12V - 7.29A ac/dc converter project Need Help

Thread Starter

Butterworth

Joined May 6, 2009
135
Sorry. I didn't know you looked at the schematic on a tiny cell phone.
Hmm well my phone isn't exactly small... its about the same size as the dell streak.

I found the following shottky diodes, 1n4508 &1n5844, i know they are not the 5822's listed but they should work still? Can I mix the two styles?
 

Thread Starter

Butterworth

Joined May 6, 2009
135
Alas, I have but 1pc of the 5844... Such is life, however, I will need to pick up the 555 Timer and the mosfet anyway, so I might as well grab a 4pk of the schottky 5822's.

I wanted to put a power indicating led (red 3mm 2.2Vf @ 10mA) Can I place this between the switch and the 555 timer? It is so I can see if the unit is on or not, being IR leds, I don't want people looking at it when it is on full blast... preventative measure.

I found a transistor comparable to the bc... it is an NTE123AP, datasheet located here http://www.nteinc.com/specs/100to199/pdf/nte123ap.pdf

I think it is higher in capacities, but will still do the job I am hoping.
 
Last edited:

SgtWookie

Joined Jul 17, 2007
22,220
Alas, I have but 1pc of the 5844... Such is life, however, I will need to pick up the 555 Timer and the mosfet anyway, so I might as well grab a 4pk of the schottky 5822's.
It never hurts to have a few extra on hand.

I wanted to put a power indicating led (red 3mm 2.2Vf @ 10mA) Can I place this between the switch and the 555 timer? It is so I can see if the unit is on or not, being IR leds, I don't want people looking at it when it is on full blast... preventative measure.
I forgot about that.

Yes, you can connect a single LED and a series resistor.

Connect it after the two diodes from the bright and dim terminals to ground (the supply negative terminal) with a series current limiting diode.
Since your supply is 12.82v, and the diodes will drop ~0.5v, a 1K resistor in series with an LED will give roughly 10mA current flow through the diode. You will need to use a 1/4 Watt resistor. Might as well use 1/4 Watt resistors for everything; they will work.

I found a transistor comparable to the bc... it is an NTE123AP, datasheet located here http://www.nteinc.com/specs/100to199/pdf/nte123ap.pdf

I think it is higher in capacities, but will still do the job I am hoping.
You can use just about any small-signal NPN transistor; 2N2222, 2N3904, 2N4401, etc - it does not have to sink much current to keep the 555 timer disabled and the output switched on.
 

Thread Starter

Butterworth

Joined May 6, 2009
135
Sorry - there's a lot of people needing a lot of help; things tend to fall through the crack.

Have a look at the attached. I didn't have a 3-position switch, so I used two SPDT switches. Don't let that throw you.

You'll only have one common switch terminal; represented by the left side of S1a and S1b.

The dim side is represented by S1a. When it is selected, the 555 timer runs, and the brightness is set via VR1.

The bright side is represented by S1b. When it is selected, the 555 timer is prevented from running by R15 pulling up the base of Q1, which keeps C1 from charging, which keeps the output of the 555 timer high, which means the LEDs are on all the time.
Ok so the test board circuit was made and it working using only a single string of 1.42V irleds. The question I propose is this, looking at the led strings you have arranged them in 7 -led strings and the last 4 strings are 6 leds... what values did you use to calculate the series resistors for each string?

*BUMP* - Sgt.Wookie, can you advise on the led order you used? I cannot get the value resistors that you did, Thanks!
 
Last edited:

SgtWookie

Joined Jul 17, 2007
22,220
Ok so the test board circuit was made and it working using only a single string of 1.42V irleds. The question I propose is this, looking at the led strings you have arranged them in 7 -led strings and the last 4 strings are 6 leds... what values did you use to calculate the series resistors for each string?

*BUMP* - Sgt.Wookie, can you advise on the led order you used? I cannot get the value resistors that you did, Thanks!
Use the values that were calculated some many posts back when I had you using 8 in series.

I'm not going to look for it.
 
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