Electronics > Beginners
Sine wave drive dc-dc converter
newbie666:
I've been reading this application note from Analog:
https://www.analog.com/media/en/technical-documentation/application-notes/an29f.pdf
Figure 4 from this app note really piqued my interest as it shows a 5 - 15V dc dc converter with output noise of 30uV (full load) and very low EM noise thanks to driving the transformer with a sine wave.
To generate drive signal app note uses wein bridge oscillator made with discrete parts which to be honest I really don't feel like doing. So my question is
is there an IC that would drive a transformer with a sine wave for me? What frequency should I aim at?
What are limitations of such a circuit?
I can imagine the efficiency won't be great, but what kind of max power output should I expect?
edit: schematic of the converter
ogden:
--- Quote from: newbie666 on February 23, 2019, 04:11:53 pm ---is there an IC that would drive a transformer with a sine wave for me?
--- End quote ---
For primary side circuit I would use microcontroller with DAC as sine generator and AB-class audio amplifier IC as driver for transformer. Other option would be to use lightbulb+opamp sine generator with audio amplifier - in case you want purely analog solution.
--- Quote ---What frequency should I aim at?
--- End quote ---
Did you read appnote carefully? Answer is there: "The sine wave’s 16kHz frequency is a compromise between the op amps available gain bandwidth, magnetics size, audible noise, and minimization of wideband harmonics."
David Hess:
The power amplifier could be replaced with a power operational amplifier or audio amplifier however this would further sacrifice efficiency because the design as shown has a rail-to-rail output stage minimizing dropout voltage. There are alternative boosted operational amplifier designs which could be used for similar performance however.
Ogden is right that a simpler Wein bridge oscillator could be used however doing so would then require an adjustment for output level. I think the author was aiming to make a design which required no adjustments.
Notice that another feature of this inverter is galvanic isolation between the input and output. This type of low noise isolated power supply is especially suitable for powering sensitive analog circuits like high resolution digital multimeter front ends.
The text says efficiency is poor at 30%. I thought it would be much higher because the class-AB linear power amplifier stage can operate close to saturation.
Output power is limited by the low efficiency producing heat and the current limit of the LT1010 based output regulators so considerably higher output power is possible if the output regulators are changed and the high power loss is acceptable. The text says as shown, the output current is 75 milliamps per output which is consistent with the LT1010.
ogden:
--- Quote from: David Hess on February 23, 2019, 09:13:35 pm ---Output power is limited by the low efficiency producing heat and the current limit of the LT1010 based output regulators so considerably higher output power is possible if the output regulators are changed and the high power loss is acceptable. The text says as shown, the output current is 75 milliamps per output which is consistent with the LT1010.
--- End quote ---
All this can be solved with modern low noise (0.8uV RMS) LDO's https://www.analog.com/en/products/lt3042.html There are complementary negative regulator as well.
David Hess:
--- Quote from: ogden on February 23, 2019, 09:26:25 pm ---
--- Quote from: David Hess on February 23, 2019, 09:13:35 pm ---Output power is limited by the low efficiency producing heat and the current limit of the LT1010 based output regulators so considerably higher output power is possible if the output regulators are changed and the high power loss is acceptable. The text says as shown, the output current is 75 milliamps per output which is consistent with the LT1010.
--- End quote ---
All this can be solved with modern low noise (0.8uV RMS) LDO's https://www.analog.com/en/products/lt3042.html There are complementary negative regulator as well.
--- End quote ---
The LT1010 has the advantage of being able to source and sink current from the output.
I think the noise argument will be a wash because noise is controlled within the loop bandwidth of the LT1013 and noise from the buried zener reference is lower than an integrated regulator with a bandgap reference can achieve alone. You do not actually need a low noise output stage for low noise with the LT1013 and LT1021 determining the output noise.
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