Hi,

Hopefully someone with a lot more experienced than me can help.

My project needs a low temp coefficient DC signal level shifting for a low production cost project (e.g. less than £5).

There is no DC supply present and the input signal is too small to power anything from it. So I am restricted to passive components.

Anyway, a schottky diode with a series PTC thermistor to compensate for the temperature variation of the diode seemed to work well. However, I need a 7 and 28 ohm thermistor and they don't seem to be manufactured less than 100 ohms.

Can anyone suggest a manufacturer who supplies a PTC thermistor down to 7 ohms or a passive alternative.

Thanks in advance,
Rob

 

You want to lower the voltage or raise it? Little more info would help.

 

Ronv, thanks for your reply.

This voltage needs to be increased by a fixed amount of around 0.22v

The temperature variation (stretch goal) is 10mV over 20-50 degC

The simplified circuit is an input from a very small PV (sensor) panel to a load resistor to create a small voltage of around 1v. The output from the resistor is then fed via a reverse connected schottky diode to a 1k pullup to 5v (the pullup and 5v is another sealed mains driven module)

Hope this helps.

 

You say "There is no DC supply present" and then "the pullup and 5v is another sealed mains driven module".
I'm puzzled. Can you make use of that 5V to power a level-shifter, or not?

 

No. Not without breaking apart the module and tapping into that circuit and it will be a production unit.