need help starting buck boost mod

[rusalka]

I really don't know where to go to start on a buckboost mod for a 18650 battery. links to sights would be most helpful, or even straight out help. But, I think I know the way this forum works; search, search, and if you can't find the info, search some more.

 

[CapeCAD]

For a single battery a boost mod would be best, search for posts using the ptn04050.

If you are set on a buck/boost you will have to design your own circuit using a pwm controller, lay out a pc board, and build it. Ti, National, Maxim, Linear Tech all manufacture pwm controllers that will work and offer sample designs to get you started.

 

[rusalka]

I need a schematic to that one. the ones that were posted have been deleted over time. Any help on that?

 

[CapeCAD]

I need a schematic to that one. the ones that were posted have been deleted over time. Any help on that?

This thread has schematics and pictures to help

 

[rusalka]

thanks for the help, but how do I go about making it variable? i want to be able to fine tune it "on the fly."

 

[rusalka]

For a single battery a boost mod would be best, search for posts using the ptn04050.

If you are set on a buck/boost you will have to design your own circuit using a pwm controller, lay out a pc board, and build it. Ti, National, Maxim, Linear Tech all manufacture pwm controllers that will work and offer sample designs to get you started.

Why would I need a pwm for this? I don't want to sound stupid or nothing, but help would be grateful.

 

[CapeCAD]

Why would I need a pwm for this? I don't want to sound stupid or nothing, but help would be grateful.

I suspected by your original post since you are using a single battery that you were really looking for information on a boost converter, but please correct me if I got this wrong.

You do not need a pwm if you use the ptn04050C, it is already included.

Voltage conversion requires a switch to turn on and off the supply voltage to allow the inductor time to charge and discharge, this is usually accomplished with a PWM controller. This can be accomplished using PWM output from an mcu, a 555 timer, or several other methods but a pwm controller is the simplest method.

A resistor/potentiometer between pin 1 and pin 3 is used to adjust the output voltage.

 

[rusalka]

Any recommended pot to use? looking for range of voltage between 4.5v to 6.4v.

 

[CapeCAD]

Any recommended pot to use? looking for range of voltage between 4.5v to 6.4v.

For the range you will first need to add a diode (~3Amp) with .5V drop to reduce the output from 5V minimum to 4.5V minimum

After adding the diode, you will need 9.5k resistor for 6.4V, and a 250kOhm pot in series to adjust down to 4.5V.

EDIT: I see what you mean, all old posts seem to have broken links to all schematics and diagrams.

 

[rusalka]

not to sound stupid, but a generalized shematic on what you are talking about would be most helpful, or even a verbal pinout would work.

Found the schematic on ti's website. I'm guessing the diode goes on pin three in series with the pot. Correct?

 

[CapeCAD]

not to sound stupid, but a generalized shematic on what you are talking about would be most helpful, or even a verbal pinout would work.

Something like this should work:

 

[rusalka]

Can you recomend some parts from electronic stores/web sites?

 

[altoids]

I also tried to make this mod got to 5 volts but as soon as I put on an atty power dropped in half chip got hot and I tossed the idea out the window. Way eaiser making a step down system to use then this

 

[CraigHB]

Doesn't surprise me. Off-the-shelf boost regulators like the PTN04050C are usually underpowered when you get into lower resistance or dual coil systems.

The dual battery with a buck regulator is going to be the best setup. They typically have much higher power outputs. You also get a wider voltage range. Boost regulators can not go much below battery voltage and are typically limited to 5.5V output.

An off-the-shelf buck-boost module is a rare animal. I have yet to see one. There are controller chips available that provide the functionality, but you'd have to design a regulator that employs one yourself. That's a job for an electrical engineer. For a layman, your choice is going to be limited to dual battery buck or single battery boost. Single battery buck-boost is going to be out of the question.

My favorite vendors for electronic components are Mouser and Digikey. Component wise, they'll have everything you need in stock and then some. For the e-cig specific stuff like atty connectors, MadVapes is who I use.

 

[rusalka]

I miss labeled the subject matter. I was after a boost system, sorry for the wrong title. I didn't, until now, what I was talking about. As far as the voltage I can settle with 6 volts, but wanted 5 volts. Also was wanting to go with a single 18650 as the power source. i don't like the fact of having to use multiple batteries, at a higher price, to do the same job.

Side Note: Anyone know of a "long life" 250k ohm pot that can be used in this application? As well as what amperage should I use for the resistors and diode?

 

[CraigHB]

I understand what you're saying. I also prefer a single battery booster.

The best pots are the worm drive ones like this

You can use 1/4 or 1/8 watt through hole resistors (1/8 watt if you want smaller physical size). Power rating for those is not going to be a concern since the currents are low.

I'm not sure about the diode. I've seen where a diode has been shown in-line with the atomizer to lower bottom end voltage range, but that also lowers the top end range. You won't want to do that since you're looking for maximum voltage output.

If you're talking about an LED indicator light, it depends on the LED. Usually, resistors in the 220 to 470 Ohm range are required. Again, 1/4 watt or 1/8 watt resistors should be fine. You can calculate an appropriate value for the LED resistor, but sometimes it's just better to try a range and see what you like best for illumination intensity.

 

[rusalka]

another question, but what type of caps should i use. the smaller the better in my situation. i'm dealing with limited space issues.

Side note: what is the power output on this booster?

 

[CraigHB]

You can get all of the information you need from the part's data sheet here.

The data sheet recommends using both ceramic and electrolytic in parallel pairs to limit ripple and increase stability, but I'm pretty sure you can get away with using just one of the other.

You can use capacitors like this if you want something cheap. For something smaller, but more expensive, you can use thesehttp://www.mouser.com/Passive-Compo.../_/N-5g8mZscv7?P=1z0wrkmZ1z0t6fn&Ns=Pricing|0 or these.

It's possible to solder the surface mount devices directly the part's PCB with short sections of solid hook-up wire. People have done that. Or, you can wire-in the leaded type.

I don't care for the tantalums that much because they have the highest ESR which is something you want to minimize, but they're going to be cheaper than ceramic and smaller than electrolytic for the capacitance value you need. Not positive, but I think they work okay with the booster.

 

[rusalka]

does it matter of the voltage on the caps? and what wattage should i use for the resistors?

 

[CraigHB]

Minumum voltage rating on the caps would be 10V. I linked to the 16V ones for the tantalum and electrolytic because they should not be operated over 80% of their rating. You could use 10V tantalums, they're cheaper, but you'd be operating fairly close to that 80% max. The ceramics are more forgiving and can operate at their full rated voltage. The high value higher voltage ones get really expensive so I linked to the 10V ones there.

You should be able to use 1/8 Watt through hole resistors if you like. You can also use 1/4W resistors. They are larger, but tend to be a little cheaper since they are more common.