UJT Oscillator current analysis

[kingh12]

Hi,

I am designing sawtooth generator circuit by using UJT. The circuit is shown below. When I look throught ossiloscope the output signals are suitable. But I don't know how to calculate the current on R1 and R2..So I cant compare the output voltages between measured and calculated. Can anyone help me about how to calculate these currents. What can be the formula? This will help me for testing the voltages on ossiloscope.

Thanks..

 

[ericgibbs]

hi,
The 3 channels on the scope have been set to AC input, this means that we can only see the voltage change.

If you select DC , knowing the supply voltage to the circuit, you should be able to work out the currents.

Repost your scope image with the readings set for DC, lets know the supply voltage.

E.

 

[kingh12]

when I try to set the channel A to DC, the signals are being lost on scope.So I left it stayed on AC mode.. the other channel b and channel c shown in figure

 

[kingh12]

As a result I cant find out how to calculate the voltages on channel a and channel c

 

[ericgibbs]

View attachment 72698


when I try to set the channel A to DC, the signals are being lost on scope.So I left it stayed on AC mode.. the other channel b and channel c shown in figure

Consider R1 first.

Set the scope to DC, connect the Chan A input to 0V on your circuit and note where the trace lies on the Y axis.

Connect the Chan A input to the lower end of R1, adjust the Chan A sensitivity until you can see the DC trace [ recheck the 0V position.]

Now knowing the supply voltage to the circuit you should be able to measure from the scope trace the difference between the v supply and the lower end of R1.

use Ohms Law to calculate the current thru R1.....

Do that first and show me what you measure.

 

[kingh12]

Thanks ericgibbs, I figured out the currents from looking at scope. But actually this is not the thing that I want. I mean if I have not scope, how could I calculate the currents or voltages by theoretically. I want to find them theoretically and compare the results with scope results. If I were using bjt transistor, I would figure it out with the beta value and would find Ie by Ib, but using the ujt I cant imagine that. There is no Ic current or there is no ratio between Ie and Ib..We have just eta value. Am I wrong? This is the point I've been lost

 

[ericgibbs]

hi,
I thought you wanted to check the parameters of your circuit UJT.

This link will give you a starting point.

https://baec.tripod.com/DEC90/uni_tran.htm

To compare any device you should have a copy of the manufactures datasheet for the device.

Its not an easy task to duplicate the manufacturers testing procedures.

Lets know how it goes.

E.