Switch mode power supplies have improved a lot over the years. I'd like to use them in my next few projects as they are small, cheap and allow me to avoid working with mains voltage. These projects will all be low current - probably a preamplifier, MM phono stage and a headphone amplifier.
Power supply will be a laptop-style SMPS (24V) feeding a triple output SMPS DC-DC converter (+/- 15V), probably a Mean Well DKMW30F-15 or similar.
What is best practice for filtering the supplies? Connection scheme is in the attached image:
Is a common-mode choke a good choice for block A?
And for block B, CLC filters on the positive and negative rails?
The Mean Well DC-DC converter in question has a switching frequency of 330kHz. I'm also considering a TDK-Lambda unit, but they do not show the switching frequency in the data sheets.
Power supply will be a laptop-style SMPS (24V) feeding a triple output SMPS DC-DC converter (+/- 15V), probably a Mean Well DKMW30F-15 or similar.
What is best practice for filtering the supplies? Connection scheme is in the attached image:
Is a common-mode choke a good choice for block A?
And for block B, CLC filters on the positive and negative rails?
The Mean Well DC-DC converter in question has a switching frequency of 330kHz. I'm also considering a TDK-Lambda unit, but they do not show the switching frequency in the data sheets.
Many converters descend to subharmonic/intermittent operation on light load which can add spurs below the nominal frequency of operation. I'd suggest using a +/-18V switchmode module into a 7815/7915 pair perhaps?
But CRC filtering will be useful too and simpler/cheaper. For low level amps such as phono/mike its good to add extra RC filters for sensitive the input stages.
But CRC filtering will be useful too and simpler/cheaper. For low level amps such as phono/mike its good to add extra RC filters for sensitive the input stages.
Yes, if your end consumers don't draw enough of current, they might go into some sort of on/off mode. Avoid this by bleeder resistors.
Use a modern regulator e.g. LT3042 after your SMPS and you have a fine DC source.
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Use a modern regulator e.g. LT3042 after your SMPS and you have a fine DC source.
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Manufacturer recommends in AN input filtering. Or show at Würth Elektronik homepage.
Linear regulators as suggested at outputs are fine.
JP
Linear regulators as suggested at outputs are fine.
JP
Thank you very much for the replies 🙂
I've read that voltage regulators aren't great at stopping high frequency noise - is it a function of the regulator's PSRR?
Good suggestion. Does a cap multiplier "look" like a big capacitor to the SMPS? They don't like to see a lot of capacitance at their outputs (for example the Mean Well model I'm looking at specifies max. 1000uF).
I've read that voltage regulators aren't great at stopping high frequency noise - is it a function of the regulator's PSRR?
Good suggestion. Does a cap multiplier "look" like a big capacitor to the SMPS? They don't like to see a lot of capacitance at their outputs (for example the Mean Well model I'm looking at specifies max. 1000uF).
I think not.
The power supply has no big capacitor to charge.
The cap multiplier gives the result of a large cap to the load.
The power supply has no big capacitor to charge.
The cap multiplier gives the result of a large cap to the load.
I'm going to start with an LCLC filter (1mH, 470uf, 1mH, 470uF). Capacitors will be bypassed with ceramic and polyester units for broader frequency interaction. The math says a cutoff frequency of 232.15 Hz.
Does this sound suitable?
Does this sound suitable?