Switch

This example illustrates how a timed switch can be used to drive a transistor. As the switch toggles at a set frequency, it alternately activates and deactivates the transistor. This switching action controls the current flowing through the collector resistor, allowing the transistor to function as an electronic switch. A voltage probe placed at the collector displays the resulting output waveform.

export default () => (
      <board schMaxTraceDistance={10} routingDisabled>
      <voltagesource name="V1" voltage="5V" />
      <resistor name="R_base" resistance="10k" schY={2} />
      <switch name="SW1" simSwitchFrequency="1kHz" schX={1.5} schY={2} />
      <transistor
        name="Q1"
        type="npn"
        footprint="sot23"
        schX={2}
        schY={0.3}
        schRotation={180}
      />
      <resistor name="R_collector" resistance="10k" schY={-2} />

      <trace from=".V1 > .pin1" to=".R_base > .pin1" />
      <trace from=".R_base > .pin2" to=".SW1 > .pin1" />
      <trace from=".SW1 > .pin2" to=".Q1 > .base" />

      <trace from=".V1 > .pin1" to=".R_collector > .pin1" />
      <trace from=".R_collector > .pin2" to=".Q1 > .collector" />

      <trace from=".Q1 > .emitter" to=".V1 > .pin2" />

      <voltageprobe name="VP_COLLECTOR" connectsTo=".R_collector > .pin2" />

      <analogsimulation
        duration="4ms"
        timePerStep="50us"
        spiceEngine="ngspice"
      />
    </board>
)

The simulation shows the voltage at the transistor's collector. When the switch is closed, current flows into the base, turning the transistor on. This pulls the collector voltage close to 0V. When the switch is open, the transistor turns off, and the collector voltage rises to 5V.