This circuit is like a bouncer for electricity.
It uses a transistor like a gatekeeper and a special diode zener diode to make sure the voltage stays steady.
The zener diode is like a set point, and the transistor copies that voltage keeping it constant for your electronic devices.
This is great for projects where ups and downs in voltage can mess things up.
The transistor can also handle a lot of power, so it is good for projects that need a bigger jolt.
What is a Voltage Regulator Circuit using Transistor and Zener:
A voltage regulator circuit using a transistor and zener diode is a simple way to regulate and stabilize the output voltage of a power supply.
This type of circuit is often used in applications where a constant voltage is required, such as in electronic devices and power supplies.
Circuit Description:
Parts List:
| Type | Specification | Quantity |
|---|---|---|
| Resistor | 1k | 1 |
| Semiconductors | Transistor TIP142 | 1 |
| Zener 11V 1W | 1 |
This is a darlington NPN power transistor.
It consists of two NPN transistors connected in a darlington configuration providing high current gain.
The Zener diode is used as a voltage reference.
When the voltage across it reaches its zener voltage, it starts conducting in the reverse direction, maintaining a relatively constant voltage drop.
There should be a resistor connected in series with the base of the TIP142 to limit the current flowing through the base.
Operation:
The zener diode is reverse biased and conducts when the voltage across it reaches its zener voltage.
This voltage is 11V in this case.
The base of the TIP142 is connected to the zener diode.
This setup biases the base of the transistor at a constant voltage of 11V.
The TIP142 is configured as an emitter follower meaning its emitter follows the voltage at the base minus a small voltage drop approx 2V for the darlington configuration.
This configuration provides a stable output voltage.
As the zener diode maintains a constant 11V at the base of the TIP142 the emitter voltage will be approximately 11V to 2V = 9V.
This provides a regulated 9V output across the emitter and ground of the transistor.
The darlington configuration introduces a voltage drop of around 2V.
This drop is taken into account when calculating the regulated output voltage.
Formulas:
Below are some relevant formulas for to regulate a DC input voltage to a fixed output voltage.
- Output Voltage (Vo):
The voltage of the zener diode (Vz) is about equivalent to the voltage of the voltage regulators output.
2. Base Resistor (Rb):
The base resistor (Rb) regulates the transistors current flow and biases it, the formula below can be used to determine its value:
Rb = (Vin – Vz) / Ib
where,
- Vin: Input voltage i.e 12V to 24V
- Vz: Zener diode voltage 11V
- Ib: Base current (typically a small value, around 1mA)
3. Power Dissipation in Resistor (Rb):
Because it restricts the amount of current that may enter the transistors base, the resistor (Rb) wastes energy, its power dissipation may be computed with the following formula:
Prb = (Vin – Vz)² / Rb
where,
- Prb: Power dissipation in Rb
Remember:
This calculation makes the assumption that the transistors base emitter voltage Vbe is around 0.7V.
To guarantee that the transistor runs in the active zone and that the zener diode current stays within the designated range, it is imperative to select an appropriate value for Rb.
The base current gain (β) of the TIP142 transistor can be found in its datasheet, and this information may be utilized to improve the Rb calculation.
Construction:
Building a simple voltage regulator circuit using a transistor and zener below mentioned are the connections steps:
- Connect the collector of the TIP142 to the positive supply Vcc.
- Connect the emitter of the TIP142 to the load resistor and ground.
- Connect the base of the TIP142 to the anode of the zener diode.
- Connect the cathode of the zener diode to the ground.
- Connect a resistor in series with the base of the TIP142.
- The value of this resistor can be calculated using ohms law mentioned in text:
- Connect your load resistor between the emitter of the TIP142 and ground.
- This represents the device or circuit you want to power.
- Connect the power supply to the collector of the TIP142.
Testing:
- Connect the power supply to the circuit.
- Use a multimeter to measure the voltage across the load resistor.
- It should be close to the regulated voltage approx 9V.
- If necessary adjust the value of the base resistor to achieve the desired output voltage.
Notes:
- Make sure to check the datasheets for the TIP142 and zener diode for their specific characteristics and ratings.
- Be cautious with the power supply voltage to avoid damaging the components.
- Use appropriate heat sinking for the TIP142 if the circuit is expected to handle significant power.
Conclusion:
The Zener diode sets a stable reference voltage at the base of the TIP142 and the transistor configured as an emitter follower ensures that the output voltage remains regulated at approximately 9V.
The darlington configuration provides high current gain making it suitable for applications requiring a significant amount of current.
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