Power Supplies

Given that more users do not have 48-50VDC readily available some sort of power supply will be needed to power the 100W and 500W amplifiers.

HIGH VOLTAGE: RF power amplifiers are connected to hazardous line voltages. When building or servicing RF power amplifiers, there may be exposed components with housings or protrusions at or above line potential. Extreme care should be taken to protect against shock. Stand on an insulating pad and make it a habit to use only one hand when checking components. Always work with another person in case an emergency occurs. Disconnect power before checking circuitry or performing maintenance. Be sure equipment is properly grounded. Wear safety glasses whenever working or soldering. AC power supplies can store voltage for minutes after being disconnected from the AC line. Wait at least 5 minutes after disconnecting power supplies from the AC line before servicing.

AC-DC Power Supplies

For the AN-1819 I recommend using three Meanwell EPP400-18 supplies in series which can provide up to 22 amps at 58-60V which is perfect for the VRF2933's and four Meanwell EPP400-15 supplied in series which can provide up to 17 amps at 62-15V for the VRF2944's. Some kind of current limiting or fusing should be used to prevent excessive current flow in case of a component failure.

For the MRF-101 amplifiers I recommend the Meanwell EPP200-48 power supply or two low cost 24V, 4A supplied in series.

The Meanwell supplies have a 12V output for a fan which controls the speed of the fan based on the output current of the supply so don't use this 12V to power a QRP rig. Since the control systems and relays operate at a nominal 12V, most amplifier projects will need second supply for this circuitry. I have used this DC-DC converter to provide 13.8V for the lower voltage components.

This supply claims to be able to produce 10A but the test reports that I have read seem to indicate with 50V input and 12V output that 4 or 5A would be a more representative rating. But even at that power level the device has ample power for control circuitry and a QRP transceiver.

DC-DC Power Supplies

Since the MRF-101 amp is so small and light, it seems like a great choice for a portable/mobile amplifier. That is until you try to power it. Fortunately there are inexpensive DC-DC converters available. I have had good results with this 1200W Boost Converter and it may seem like 1200W is overkill for a 100W amplifier but when you dive into the ratings you can see where the problem is.

It's rated at an input of 10-60V and an output of 12-83V. The MRF101 amp needs 50V at 4 amps, which is well under the device's output rating of 10 amps. But if the input voltage is 12V and the supply is 90% efficient, the input current will be 18.5A wich is dangerously close to the 20A max input rating of the device. If you are using a decent 13.8V power source this converter should be fine but if you intend to use a battery that will drop below 12V as it discharges, you might want to lower the output voltage to 40-45V to prevent blowing the input fuse or tripping the current limit.

A better choice might be to use a higher voltage battery, running a 24-28V pack will eliminate input current limit issues, you can use the buck converter above to provide 13.8V for the control circuitry and QRP transceiver.

Power Supplies Monitoring

I recommend monitoring/metering the power supply's output voltage and current to aid in setting the bias and keep tabs on how the amp is running. A 10:1 resistive voltage divider can scale the 50V to 0-5V input for input to an Arduino or other controller. For current monitoring, Adafriut makes a 60V 5A, INA-169 Breakout Board which is perfect for the MRF-101 amplifier.

If anyone has any input on powering these amplifiers that you would like to share, send me an email info@RFPOowerTools.com and I'll include it.