Aim
The aim of the experiment is to construct the Voltage Regulator and measure the load regulation of the circuit.
Introduction
Series/Shunt Regulators
A Linear regulator is a system where the output voltage remains constant regardless of the input voltage fluctuations or variations in the load current.
Theory
Zener Diode behaves similar to a small signal diode when it is forward biased. The major difference is that when a Zener diode is reversed biased and the voltage reaches the avalanche breakdown or Zener voltage of the diode. Current starts to flow through the diode and for a certain value of current known as the Knee current the diode will maintain a constant voltage between its terminals. This characteristic of Zener diode
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Figure 1 shows,
Figure 1 – Positive side of Voltage Regulator
It is ensured that capacitor C1 is connected the right way around. An ammeter is connected between test points A and C. +24V and 0V points are connected to the unregulated PSU. (The +ve terminal of PSU is to the left of 0V terminal when looking at the terminals). The unregulated PSU is switched on and a voltmeter or oscilloscope is used to record the +Vcc voltage. The PSU is switched off and a 22.5 load is connected across the regulator output. The PSU is switched on and the base current at transistor Q2 is recorded. (The PSU is left on for 60s to allow the regulator to stabilize but not for very long). The process is repeated using a 30 load. A link is soldered between test points A and C. Loads 22.5 and 30 are used in separate tests to measure IL and VL , i.e., load voltage and current . Also VCE , VR1 and VUNREG for Q2 is measured. The link between A and C is removed. L2 and BC337 are soldered with wire lead from B. 22.5 load is connected and an ammeter is connected between A and B. The PSU is switched on and IAB is recorded. The same process is repeated for 30
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A = Vcc
Hence maximum efficiency obtained, η = π / 4
= 0.785
Thus at least 20% of the power supplied to an amplifier is dissipated as heat in the output transistors. Heat sinking ensures that the temperature of a transistor is kept below its maximum operating temperature. The collector dissipation temperature is 65°C at room temperature (25°C). The junction to case thermal resistance (RθJC) is 1.4°C/W and junction to air thermal resistance (RθJA) is 62.5°C/W. Effective θja is reduced using heatsink with low thermal resistance and making a good connection between case and heatsink (θsa). Ambient temperature is 25°C. power of 22.5 Ω load is 5.365W. The temperature of a junction,
Tj = Ta + Pθja
Tj = 25 + 5.365 (62.5)
Tj = 360.31°C
The limit of the transistor is 150 °C and since junction temperature exceeds this value, we definitely need a heatsink or the regulator can’t be left running.
The graph below shows the safe working temperature for given power ratings. For example at 65W the maximum safe operating temperature is