# Confusion with resistor and diode voltages when heated in a series circuit

Below there are two circuits supplied by a 10V supply. The only difference is the one on the left is 10k in series with 1k; and the one on the right is 10k in series with a diode.

If the resistor is heated its resistance increases. And if the current would remain the same we would say that the voltage across the resistor would increase. But the current will not remain same because the total circuit resistance increase will decrease the current. Will the voltage across the 1k resistor increase or decrease? Which one will dominate? Increase in resistance or the decrease in current?

If the temperature of the resistor increases resistance increases and this yields current decreases according to Ohm's law V = R * I. R is increasing and I is decreasing. In a practice which one dominates and what happens to the voltage across the 1k resistor?

If the diode is heated its DC resistance decreases. If the current would remain the same the voltage across the diode would also decrease. But since the circuit current will increase I'm again facing the same difficulty here. The diode DC resistance is decreasing which immediately should increase the circuit current. Again something is very cloudy for me to decide what happens to the voltage across the diode when it is heated in practice. Which one will dominate? Increase in current or decrease in DC resistance? How can it be explained step by step manner?

• 10k@10V limits the current to 1mA. At this current, self-heating of the diode is irrelevant, the power is at maximum 600mV*1mA=600µW. Commented Jun 4, 2018 at 0:58
• i dunno why u guys wanna change my question and answer something else ..
– cm64
Commented Jun 4, 2018 at 1:04
• This usually means your question isn't well-defined and takes a lot of abroads into the brush. Commented Jun 4, 2018 at 1:08
• I will make one other observation. If you want to create a voltage reference, the resistor circuit is better when the input voltage (10V) is well-regulated. But if the input voltage is variable, it may be better to use the diode as a voltage reference in spite of the temperature effect, because the diode is not very sensitive to input voltage. You can also look into temperature compensation techniques. Commented Jun 4, 2018 at 1:10
• @cm64 - "i dunno why u guys wanna change my question and answer something else" I don't think they're doing it deliberately. Obviously you understand the question, but I also interpreted it differently to you, due to the diagrams. Where they say "HEAT", they don't say "External heat applied here" and I thought they were trying to tell us which components would get hot by self-heating in the circuit. Your question also says "If the resistor [/ diode] is heated [...]" without saying the important word externally, so mis-interpretations could continue. Glad it was answered in the end! Commented Jun 4, 2018 at 1:13