14 to 40 or 50 volt boost circuit

[kinarfi]

Small 555 circuits

Update, after building several boost circuits with the 555 timer, I have come up with a few ideas that need to be bounced off of others, Please take a look at the following attached drawing and see if you can find errors and add comments if needed.
It is drawn to represent installation on a Vector 8022 board which has the "P" pattern or the traces running end to end. The breaks in the lines represent where the traces need to be broken. This makes for a board that is about 1" x 2".
Thanks,
Kinarfi

 

[Ubergeek63]

Update, after building several boost circuits with the 555 timer, I have come up with a few ideas that need to be bounced off of others, Please take a look at the following attached drawing and see if you can find errors and add comments if needed.
It is drawn to represent installation on a Vector 8022 board which has the "P" pattern or the traces running end to end. The breaks in the lines represent where the traces need to be broken. This makes for a board that is about 1" x 2".
Thanks,
Kinarfi

did you see my post ( web site was screwing up that day so there are were a bunch dupe msgs)? https://www.electro-tech-online.com/custompdfs/2012/02/tps61041.pdf with a dual inductor (center tap to the sw pin) should be able to do the whole thing with the LED string in place of R1 and R2 set to 125 ohms.

Dan

 

[kinarfi]

Yes, I looked at it, 6 volt max in, mostly, I'm working with 12.6v, engine off, to 14.4v, engine running. It is that extra 1.8 volts from the alternator that needs to be dealt with. If you set up a LED for 12.6, you fry it at 14.4. My solution has been to series several and boost the voltage and control the current. Serves me well so far. The use of the 555 appears to a very good base and the addition of the correct FET and feedback allows for control from ma to amps and voltages from 20 to 200 or more. My favorite store bought device so far is the LT1320a, but I enjoy the designing and building from discrete components.
Kinarfi

 

[Ubergeek63]

i did not catch that the 12V was the input voltage... you are aware of the 60-80V load dump spec on the automotive power rail?

 

[kinarfi]

i did not catch that the 12V was the input voltage... you are aware of the 60-80V load dump spec on the automotive power rail?

Not sure what you are referring to.

 

[Ubergeek63]

Not sure what you are referring to.

sorry ... suspected that...

https://www.electro-tech-online.com/custompdfs/2012/02/an9312.pdf

 

[kinarfi]

1st, I said that the current could be controlled using a resistor that was chosen so the voltage drop at the desired current equaled about 1 volt and then use a pot to feed the Q1 transistor, haven't made that work yet at higher currents!
2nd Refer back to the drawing in post #32, Q2 current limiting transistor on pin 4 of the timer, built that and the 40 volts came up and the 900ma current only came up to about 500 to 700 ma depending on which build I was running, then after a short time the current would drop and lights would dim. Some times, they would pulse on and off are a rate of about one or two hz, and with these LEDS, that's lots of very bright light flashing. Tried various fixes and nothing worked. Finally, I decided to try running the circuit as a voltage device instead of a current device and used a pot to control the voltage without any load, worked great, set the voltage to what I knew the LEDs could handle and then hooked up the LEDs while it was running, the lights came on, the current came up and all was good, for about 5 seconds, then the current started dropping and lights went dim. After several repeats and watching the scope as I did so, I noticed Vrst would be at ~2 and then drop to near 0 after I hooked the lights up, finally pulled Q2 and all was happy, I could set the voltage where I wanted so the current was what I wanted and every thing was basically stable except for changes as things heated up. The components did not get warm enough to be of concern, just the LEDs.
I think the design is good, but the oscillating of the inductor caused enough spikes to keep turning on Q2 which slowly draind C4 to the point that Vrst was too low to allow the timer to operate.
More playing tomorrow. Pretty neat, I was getting a full 40 watts out of it, guess I'll have to see how much I can get once I get the Q2 problem ironed out.
Kinarfi

 

[Ubergeek63]

functional but sloppy.... LEDs dimming out as 317 goes into thermal shutdown ... bare minimum regulate the current directly... BTW you will NEVER get the full 40W out of it with linear current regulation