Voltage Regulator Design with BJT Darlington Transistors and Zener Diodes
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- เผยแพร่เมื่อ 20 ก.ย. 2024
- Design of a minimal Regulated Voltage Supply is discussed in this video along with the Analysis and Practical choice of parameters for a near-minimal component power supply. For more circuit examples please see • Voltage Regulator Desi... and • Voltage Regulator desi... .
Note that the analog circuit discussed in this example does not require Op Amp. The input unregulated voltage is varying considerably in the range of 20 to 30 volts. This minimal regulator design requires two Zener Diodes, total of four Bipolar Junction Transistors in the form of one BJT Darlington Transistor pair and one semi Sziklai transistor pair and one towered transistor pair. The bottom Zener Diode with 5.1v Zener break down voltage and minimum Zener current of 1 mA sets the reference voltage for the regulated 16v at the output. The circuit components are designed to support up to 2A maximum current for the output resistor load. A combination of Kirchhoff's circuit laws and BJT current gains is applied to analyze and design this voltage regulator circuit.
Thanks for watching & your comments. NOTE: supported input unregulated supply voltage is ~21-30v. For more Analog Circuit, Op Amp and Regulator Examples please see:
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As always I enjoyed your analysis of the circuit, thank you for that. I also wonder if the explanation of intuitive understanding of sub-circuits of this voltage regulator would be helpful for some people. For example, the role of the T4 and the Zener diode Vz2 in this circuit.🙂
Thanks for watching and your good follow-up questions and comments. Sure, BJT transistor T4 and Zener diode with reverse breakdown voltage Vz2 are establishing the reference voltage (sort of like what bandgap circuit does) in the sense that this Zener Diode set the baseline voltage at nominal 5.1 volt then the T4 BJT transistor adds another 0.7 volt of Vbe or Base-Emitter to get to 5.8 volt reference voltage at the base of T4 which then is scaled up by the two resistors R1 and R2 to get to the target 16 volt fixed output DC voltage that we desire for this Regulated Voltage Supply circuit design. I will post more voltage regulator examples in the analog curcuit playlist th-cam.com/play/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt.html . Please note that this example is a relatively minimal regulator circuit without any Op Amp. More comprehensive and more practical regulator designs require more components including operational amplifiers. I hope this is helpful. 🙏
The interesting, and more unusual, part of the circuit is the transistor T3 and its associated Zener diode 1, which form a constant current source, ensuring a high impedance load for the transistor T3 and increasing its voltage gain. That improves the ability of T4 to keep the output tightly regulated though the negative feedback via its base.
@@RexxSchneiderThanks Rex for watching and sharing your insights. I will post more voltage regulator examples in the analog curcuit playlist th-cam.com/play/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt.html . This example is a relatively minimal regulator circuit without any Op Amp. As you know, more comprehensive and more practical regulator designs require more components including operational amplifiers. Thanks again for watching 🙋♂️
Very interesting. And amazing how you managed to cram all the formulas on one page :)
Thanks for watching. Glad that you like this Voltage Regulator Design Example video and its format. I appreciate your noticing of compact analysis approach with the main reason that circuit schematic is easily and always available in the view side by side the presented circuit analysis. For more Analog Circuit, Op Amp and Regulator Examples please see: Voltage Regulator Example: th-cam.com/video/rI9f6-DyXxQ/w-d-xo.html
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thank you verry much i learn a lot
You are Welcome. Thanks for watching. Glad that this Voltage Regulator Design Example video is useful. For more Analog Circuit, Op Amp and Regulator Examples please see: Voltage Regulator Example: th-cam.com/video/rI9f6-DyXxQ/w-d-xo.html
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Thank you 🙏
You really don't want to run low voltage Zener diodes at 1mA. They have poor "knee" characteristics at breakdown, and as you saw on the data sheets, they can have have a slope resistance of as much as 600R at 1mA, and that badly affects the voltage regulation. It's best to set both of them to 5mA at least and work from there. I would select Rz2 around 1.5K to 2.2K.
The real problem with the circuit, though, is that the voltage at the base of T2 has to be at least 16V + 2 x 0.7V = 17.4V. That is the voltage at the collector of T3. However, if the supply rail is at 20V, you showed that the base of T3 would be at 16.4V and that won't allow T3 to operate. Your minimum supply voltage for the circuit is likely to be more like 22V.
Thanks Rex for watching & surely for your detailed attention. You have a valid point and KVL analysis about the lowest acceptable level for the unregulated input supply voltage. I will be more careful about the claimed supported range for the input voltage supply. Regarding the Zener Diode bias current, while 5mA is more preferred to 1mA, ultimately it depends on specific Zener Diode selected for the design. Some of them are pretty fine with bias currents as low as 0.25mA.
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Thanks again for watching & your insights 🙏🙋♂️