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Q&A

General Q&A about the design and function of electronic systems, electric power systems and infrastructure, their theory, and tools specific to those fields. Read these guidelines before posting.

Filters (None)
71%
+3 −0
Purpose of emitter resistor in a common collector amplifier

I see a lot of common collector amplifiers with the output taken across an emitter resistor. What is the purpose of doing it this way instead of connecting your load directly to the emitter? I sh...

4 answers  ·  posted 4y ago by jm567‭  ·  edited 1y ago by Lorenzo Donati‭

66%
+2 −0
Select resistor for a diode

Suppose we have this circuit How do I pick a appropriate value for the resistor R1?

3 answers  ·  posted 3y ago by MissMulan‭  ·  edited 1y ago by Lorenzo Donati‭

33%
+1 −4
Floating circuitry and diodes

In both cases, is the "X" point floating when there is no 12V applied ?

1 answer  ·  posted 1y ago by kellogs‭  ·  edited 1y ago by Lorenzo Donati‭

50%
+0 −0
Modelling tunnel diode relaxation oscillator

I have been trying to model this oscillator I was wondering if we can somehow predict the frequency of the oscillations.For small currents inside a diode from the Shockley diode equation $$ e^{x...

1 answer  ·  posted 2y ago by MissMulan‭  ·  edited 1y ago by Lorenzo Donati‭

50%
+0 −0
Tunnel current equation

The current through the tunnel diode is: where $I_{f}$ is the current from the Shockley diode equation and $I_{tunnel}$ is the tunnel current. Is there an expression for the tunnel current or i...

0 answers  ·  posted 3y ago by MissMulan‭  ·  edited 1y ago by Lorenzo Donati‭

62%
+3 −1
How to plot the I-V curve of a tunnel diode?

I am trying to understand tunnel diodes by experimenting with them. Research tells me they can have negative resistance, and can be used to build a high frequency oscillator. Tunnel diodes are su...

4 answers  ·  posted 4y ago by tlfong01‭  ·  edited 1y ago by Lorenzo Donati‭

84%
+9 −0
Why do DC/DC switching controllers seem to favour the buck-boost topology over similar ones like Cuk, SEPIC and Zeta?

I am looking at various DC/DC converter topologies for a power system I am designing. The most suitable topology for me is one that can perform both step-up and step-down functions, so I am looking...

2 answers  ·  posted 3y ago by Mu3‭  ·  edited 1y ago by Lorenzo Donati‭

71%
+3 −0
Flyback converter design

Hi guys,I'm designing a multiple output flyback converter with 2 outputs at 10v@1 Amp and 5v @ 2 Amps .Input is 20 V dc Im having some problem with the implementation of closed loop. Open loop res...

2 answers  ·  posted 3y ago by Sriram14‭  ·  edited 1y ago by Lorenzo Donati‭

25%
+0 −4
DC-DC converter using Hartley oscillator and transformer [closed]

Instead of using a buck or a boost converter can we use for DC-DC conversion the circuit Im going to describe in the next lines? First we begin with a Hartley oscillator whose output is fed into ...

0 answers  ·  posted 2y ago by MissMulan‭  ·  edited 1y ago by Lorenzo Donati‭

75%
+4 −0
Design considerations for a synchronous DC/DC converter

In the field of DC/DC conversion, one can build a synchronous DC/DC converter (also referred to as synchronous rectification). This practice involves replacing a diode with a MOSFET switch. As far...

2 answers  ·  posted 3y ago by Mu3‭  ·  edited 1y ago by Lorenzo Donati‭

60%
+1 −0
Max V/Hz value for motor

I want to run a specific motor in the open loop. How to calculate the maximum ratio of V/f to run it? Am I looking at Ld or Lq value for this? Let's say these are the characteristics - haven't ch...

2 answers  ·  posted 3y ago by 2kind‭  ·  edited 1y ago by Lorenzo Donati‭

60%
+1 −0
Estimating the input capacitance of an BLDC motor controller

Problem Description I am trying to design a BLDC inverter and I am in doubt of what would be the right approach for estimating the input capacitor size/type. Doing it empirically or throwing every...

2 answers  ·  posted 3y ago by 2kind‭  ·  edited 1y ago by Lorenzo Donati‭

75%
+4 −0
Limiting current to DC brushed motor

This question is related to my previous question. I want to drive a brushed DC motor using H-bridge. To power the motor two 18650 cells will be used in series. The issue is that I want to limit th...

1 answer  ·  posted 2y ago by Stefan‭  ·  edited 1y ago by Lorenzo Donati‭

20%
+0 −6
Band pass filter given cutoff frequency and bandwidth

I have decided to try design a band-pass filter with a cut-off frequency of 10kHz and bandwidth of 2 Hz. $$ \frac{1}{\sqrt{LC}} = 10001 \rightarrow LC = 1/100020001 sec^{2}$$ $$ \frac{R}{L} = 2...

2 answers  ·  posted 2y ago by MissMulan‭  ·  edited 1y ago by Lorenzo Donati‭

71%
+3 −0
Cable voltage rating

I was looking for guidelines of how to select appropriate cables for applications (I am interested in DC), I found IEC 183 standard which talks about high voltage cable selection for AC. Also, the ...

1 answer  ·  posted 1y ago by Elleanor Lopez‭  ·  last activity 1y ago by Sclrx‭

20%
+0 −6
Electrolytic vs ceramic capacitors about self-resonance frequency

Which capacitors have smaller self resonance frequency?I would bet my money on electrolytic capacitors because they are usually much bigger than the ceramic capacitors however I don't know if they...

1 answer  ·  posted 3y ago by MissMulan‭  ·  edited 1y ago by Lorenzo Donati‭

33%
+0 −2
Voltage of tank circuit is invalid

In a previous question we found that for a critically damped oscillation: $$ I(t) = 2 t e^{-0.5 t} $$But if we integrate to find the voltage through the capacitor: $$ V_{CO} + \frac{1}{C} \cd...

1 answer  ·  posted 3y ago by MissMulan‭  ·  edited 1y ago by Lorenzo Donati‭

71%
+3 −0
Two way circuit breaking capability for ideal diode controllers

I would like to save some costs with ideal diode controllers. Basic requirement is for the diode controller to block overcurrents (short circuits) in both directions. The MAX16141A IC can do it a...

1 answer  ·  posted 1y ago by kellogs‭  ·  edited 1y ago by kellogs‭

75%
+4 −0
Capacitor in 2nd stage of opamp

Inside a op-amp after the stage where the differential signal is converted to single ended , there is further amplification of the DC signal.For AC signals there is a capacitor parallel to the tran...

1 answer  ·  posted 3y ago by MissMulan‭  ·  last activity 1y ago by Lorenzo Donati‭

66%
+2 −0
Digital multimeter display count range

The display counts range is one of the digital multimeter characteristics. We know that a DMM is based on an analog/digital converter, and we know too that each ADC has a certain resolution in bit...

1 answer  ·  posted 4y ago by Pacifist‭  ·  edited 1y ago by Lorenzo Donati‭

71%
+3 −0
Is it possible to calculate the rise/fall time of an operational amplifier ?

I am planning to use the LM318 operational amplifier to generate a PWM signal and I need to know how to calculate the rise/fall time. LM318/LM218/LM118 datasheet -The slew rate is 70 V/µs maximum...

1 answer  ·  posted 2y ago by deleted user  ·  edited 1y ago by Lorenzo Donati‭

60%
+1 −0
Darlington or Sziklai configuration - why and when using complementary pairs?

Why does the Darlington or Sziklai configurations need complementary transistors? For these configurations, when should I use complementary pairs and when could I use not complementary pairs ?

1 answer  ·  posted 4y ago by coquelicot‭  ·  edited 1y ago by Lorenzo Donati‭

57%
+2 −1
What is causing this massive discharge traveling down a power line?

What is causing this [ABC-news video via Twitter] spectacular power-line phenomenon? [image: still from ABC News]

1 answer  ·  posted 3y ago by Pete W‭  ·  edited 1y ago by Lorenzo Donati‭

71%
+3 −0
Why Ib=const. for BJT output characteristics Ic=f(Vce)

Introduction: In some books and other technical papers (also from universities) it is - surprisingly - still claimed that the bipolar transistor (BJT) would be a current-controlled element. This is...

4 answers  ·  posted 4y ago by LvW‭  ·  edited 1y ago by Lorenzo Donati‭

75%
+4 −0
Electrolytic capacitor lifetime rating

If you search through the electrolytic capacitor offerings from distributors like Farnell, RS, Digikey or Mouser, you find that the maximum life-time rating is commonly quoted as 5,000 or 10,000 ho...

1 answer  ·  posted 4y ago by Andy aka‭  ·  last activity 1y ago by Lorenzo Donati‭

75%
+4 −0
Why there is a body diode in mosfets?

In theory (I mean in my engineering curriculum) I never found a diode in a mosfet symbol but in datasheets there is a diode called as body diode in both pmos and nmos.Please explain its significan...

3 answers  ·  posted 4y ago by aditya98‭  ·  last activity 1y ago by Lorenzo Donati‭

71%
+3 −0
Cleaning flux out of USB connectors after soldering

When soldering Micro-USB or USB-C connectors by hand, flux is applied generously. This sometimes results in flux getting inside the connector housing, making it sticky and creating high physical re...

1 answer  ·  posted 4y ago by Kranulis‭  ·  last activity 1y ago by Lorenzo Donati‭

81%
+7 −0
When do I need to put anti-aliasing filter in front of SAR ADC?

Signal characteristics are: 0 to 3.3V span 0 to 100Hz range( there will be noise superposed on top with unknown characteristics) Output resistance Rout=4700 ohm I want to sample that with a...

2 answers  ·  posted 2y ago by 2kind‭  ·  edited 1y ago by Lorenzo Donati‭

75%
+4 −0
MOV vs. TVS diode

Simple thing that I realized I should know but do not -- when is an MOV preferable to a TVS diode (with some associated network to really make it work, in both cases)? Is it even something to routi...

2 answers  ·  posted 3y ago by Pete W‭  ·  edited 1y ago by Lorenzo Donati‭

60%
+1 −0
What is the difference between differential amplifier and differentiator?

Since am interested in how a delta sigma modulator works, I need to know what is the difference between differential amplifier and differentiator if there is a difference of course.

3 answers  ·  posted 4y ago by Pacifist‭  ·  edited 1y ago by Lorenzo Donati‭

66%
+2 −0
Complementary transistor pairs - what is the point ?

I understand that some applications require NPN-PNP pairs with identical electrical characteristics. But I would like to understand why.

2 answers  ·  posted 4y ago by coquelicot‭  ·  edited 1y ago by Lorenzo Donati‭

71%
+3 −0
Is there an easy way to measure the characteristic impedance of a cable using basic lab instruments?

As the title says, I'm interested in a simple technique to measure the characteristic impedance of a cable using only the instruments available in a school lab or to a (somewhat advanced) hobbyist....

1 answer  ·  posted 1y ago by Lorenzo Donati‭  ·  edited 1y ago by Lorenzo Donati‭

77%
+5 −0
Substituting multiple lower voltage resistors for a high voltage resistor

Certain high voltage resistors are fairly hard to get, such as the HVR37 series from Vishay. I'm looking at redesigning a board that produces 1000V via a transformer, but I want to use parts that ...

1 answer  ·  posted 4y ago by TimH‭  ·  edited 1y ago by Lorenzo Donati‭

28%
+0 −3
Thermal stability coefficient [closed]

The thermal stability coefficient is defined to be: $S = \frac{dI_{C}}{dI_{CBO}}$ where $I_{CBO}$ is the reverse current of the BJT when voltage isnt applied to the base of the BJT. In case of a ...

0 answers  ·  posted 2y ago by MissMulan‭  ·  closed 1y ago by Nick Alexeev‭

60%
+1 −0
Are a JFET's Idss and Vgs(off) values correlated?

I know that many JFETs parameters have a very large manufacturing spread, in particular, $I_{DSS}$ and $V_{GS(off)}$, as one can see (for example) in this datasheet excerpt: ... My question i...

1 answer  ·  posted 1y ago by Lorenzo Donati‭  ·  edited 1y ago by Nick Alexeev‭

77%
+5 −0
What effect will extreme temperatures have on characteristic impedance of a wire?

My scenario is this: radio equipment controlling an overhead crane inside a steel mill. Specifically it is used for transporting melting pots. With the current, unfortunate installation, the antenn...

2 answers  ·  posted 2y ago by Lundin‭  ·  last activity 1y ago by Lorenzo Donati‭

77%
+5 −0
Low-pass filter after the output DAC in CD players

[Disclaimer. This is not for an academic class. I'm self-studying.] I’m reading an introductory book on DSP for audio and computer music [Steiglitz 1996, ISBN 0-8053-1684-1 p. 287]. One of the ...

4 answers  ·  posted 2y ago by Nick Alexeev‭  ·  last activity 1y ago by Lorenzo Donati‭

77%
+5 −0
Possible stray current corrosion in reinforced concrete

I have a question about stray current corrosion in reinforced concrete. I am working on a project in a parking garage with PV-panels on top of the roof. The ground is directly connected to reinforc...

1 answer  ·  posted 2y ago by Willem ‭  ·  edited 1y ago by Lorenzo Donati‭

50%
+0 −0
Pulse disappear in digital scope just by looking at different signal in other channel.

I have a HANTEK 6022BE oscilloscope and I'm monitoring three signals with it: FS (Frame sync clock). Pulse. Transfer complete. I'm using two channels of the scope to monitor a pair of these...

1 answer  ·  posted 2y ago by mohammadsdtmnd‭  ·  last activity 1y ago by Lorenzo Donati‭

80%
+6 −0
DC offset correction loop (DC servo loop). What's its advantage, compared to a high-pass RC filter?

Once in a while in literature I see a DC offset subtraction loop. Here are a few more examples. DC servo loop removes a DC offset after an op-amp. DC servo loop removes DC current from a photo...

2 answers  ·  posted 1y ago by misk94555‭  ·  edited 1y ago by misk94555‭

69%
+7 −2
Why is the resistance of water so high and still so dangerous?

Measuring the resistance of water from my tap I got 500kOhm. Adding considerable amount of salt brought it down to 20kOhm: The question I have is why water is such a danger for short circuits if t...

4 answers  ·  posted 3y ago by Kranulis‭  ·  edited 1y ago by Lorenzo Donati‭

66%
+2 −0
Is the noise of op-amps and ADCs Gaussian, possibly with zero mean?

I understand that white noise is not always Gaussian. In general, is the $V_{pp}$ and $V_{RMS}$ noise stated in operational amplifier and ADC datasheets Gaussian? And is its mean zero? Any exemptio...

1 answer  ·  posted 1y ago by Joel‭  ·  last activity 1y ago by Lorenzo Donati‭

83%
+8 −0
Is ESD overhyped?

I have seen many engineers talk about ESD protection but I had never seen its effects myself. I made many small DIY projects and I have used bare hands to touch ICs and their pins,but nothing got d...

10 answers  ·  posted 4y ago by aditya98‭  ·  last activity 1y ago by rdtsc‭

66%
+6 −2
Titanic submarine control considerations

The submarine built by OceanGate went missing on 18th June 2023. A lot of online criticism was directed towards the control hardware of the submarine - Logitech F710 controller. However, why i...

3 answers  ·  posted 1y ago by Elleanor Lopez‭  ·  last activity 1y ago by Pogo‭

75%
+4 −0
Is concentric twist a common practice?

I have seen multiple sources on the web discussing what they call concentric twist harnesses. It boils down to having a wiring harness built in layers, where each layer is twisted around the previo...

0 answers  ·  posted 1y ago by Sclrx‭

84%
+9 −0
Flyback transformer with Intrinsic Safety

I have no experience designing for Intrinsic Safety (IS), but need to do that now. I have read thru IEC 60079-11, which seems to be the relevant standard for my purposes. The board I need to desi...

4 answers  ·  posted 3y ago by Olin Lathrop‭  ·  last activity 1y ago by Lorenzo Donati‭

77%
+5 −0
How to perform initialization of static storage variables in embedded systems?

Whenever declaring a variable in C outside a function at file scope or when specifying it as static, it gets assigned a life time known as static storage duration. Meaning it will be accessible thr...

1 answer  ·  posted 2y ago by Lundin‭  ·  last activity 1y ago by Lorenzo Donati‭

71%
+3 −0
Choosing between common-drain JFET amplifier, and common-source

Do common-source JFET amplifiers have an advantage over common-drain? The JFET would be in a low noise photodiode amplifier. The signal is 100us pulses with 10us raise times. Here are the schema...

1 answer  ·  posted 1y ago by misk94555‭  ·  last activity 1y ago by Olin Lathrop‭

77%
+5 −0
What material is used in the tabs of power packages? (TO-220, D2PAK, etc.)

What material is used in the tabs of power packages? (TO-220, D2PAK, etc.) I would assume probably a tin-plated copper alloy, but I can't find a reference. Datasheets don't seem to mention the mat...

1 answer  ·  posted 1y ago by Jason S‭  ·  last activity 1y ago by Lorenzo Donati‭

66%
+2 −0
High power LC circuit with programmable resonant frequency

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is a...

1 answer  ·  posted 1y ago by dcsuka‭  ·  edited 1y ago by dcsuka‭