No, zener is a shunt device. It will not withstand 5 ampere peaks, which converter can provide , and tablet consume ,for short peaks. And 4,2v zener will leave you with 0,7v output instead of 4,3v you expect. You can add powerful schottky diode in series with output, thats much better , but diode voltage drop varies with current , so reguliation will worsen. At first, when you get converter, adjust voltage to minimum. Because you have removed battery, there is no risk to overcharge it, so some small overvoltage should not cause damage i think. In example , if it will adjust to 4,4V minimum , you can connect it , just watch polarity. Also wires from converters output will have some voltage drop, so under load voltage will sag anyway.
Ok, thats good. I was doing the research some time ago and I settled with 4.2v. I can't remember agruments for my decision anymore.
But lately I started searching a bit and I seen that some are using 4.4v indeed.
Maybee I just went a bit lower for tolerance purposes.
Will try the trimming when I get it and see where I am. Calculated is 4.35v...
But lately I started searching a bit and I seen that some are using 4.4v indeed.
Maybee I just went a bit lower for tolerance purposes.
Will try the trimming when I get it and see where I am. Calculated is 4.35v...
Also some small tip. How did you measured tablet consumption? I would recommend not to trust measurement tools ,because they display averaged values. If current varies from 5A to 0A , tool will display 2,5A . Try to put small resistor like 0,1 or even 0,01 ohm in series and measure voltage drop with scope , watch for peaks.
I had just received the converter.
Will see what is the voltage and drop it further if needed.
I measured consumption with DMM. I think that consumption should be pretty even with tablet with locked screen... no serious activity.
Will see what is the voltage and drop it further if needed.
I measured consumption with DMM. I think that consumption should be pretty even with tablet with locked screen... no serious activity.
Voltage won't drop bellow 4.58v... thats with Vo+ connected directly to TRIM...
Adding load won't lower it as expected since it is regulated output...
Will get the shottky diodes tomorrow...
Adding load won't lower it as expected since it is regulated output...
Will get the shottky diodes tomorrow...
So there are two possibilities: datasheet lie's about range of adjustment possible ,or your measurement equipment not accurate , maybe bad battery ? The choice is then schottky diode or special LDO ...
Wait a minute... Bad battery? Battery in DMM? It's low yes, I have low batt simbol on for some time now... let me change it real quick...
No luck, but it was worth a try... But I did noticed that voltage fails when I push range selector inwards....
It's a fairly new DMM (1st time I had changed the battery)...
I have another on in the garage... will get and grab it.
It's a fairly new DMM (1st time I had changed the battery)...
I have another on in the garage... will get and grab it.
For checking voltages like Li-on battery , every milliVolt is important ,to not overcharge battery .Not all tools have that accurancy. Had also once noticed strange voltage at li-on charge ic output , with dead battery fully charged ,my dmm displayed 4.25V , which could mean battery was killed by ic ,that was more than allowed by datasheet. But then i didn't knew , that it's my dmm was not properly adjusted ,or aged , and displayed higher voltage that it was actually .So sometimes don't trust your tools .
Nobody noticed or calculated ,that 5V adjustment range actually is not so wide ,to reach 4,35V ( 15% needed ).
Nobody noticed or calculated ,that 5V adjustment range actually is not so wide ,to reach 4,35V ( 15% needed ).
I'm out of luck, the other DMM shows the same...
I had calculated (5v ÷ 100%)*87% = 4.35v...
If only I could make sure 4.58v won't harm the device on the long run... but I cannot find any specs online.
I had calculated (5v ÷ 100%)*87% = 4.35v...
If only I could make sure 4.58v won't harm the device on the long run... but I cannot find any specs online.
Then probably adjustment range is not important parameter of converter ,and may vary from unit to unit .Datasheet just specifies maximum possible range,which is not guaranteed.
Try with schottky diode in series then ,and add some capacitor after it . With calculations you are right , i've mistaken somewhere .
Try with schottky diode in series then ,and add some capacitor after it . With calculations you are right , i've mistaken somewhere .
Ok, will go and buy them tomorrow. Will try to get 1N5823 as Osvaldo suggested.
Cap would be something around 100uF, or more like 1000uF?
Cap would be something around 100uF, or more like 1000uF?