Voltage Shunt Circuit

Thread Starter

wbhowarth

Joined Mar 9, 2021
9
Hello friends,

I am working on a solar powered battery charger for three NiMH cells. Panasonic recommends a few different charging methods, while not ideal I have opted for upper battery voltage limited for simplicity's sake.

So, with each cell at 1.2V I would like to create a shunt to ground that will engage at 5V and an additional shunt that will disengage at 2.4V.

My initial thought was diodes, but I'm not sure this is practical. I was thinking of multiple diodes in series to create 5V total forward voltage, but this would be several diodes and my gut tells me this is not a good solution. Are there diodes designed for specific forward voltages to accommodate a shunt like this?

Thanks!
 

crutschow

Joined Mar 14, 2008
29,519
with each cell at 1.2V I would like to create a shunt to ground that will engage at 5V and an additional shunt that will disengage at 2.4V.
Why two shunts?
Don't you just want to engage one shunt at 5V and disengage it a 2.4V?

How much current do you need to shunt?

Why a shunt regulator instead of a series regulator?

A TL431 programmable accurate shunt voltage reference can be adjusted to the desired shunt voltage using two resistors.
 
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Thread Starter

wbhowarth

Joined Mar 9, 2021
9
Why two shunts?
Don't you just want to engage one shunt at 5V and disengage it a 2.4V?
Hi crutschow, thanks for the reply. You are right to question, my thought was half baked. The "switch" at 2.4 volt should not be a shunt. It will be tied to a uC pin to initiate charging upon going low. Obviously shunting the charging current would not be ideal!

How much current do you need to shunt?
Approximately 500mA, so a shunting IC with a higher current rating might be ideal for the upper limit, but the lower will require another solution.

One of the main obstacles I have encountered is the lack of a constant voltage in the circuit. The solar cell voltage will vary considerably up to a maximum output of 5.5V. If I am understanding correctly, the TL431 provides a ~2.5V reference voltage so long as the anode voltage is 2.5V or greater?
 
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