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The module as advertised on ebay.
This non isolated step-up DC-DC converter is rated at 40 Watts continuous and for the Dynaco amplifier around 20 Watts is needed - around half of the stated maximum. With all such modules it has been found that under running them obviates the necessity for additional cooling and will prolong the module life. Also the die-cast box used for the project is not ventilated and minimum heat generation is thus important.
The input voltage range is 8 - 32 Volts and our application will fix the input at 19.5 Volts from a laptop power supply.
Output voltage is variable up to 350 Volts or so and our design requiring 255 Volts will not stress the capacitors. The operating frequency is given as 75 kHz. The module measures 60 x 50 x 20 mm.
These modules are designed for charging duties for flash guns etc. The provision of a perfectly clean DC output is not a requirement - for an amplifier the reduction of noise in the output is important.
It has been found that with a 160 μH inductor on the output feeding a pair of 110 μF electrolytics the noise can be considerably reduced.
Image from the Tektronix TDS 2012 oscilloscope..
The above image shows the noise on the 255 Volt HT rail under load running the amplifier. The spikes are at more than ten times the frequency range of human hearing and have an amplitude of less than one Volt pk-pk. The amplifier is silent with no audio input.
For comparison the voltage ripple from the Heathkit IP-47 HV stabilised bench power supply was measured also driving the amplifier at 255 Volts. As expected the trace was virtually noise free.
Noise from the stabilised power supply.
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