modified 10 years ago

Cannot find solution - opamp current source transistor matcher

01:31:00

The circuit is supposed to pull about 100 microamps through the top NPN transistor through the 6.8k resistor. If you know opamps its very easy to see this assuming an ideal opamp. Opamp imposes 5V across 51k resistor where the majority of the current must be drawn through the collector of the bottom NPN and consequently also through the top NPN. I am wondering why a circuit that is so easy to be solved by "inspection" cannot be solved by EveryCircuit. Anyone have any ideas? 

Well it turns out that you have to put switches across the collector and emitter of each transistor to get the simulation started up. Once the simulation is started you open the switches to see the actual circuit.

published 10 years ago

Timko

10 years ago

Delete 10 k resistor

Timko

10 years ago

And ground

Andrijlocarno

10 years ago

You can put the battery on the bottom left at -50V.

hurz

10 years ago

Not much time for this again, but a quick solution is apply a switch from emitter to collector across both transistors and keep it close while sim strat. After start you can open it. Hope this helps.

eeveleigh

10 years ago

The idea using switches works, thanks.

hurz

10 years ago

A single switch is also ok and makes life easier 😉

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