The zero gain amplifier (Q1, R2) and stabilized current source (Q2, R3) can be used in conjunction with a common emitter amplifier stage (Q3) in negative feedback to build a two terminal circuit which provides a constant or regulated output voltage over a range of input currents.
As in all the ALM labs we use the following terminology when referring to the connections to the M1000 connector and configuring the hardware. The green shaded rectangles indicate connections to the M1000 analog I/O connector. The analog I/O channel pins are referred to as CA and CB. When configured to force voltage / measure current -V is added as in CA-V or when configured to force current / measure voltage -I is added as in CA-I. When a channel is configured in the high impedance mode to only measure voltage -H is added as CA-H.
Scope traces are similarly referred to by channel and voltage / current. Such as CA-V , CB-V for the voltage waveforms and CA-I , CB-I for the current waveforms.
ADALM1000 hardware module
1 - 2.2 KΩ Resistor (or any similar value)
1 - 100 Ω resistor
1 - 1K Ω resistor (or similar value)
1 - 10 KΩ variable resistor (potentiometer)
3 - small signal NPN transistors (2N3904 and SSM2212)
The breadboard connections are as shown in figure 1. The output of the channel A voltage generator drives one end of resistor R4. Resistors R1, R2 and transistor Q1 are connected as in previous zero gain amplifier section. Resistor R3 and transistor Q2 are added as in the stabilized current source section. If the SSM2212 matched NPN pair is used it is best that it be used for devices Q1 and Q2. Q3is added with its emitter grounded, its base connected to the collector of Q2 and collector connected to the combined node of R1, R3 R4 and channel B scope input CB-H.
Figure 1 Band-gap shunt regulator
Channel A voltage generator CA-V should be configured for a 100 Hz triangle wave with 5 volt Max and 0 V Min. The channel B scope CB-H in Hi-Z mode is used to measure the regulated output voltage at the collector of Q3.
Plot the output voltage (as measured at the collector of Q3) vs. the input voltage. At what input voltage level does the output voltage stop changing i.e. regulate? This is called the “drop out” voltage. For input voltages above the drop out voltage, how much does the output voltage change for each volt of change at the input? The shunt type of regulator is powered by an input current. As the input voltage changes the current in R4 changes. Translate the change in voltage across R4 to the change in current flowing into the shunt regulator. The change in Vout / change in Iin is called line regulation.
The regulated output voltage should be observed as the variable resistor R3 is adjusted. How does a change in R3 effect the performance of the shunt regulator?
What affects the regulated output voltage as a load to ground is applied to the output voltage?
What determines or limits the current available to an output load?
The CA3045,46 ( LM3045, 46 ) NPN transistor array is a good alternate choice for building this example circuit. See pinout below.
All the emitters can be tired to ground ( pins 3,7,10,13 ). Devices Q1, Q2 and Q3 can be connected in parallel and serve as Q2 in figure 1. Q4 and Q5can be used for Q1 and Q3in figure 2. The 3 to 1 emitter area ratio will result in an output voltage very nearly 1.2 volts if R1 and R3 are both equal to 2K.
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