we recently bought a set (4 of them) of 15VDC, 3A linear power supplies from a well known manufacturer. This is not a new thing, we have been buying these supplies for years, all the way back to the 1990's. Every time we buy them, we test them before installing them. We would apply a resistive load and test it to 100% of its rated output. Only this time, on all 4 of the power supplies, the output voltage would not come up to 15V. So we figured we got a bad batch, sent them back, and got a new set of 4. These would not work either. The outputs would only come up to about 0.3V. Eventually we found that if we waited long enough, like between 45 seconds to 2 minutes, the outputs would come up to 15Vdc. This wasn't a slow transition, over 30 seconds the output would rise from 0.3V to about 0.6 volts, and then suddenly jump to 15V, and would behave normally. Also, we found that if we only loaded it to 50 or 60% of its rated load, it would turn on immediately. we don't observe the delay unless the load is between 70 to 100%.
We called the manufacturer and explained this to them, and after a few days they claimed that there is nothing wrong with them. they said that the turn on time is not defined in the datasheet, so we should always assume it might take several minutes for them to turn on.
this seems fairly weird to us, is this just how things work and we can't do anything about it?
Also, we have at least 6 of the power supplies of the same type, just older from 10 years ago, and we tested them the same way right next to eachother, and the older ones turn on immediately under full load. Note that all of these power supplies use the lm723.
we use these power supplies in fairly sensitive equipment, and normally they're not under 70% load, but occasionally they are, and if they don't turn on it could cause some damage. Does anyone have any thoughts on this situation? is there an implicit understanding that linear power supplies might not turn on immediately, for as long as 2 minutes? shouldn't this be reflected in the datasheets?
We called the manufacturer and explained this to them, and after a few days they claimed that there is nothing wrong with them. they said that the turn on time is not defined in the datasheet, so we should always assume it might take several minutes for them to turn on.
this seems fairly weird to us, is this just how things work and we can't do anything about it?
Also, we have at least 6 of the power supplies of the same type, just older from 10 years ago, and we tested them the same way right next to eachother, and the older ones turn on immediately under full load. Note that all of these power supplies use the lm723.
we use these power supplies in fairly sensitive equipment, and normally they're not under 70% load, but occasionally they are, and if they don't turn on it could cause some damage. Does anyone have any thoughts on this situation? is there an implicit understanding that linear power supplies might not turn on immediately, for as long as 2 minutes? shouldn't this be reflected in the datasheets?