When the switch is connected to ground (on), the emitter-base voltage equals 12V.Why does this happens? Because there is still a differential voltage in the PNP transistor, between the emitter and the base. When using two different power supplies and PNP transistors, it could happen that the transistor is still on, even if you already have turned it off! It's very common when using microcontrollers. Since PNP transistors are polarized oppositely, it requires a clear path to ground. The equivalent schematic is displayed below and it requires an additional transistor to work. How to Drive the DC Motor with the PNP Schematic Then, the transistor is switched on and the motor begins to rotate. When the switch is turned on, (enough) current flows from the 5V power source from the base to the emitter. How to Drive the DC Motor with the NPN Schematic The emitter (for this switching model schematic) should be connected either to the ground (NPN) nor to the power source (PNP).ĭepending on the quantity of the base current, regulated by the base resistor Rb, the collector will allow a proportional amount of current to flow from the collector to the emitter (NPN) or vice versa (PNP). In both cases, the collector is connected to the circuit that we actually want to switch, where more current flows. The NPN is switched on when (enough) current is flowing into the base of the transistor, while the PNP is switched on when (enough) current is drawn from its base. The schematic is very similar except that for this circuit two power sources are used. In the previous post, we used a transistor to switch a LED. The Circuit to drive a DC Motor Switching Schematic of the Transistor Final ValuesĪfter the tests, here are the results that we have interest in. For the calculation, let's leave it at 20mA as midpoint but feel free to use any value between both measures. By using this tool, designers can select the most appropriate transistors for their circuit applications and minimize the risk of circuit failure.As you can see, the measures varies from 19.1mA to 159.9mA. It helps engineers and designers to optimize the BJT's operating conditions, ensuring that the device operates within safe and reliable limits. In conclusion, the BJT transistor bias voltage calculator is a valuable tool for designing and analyzing electronics circuits that use BJTs. This information can help the designer select the most appropriate transistors for their circuit application and ensure that the circuit operates within safe and reliable operating conditions. The user must also input the circuit parameters, such as the desired output voltage and current, as well as the load resistance.īased on these inputs, the calculator will generate the optimal bias voltage values for the BJT transistor, taking into account the transistor's voltage and current ratings, as well as the load requirements. To use the calculator, the user must input the transistor's datasheet parameters, such as its current gain (also known as hfe or beta), the maximum voltage and current ratings, and any other relevant information. The calculator takes several factors into account, including the desired operating point, the load resistance, and the BJT transistor's datasheet specifications. The BJT transistor bias voltage calculator is a tool that helps designers and engineers determine the correct bias voltage values for a given transistor and circuit configuration. The amount of bias voltage used is critical to the BJT's operation and can determine its amplification, switching, and operating characteristics. The basic operation of a BJT transistor involves applying a voltage difference between two terminals, called the base and emitter, which controls the current flow through the device. BJTs are electronic devices that can amplify or switch electronic signals, and they are commonly found in a variety of electronics devices such as amplifiers, oscillators, and power supplies. A BJT transistor bias voltage calculator is a useful tool for designing and analyzing circuits that use bipolar junction transistors (BJTs).
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