@Robert93820
Hi Bob, you really are a great help for newbies like me i feel lucky to have you looking over my shoulder. Thank you.
Yes of course it is easy to have all these ideas but then suddenly realise when someone like you comments there is a finite amount of power available and a bit her and bit there and pretty soon there is non left for the primary job.
Before i changed the circuit to include a Tranistor i had thought a Mosfet would work and did research that option but then was worried i was making mountains out of molehills but given your comments regarding the voltage drops it certainly is an option worth looking at and thank you for your thinking and input.
Could the Tranistor just be replaced with a NO mosfet and a similar power process be used to power the gate?
Cheers
Hi Leslie
Not Really
It is the 1N4007 Di that is the problem.
Cheers Bob
@Robert93820
Bob, my apologies, I misread your previous post and obviously misunderstood the Diode you were referring to although you made it pretty clear in your post. So I now understand the problem and have done some reading and exploring. As I understand it and as you mentioned if I replaced the D1 with a B0530W Schottky diode which according to its data sheet has 435mV Vf at 0.5A and 375mV at 0.1A then the LIPO battery will only charge to a maximum of 4.2v-0.435v=3.765v. Is that correct? And the charger will sense that the battery is at 4.2v when in reality it will only be 3.765v so there, at least, should be no overcharging problems with the LIPO. Downside I imagine is the battery will need to be recharged more frequently. At least that is what I think but hopefully you may advise.
Cheers
Les
Hi Leslie
Where and what is the LIPO charger located and is it powered by 5V with a USB type connection as most are.
If it is on the same mother board as everything else and the 5V (I am assuming 5V) input to it is accessible there may be a way to get rid of that diode and still disable the converter when the battery charger is powered.
Cheers Bob
Hi Leslie
I am assuming what I replied above re LIPO charger is correct and it is one of these stand alone boards powered bu 5V with USB type input.
The little modification should work.
If you want to use a Mosfet instead of the transistor change the base (gate) resistor value to about 1K
The resistor base (gate) to ground remains 10k
Cheers Bob
@Robert93820
Hi Bob,
That is a very clever solution to the problem. In my case because the charger is in a separate casing from the lamp BuckConverter and Battery I will need to look at an additional connection from the charger to carry the 5v. Cuently the design uses 2 pogo pins (PP1 &PP2)to connect the cahrger base and the portable lamp when recharging is required so I will need to add a third pogopin to connect that 5v. I will see how I can work that in to the design.
On another question when I developed my previous schematic with D1 in use I had wondered about putting a Resistor from the Transistor base to Gnd as I had seen that done elsewhere but without knowing why it was there I left it out. You have put it in. What is its purpose in the circuit. Just trying to learn as I go so hope its not a silly question.
Cheers
Hi Leslie.
A bit of insurance to make sure the transistor is off when no voltage on the base and therefore no current into it.
This is essential with a Mosfet as the gate capacitor will charge and if there is no resistor to discharge it it will never turn off. Even if power is removed and restored. If a Mosfet is DRIVEN both high and low there is no need for this resistor as the driving circuitry both charges and discharges this cap. Having said that it is a good idea to include this resistor as a safeguard.
Cheers Bob
I didnāt realise that. I thought the charger might be with the buck converter and battery and you were just plugging in a 5V source. Makes things a bit more difficult. Another hurdle ??
@Robert93820
Thank you Bob, not a hurdle but a challenge and i have been so enjoying all of them on this journey and have learnt so much along the way much of it from yours and similar posts.
The use of resistors and caps as insurance and filters is still very much of a mystery to me as while i can see and understand circuit logic and the actions of components I havenāt yet discovered the logic in resistors and caps sometimes seemingly used randomly. Maybe it is only something experience can teach you.
Recently i came across a IC i did not know of. It is a constant current LED driver and from what i have seen it might be a far better solution to my requirements than the buck converter circuit i have currently used. Given all i am doing is powering an LED from a Li-ion battery have a built a mercedes where a VW would do? Love to have you opinion.
Cheers
Les
Hi Leslie
If only 1 or 2 LEDs a resistor would do.
Constant current LED drivers have been around for a long time. Usually used to drive large LEDs with a constant 700mA or I think 300mA. I think the voltage gets up around 36V or so.
A constant current source is not difficult to make and can be simply a transistor, 2 resistors and some sort of reference voltage.
You should do some study of the basics, Volts, Amps (current), ohms (resistance) and power (watts) plus capacitors, inductors and their uses. Just a bit of basic knowledge will make it far easier to understand what is going on. There are a couple of useful snippets worth remembering and thinking about.
Batteries DONāT āstoreā electricity. The charge and discharge cycles are chemical actions. The only thing that āstoresā electricity is a capacitor. But for the sake of simplicity batteries are considered storage devices as you put electricity in and get electricity out (rechargeable anyway). But it doesnāt hurt to know the ātrueā state of play.
Fuses donāt āprotectā a piece of equipment. That equipment is usually faulty and is the cause of fuse failure. A fuse protects the supply and wiring to that equipment. Most semiconductors will fail long before a fuse will blow.
and sometimes ARE used randomly. Just chucking a few caps around a circuit to get rid of so called noise etc can sometimes lead to some very obscure problems. You really need to think about where you put them and what type of cap to use.
There is lots and lots more but you will find a basic understanding of the fundamentals will make your journey down this path a lot easier.
Cheers Bob
Hi Bob,
Thank you for your reply and advice. I feel I do have a pretty good understanding of the basics you suggested and have learnt that over many years during which I have gained a good understanding of power, volts, current, capacitors and resistors and the parts they play in any circuit. In more recent times I have read, studied and learnt about inductors, diodes, transistors, op-amps, mosfets, logic gates and much of the modern electronics as my early basic knowledge was gained nearly 60 years ago ( I am 78 yo) when I was in my 8-20 years age period and building crystal sets then vacuum tube receivers and transmitters from parts and help I was given by Dr Peter Jeffreys (UWA professor of Electrical Engineering) our friend and neighbour at that time. Back then I was intent on being an electrical engineer and took all the science classes at my school with that ambition in mind. I subsequently chose Architecture as my profession instead of EE and in that process I received a very good education in basic electrics and advanced maths and calculus and logic so am fairly comfortable with the maths and the processes of schematic interpretation and understanding.
It is however the basic nuances of the schematics I study that I am trying to better understand.
Terms such as ānoiseā and āfiltersā etc and their effect on a circuit and in that you are right as I do need to get a better understanding of why they are in the place they are in the circuit and what their intended to achieve, why they achieve it and how to determine sizes etc to meet the intended requirements and, most importantly, what their effect will be on the circuit. So I will continue my studies no doubt asking more questions as I go:-)
Regards and please know I really do appreciate your generous help, advice and assistance.
Les
Hi Leslie
Interesting times. I too am getting a bit long in the tooth (86 last month).
A little scenario to get you thinking.
On a piece of paper draw a wire (straight line will do).
Draw a capacitor from one end to ground. Depending on size and type this should bypass interference to ground at that point.
Draw another capacitor from the other end to ground. This appears to be a piece of wire with a cap at both ends and should bypass interference at both ends, right?
Wrong!! Not so. That wire is an inductor (and yes the inductance of a piece of wire can be measured).
Now redraw that straight wire as a coil. What do we have? A tuned circuit.
Now it does not take much imagination to see that problems could occur if this tuned circuit is excited at or near its resonant frequency. Circulating currents and voltage across such a circuit could be substantial.
Remove one cap and the tuned circuit disappears.
This is an example where throwing capacitors around at random is not the answer. Particularly if you are trying to filter out unwanted interference. a general rule would be to only use 1 cap on any length of wire. Choose the point closest to where the interference could cause problems.
Cheers Bob
I had a think about the charger connected while discharging problem. I donāt think it is a problem. The mode of the charger is determined by the battery voltage. If the battery shows 3V or less, the charger uses a low current to try to recondition the battery to bring it to 3V. If it is 3V to 4.2V it charges at constant current. When it reaches 4.2V it switches to constant voltage.
The maximum current the charger provides is 100mA or 500mA (there is a link to change this). The current draw is more than 500mA when the LED is on, so the charger will go into constant current mode delivering 500mA when the battery voltage falls below 4.2V and the battery provides the rest. When the LED is switched off, the charger will continue to provide 500mA until the voltage goes back to 4.2V when it will switch back to constant voltage mode.
Without looking at the specification of the IC used in the charger, this is supposition. But given the price of the charger, it isnāt going to be smart. Iād be confident it works as Iāve described.
If the current drawn by the load were less than the charger current, the situation may be more complex. The charger would switch between constant current and constant voltage repeatedly. Maybe that could cause a problem, I donāt know.
back conversion is a very wide topic that requires a lot of time to master. You need to have basic information about the back converters and also have other information on how to do tis through simulation using the EDA software. You dont need to guess around, just let the EDA software do you the tough job. Learn more about inverters on Introduction to Multilevel Inverters - The Engineering Projects
