5V Stabilised Supply for USB Hub

Intro: 5V Stabilised Supply for USB Hub

This is a stabilised supply intended to be used with a bus powered USB hub in order to deliver a stabilised + 5 volt supply to the devices connected to it.

Due to the resistance of the connecting cable, and the resistances introduced for current sensing for overcurrent protection, the voltage at the hub can be anywhere between +4.5 V(loaded) and +5.5 V. This circuit will deliver a stabilized +5 V in both the cases, ie, it is a buck/boost design, using the TPS63000 switch mode regulator chip manufactured by Texas Instruments.

It can deliver +5 V at 500 mA from input voltages as low as 2 Volts so a rechargeable battery and its (USB powered) charger can be added to make this into a USB UPS for the USB hub.

STEP 1: Preparing the Circuit Board

I decided to do a ground plane based layout. The chip has ten solder pads and a thermal pad to be soldered, and this was a different method to try with these types of leadless packages.

A scrap of single sided paper phenolic copper clad was cut to size and the outline of the chip drawn on its unclad side.

Then with a small screwdriver sharpened into a chisel, material was removed, making a niche for the chip to sit in.

STEP 2: Gluing the Chip In

The chip is then glued into the space so dug out.

This is, strictly speaking, unnecessary but I liked the feel of gouging out the PCB material, and it was fun to add some three dimentionality to the circuit.

STEP 3: The Ground Connections

Now that the chip is firmly inside the board, it is time to plan on connecting the ground leads.

Since the other side is an unbroken ground plane, this is easy: just drill holes and solder a wire.

STEP 4: Drilling Holes

Looking at the schematic, three pads of the ic have to be connected to ground. So three holes are drilled at the appropriate places.

STEP 5: Soldering Ground Leads

Three wires are first soldered at the copper side, then bent over the ic, cut to size and soldered to the pads and the central thermal pad.

STEP 6: Preparing the Inductor

A moulded 2.2 microhenry inductor was heated in a flame, its encapsulation removed, and the turns counted (there were 12). It was then rewound using fresh wire over the bare ferrite core.

I decided to dig the inductor in (for protection) so its shape has been marked on the board.

All this is, of course, really unnecessary.

STEP 7: The Inductor

This is another wiew of the prepared inductor.

STEP 8: The Hole for the Inductor

I have carved out a nice hole for the inductor to sit in.

STEP 9: The Inductor in Place

This is how the inductor looks when fitted into place.

STEP 10: The Input Filter

The power to the Analogue section of the chip has to be filtered by a series resistor and capacitor to ground. These components have been fitted in position. Copper foil from another scrapped board was lifted, cut into shape and stuck in place to connect the components.

This makes the layout into a double sided board - sort of.

STEP 11: The Output Connector and Capacitor

A pair of pins from an old motherboard was pressed into service for the 5 volt regulated output. The 10 microfarad tantalum surface mount capacitor was soldered across it.

All the resistors and capacitors were rescued from junked hard disks.

STEP 12: The Feedback Resistors

The feedback input of the TPS63000 has to be fed a voltage of 500 millivolts derived from the output. With a 5 volt nominal output, this means a division ratio of ten or two resistors, one nine times the other.

Ransacking all my surface mount boards (in my junkbox) threw up the pair you see in the figure. They were connected together as shown, then connected to a battery and my trusty multimeter verified that the division ratio was indeed ten.

If you are confused, on the left is a 523K resistor ie, 5, 2 and 3 followed by three zeroes, in ohms. On the right is a 4.7 Megohm resistor, ie, 4 and 7 followed by five zeroes, in ohms.

47 divided by nine is approximately 5.23.

STEP 13: The Resistors in Place

The resistors have been soldered into place, though due to limitations of space they had to be stuck upright to the output capacitor.

The whole thing is held together with liberal applications of superglue - otherwise the solder joints might come apart each time the board fell off the table.

Now all that remains is for the inductor and input capacitor.

STEP 14: Niche for the Capacitor, Too.

I decided to cut into the board for the input capacitor, and use solder pins for the input connection.

The outline of the capacitor has been marked on the board for cutting out.

STEP 15: Capacitor Trench

The capacitor trench is ready for use.

STEP 16: The Finished Board

The board is finished, all components are in position.

It was tested.

First with two rather weak penlight cells - I did not trust my handiwork that much - and the output was 5.04 volts

Elated with the success, I tried it with three good cells - an input voltage of 4.5 volts - and the output was still 5.04 volts

Then I tried the voltage from the USB port of my computer - around 5 volts, though liable to jump around on the lower two digits - and still the output held steady at the same old 5.04 volts.

So it would seem that this thing works, at least during preliminary tests.

According to the datasheet it will start at 1.9 volts and accept a maximum of 5.5 volts, and hold its output voltage steady.

It is a buck - boost converter, which means it can accept input voltages above and below its output voltage, switching between modes automatically in order to keep the voltage steady.

It could be fed from a rechargeable cell in order to maintain the USB supply voltage even when the cable is disconnected from the computer - if that is any good.

Comments

[siytek]

Thanks for posting. I was wondering why you might have changed the value of C1 to 22uF? The reference schematic in the TPS63000 datasheet shows 10uF, which is the maximum allowable decoupling capacitance between Vbus (or Vin in your schematic) and GND. My understanding is if your capacitance is too high, the inrush current which initially charges the decoupling capacitor will exceed the maximum allowable 100mA. This will occur as soon as you plug in, ie before the device has authorised the use of up to 500mA. It probably doesn't matter too much for a DIY project, its just im looking to stay within the USB spec. I was just curious as to whether you are getting better results with 22uF?

[GENERALCHAOS]

i have a 7 port chip gate from Ti would it work for all 7 port or 4 only ?

[Esmagamus]

I liked the design of the circuit, but the final result... You should try ExpressPCB. It's really easy to use and you can design every circuit you want easily and make pro-looking boards with the toner method. Keep up the effort.

[raykholo]

um, what does this do? it does look cool and high tech though but i dont get any of it

[neelandan]

It is intended to be a "supply booster" compensating for the inevitable voltage drop along a long USB cable.

[raykholo]

much better thanks

[Xellers]

Although this project is great, I must admit that the pictures arn't great and it looks as if you did a somewhat messy job with the wiring.

[neelandan]

Yes, if I had to do it again I would use a regular printed circuit and take better pictures of the result.

[Xellers]

I understand...

[PointyOintment]

Two questions: 1. What is the red wire for around the inductor? 2. Why did you unwind and rewind the inductor?

[neelandan]

That red wire goes twelve times round the black core. It IS the inductor. The encapsulated inductor was too large (in relation to the chip) so I was trying to make it smaller by removing the encapsulation. Removing it damaged the winding, so I had no alternative but to rewind it.

[dwarven]

the schematic diagram was preety ..the part component was complex

[neelandan]

The circuit diagram has been copied from the data sheet by Texas Instruments. The component values were added by an image editor (MS paint). Now that's funny - M/s TI have not yet set up a high squeal about me "stealing" their circuit diagram. Perhaps it might be that their ic will not work if I get too creative with the circuitry around it. What I can get creative with is the way those components can be connected, and I am exploring new ways of prototyping circuits. You do not have to be intimidated by the unorthodox means I have adopted. Texas Instruments, again, have guidelines for PCBs for their ICs and they frequently include layouts in their datasheets. Reading those datasheets will help you decide on a suitable method of construction.

[LasVegas]

stabilize |ˈstābəˌlīz| verb make or become stable : [ intrans. ] his condition appears to have stabilized | [ trans. ] an emergency program designed to stabilize the economy. • [ trans. ] cause (an object or structure) to be unlikely to overturn : the craft was stabilized by throwing out the remaining ballast. DERIVATIVES stabilization |ˌstābəliˈzā sh ən| noun :)

[BruceR]

Britain and America, two nations separated by a common language.

[rotor]

I am 200% in love with these destroyed-looking devices. Please do an instructable on the saltwater etching process you used in your other usb hub.