Bench Power Supply Part 1

Graduation is on the horizon, and I’ve spend too many years using wall-warts as my primary bench power supplies. I’m ready to finally build something I can be proud to have on my bench. So, I’m setting out to build a really high quality bench power supply click this link here now. Every good project starts with a list of goals and in this case that means setting the specifications for my power supply. I think it’s good design practice to decide what you seek to accomplish before you spend too much time designing. So, without further delay, here are the initial specs that I’ll be designing to. Design Specifications:

Dual Floating Outputs
Adjustable Voltage, 0-30V, Steps of 10mV
Adjustable Constant Current 0-5A, Steps of 1mA
Soft output On/Off Switches (Default: OFF)
Output On/Off Indicator LEDs
OLED Text Display
Voltages/Currents set with single rotary encoder
Serial Computer Interface (Read/Set Voltage/Current)
High power efficiency, switching knock-down stage, regulated final stage
ICSP Header for firmware updates
Made from low cost parts
Now that the specs have been written down, I’ll begin designing the circuitry. Stay tuned for part 2.

Weather Station

I’ve been spending some of my spare time tinkering with the famous Arduino again. This time I’ve managed to build a network enabled weather station platform. It’s pretty simple so far. It is currently only measuring temperature using an LM34 temperature sensor. It’s just strung out my window, and is programmed to take a reading every 15 minutes.
The communication is done through an Ethernet Shield. This device sits on the Arduino and allows it to make basic HTML requests and pushes data to a PHP script on my website using the URL and the PHP _GET function. The data is then stored in a CSV file and displayed via a Google Graphing API. BTW, this is live data you’re seeing and the time is local time (Pacific). View the weather station page.

How to choose a power supply

astronMeterMany modern ham radios operate on low voltage DC instead of high voltage AC. This is done for several reasons. First, most of the circuits inside these radios actually run on low voltage DC, so high voltage AC isn’t needed. Second, running the radio on low voltage DC saves space inside the radio. This is because the radio can directly accept the low voltage DC it needs, and dosen’t need an internal power supply to convert from high voltage AC to low voltage DC. Finally, the last advantage is that these radios can easily be installed in a car or run on a car battery.

So, this leads to the main point. What power supply do I need for my radio if it says it requires DC? The short answer is: Many different supplies will be adequate. The two most important things to pay attention to are the following:

  • Does it produce the proper voltage?
  • Can it supply enough current?

Many DC power supplies on the market today provide 12 Volts DC (Actually 13.8 Volts is considered “nominal”). It is important to check the specifications and make sure that the output voltage on the supply is close to what your new radio calls for. A few volts difference is usually OK.

Next, check the maximum continuous current rating of the power supply. The power supply should provide at least the amount of current your radio needs plus 10%. The extra 10% is headroom to prevent your power supply from overheating. Most hams follow this extra 10% rule and some go even higher. Remember that you radio will not always need the max current that is listed on the radio’s specs. This is usually the current drawn when the radio is transmitting on full power. The current the radio requires when it’s receiving is typically much less.

So, in conclusion, you will need a power supply that matches the voltage of your radio, and can supply enough current to keep your radio running. Extra features like meters aren’t absolutely necessary, but can be nice for troubleshooting problems, however, they cost more!