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Can't find that power iron?




 
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Author Topic: Can't find that power iron?  (Read 288 times)
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« on: April 25, 2019, 01:19:07 PM »

I couldn't find the power supply for my 32S1, so I made a small AC-DC converter. Here are the first results. Not shown is the 115V rectifier and the capacitor. and the output filters. It should be a big capacitor to get a low ripple, I use 1000 uF 250VDC and a step-start to get it charged.
The transformers are EFD27 , but just because I had them laying around. Bigger transformers may run cooler. The driver is a IR2153D and 2 x 20 AMP FET's. You can add more transformers just in parallel to the other one. I will use a 42mm core for the 800 Volts, but I am waiting for the cores. .
The frequency is approx 80 kHz so I could use 3,8Volts per turn. VERY easy to wind, the HV has only 78 turns and the primary 2 x 44 turns.  With a 42 mm core you can increase to approx 5V / turn, but lowering to 4 Volrts will results in a lower core temperature. It is better to wind for 400 Volts and double the voltage. This in order to have a high self resonance of the HV winding.
When you use 42 mm cores in stead of the 28 mm, the core temperature will be lower. These transformers run up to approx 85 degrees C with a respectable 270 VDC at 300 mA and 6,4 Volts at 6 amps as a load.
The converter should be WELL shielded and filtered in order to minimize RF interference. But it is very small what makes shielding a bit more easy.
You may get an improvement and a lower transformer temperature by using Litz wire. I wound the 6 Volts with 4 wires in parallel to minimise losses at 80 kHz. But I used normal wire
Using a bigger ferrite core the converter may deliver a few kW at 2 - 4 kV. The main advantage is simplicity. At kV range outputs it is better to make various sec windings for lower voltages and rectify each one  and  put them in series. That is to minimise risk of resonace problems. The core should NOT have a gap and the primaty should be in balance, so do NOT make an error counting the turns.
In order to start the converter or switch it off, simply short circuit the 1000 pF capacitor of the IR2153 with a relay or so.
That makes is pretty easy to power linear amps because there is no RFI during reception with a switched -off converter.
There is NO need for stabilisation, the output is a lot more constant than using a normal iron with rectifiers.


* ac-dc converter.JPG (2024.86 KB, 2592x1944 - viewed 98 times.)
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