Monthly Archives: April 2013

Transistor biasing in amplifiers and Opamp Voltages

This applies to the problem of proper biasing in transistor amplifiers. Take a look at the diagram shown below:

The biasing on the left is the correct biasing while the one on the left is the incorrect one. The wire from Ci should be should be shorted with the resistor network as shown in the circuit and should not overlap it like the second example. In the case of the wrong biasing, since the base-emitter junction had got no biasing at all, the BJT never gets on and you will not get any output at all from the amplifier. Many people tend to make this mistake and thus the biasing of the BJT is not proper.

Opamp input voltages

When connecting a circuit with an opamp remember that the input voltages given to the opamp should not exceed the Vmax and Vmin values set in the opamp properties. Alternatively while using a five-pin opamp, the input voltages should not exceed the voltages set for the supply voltages for the opamps. If the opamp uses a supply of +15 to -15 V then the input should not cross this threshold. If it does happen  to then the circuit simulation may happen to fail. While designing the circuit, ensure that you give input voltages that do not exceed the voltage limit set by the opamp.

For any queries feel free to leave your comments.

Don’t forget the ground on both sides of a transformer circuit!

Hi folks, greetings from DoCircuits! It’s great to see everyone having fun learning with DoCircuits. As promised we have been introducing new features and components to enrich your learning experience on a regular basis. We hope you have found them useful and user-friendly. That on one side, we have found some recurring issues related to some type of circuits from the simulations you have run. Let’s try to get those issues addressed in this blog and the ones that follow.

Consider a basic full wave rectifier as shown below:

Note the ground that is connected at the transformer primary to the negative terminal of the input supply. Most circuits that you find online or in text books don’t show this ground and so you may not use it while connecting the circuit. But for our simulator to understand the negative terminal as a reference point a ground has to be connected. If that ground is missed the output will be zero when measured at the input. Similarly if ground is not connected at the secondary you will get an erroneous output.