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USB Power Adaptor USB Power Adaptor Project by Nicholas Vinen This simple and cheap PCB provides an easy way to add a USB socket to a 5V DC powered device. It accepts a Type-C or mini/micro Type-B socket and provides optional reverse power flow/reverse polarity protection and LED power indication. I wanted to add a USB socket to my RGB LED Clock (the article just before this one) for power, but I couldn’t fit one near the PCB edge as it is totally occupied with LEDs. Horizontal USB connectors won’t work if placed in the middle of the board. Tim Blythman suggested I mount the socket on a small, separate PCB and suggested that it could have other uses. Hence this project. To make the board as flexible as possible, I have placed four different USB socket footprints on this tiny 12.7 × 26.5mm board. You can attach the very common SMD mini Type-B socket, one of two readily available micro Type-B sockets or one of two fairly standard Type-C sockets. Use whichever suits your needs. The resulting 5V DC is available on a set of four pads in the middle of the PCB. These allow a two-way pin header to be fitted in eight orientation and polarity combinations. This is especially handy if you’re mounting this PCB to another one via a pin header, as you can choose which direction the USB socket will face (north, south, east or west) regardless of the header polarity. You don’t have to attach this board to another one; you can solder a pair of wires, or a header and use jumper wires. In fact, it’d be a convenient way to feed 5V to a breadboard from a computer or USB charger. If using a micro Type-B socket, you can choose one with or without through-hole mounting pins; the PCB will accept either. Having said that, we’ve specified the type with pins in the parts list as it is easier to mount and more secure once soldered. Similarly, for USB Type-C, you can use a six-pin power-only socket or a 12-pin power-plus-data socket (the data pins are not connected). The circuit is very simple, as shown Practical Electronics | June | 2026 in Fig.1. You can use a 1A or 3A schottky diode for D1, or a 0W resistor (shown as a dashed link shorting D1 out). USB connectors are polarised, so in theory, you don’t need D1 for reverse-polarity protection. Its main purpose is to prevent power from feeding back into the USB power source if the target board is separately powered. So whether you fit D1 or a 0W resistor will depend on whether that is possible in your application. If you’re wiring up the USB cable yourself, or if its forward voltage is irrelevant (eg, the target board immediately reduces it to 3.3V with a low-dropout regulator), you may still want to fit D1 for reverse polarity protection. You don’t need to fit the LED and its series resistor if you don’t need a power-on indicator. As for the other two resistors, they are only required if you are fitting a USB Type-C socket, to signal to the power source to supply 5V. For Type-B sockets, you can just leave them off. Construction Depending on which socket you are using, follow the relevant overlay diagram: Fig.2(a) for USB-C power only, Fig.2(b) for USB-C power and data, Fig.2(c) for mini-B or Fig.2(d) for micro-B. All other required or optional components are shown fitted. If you don’t need LED1, leave it and the resistor on the opposite side of the board off. If you don’t need D1, replace it with the 0W resistor. Start by fitting the USB socket. It will make soldering easier if you spread a thin layer of flux paste over all the pads for your particular socket before you place it on the board. Only the USB-C power-only socket lacks locating posts; the others should snap into place and you can then tack Fig.1: the four possible USB sockets are wired in parallel and it has provision for the two 5.1kW pull-down resistors needed for a Type-C socket to receive 5V. D1 prevents power flowing back into the USB socket, while LED1 provides power-on indication. 25 Constructional Project From left-toright: the Mini USB, USB-C & Micro USB versions. one pin and check that all the pins are aligned. For the USB-C poweronly socket, you’ll have to position it by eye initially. Remelt that initial solder joint and nudge it until its six relatively large leads are over their pads. Add a bit more flux paste over the remaining leads and then solder them. Once those leads have been soldered, you can solder the mechanical mounting pins or tabs. The USB-C power+ data socket is designed for 1mm-thick PCBs, which is why we’ve specified this board that way. Otherwise, its mounting tabs won’t go all the way through the board. You may need to turn your iron up a bit while soldering the mechanical mounting tabs as the USB socket case will draw heat away from them. Turn it back down when you’ve finished. Most sockets have pins that are closely spaced, so it’s likely you will have some bridges between them now. If you do, add some more flux paste and then press solder-wicking braid down on them with the tip of your soldering iron. Wait for the solder to flow, then slide the braid away from the pins. It should remove the excess solder and leave behind nice-­ looking joints. Now is a good time to clean off any flux residue, either with a specialised flux remover, isopropyl alcohol or methylated spirits. Then inspect the board under magnification and good light. Verify that all the USB socket solder joints are good. If not, add some more flux paste and rework them, either by adding more solder or removing excess solder with the wicking braid. If you fitted either of the USB-C sockets, you’ll now need to install the two side-by-side 5.1kW resistors. Without them, you may not get power. Now move on to diode D1. If fit26 ting it, make sure it’s orientated as shown. Otherwise, replace it with the 0W resistor, so there is a path for current to flow from the USB socket to CON3/CON4. If you want the power indicator LED, solder it now. It is also polarised. The best way to do this is to use a DMM set on diode test mode to probe the ends of the LED until it lights up. The black probe will be touching the cathode when it does, so that is the side you solder to the pad marked K on the PCB. If fitting this LED, don’t forget its series resistor; otherwise, it can be left off. That just leaves pin header CON3/ CON4. There are two + symbols shown in two corners; the other corner pads are ground (ie, negative). There are four possible positions that you can solder a two-pin header here, on either side of the board. Whichever one you choose, one of its pins will go to a pad marked with a + symbol. So choose the location that gives your required polarity (if it matters). Fig.2: follow the appropriate overlay diagram for the socket you are using. All show D1 and LED1 fitted but you can replace the former with a 0# resistor or wire link, or omit the latter, if you want. The presence and location of CON3/ CON4 will also depend on your requirements. Practical Electronics | June | 2026 USB Power Adaptor Parts List – USB Power Adaptor 1 1mm-thick black double-sided PCB coded 18101251, 12.7 × 26.5mm 2 5.1kW M3216/1206 SMD resistors (only required for Type-C USB sockets) 1 0W M3216/1206 SMD resistor/link Pick one of these sockets: 1 SMD Type-C USB power-only socket (CON1) [GCT USB4135 or equivalent] 1 SMD Type-C USB 2.0 socket (CON2) [GCT USB4105 or equivalent] 1 SMD mini Type-B socket (CON5) [Molex 0675031020 or equivalent] 1 SMD micro Type-B socket (CON6) [GCT USB3080-30-01-A or equivalent] Optional parts 1 2-pin header (CON3/CON4) 1 SS14 (1A), SS34 (3A) or equivalent schottky diode, DO-214AC (D1) 1 M3216/1206/SMA SMD LED plus 5.1kW M3216/1206 SMD resistor (LED1) Fig.2 shows four of the possible locations for that header. Alternatively, simply solder two wires to these pads, one to a pad marked + and the other to an unmarked (ground) pad. The accompanying photo shows the USB Power Adaptor fitted with a Type-C socket mounted on our RGB LED Analog Clock (presented earlier in this issue) using CON3. That position was chosen as it matched the polarity of the power header on the Clock PCB. Testing Plug your assembled board into a USB power supply and use a DVM to check the output at CON3/CON4. If you connect the red probe to a + pad and the black probe to one of the other two, you should get a reading of about +5V, or +4.7V if you fitted D1 rather than a 0W resistor or wire link. If you don’t get a voltage reading, check that your supply is on and that diode D1 is orientated correctly or linked out. If you have fitted LED1, it should light up. If you can measure voltage but it isn’t on, it may be backwards or have a bad solder joint. Also check the series resistor’s solder joints. All that’s left is to wire this up or solder it to your target board, apply power and check that it works. Make sure you get the output connection polarity right! Note that the final version of the PCB fixes a couple of minor problems with the prototype ones shown in the photos. It’s a little bit shorter so the plugs can reach the sockets more easily, the USB-C 2.0 connector has four solder pads to secure the shell The power + data version of the USB-C Power Adaptor. We didn’t have a 0W resistor on hand so used a piece of wire instead. rather than two, and the micro-B footprint was improved to make it easier to solder and more secure. Using it Besides the RGB LED Analog Clock, some of our recent projects that this board could potentially be used with include: • Coin Cell Emulator (November 2024) • TQFP Programming Adaptors (October 2024) • Dual-Channel Breadboard PSU (December 2023) In some cases, the connection would be made via the ICSP (in-­ circuit serial programming) header, which has VDD and GND pins next to each other, suitable for connection PE to CON3/CON4 on this board. One of the USB-C versions of the Power Adaptor attached to our new RGB LED Clock. USB Power Adaptor Kit (SC7433, ~£5 + P&P) from Siilcon Chip (sent from Australia) Includes everything in the parts list; choice of one USB socket: 1. USB-C power only 2. USB-C power+data 3. mini Type-B 4. micro Type-B. https://siliconchip.au/ Shop/20/7433 Practical Electronics | June | 2026 27