*Boosting 3V to 5V (using discrete components)

retched

Joined Dec 5, 2009
5,207
Battery charging ICs will vary charging output based on the batterys chemical make-up, temperature, voltage, current, and even time.

It is an all in one deal.
 

Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
Battery charging ICs will vary charging output based on the batterys chemical make-up, temperature, voltage, current, and even time.

It is an all in one deal.
Absolutely sir, charging ICs is an all in one deal. . .but if you cannot avail those ICs just like me, I think you will do the same :) What do think is needed to adjust the 0pt current of the ckt. automatically according to its load? Thank you
 

Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
Hello,

The start of the turns are on the right side for both coils.
I think AWG 22 wire will work.
http://www.hardwarebook.info/AWG
You can use enamel wire on a toroid.

Greetings,
Bertus

Hi there,
0k I will look for AWG 22 magnetic wire.
Regarding the diagram, do you think RC ciruit in the zener is needed to improve it?
LOW ESR capacitor is essential in this ckt.? That is low voltage rating capacitor?
1000uF/ 12V is better than 670uF/ 25V?

Thank you.
 

retched

Joined Dec 5, 2009
5,207
You should at least use a diode to drop the voltage to a proper level for charging.

You will need a way to disconnect the charging circuit for a moment to get the voltage of the battery throughout the cycle. The easiest (not the best AT ALL) Would be to set your output by chart. and timer. Many el-cheap-o battery chargers use a timer circuit and thats about it.
 

Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
You should at least use a diode to drop the voltage to a proper level for charging.

You will need a way to disconnect the charging circuit for a moment to get the voltage of the battery throughout the cycle. The easiest (not the best AT ALL) Would be to set your output by chart. and timer. Many el-cheap-o battery chargers use a timer circuit and thats about it.
A 4V7 ZENER? Anyway, do you think 3v can be boost to 5v without using a inductor? I only need 500ma 0pt. current.
 

retched

Joined Dec 5, 2009
5,207
You only need 500mA? Without an inductor? When you figure that one out, we can go into business together. The largest IC I can find is a Voltage pump that will give you 250mA at 5v.

You do not have access to any ICs?

If you have access to any broken equipment or old transformers, you can use the wire out of it to wind your inductor.

Maybe you should open an electronics supply store instead! Think about all the customers you could serve, and how easy it would be to grab an IC off the shelf.
 
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ifixit

Joined Nov 20, 2008
652
I put together this booster circuit that seems to do the job, although it needs more testing and a circuit to detect full charge voltage.

I have more details if there is interest.

Good Luck
 

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Audioguru

Joined Dec 20, 2007
11,248
I put together this booster circuit that seems to do the job
If you don't limit the current, regulate the voltage and stop overcharging when the battery is fully charged then the battery might catch on fire. Maybe the 2 ohm resistor will limit the current enough.

It looks like the output is 5.4VDC with a 3.0V square-wave input and will be higher when his Lithium input battery is fully charged..
 

ifixit

Joined Nov 20, 2008
652
Audioguru:

C3, C4, R4, & R3 are choosen to transfer only enough energy to charge ~500mA to a flat (3.7V) battery. The current reduces to 300 or 400mA as the voltage approches 4.2V. The voltage doesn't need regulation during charging, but of course more circuits need to be added yet to stop the charge when 4.2V is reached. This crude method does not ensure a fully charged battery, or that it won't be slightly over-charged. Hopefully, it is good enough for Juan needs.

Juan:

This is definately not the best way to charge lithiums, but you seem to have limited resources and asked if it could be done without inductor or special IC.

Whatever design you decide to use, do the control circuits all have to run from a 3V supply, or is a higher voltage available? 5V at 50mA would be nice. Cheap mosfets need more than 3V on the gate. You may need another charge pump to get an auxilary voltage at low current.
 

Audioguru

Joined Dec 20, 2007
11,248
Juan does not have a 3V supply. He is using another 3.0V to 4.2V Lithium rechargeable battery to drive the voltage stepup circuit so the output will be a voltage that is too high to charge the other Lithium rechargeable battery.

Maybe he is making a perpetual motion machine. The battery voltage is stepped up and this voltage charges the same battery.
 

Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
I put together this booster circuit that seems to do the job, although it needs more testing and a circuit to detect full charge voltage.

I have more details if there is interest.

Good Luck
Thank you sir for your reply I really appreciate it. Could your ckt. can be modified to charge LI-ION battery with lessen component without the use of a inductor. What I mean is a charge-pump ckt. using BJT discrete components. So, I think if I will need only 300mA or less charging current to charge a LI-ION battery from a source of 3V7/ 1800mAh, can we make a charge pump ckt. with lesser component and using only BJT discrete components? Thank you
 
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Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
Hi everyone,

Regarding the boost circuit with inductor schematic diagram. .Can you please explain to me the function of each component and its operation in the circuit because I am very curious how it is functioning. I hope you can help me out. Thank you.
 

SgtWookie

Joined Jul 17, 2007
22,230


C1 effectively decreases the impedance of the battery labeled "Vin". Without it, more power would be dissipated in the battery due to it's internal resistance.

T1 and Q1 basically form an oscillator. R1 limits the maximum current through the base of Q1. Initially, current flows through both windings of T1; some current goes through the main winding through D1 to charge C2 via the upper winding, and some goes through the trigger winding via R1 to the base of Q1.

When Q1 finally turns on due to it's base current via R1, the output of the main winding is pulled to 0v. As current starts flowing through the main winding, the trigger output goes low, turning off the transistor Q1. Since there is no longer a current path through Q1 to ground, the output side of the main winding increases in voltage until it exceeds the forward voltage of D1 + the voltage on C2, and the charge on C2 is then increased via current flow through D1.

As current through the main winding decays, the current on the trigger winding starts flowing back through R1 to the base of Q1, turning it on, repeating the cycle.

This continues until the current flow through D2/R2 exceeds about 1.91mA, at which point the voltage on the base of Q2 is about 0.63v, which starts to turn Q2 on. When Q2 is turned on, it starts sinking current from R1, which prevents Q1 from being turned on.

Standard Zener diodes are rated for breakdown voltage at 10mA to 20mA. In order to get a reasonably accurate output voltage, it will be necessary to select a low-current Zener, and add it's value to the Vbe of Q1 when it's conducting.
 

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ifixit

Joined Nov 20, 2008
652
Hi Juan,

Here is version 2 of my pump charger. It does not use MOSFETs, inductors, or 555 chips. Hopefully, you have access to transistors, resistors, caps, & diodes.

Circuit Operation

Q7 & Q6 are a multiviberator running at ~1KHz from a 3.7V supply. Q8 buffers the multi's square wave signal. Q3, Q4, Q5 and related components provide extra gain and drive Q1 & Q2 such that Q1 & Q2 are never on at the same time.

Q1 & Q2 drive the pump capacitor C3. C4 stores the charge, which can go up to ~7 volts with no load, or no battery to charge, and no limiter. C4 also smooths the charge pulses to an average of 300 to 400mA into a 3.7V lithium battery. R3 and R2 can be changed to adjust the charge current to suit, which remains relatively constant throughout the charging cycle.

Once the battery voltage reaches ~4.1V, D3 conducts turning on Q9, and inhibiting Q2 from turning on, which therefore limits the charge current to hold the voltage at approximately 4.1 volts. D3 is a 3.9 volt zener, which can be a 1N5228 or 1n748. The current limit point can be adjusted by changing R15 or R16. This is not the best way to determine if a battery is fully charged, but since you have limited resources, it will have to do.

You don't have to use the devices I used, they can be subsituted with whatever you have that is equilivent, or better. C3 or C4 can be made up from five 1000uF caps in parallel.

Inductors or not, that is the question. The pump circuit has alot more parts, but at least you don't have to wind any of them.:)

Good Luck
 

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Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
Greetings,

Thank you guys in supporting me. I really appreciate all the knowledge that I have learn from you.
Sorry for not updating this passing days 'coz we had an internet connection problem here in our province.
Regarding the ckt. I've decided to construct those two circuits. That is, the one with inductor and the charge pump by ifixit. I wil diffentiate between those two ckt. that will fit to my needs.
 
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