vintage style led bulb DC-DC step up for my boat (12v input)  - Page 1
Forum section: electronics / beginners

author: dusta
author_rank: Newbie
timestamp: March 01, 2018, 11:18:26 pm
content: I have looked through multiple IC data sheets and am very confused. I started building a circuit based on this (https://learn.adafruit.com/diy-boost-calc/the-calculator) with an arduino to read the output voltage (through a voltage divider of course) and varying the brightness with a pot as the light dimmer. I then got dissuaded by reading a few forum posts and started looking for ICs to do the job. I would like to have a 10-14vdc input boosted to 100v-130vdc output. The leds switch on at 100V and are at max at 130V 0.1A. I have looked at the data sheets at most of the ICs on this page:https://uk.rs-online.com/web/c/semiconductors/power-management-ics/boost-converters/?applied-dimensions=4294506514,4293615121&sort-by=P_breakPrice1&sort-order=asc&pn=1Could someone please point me in the right direction?

author: katzohki
author_rank: Frequent Contributor
timestamp: March 02, 2018, 12:20:40 am
content: So you want to boost 12V DC to 120V DC? Linear Technologies is really good at providing cookie cutter solutions for stuff like that, you might try looking at their parts.

author: Paul Price
author_rank: Super Contributor
timestamp: March 02, 2018, 12:37:26 am
content: Stick to the original Adafruit circuit because it is so much more simpler to build and use and cheaper. You don't need the precision and complexity of circuit of the TI chips for your very modest goals. Just add a CMOS 555, a pot, a 10-ohm sense resistor, a 1K brightness pot and a BC547/2N3904 transistor(LED current feedback control for the 555), and a timing capacitor and resistor to make an astable 555 oscillator to drive the HV MOSFET.Even more simple, just use a CMOS 555 timer as an astable oscillator to drive the gate of a 120V+ MOSFET and adj. the duty cycle of the 555 timer output driving the MOSFET gate to achieve the required voltage output. The 555 basic MOSFET driver circuit would only require two capacitors, a pot, 3-additional resistors. This circuit is unregulated and LED brightness will vary with temperature.You can easily add feedback for voltage control with a sense resistor at the ground return of the LED string to control the base-emitter voltage and the NPN transistor collector turns off the 555 timer by connection to its reset pin when the desired convertor output voltage has been reached. This gives voltage regulation that controls accurately the voltage applied to the LED string. A pot across the sense resistor sets the current fed back to the transistor base to set your desired LED current (LED brightness). A 1-meg resistor from the reset pin on the 555 to the 555 Vdd terminal is required.The TI chip TPS40210DGQR would do the same thing with a much more complicated circuit requiring at least 18 components.In either case you might need an additional series 1N4001 diode and a LM317 or LM7812 regulator and two 100uF electrolytic caps to filter your power and maybe even a 24V 1W zener to protect your LED driver circuit from power surges on your boat.

author: dusta
author_rank: Newbie
timestamp: March 02, 2018, 04:54:31 pm
content: Thanks for your insight Paul, have just built a fairly dodgy circuit with what is laying around and it works!. Is the circuit you described like this?:I have just read this page (http://www.dos4ever.com/flyback/flyback.html) and thought maybe a flyback converter would be more efficient, would there be much difference in effeciency considering the LEDs are max 8W. Are these series LED strings in these bulbs much different from NIXIE tubes as a load?

author: Seekonk
author_rank: Super Contributor
timestamp: March 02, 2018, 11:33:20 pm
content: I bought 120V flush mount 18W LED fixtures for my camp and took out the inverter in them. The LED operated at 41V and I just used a $3 boost converter to get 36V. That made it about a 6W LED which is bright enough. It operates cool enough and has so much margin that running it in strictly in voltage mode is safe.

author: dusta
author_rank: Newbie
timestamp: March 03, 2018, 11:28:29 am
content: Unfortunately I cant access the LED strings to break them apart into 50V strings. Would have to break the glass. Unfortunately low wattage boost modules off the shelf seem to stop at the 40V mark.

author: Seekonk
author_rank: Super Contributor
timestamp: March 03, 2018, 01:38:53 pm
content: There are some $5 modules that will adjust up to 400V. I have a little AC module that is 300W and just needs a transformer added to it about the same price.

author: dusta
author_rank: Newbie
timestamp: March 03, 2018, 02:03:41 pm
content: $5 DC-DC modules that will do 12vdc->130vdc? could you link them please?

author: ebastler
author_rank: Super Contributor
timestamp: March 03, 2018, 03:21:15 pm
content: I understand that your application is to run "vintage look" LED lamps (glass bulbs and filaments, I assume?) on a boat, where you have only a 12V supply -- right?Why not use 12V filament LEDs right away? Seems like the more elegant and simple approach? This is just a random Google hit, can't vouch for them:https://www.12vmonster.com/collections/lighting-classic-filament-halogen-bulbs/products/dc-12v-6w-led-filament-wire-light-bulb-retro-edison-style-lamp

author: Paul Price
author_rank: Super Contributor
timestamp: March 03, 2018, 03:48:48 pm
content: Yes, that's almost exactly the circuit. It is a flyback converter, simple and it works well. In my design I connect the collector of the transistor to the reset pin and this allows the 555C to completely shutdown and regulate over a very wide range of output voltage.You won't find a circuit more efficient than this. To increase the efficiency of the circuit shown I would have increased the values of the resistors shown by approx x100 and decreased the value of the timing capacitor /100 to achieve the same output freq. and duty cycle. This results in a very power thrifty 555 MOSFET driver. This MOSFET driver circuit would be very more efficient usng a CMOS 555.

author: Zero999
author_rank: Super Contributor
timestamp: March 04, 2018, 10:06:55 am
content: Quote from: ebastler on March 03, 2018, 03:21:15 pmI agree. Lots of mains LED lamps won't work from 120VDC anyway, because they often use a capacitive voltage dropper, which is AC only.