Battery Charger questions

Products & Technology DSO Nano
#1

Good day to all.

Just looking a little more closely at the hardware schematic and see something that scares me: Diode D3 bypasses the Lithium Battery Charger circuit and dumps raw USB supply voltage directly into the battery.

This just seems wrong!

Vusb ranges anywhere from 4.2V on up to 5.2V (cell-phone charger). Most common is somewhere near 4.4V - 4.9V.

I have 2 issues with the diode:

  1. No current limit. If the battery want to, it can suck as much current as it wants. With some PC motherboards, that can be several Amps (they cheaped-out and didn’t put in current limit).

  2. Battery voltage too high if Vusb exceeds 4.7V or so.

I’m curious: why is that diode there?

dwayne

#2

Here you can get the data sheet for the charge controller:

http://www.datasheetcatalog.org/datasheet/lineartechnology/405442xf.pdf

And yes: I also think that you don’t need the Diode D3/S34 but maybe the designer wanted to override the charge ciruit to drive the DSO Nano with USB power if there is an usb connected.

…

Another hint: You can attach a charge indicator LED at Pin 1 (open Collector)

Form the data sheet:

“The CHRG pin (Pin 1) can sink up to 10mA to drive an LED that indicates that a
charge cycle is in progress.”

That’s a useful modifcation i think.

#3

If i got my DSO nano with V1.1 oder V1.3 hardware revision i will remove this diode completly.

The main question is: So why do you use a charge controller if you override its function with a diode ? The controller can’t control the charge current if the diode pushes the current of her own as in V1.1 oder V1.3 of the circuit.

The controller knows best what to do with the accu.

#4

There is not a charge controller on the board … Now VBus pass the D3 and connect to the Battery .

If we use the charge controller, the D3 will not solder in the board. But now the DSO just use the diode not the charger circuit.

#5

There is not a charge controller on the board …

There is no LTC 4054 on the board ? Removed to save money ?

Because on the circuit plan i can see this IC.

#6

There is some discussion related on this, perhaps this will give some info.
Im not sure though if this is the main reason why the IC is bypass.

viewtopic.php?f=12&t=495&start=30

#7

Because on the circuit plan i can see this IC.

There is a dotted line block around the charge circuit , it means that this circuit is reserve.