# Digital thermometer

Discussion in 'Homework Help' started by JoyAm, Sep 10, 2014.

1. ### JoyAm Thread Starter Member

Aug 21, 2014
112
4
I am supposed to be able to calculate the room temperature using this two diode circuit but i have no idea how, can you give me some hints ?

2. ### dalam Member

Aug 9, 2014
58
6
Voltage drop across diodes depends on temperature.

JoyAm likes this.
3. ### JoyAm Thread Starter Member

Aug 21, 2014
112
4
By the factor VT=K*T/q ?
and i will use this VD=VT*ln(ID/IS)
in that case idk what the value of IS is

4. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
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Not sure that V(x)-V(y) is any better than V(x) or V(y) by itself...

5. ### JoyAm Thread Starter Member

Aug 21, 2014
112
4
The V(x)-V(y) represents the Vp .But well i still dont know how can i solve it

6. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,066
Start here...

The simulation shows the temperature dependence of the forward voltage drop of two ideal diodes with different forward currents. Vp = V(x)-V(y)

7. ### JoyAm Thread Starter Member

Aug 21, 2014
112
4
T=vp*q/(ln(I1-I2)*k) is that right ?
Oh i think i got it just give me some minutes

8. ### JoyAm Thread Starter Member

Aug 21, 2014
112
4
Or not...
Vp=(k*T/q)*ln(I1/I2)
dVp/dT=0.139=(k/q)*ln(I1/I2)
so from that we can calculate the k/q
and then i dont know

Feb 17, 2009
3,995
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10. ### JoyAm Thread Starter Member

Aug 21, 2014
112
4
this looks like what i got on post #7 but still how can i use the gived dvp/dT to solve the problem ?