Power 8 x SSL9K

[darkcharly]

Hello! I wanted to ask a question: I can use the keith´s PSU to feed eight preamps SSL9k?
I have a transformer 50VA 20 + 20. It can be useful?
Thank you!

 

[Whoops]

Hello! I wanted to ask a question: I can use the keith´s PSU to feed eight preamps SSL9k?
I have a transformer 50VA 20 + 20. It can be useful?
Thank you!

Hi,
don't know if you already solved your problem or not.

I don't remember the current draw right now of the SSL9k.

I know Ive used 1 Keith PSU for powering 4 of them,  and the supply was fine. the 7818 and 7919 go up to 1.5 Amps

For 8 units I would use 2 Keith PSU's, one for each 4.

 

[Rob Flinn]

I know Ive used 1 Keith PSU for powering 4 of them,  and the supply was fine. the 7818 and 7919 go up to 1.5 Amps

Looking at the National semiconductor date sheet it says output in excess of 1A for78xx.  So it seems if you want 1.5A rating you will need to select a particular brand of 78xx.

The current you can draw also depends on how much voltage you are dropping across the regulator too.  The more you drop, the hotter it gets, & the less current capability it has.  It will also only have the maximum specified current rating when bolted to a good heatsink. 

The LM317/337 combination do have a 1.5A rating, but will still be subject to the above.

 

[Gareth Connor]

One options as to the suitability of the transformer you have, as well as the choice of PSU/regulator system is to calculate your way to an answer:

Start by calculating the current required for each channel:
IC data sheets state the supply current in mA. e.g. NE5534 has a supply current of max 8mA.
Factor in the current drawn by LEDs.
Is there any transistor circuitry? Factor it in as well.

When all currents are added together you will get a total of "N" mA.
Is this greater than the capability of your chosen PSU/regulator? If yes, put in 2 PSUs; if no, by how much is "N" under the PSU's limits? A rule-of-thumb allowance is 30%. So if your calculated currents add-up to 1 amp, and your regulators are LM317/LM337 (rated at 1.5A with suitable heatsinking), you are well-within the regulator's capability provided that the regulators are suitably heat-sinked....... again, reference to the regulator and heatsink manufacturer's data sheets on their products will provide answers, or at least the raw info from which answers can be worked out.

Finally, is the transformer up to the job? Back to the calculator and the Laws of Mr Ohm.


Hope this helps.

 

[Rob Flinn]

So if your calculated currents add-up to 1 amp, and your regulators are LM317/LM337 (rated at 1.5A with suitable heatsinking), you are well-within the regulator's capability provided that the regulators are suitably heat-sinked....... Hope this helps.

Generally as a rule of thumb, yes, but it still depends on how much voltage is being dropped across the regulator.  Normally there is a graph on the data sheet, which tells you how much the regulator derates as Vin-Vout increases.  If Vin-Vout is a lot the regulator might for example only have a 1A rating & therefore wouldn't have the 1.5x safety margin if the circuit draws 1A.