DC Operating Point

Your Guide To LTspice. Learn DC Operating Point

DC Operating Point

DC Operating Point is a simple, but incredibly useful analysis. It will not give you anything to plot, but it will indicate voltages at all nodes and DC currents through all devices in the circuit.

Biasing in electronics means establishing predetermined voltages or currents at various points of an electronic circuit for the purpose of establishing proper operating conditions in electronic components. Many electronic devices such as transistors and vacuum tubes, whose function is processing time-varying (AC) signals also require a steady (DC) current or voltage to operate correctly — a bias. The AC signal applied to them is superposed on this DC bias current or voltage.

The operating point of a device, also known as bias point, quiescent point, or Q-point, is the steady-state (DC) voltage or current at a specified terminal of an active device (a transistor or vacuum tube) with no input signal applied. A bias circuit is a portion of the device’s circuit which supplies this steady current or voltage.Let’s consider an example for finding the dc operating point in LTspice shown below.

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This is a common emitter amplifier using 2N2222 npn transister. Common emitter amplifier is normally used for amplifying the signal strength. Here we are giving

Dc supply voltage Vcc=15v

collector resistance Rc=4.7k

Emitter resistance Re=4.7k

Resistance  R1=100k

Resistance R2=57k.

In order to do DC operating point  analysis in LTspice, first click on the simulation button. Then click on the edit simulation command. Then a pop will appear and click on the DC operating point as shown above. Next click on the  run button then result will appear. See the below result.

lt spice
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The result  shows all the current through the resisters (I(R1),I(R2),I(Rc),I(Re) ),current through terminal like (I(b),I(c),I(e)),and all node voltages.

Let’s know your comments and suggestions. happy reading..

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