# BJT Voltage Divider Bias Design Template

## BJT Voltage Divider Bias Design Template – Mathcad

This design template comes in two formats. First is in Mathcad and the second one is in excel. The equations are derived in Mathcad. This is all you need to design such circuit. No need to go back to basics and perform research again on how to derive equations. It is all done in this BJT Voltage Divider Bias Design Template.

The derivations are based on the circuit above. Just neglect the values, only the variables are useful during derivations. The circuit is obvious a voltage divider configuration as we learn from the universities. The derivation of the equations can be difficult to others especially when they already forget what they learn from the universities or simply to those not an electronic engineer or technician. However, that is not an issue anymore. All the equations are derived. Despite, both the templates are automated, no need to learn the equations. Just put values into it.

### Some Snapshots of the Derivations

Once you download the Mathcad template, you can see all the derivations. To those who do not have the Mathcad tool, don’t worry, there is a PDF version of the derivations. You can still check the equations if you doubt it.

### How the BJT Voltage Divider Bias Design Template Works

There is nothing special to do. Just download the Mathcad template. All the green fields are inputs. the user will provide data for that. On the other hand, all the yellow fields are computation results. That must not be altered.

Once you supply the values in the green fields, the template will do its job. Your design is done. As simple as that!

## BJT Voltage Divider Bias Design Template – Excel

If you have no Mathcad tool, nothing to worry. The template has an excel version. The same with the BJT Voltage Divider Bias Design Template in Mathcad, all the green fields are user inputs while all the yellow are calculation results.

Excel is a very common office tool. Thus, everyone have access on it.

The template computes the current of each device, it calculates the power dissipation and also give the power stresses. The template will also indicate the transistor circuit operation which is either linear or saturation. It will also give the VCE and Vout information.

## Design Sample Using the Excel Template

In this example, we will use the transistor PBSS4160T-QR from Nexperia. Assuming the ambient temperature where the design is to put is 50’C, then the resulting power dissipation of this transistor is

Power dissipation, de-rated = (Tjmax – Tamax) / Rthja = (150’C – 50’C) / 312K/W = 0.321 W

Where Tjmax and Rthja are both provided in the datasheet as below image.

We will put the 0.321 W under the field Q1 Power Rating of the NPN Fixed Bias Design Template in excel. From the datasheet also, the minimum beta is 100, and put this to the excel template under Beta_device_minimum.

For the VCEsat and VBE, I am considering for both the maximum values and put to the designated fields.

With the other inputs in green fields, the power stress on Q1 is 1.41%. As simple as that!

The download package has three files with all same file name. They are for excel template, mathcad template and the PDF copy of the derivation in mathcad.

When you download the BJT Voltage Divider Bias Design Template and run into troubles, please email to [email protected]. We are happy to help you. We are also open for consultations.

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