ATTEN PPS3005S observations - Page 1
Forum section: electronics / general

author: grevillea
author_rank: Newbie
timestamp: October 02, 2012, 07:45:51 am
content: Having benefited from others posts, I thought to add some observations and discussion starters on my recent purchase of one of these units.Location: Australia. AC power is 240VAC (+/- 10%), but the unit is rated for 220VAC. I wonder how long it may take to burn it out :-). I can purchase a 240V-220V autotransformer, for about half the price of the unit.Computer control: This was a key requirement for my application, and I am quite pleased with the result. It did not take long at all to implement the 24-byte fixed frame protocol which is the same as used by the the 3 channel ATTEN unit. Documentation is minimal but adequate if you understand binary data. Under Win 7 I did not need a special driver; the supply appears as a USB virtual COM port and I found it accessible at 9600 baud. One difficulty: it does not seem to send regular updates to the PC but it will respond when the PC sends it a command. So, to monitor what is happening one needs to keep resending the same command. Successfully used this approach to monior the settling after changing the parameters. Having to send a command each time is a small inconvenience, but it makes it more difficult to auto-detect the port number to use in the first place.So far, I have only played with OCP mode (not CC mode). I am driving LEDs, so set the maximum safe voltage (12V) and the desired current level and turn on the output power. There is a flash from the LEDs as the voltage is initially set to 12V and then the OCP cuts in and drops the voltage. Of course, with computer control, one can ramp the output voltage up gradually. The issue is the cut-in of the OCP, so it does not help to turn on the output power at 6V and then jump to 12V. It seemed that I had to get to a significant level above the optimum voltage before the OCP would cut in and reduce the voltage; in my observations 0.5-1V above the final settling value, but I guess the real issue is how much current is drawn above the set value before OCP cuts in. I also observed some instability in the OCP, with the current levels (and voltage levels) fluctuating for small output currents (10mA). Once OCP is activated, the desired current level can be changed up and down and there is no flash from the LEDs. Setting the desired current to 0 does not actually stop all output current, and the LEDs still manage to glow dimly.It would be interesting to explore CC mode, which seems to be available through computer control. I am guessing that the current output would be held stable at the desired level and the voltage would be limited to the value specified (OVP). That should mean that an LED can be driven safely and without flashing it at turn on but I have yet to prove this.Powering the unit off can produce a flash from the LEDs also, and I have not attempted to determine the voltage level during those events. As noted in other posts, it seems unwise to turn the unit on or off with load attached.Noise: I measure 53dbA at 300mm (1 foot) from the side of the case. That is about the same as my Brother laser printer. I am thinking about the fan speed control mod, but its probably not worth my while for the present.Output banana sockets: I was surprised that standard 4mm banana plugs would not fit the outputs. The inside diameter is close to 3.5mm so I think perhaps that these output sockets are for 1/8 inch banana plugs. I am currently looking for a supply of suitable plugs because jamming 4mm plugs into 3.5mm holes does not work very well and certainly discourages one from disconnecting the load for switch on and off.

author: Datman
author_rank: Regular Contributor
timestamp: October 11, 2012, 08:27:34 am
content: Quote from: grevillea on October 02, 2012, 07:45:51 amYou could use a 240-20V (or 18V) transformer, connecting secondary winding in series to the 240V to obtain 220V. Check the phase to obtain 220V, else you'll have 260V! The secondary have to be suitable for the current needed. The transformer power needed will be the current x 20V (or 18V).