Low Voltage Regulator Circuit Design with Op Amp, Zener Diode, JFET, BJT Transistors

How to design a Low-Voltage Regulator? How does the regulator analog circuit work? How should we select the circuit components? How does temperature compensation work in this circuit? These questions are discussed in this low voltage supply regulator analog circuit design using an example implementation of 2-volt regulated supply at the output of the circuit given an unregulated supply voltage at the input. This circuit is implemented with one operational amplifier, on Zener Diode, one N-channel JFET or Junction Field Effect Transistor, one low-current NPN BJT and one high current PNP Bipolar Junction Transistors. The NPN BJT transistor is wired to operate as a PN junction diode. The negative feedback for op amp circuit is intuitively analyzed and shown that virtual short is enforced for the positive and negative input terminals of the OpAmp. Example of potential choices for op amps are Texas Instruments OPAx607 or THS4051 or analog devices LM108 or more recent FET input op amps with low offset current and noise. The choice of Zener Diode is discussed with temperature coefficient of nearly -0.085% per degree Kelvin. It is recommended to have 1% tolerance resistors (or better) in this circuit.

[@STEMprof]

How to design a Low-Voltage Regulator? How does the regulator analog circuit work? How does temperature compensation work in this circuit? These questions are discussed in this video. For more examples please see: Voltage Regulator with MOSFET, JFET & Temperature Compensation kzbin.info/www/bejne/hJXJqnulrc9-qLs Current Foldback Voltage Regulator with Op Amp, Darlington Transistors kzbin.info/www/bejne/iHfJg6WYprKSY9U Current Limiting Foldback Voltage Regulator Circuit kzbin.info/www/bejne/jH-XkKR8bqmpeK8 Voltage Regulator Circuit Design with Op Amp and BJT Transistor kzbin.info/www/bejne/qHqcl2ljed6LrrM Push-Pull Power Amplifier with Darlington Transistors kzbin.info/www/bejne/bmeZfoyfl9Rrr6c Voltage Regulator design with Op Amp BJT JFET and Zener Diodes kzbin.info/www/bejne/eXvPXqior8qcitE For more analog circuits and signal processing examples see my analog design videos playlist kzbin.info/aero/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt . I hope these Circuit design and analysis videos are helpful.

[@paulthomas4917]

Geat video, on first seeing the circuit my eyes were drawn to the positive feedback on the op amp, me thought, stable output, more like a demented pinball machine output, lol We are conditioned to seeing the terminals of bjts being shorted and just thinking temp compensation going on but the non inverting input being connected to the output made me hover over the delete trace on the schematic editor. like the way you teach, thank you so much. liked and sub'ed .

[@STEMprof]

You're welcome. Glad that you enjoyed this Voltage Regulator circuit video. Thanks also for sharing your observations. To watch an alternative design of voltage regulator please see kzbin.info/www/bejne/iHfJg6WYprKSY9U which is a Current Foldback Voltage Regulator Design with Op Amp and Darlington Transistors. I hope you enjoy this video as well.🙂

[@frunsebischkek1050]

👍 Very nice! Thank you. Using this principle you can create a push-pull stage of 2 bjts after the OpAmp. It works very stable.

[@STEMprof]

You are welcome! Glad that this video is interesting. The Push-Pull Amplifier stage that you mentioned is discussed in kzbin.info/www/bejne/bnOpq6afbJKJmNU which is the video of Push-Pull Power Amplifier Design with Op Amp, Sziklai Darlington Transistors. I hope it is interesting as well. 🙂

[@frunsebischkek1050]

@@STEMprof 👍

[@louco2]

Tank you so much for taking the time to do these videos!!

[@STEMprof]

My pleasure. Glad that you liked this voltage regulator video. Here are a few more related circuit examples: Voltage Regulator Circuit Design with Op Amp and BJT Transistor kzbin.info/www/bejne/qHqcl2ljed6LrrM Voltage Regulator designed with MOSFET, JFET transistors kzbin.info/www/bejne/hJXJqnulrc9-qLs Current Foldback Regulator Design kzbin.info/www/bejne/iHfJg6WYprKSY9U

[@electroquests]

Can you please explain how the current through the positive supply voltage i.e. through 680 ohms reduces when voltage at inverting terminal is higher than the non inverting terminal?

[@electroquests]

Thanks for the video, it is an interesting circuit

[@STEMprof]

Sure, this technique is similar to the Push-Pull design in kzbin.info/www/bejne/bnOpq6afbJKJmNU. As I mentioned in the video around minute 3:50, the internal output stage inside the op amp looks similar to the NPN-PNP output stage of a power amplifier circuit (albeit with orders of magnitude less current). When voltage at inverting terminal of Op Amp is higher than the non inverting terminal, Op Amp immediately attempts to reduce its output voltage toward the negative supply voltage (in this case ground). This is achieved by reducing sourcing current from Vdd (hence reduced current through 680 ohms resistor) so that less current is provided to op amp output (resulting in reducing output voltage). This reduction of current through the 680 ohms translates to reduced voltage drop across 680 ohms resistor which means reduced voltage across the emitter-base PN junction of the main PNP BJT transistor. That translates to exponential reduction of the collector current of the main PNP transistor. which results in reduction of the voltage across the series of feedback resistors R3+R4 and hence reduced emitter voltage of the small NPN BJT transistor (which is effectively a Diode). The reduction of emitter voltage results in reduction of the voltage at the inverting terminal (counteracting the initial voltage increase) indicating a negative feedback. I hope this explanation is helpful

[@STEMprof]

@@electroquests You are welcome. Thank you. Glad that this analog circuit video is interesting. To watch an alternative design of temperature compensated regulator circuit please see kzbin.info/www/bejne/hJXJqnulrc9-qLs which is Voltage Regulator designed with MOSFET, JFET transistors.

[@bob_mosavo]

Thanks 👍

[@STEMprof]

You are welcome. Glad that you liked this video.

[@h7qvi]

Screwwy but interesting

[@sc0or]

Good day Sir. Do you have any notes about a stability with using an open loop on an op amp in this schematic? It could easily oscillate in case of improperly selected/added/missed capacitors and their values IMHO.

[@STEMprof]

Good day to you as well. Thanks for sharing your thoughts. The Operational Amplifier in this circuit is wired in an overall closed loop negative feedback circuit scheme as explained in the video starting at 3:50. Nonetheless, to your point, depending on the selected Op Amp extra care is needed regarding any extra stablizing capacitors (say 10pF to 100pF) required between terminals of the selected op amp (as described in op amp datasheet).

[@yjweaver5108]

I didn’t watch the entire video- did you mention what is advantageous about this circuit compared to a simple buffered voltage divider, other than temperature compensation?

[@STEMprof]

Aside from temperature compensation, this circuit has a negative feedback loop that keeps the output voltage fixed at desired voltage while also providibg high current to the output load via PMOS transistor.