need some help with resistor values

[petehall347]

Re: need some help with resistor values

any thoughts on correct value for R4 ?

[R_J]

Re: need some help with resistor values

I can make out a 4 and a 0 so it might be a 470 (47Ω) try cleaning it off and see if you can read the number.
Is it between the ic drive output and the fet gate?

[petehall347]

Re: need some help with resistor values

i thought 470 too . think its across D7 will check later

[petehall347]

Re: need some help with resistor values

ok R4 connects from IC to gate so must be gate resistor .
it also connects to R5 and R11 .
D7 also connects to ic same pin then to R5 then to gate
so need to now know correct value for R5 as was earlier thought to be gate resistor i think .

[petehall347]

Re: need some help with resistor values

looks like same as R27 on this schematic ....page 17

[R_J]

Re: need some help with resistor values

I suspect R5 would be a low value also, maybe in the 30~50 ohm range? This is just a guess based on other schematics.

[petehall347]

Re: need some help with resistor values

i cant even find any schematics with values on the resistors . most schematics i have looked at dont even have the diode and resistor in series . what is the purpose of them i wonder ?

[R_J]

Re: need some help with resistor values

The resistor is used to adjust the mosfet turn on speed and stop gate loop ringing, basically the diode is used to help turn off the mosfet. I suspect the resistor in series with the diode is to adjust the turn off speed.
See page 2, it shows this configuration
In post #19 I mentioned the ncp1251, It is not a replacement I only mentioned it because the way it operates is similar and the datasheet is in english

Here is a Chip-Rail CR6853 datasheet, in english. I suspect it is very close to the CR6855, and you can see how it operates.

[petehall347]

Re: need some help with resistor values

thanks for the info .
i am not too good at following the calculations . what value resistors would get me in the ballpark ?

[R_J]

Re: need some help with resistor values

The Chip-Rail datasheet was so you could see what voltages (ie:VDDon) are required to get the ic working which should be similar to the ic on the board (which is likely dead) R6 seems to be 47Ω so I would try a 47Ω for R5 as well.
I doubt you would be able to calculate the values from the datasheet, they likely picked them with the operation of the mosfet in mind. Without another board or schematic I don't know how else you will find the exact values.
On R9 I can make out a 5, my guess would be it was a 0.5Ω 1~2 watt but I could be wrong.

[petehall347]

Re: need some help with resistor values

nice one thanks . will update as to what happens when i have the parts and fitted them . might take a while as have to go away soon .

[R_J]

Re: need some help with resistor values

Have you priced out a new charger or looked for a good used one? it might be cheaper to go that route then trying to repair this one.

[petehall347]

Re: need some help with resistor values

nothing available at all .
i did think like i mentioned earlier to get a plug in supply and wire to charging terminals . just need to know the right one to get . original is 18v 1500ma . i guess it should actually be higher than 18v though with the battery being 18v . just crossed my mind with that is there wont be a light to say the battery is charged .

[petehall347]

Re: need some help with resistor values

am thinking i could use this . all i need to do is transfer the led part and wire the charger to original box . https://www.ebay.co.uk/itm/Workzone-...ess-Batteries-

[redwire]

Re: need some help with resistor values

I found typical part values for CR6855 in a 12V 3A power supply and 5N60 MOSFET, and laptop 19V 2.1A application.

R9 Current-sense I see a "5" and guess it was 0.56 ohms.
R6 Gate drive on I see a "4" and guess 4R7 as datasheet says its 1-5 ohms.
R5 Gate drive off ... I would guess the same