Hi Guise.
Lovely facility, this. Well done.
Okay - I've checked existing threads and posts and found nothing that specifically addresses my challenge. I have a 555 PWM circuit from Tony van Roon ( http://www.sentex.ca/~mec1995/circ/pwm555.html ) that I used some years back on a hydrogen project. Works perfectly.
Although Tony's design is primarily a motor control, I've also successfully used it as a dimmer for 12v lighting systems. But now, I have an added challenge. Here in South Africa we have intermittent and dirty utility power most of the time, so battery backup systems are the rage - if not absolutely essential.
I'm helping an artist friend who has a huge house (3 levels with guest cottage). He designs and builds amazing LED chandaliers and perspex lamps out of LED strips, which draw anything from 250mA for the smaller lamps to around 3A for the bigger arrays. His entire home lighting system was supposed to be designed for DC but our local electrical engineers got it all wrong and, as a result, the 30Amp 12v DC supply only delivers 9 - 10v by the time it gets to the lamps at the furtherest part of the house. There is voltage drop everywhere - even in the same room as the supply!
So we decided to use a 24V grid and build a small regulator (based on the same design) into each lamp to keep power rock steady at exactly 12.5v DC. I have changed the circuit slightly. An LM7812 is feeding the 555 circuitry with no problem or heat from the 15v difference. The FET is an IRFZ44 and the lighting load is connected directly to the 24v supply. Now here's the problem:
When utility power is available, the PSU puts out 27V because it has to maintian the 4x 60A/h batteries (configured for 24V). So any setting on the PWM regulator will hold steady as long as the supply remains at 27v. But when the utility power fails, the input to the PWM regulator drops to battery float (approx 25v) and then, depending on how long the utility power is out, the battery will drain steadily down to a minimum of 21v.
There is no compensation by the FET and so the voltage to the lamps also drops, causing the llamps to dim accordingly. You probably know that LED lighting is very sensitive to voltage.
So my question is: keeping component count down (and size), how do I get the 555 to compensate for the changing imput voltage at the FET. Remember that the 555 is steady at 12 v via the 7812 but the supply voltage to the lamps is varying.
To reiterate: circuit size and component count are considerations and parts are hard to come by in our small town - so this is pretty much what have to work with. I do have some 5w 13v zeners and a TL431 adjustable shunt on hand. I tried a few angles with them but without success - I could only get the 555 to change its frequency but not its duty cycle.
Help?
PWR2U
Lovely facility, this. Well done.
Okay - I've checked existing threads and posts and found nothing that specifically addresses my challenge. I have a 555 PWM circuit from Tony van Roon ( http://www.sentex.ca/~mec1995/circ/pwm555.html ) that I used some years back on a hydrogen project. Works perfectly.
Although Tony's design is primarily a motor control, I've also successfully used it as a dimmer for 12v lighting systems. But now, I have an added challenge. Here in South Africa we have intermittent and dirty utility power most of the time, so battery backup systems are the rage - if not absolutely essential.
I'm helping an artist friend who has a huge house (3 levels with guest cottage). He designs and builds amazing LED chandaliers and perspex lamps out of LED strips, which draw anything from 250mA for the smaller lamps to around 3A for the bigger arrays. His entire home lighting system was supposed to be designed for DC but our local electrical engineers got it all wrong and, as a result, the 30Amp 12v DC supply only delivers 9 - 10v by the time it gets to the lamps at the furtherest part of the house. There is voltage drop everywhere - even in the same room as the supply!
So we decided to use a 24V grid and build a small regulator (based on the same design) into each lamp to keep power rock steady at exactly 12.5v DC. I have changed the circuit slightly. An LM7812 is feeding the 555 circuitry with no problem or heat from the 15v difference. The FET is an IRFZ44 and the lighting load is connected directly to the 24v supply. Now here's the problem:
When utility power is available, the PSU puts out 27V because it has to maintian the 4x 60A/h batteries (configured for 24V). So any setting on the PWM regulator will hold steady as long as the supply remains at 27v. But when the utility power fails, the input to the PWM regulator drops to battery float (approx 25v) and then, depending on how long the utility power is out, the battery will drain steadily down to a minimum of 21v.
There is no compensation by the FET and so the voltage to the lamps also drops, causing the llamps to dim accordingly. You probably know that LED lighting is very sensitive to voltage.
So my question is: keeping component count down (and size), how do I get the 555 to compensate for the changing imput voltage at the FET. Remember that the 555 is steady at 12 v via the 7812 but the supply voltage to the lamps is varying.
To reiterate: circuit size and component count are considerations and parts are hard to come by in our small town - so this is pretty much what have to work with. I do have some 5w 13v zeners and a TL431 adjustable shunt on hand. I tried a few angles with them but without success - I could only get the 555 to change its frequency but not its duty cycle.
Help?
PWR2U