EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: BeBuLamar on May 11, 2021, 01:41:29 pm
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I just bought a Matrix MPS-3605LP last month. It's a 36V 5A power supply. I found it's OK for the price of $129 but I notice something. I hear relay clicking when I adjust the voltage between 12-13V and also between 25-26V. So do you think that it switches the input voltage so to reduce the voltage difference between input and output which can cause it to get very hot?
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I just bought a Matrix MPS-3605LP last month. It's a 36V 5A power supply. I found it's OK for the price of $129 but I notice something. I hear relay clicking when I adjust the voltage between 12-13V and also between 25-26V. So do you think that it switches the input voltage so to reduce the voltage difference between input and output which can cause it to get very hot?
Yes, many linear power supplies has relays to change input voltage.
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Yes, this is very common for lineair power supplies.
Ever since the '70-ies or earlier they use transformers with multiple taps to reduce dissipation in the power supply.
Dave has made a teardown of the Korad 3005 power supply long ago, and you will find something similar in almost any variable output lab power supply.
A more modern approach would be to use an SMPS with variable output voltage as a pre regulator, and then a linear regulator (which drops just a few volts) to clean up the switching noise, but these are not so common. My guess is that if you want to make a low-noise power supply, then the cost and weight of a chunk of iron in a transformer is still attractive because it just does not generate any HF noise by itself. The weight is also not an issue for a power supply that just sits on a shelf.
There are lots of SMPS modules, which are cheap and practical for delivering lost of raw power, but these have quite some switching noise.
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So do you think that it switches the input voltage so to reduce the voltage difference between input and output which can cause it to get very hot?
yes, high voltage drop on linear regulator leads to a high heating and low efficiency. Reduce voltage with relay switch between different transformer output allows to reduce voltage drop and heating. Relay switch doing this job.