A problem in the calculation for a hardware design

[ptc-4622978]

Hello,

I try to use Mathcad to calculate the resistor value in a NPN transistor switch circuit as below:

What I have done is as below:

1. First I define two variable, Upin which is the output voltage of MCU output pin, and Ube which is the voltage between transistor's base and emitter.

Normally these two voltages are constant, but I want to define them as variable that I can reuse this calculation.

2. Then I define the equation.

3. I provide the initial value of R1 and R2.

4. I define the constraint as Ib should be 10mA, and R1 should be equal to R2.

5. I invoke the 'find' function to get the value of R1 and R2. But it fails.

Attached please find the .mcdx file, could you please help me figure out the cause of this problem? Or let me know what I should do in Mathcad for my case?

Thanks.

[MikeArmstrong · Accepted solution]

Does the attached help?

Mike

[ptc-4622978]

Hello Mike,

It works. Thanks for your great help!