Voltage Regulator Op Amp Circuit with Foldback current limiting
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- Опубликовано: 3 окт 2024
- A voltage regulator circuit is analyzed in this Op Amp BJT circuit design example. This regulator is designed with operational amplifier, Zener Diode, Darlington transistor pair and a set of PNP-NPN BJT as foldback current limiter. For more Analog and OpAmp circuit examples including Analog Computers and signal conditioning please see • Electrical Engineering...
Note that the unregulated voltage supply at the input of this regulator is varying considerably between 14 to 20 volts. The low power 6 volt Zener diode (for example 1N5233 or MMBZ52xxBLT1G Zener Voltage Regulators) sets the reference voltage (like a bandgap) and the non-inverting op amp circuitry enforces a scaled version of the reference voltage at the output that can be adjusted by the value of the potentiometer (aka adjustable resistor). The presented voltage regulator circuit analysis shows that the regulated output voltage can be programmed between 6 to 12 volts. The minimum acceptable resistor load and the current limiting high power feedback resistor are computed as well. The Foldback current limiter functionality is explained by analyzing the roles of the set of PNP and NPN bipolar junction transistors in the current limiter feedback path that steers away op amps current when limiting output current of regulator is required. The power consumption and dissipation of the power BJT transistor in the Darlington pair is also computed.
Thanks for watching. For more Analog Circuit, Op Amp and Regulator Examples please see: Voltage Regulator Example: ruclips.net/video/rI9f6-DyXxQ/видео.html
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I hope these Analog Circuit Design and Analysis Examples are interesting and helpful. 🙏
Yes, indeed it was helpful. Never before have I analyzed that type of voltage regulator. Thank you for this great lesson.
You're welcome. Thanks for watching & your encouraging comment. Glad that you liked this video. Please let me know the circuit topics that you are interested in seeing more in this channel 🙂. For more Analog Circuit, Op Amp examples please see: Voltage Regulator Example: ruclips.net/video/rI9f6-DyXxQ/видео.html , Op Amp BJT JFET in Voltage Regulator design ruclips.net/video/CJl-urzeiTo/видео.html
Push-Pull Power Amplifier ruclips.net/video/866MYibo8yE/видео.html
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And my Analog playlist ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
Thanks again 🙋♂
I need to analyse circuits like you Prof. My problem is knowing where to start on a given cct, at the moment I couldn't get very far on my own, but am learning fast thanks to your videos.
Thanks George for watching and your encouraging comment. Glad to hear that you are making good progress and my videos are helpful.🙏 For more Circuit and Op Amp Examples please see my Circuit Videos playlist ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
I hope these Analog Circuit Design and Analysis Examples are interesting and helpful. 🙏
Thanks for watching this voltage regulator circuit analysis example. I appreciate your feedback and follow-up questions. Please note that there are many ways to wire components & transistors to build current limiting feedback (method shown here is not unique). With that in mind, Notice that current limiting PNP-NPN transistors are high-beta transistors with low 10 micro amp to max ~10-20 mA current levels that are completely negligible compared with the output current levels.
And regarding response time of the regulator (say to a sudden current surge due to for instance inadvertent shorting of output to ground) is mainly defined by the Op Amp KPI (e.g. slew rate, max current, settling time, etc.) of the operational amplifier selected for this circuit. The low-current PNP and NPN BJT current limiting transistors respond very fast as they just need the minimal turn-on voltage across the PN junction of emitter-base of PNP transistor. The cascade BJT pair (while in linear region) has a current amplification beta of at least 100. Hence a mere 50 micro amp emitter current of PNP BJT translates to 5 mA current steering from the output of Op Amp by the NPN BJT transistor. Note that in nominal operation, the Op Amp only needs to provide 1.2 mA to the base of the high-power Darlington transistor pair to support up to 1.2 A current at the output of this regulator. We can also adjust the value of the nominal 600 ohm resistor at the output of the Op Amp to optimize the response of the circuit. Both Analog Devices and Texas Instruments offer a number of good op amp choices that can be used for this voltage regulator design application (please see Analog Devices Op Amps www.analog.com/en/product-category/operational-amplifiers.html ).
Please see more circuit examples in the analog circuit collection ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
I hope these explanations and additional information are helpful. Thanks again for watching. 🙏
Neat video and circuit analysis! If I may add: I would replace the Zener Diode with a TL431 or any other reference to get more stability on the output voltage throughout the temperature range!
Thanks Matthias for watching and sharing your thoughts and suggestions. Glad that you liked this regulator circuit analysis video. Your TL431 Shunt Voltage Regulator from Texas Instruments is a good alternative solution with more temperature stability instead of Zener Diode 1N5233 (from Vishay Semiconductor) if its 0.038% temperature coefficient (70mV change in 6V reference per 30 deg C junction temp change) is not low enough for a given application. For more examples please see ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
I hope these Examples are interesting and helpful. Thanks again 🙏
You are helping us
My pleasure. Glad that this voltage regulator video is helpful.
Nice explanation. But I see one mistake, or I consider it a mistake. RLmin is calculated and valid only for alpha=1. For lower alpha there will be different allowable RLmin (lower). And then the calculations for max power dissipation is wrong. If alpha=0, the Vo=6V, and RLmin=5ohms. Voltage drop on pass transistor is 13.4V, current 1.2A, and maximum power dissipation will be 16.08W
Thanks for watching and sharing your thoughts. I appreciate your detailed attention. One could even state that RLmin is zero because we already have foldback current limiter in this circuit that quickly protect the circuit. But, aside from the fact that I wanted to show how RLmin is calculated, it is not recommended to plan RLmin for different output voltages due to possible current spikes and surges beyond planned limits for transistors in this circuit in addition to requiring higher power BJT as you also noted. I will post more Voltage Regulator examples soon. In the meantime, please see more examples in the analog circuit collection ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
I hope this explanation is helpful. Thanks again. 🙏
Thanks for the excellent review. How are the response times calculated for this circuit.
Thank you for watching & your good question. Glad that you liked this voltage regulator circuit analysis video. For more example please see the Circuit Videos ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt . Regarding your question,
Response time of the regulator (say to a sudden current surge due to for instance inadvertent shorting of output to ground) is mainly defined by the KPI (e.g. slew rate, max current, settling time, etc.) of the operational amplifier selected for this circuit. The low-current PNP and NPN BJT current limiting semi Szkilai pair transistors respond very fast as they just need the minimal turn-on voltage across the PN junction of emitter-base of PNP transistor. The cascade BJT pair (while in linear region) has a current amplification beta of at least 100. Hence a mere 50 micro amp emitter current of PNP BJT translates to 5 mA current steering from the output of Op Amp by the NPN BJT transistor. Note that in nominal operation, the Op Amp only needs to provide 1.2 mA to the base of the high-power Darlington transistor pair to support up to 1.2 A current at the output of this regulator. We can also adjust the value of the nominal 600 ohm resistor at the output of the Op Amp to optimize the response of the circuit. Both Analog Devices and Texas Instruments offer a number of good op amp choices that can be used for this voltage regulator design application (please see Analog Devices Op Amps www.analog.com/en/product-category/operational-amplifiers.html ).
For more Analog Circuit, Op Amp examples please see: Voltage Regulator Example: ruclips.net/video/rI9f6-DyXxQ/видео.html , Op Amp BJT JFET in Voltage Regulator design ruclips.net/video/CJl-urzeiTo/видео.html
Push-Pull Power Amplifier ruclips.net/video/866MYibo8yE/видео.html
Voltage Regulator Design with Darlington Transistors ruclips.net/video/ArisQp7V0Ac/видео.html
Op Amp Analog Computer circuit that solves Differential Equation: ruclips.net/video/ENq39EesfPw/видео.html
And my Analog playlist ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
I hope this explanation and additional videos are helpful in answering your question. 🙋♂
Thanks again
Nice as usual. Quick question here though, how can you say OP amp is operating with feedback when said feedback is done through OFF transistors .. ? Thanks
You're welcome. Thanks for watching & your good question. Negative Feedback for op amp is provided via voltage division across two 10k ohm resistors in series that feed the negative input terminal of the operational amplifier. For example, if output voltage suddenly increases then the voltage at negative terminal of op amp increases as well that results in op amp reducing its output voltage that then reduces voltage at base o Darlington transistor and hence results in reduction of output current and voltage (basically counteracting the initial voltage increase as expected from negative feedback). For more Op Amp & Analog Circuit examples please see:
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I hope these videos are interesting as well. 🙋♂️
Thank you for video. I’m new to electronics, are most voltage regulators designed this way?
You're welcome. Thanks for watching and your question. There are different methods for designing voltage regulators that depend on target design requirements and Key Performance Indicators (KPI). For more regulator examples please see: Voltage Regulator Design with BJT Darlington Transistors and Zener Diodes ruclips.net/video/ArisQp7V0Ac/видео.html
Voltage Regulator Design with Op Amp ruclips.net/video/rI9f6-DyXxQ/видео.html
Voltage Regulator design with Op Amp BJT JFET ruclips.net/video/CJl-urzeiTo/видео.html
I will post more voltage regulator circuit design examples soon. I hope this is helpful. 🙏
@@STEMprof thank you for answering
You are welcome. For more Electronic circuits examples please see ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
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If I'm not mistaken, this one will have issues sinking currents (e.g. variable reactive loads) . Assuming an overvoltage injected in/by the output, the PNP is blocked (its base is at higher voltage than its emitter) and the overvoltage can only try to drive the current through the darlington in reverse.
Thanks for watching and sharing your thoughts and feedback. It is helpful and encouraging to hear back and further learn. This regulated DC voltage supply is mainly designed for resistive load. Using and analyzing it for a reactive load require further evaluation, modification and potentially additional restrictions. I will try to post videos about more flexible Voltage Regulators. In the meantime, please see more circuit examples in the analog circuit collection ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
I hope this is helpfull. Thanks again for watching. 🙏
@@STEMprof Thank you.
"I will try to post videos about more flexible Voltage Regulators." I'm waiting for them, then.
In re: "is mainly designed for resistive load" - wouldn't hurt to mention this in the video comments.
Thanks again for watching and your good suggestions and feedback. I am thankful. Sure, will post more videos soon and will try to mention details as much as I can. 🙋♂️
Wouldnt the max power of the Darlington pair be when alpha = 0?, this would mean output voltage is 6V, and the voltage drop across r would be 0.6 V then VCE would be 20V - (6V + 0.6V) = 13.4V and power would be 13.4V * 1.2A = 16.08W, all of this while staying within expected ranges
@@josemanuelromo6832 thanks for your good question. This problem states that the minimum load resistor allowed is 10 Ohm. Hence the max output current is 1.2 Ampere that ONLY happens when output voltage of regulator is 12 Volts (meaning alpha is one). When alpha is set to zero, then output voltage is 6 Volts which results in max output current of 600 mA when minimum allowed load resistor of 10 Ohm is applied. I recommend that you also watch minute 21:10 onward that further explains by showing and plotting the Transistor Power Formula. I hope this is helpful.
Why do you write units as a superscript?
Thanks for watching and your follow-up question. I appreciate your interest. I don't mean to indicate units should be written as superscript. It is just mostly matter of lack of space (in front of the number) and/or a way to highlight the unit and scale (e.g. mV, uA, etc.). For more Circuit examples please see ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
I hope this explanation is helpful. 🙋♂️
Your current limiting transistor is connected incorrectly.
Thanks Dennis for watching and sharing your thoughts and feedback. I am thankful. There are many ways to wire components & transistors to build current limiting feedback (method shown here is not unique). With that said, please let me know why do you think the PNP-NPN transistor pair is not right? Notice that they are high beta transistors with low 10 micro amp to max ~10-20 mA current levels that are completely negligible compared with the output current levels. I will post more Voltage Regulator examples soon. In the meantime, please see more examples in the analog circuit collection ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
I hope this explanation is helpful. Thanks again for watching. 🙏
Your microphone is doing some funny thresholding midway through the video
Thanks for watching and your thoughtful comment. I just checked again and could not observe any major issue. Please refresh your page and watch again possibly in Firefox browser and if you still observe any issue then please let me know at what moment or minute you observe it happening. For more Analog Circuit, Op Amp examples please see:
Voltage Regulator Example ruclips.net/video/rI9f6-DyXxQ/видео.html , Op Amp BJT JFET in Voltage Regulator design ruclips.net/video/CJl-urzeiTo/видео.html
Push-Pull Power Amplifier ruclips.net/video/866MYibo8yE/видео.html
Voltage Regulator Design with Darlington Transistors ruclips.net/video/ArisQp7V0Ac/видео.html
Op Amp Analog Computer circuit that solves Differential Equation: ruclips.net/video/ENq39EesfPw/видео.html
And my Analog playlist ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
Thanks again 🙋♂
I tried and tried to respond directly to your comment below, bur for some reason the system was completely ignoring me when I hit the reply button, so I am doing it this way.
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I must have misread your schematic, thinking you were using all NPN transistors.
I can see how your PNP/NPN combination would work for current limiting.
I apologize for my error. I thought I had checked the transistor type multiple times before making my comment.......
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If you HAD used an NPN for the current sense instead of a PNP you could have performed the same function with one less transistor.
Your series pass Darlington configuration needs a resistor from base to emitter to minimize or eliminate the effects of leakage on the second transistor in the pair, and your current limiter might ground the base of the first transistor, but would not be able to eliminate the leakage current in the second transistor. And since it will be the one generating all the heat, the leakage really has to be considered.
If you use an off-the-shelf darlington power transistor instead of creating your own, you will not have to worry about leakage because the off-the-shelf parts have those resistors already in the part.
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I will be looking for those future videos you mentioned.
Thank you.
Thanks again Dennis for watching and for sharing your thoughts and feedback. I appreciate your follow-up comment. Glad that the issue is resolved. Thanks also for sharing your practical advice regarding base-emitter resistor to counter leakage. I will post more examples and I hope that you find them interesting as well. In the meantime, please see more circuit examples: Voltage Regulator Example: ruclips.net/video/rI9f6-DyXxQ/видео.html
Voltage Regulator Design with Darlington Transistors ruclips.net/video/ArisQp7V0Ac/видео.html
And the Analog / Op Amp circuits videos playlist ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
I hope you enjoy the circuit videos 🙋♂️
I also think the current foldback function could be implemented with only NPN transistor, but in that case the current sense resistor would have to be installed on the negative side of the supply and that would affect the voltage control (the voltage applied to load would not be the same as intended. One correction would be to change the voltage reference accordingly and take the zener anode from the current sense resistor
@@anoimo9013 Thanks for watching & sharing your thoughts. Glad that this video is bringing these good comments. To your point there are many ways to design a target voltage regulator. For more examples pls see: Voltage Regulator Example: ruclips.net/video/rI9f6-DyXxQ/видео.html , Op Amp BJT JFET in Voltage Regulator design ruclips.net/video/CJl-urzeiTo/видео.html
Voltage Regulator Design with Darlington Transistors ruclips.net/video/ArisQp7V0Ac/видео.html
Push-Pull Power Amplifier ruclips.net/video/866MYibo8yE/видео.html
And my Analog playlist ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
Thanks again 🙋♂