB connectors, some power-pole, and binding posts.? Each does an amp easy. and the transformer, rectifier and filter (times two) feeds each of three so?I can have two floating sources without common ground. Electrical noise at the bench can be an annoying. Allison
Arv Evans All Messages By This Member #248 Allison Agreed about noise from all sort of electronics.? We live in a world full of it, some of our own making.? I broke open the USB charger module (1) to see what was in it, and (2) so others would not have to do the same.? Now that I know what is inside and how it works I can simply purchase those little 5V chargers and use them much like we have done with wall-warts for many years.? A USB cable from the dollar store and small test equipment is easily and conveniently powered.? These USB chargers seem to operate at around 50 KHz (the pulse rate varies depending on current load), but do not radiate strongly.? Opening one up and adding 0.1 mfd across the 5V output quieted it down to almost nothing being radiated.? The 5V output is unexpectedly stable with varying load, at least on these units from a local Dollar Store.? Since Li-ion cells act like big capacitors I tried using one of these 5V chargers to power a Pixie based telemetry system that has Li-ion backup power.? Result is gratifying, no switching transients, and It works just like it does when running on Li-ions charged by a pair of small solar cells.? The telemetry system runs on Pixies at 160 to 190 KHz but no noticeable interference from the 5V charger.? Of course the 5V output is excellent for Arduino Nano? or Arduino Pro-mini based test equipment.? Arv _._ toggle quoted message Show quoted text On Wed, Sep 19, 2018 at 8:28 PM ajparent1/kb1gmx <kb1gmx@...> wrote: Arv, as an actve ham on MW, HF and VHF? II can say those things and may other not USB are Banned in teh hose till verified RF non interfering.? Can't control the neighbors but I try to not do it to myself.? For bench use USB power I have a box with six 7805 analog regulators, some with USB connectors, some power-pole, and binding posts.? Each does an amp easy. and the transformer, rectifier and filter (times two) feeds each of three so?I can have two floating sources without common ground. Electrical noise at the bench can be an annoying. Allison

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