HOME     STORE     BLOG     SCHEMATICS     TUTORIALS     DOWNLOADS     CONTACT

Using a single 7812 IC voltage regulator and multiple outboard pass transistors, this power supply can deliver output load currents of up to 30 amps. This circuit is a fine example of Kirchoff's current and voltage laws. To summarise, the sum of the currents entering a junction, must equal the current leaving the junction, and the voltages around a loop must equal zero. For example, in the diagram above, the input voltage is 24 volts.

As you might expect, I have several power supplies that have more than enough capacity to power my new KN-Q7 transceiver. However, my largest power supply is normally connected to my main 100W PEP SSB transceiver. It is capable of 20A and more, but it’s not easy to connect other equipment to it. I also have a smaller 8A power supply, but I use this to power some other VHF and UHF transceivers. In short, I wanted a simple power supply which I could dedicate to this new transceiver.

12V dual power supply has symmetrical voltage output +12V and -12V with limited current to 100mA. It has been built to power three OPA627 opamps of Audio DAC I am building with PCM1792 & PCM1794 chips. Circuit has on the primary side only fuse. I couldn't find smaller than 50mA. We can connect power cord directly to the X1 connector or via power switch on the chassis. On the secondary side of transformer are connected two fuses 100mA and after them is bridge rectifier. For filtering of rectified voltage there are C1 and C2. Next are positive and negative voltage regulators 78L12 and 79L12 with decoupling capacitors C3 to C6 close to regulators. Next are small filter capacitors and also signaling LEDs connected via resistors. Output voltages are connected to 3 pin connector. For signaling of presence of voltage is enough only one LED. We can also use 2 pin connectors for LED connecting.

This is high current 12V power supply. Power supply uses LM7812 IC and can deliver up to 30A to the load by the help of the TIP2955 pass transistors. Each transistor can handle up to 5A and six of them result an total output current of 30A. You can increase or reduce the number of TIP2955s to get higher or lower current outputs. In this design the IC delivers about 800mA. A 1 amp fuse is connected after the LM7812 to protect the IC against high current transients. The transistors and the 12V regulator IC both require adequate heatsinking. When the load current is high, the power dissipation of each transistor also increases so excess heat may cause the transistors to fail. Then you will need a very large heatsink or fan cooling. 100Ω resistors are used for stability and prevent current swamping as the tolerances of dc current gain will be different for each transistor. The bridge rectifier diodes must be capable of passing at least 100 amps.

As is commonly the case, this supply was born of necessity. There is absolutely nothing special about the circuit, except that as shown, it is quite capable of up to 20 Amps intermittently or 10A continuous. Simply use a bigger transformer, bridge rectifier and more capacitors and output transistors to get more current. The basic circuit should be good for up to 100A or so, using a 5A TO3 regulator IC, but it can obviously be increased further (if you really do need a 500A supply!).

Linear power supplies for communication equipment are among the most commonly built electronic projects. Almost every technically inclined radio amateur has built at least one. But unfortunately most designs, even those published in well respected books, are unnecessarily complicated, or have some specific drawbacks. The design presented here is a little bit unusual in its arrangement, but offers some advantages over the usual designs that I will explain in the following paragraphs.

Amateur radio has been somewhat slow to accept switching power supplies for powering communication equipment. This is a pity, because "switchers", as they are often called, offer very attractive features, like small size, low weight, high efficiency, and low heating. True, they are generally more complicated than linear power supplies, but this is easily compensated by the fact that they can be built for a lower cost. Some early switchers produced an objectionable amount of RF noise, bringing the whole switching technology into bad reputation. But by proper design techniques and careful EMI filtering it is possible to build very quiet switchers. In this article I will describe the construction of a switching power supply designed to power a complete ham station, with several radios and accessories. This power supply produces 13.8V regulated to better than 1%, at a continuous load current of up to 40A. It has current limiting, making it appropriate for direct connection to a 12V backup battery. If the current limit potentiometer is turned up, the power supply can deliver up to 60A on an intermittent basis, while maintaining regulation. No minimum load is required. The ripple on the output is about 20mV, and the efficiency is 88%. A cooling fan operates depending on the average current drawn, and a tricolor LED tells you if the voltage is normal, too high or too low. It produces no detectable RF noise at any frequency higher than the main switching frequency of 50kHz (I checked it with an antenna wire looped around the operating power supply, tuning my TS450 from 30kHz to 40MHz). And you get all this in a box that measures just 306 x 150 x 130mm, including all projections, and weighs only 2.8kg!

Amateur radio has been somewhat slow to accept switching power supplies for powering communication equipment. This is a pity, because "switchers", as they are often called, offer very attractive features, like small size, low weight, high efficiency, and low heating. True, they are generally more complicated than linear power supplies, but this is easily compensated by the fact that they can be built for a lower cost. Some early switchers produced an objectionable amount of RF noise, bringing the whole switching technology into bad reputation. But by proper design techniques and careful EMI filtering it is possible to build very quiet switchers.

Power supply used for professional FM broadcasting transmitter.

I normally use a USB port as power supply for my projects but some ICs need 3.3V instead of 5V. Therefore I decided to build this small dual power supply. Power supply uses two low dropout voltage regulators that provide up to 800mA of output current and come in TO-220 package. LD1117V33 is used for 3.3V and LD1117V50 for 5V. Input voltage is 6V-15V and both regulators can be switched on/off individually.