Swapping trim potentiometer with a digiral resistor on a Step Up Converter

Other Hardware General Electronics
21

OK. Zero volts if no drains are selected plus some bonus voltages, clustering around the existing values, if multiple drains are selected.

For the calculation, what I mean for example is that if you want a choice of 3 specific output voltages, you may just get lucky and be able to use only two drains pulling either one or both resistors to ground. It just depends on the required output voltage set. In practice, you are also limited by standard resistor values.

I should have said also that the maximum voltage is limited to the clamp diode voltage of the TPIC6B595 (50v). But the OP is working with a 35 volt boost converter so that should not be a problem here. A Zener diode across the top resistor may also be good.
Anyway, I've not tested it but I would be curious to see if someone can get it working in practice.

22

Why? It is only ever subject to the reference voltage as it is the low side of the divider, is it not?

That would depend on what "standard" series you are using, would it not?

23

Thank you for your explanation. I'll try to get my hands on some shift registers (and a few new Arduino boards) and play around with this setup.

I'll keep you updated with some results as soon as I had a chance to try it.

24

OK. Just remember that the circuit in post #15 was designed for the TPIC6B596 TPIC6B595, a high voltage low side (sink) shift register with 50v clamp diodes. It may not work with general purpose shift registers or for voltages which exceed 50v.

25

TPIC6B596 are actually quite expensive I just found out. They cost more than the entire XL6009 :sweat_smile:.

26

So you are ignoring my question. :face_with_raised_eyebrow:

27

Sorry. I've looked at it again. You appear, in this case, to be correct. The clamp diodes will have no effect on the voltage divider for the range of reference voltages which are relevant for most boost converters.

As for the resolution of resistor values, yes this does depend on the series and you can even probably create every desired value to a resolution of 1 ohm by combining series and parallel networks. However, in practice, you are limited to a specific value from the series. Yes, that does depend on what series you use.

28

They probably are. TPIC6B595 OTOH are relatively cheap, particularly if you source them from the same place as your XL6009. Care to explain where?

29

I corrected the typo inpost #24 . Yes it TPIC6B595. However, your main problem may availability rather than cost.

30

Just ordered some TPIC6B595 from AliExpress, just like the XL6009.

31

Thought as much. :grin:

Slow (though I am getting some things within two weeks recently, through a "combining" service) but generally reasonably inexpensive, especially compared for example to Amazon for what must be identical items.

How much different the quality control is for the traditional electronics suppliers (Mouser etc.) is a fascinating discussion.

It is possible that people are just beginning to wake up to the concept that we should not be having everything (or indeed anything) manufactured in China. :roll_eyes:

For example, X-ray contrast dye.

32

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