This circuit is like a bouncer for electricity.
It uses a transistor like a gatekeeper and a special 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 a great project where ups and downs in voltage can mess things up.
Also a transistor can handle lot of power so it is good for projects that need a bigger shock.
What is a Voltage Regulator Circuit using Transistor and Zener:
A simple way for controlling and regulating a power supplies output voltage is to use a transistor and Zener diode in a voltage regulator circuit.
Applications requiring a steady voltage in power supply and electronic equipment often use this kind of circuit.
Circuit Working:
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 reaches its Zener voltage it starts conducting in the reverse direction maintaining a relatively constant voltage drop.
A resistor is connected in series with the base of the TIP142 to limit the current flowing through the base.
Circuit Operation:
When the voltage across the zener diode reaches its zener voltage the reverse biased diode conducts.
11V DC is used to power the circuit.
The zener diode is connected to the TIP142s base.
In this configuration the transistors base is biased at a steady 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 basic formulas to regulate a DC input voltage to a fixed output voltage.
Base Resistor (Rb):
The base resistor (Rb) regulates the transistors current flow and biases it the formula below is used to calculate its value:
Rb = (Vin – Vz) / Ib
where,
- Vin is input voltage i.e 12V to 24V
- Vz is the Zener diode voltage 11V
- Ib is the base current around 1mA
Power Dissipation in Resistor (Rb):
Since it limits the amount of current that may reach the transistors base the resistor (Rb) loses energy.
The below formula is used for calculating its power dissipation:
Prb = (Vin – Vz)² / Rb
where,
- Prb is the power dissipation in Rb
Remember:
The base emitter voltage (Vbe) of the transistor is roughly calculated around 0.7V.
To function transistor in the active zone ensure that the Zener diode current remains within the specified range
Its important to choose the right value for Rb.
The datasheet for the TIP142 transistor includes information about its base current gain (β) which is used to enhance the Rb calculation.
How to Build:
Building a simple voltage regulator circuit using a transistor and Zener below mentioned are the connections steps:
- The collector of the TIP142 is connected to the positive supply Vcc.
- The emitter of the TIP142 is connected to the load resistor and ground.
- Connect the base of the TIP142 to the anode of the zener diode.
- Wire the cathode of the zener diode to the ground.
- The base of the TIP142 is connected to resistor in series .
- The value of this resistor is 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:
- Join the circuit to the power source.
- To find the voltage across the load resistor use a multimeter.
- It should be around 9V which is the regulated voltage.
- To get the desired output voltage change the base resistors value if needed.
Notes:
- Be sure to check the TIP142 and Zener diode datasheets for their particular ratings and features.
- Use the power supply voltage carefully to prevent component damage.
- If the circuit is meant to carry a lot of power use the TIP142s proper heat sinking.
Conclusion:
At the base of the TIP142 the Zener diode provides a steady reference voltage and the transistor sets up as an emitter follower makes sure that the output voltage stays controlled at about 9V.
Because of its high current gain the Darlington design works well for applications that need a lot of current.