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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.

33%
+0 −2
Re model of transistor is the same in 2 different configuration

I was studying the Re model of a transistor: But the Re model for 2 different configurations (common emitter and common base )turns out to be the same! I don't know why I am really confused.How...

2 answers  ·  posted 6mo ago by MissMulan‭  ·  last activity 6mo ago by LvW‭

66%
+4 −1
PCB ground planes with isolated voltage

I have designed a PCB that I need to work in which a microcontroller drives a 24 V brushed motor. The input power to the board is 24 V, this is then lowered to 5 V by a step down converter, and thi...

3 answers  ·  posted 10mo ago by Alinik‭  ·  last activity 6mo ago by KalleMP‭

77%
+5 −0
Unexpected impedance spike when paralleling capacitors

I was watching a video from EEVBLOG about bypass capacitors, and he presented a theory that randomly connecting different values of capacitors in parallel can create unexpected impedance spikes: ...

3 answers  ·  posted 6mo ago by Elleanor Lopez‭  ·  last activity 6mo ago by Andy aka‭

71%
+3 −0
Thévenins Theorem for Transistor Circuit

I am calculating the base current of transistor Q1. To simplify the circuit equations, I applied the Thévenin's theorem twice and converted V1 and R1, R2 into Vth and Rth as shown in the image. Vt...

2 answers  ·  posted 7mo ago by kadamrohan16‭  ·  last activity 7mo ago by Olin Lathrop‭

77%
+5 −0
What is this fourth connection in NMOS device?

I know that in transistors there is base, collector and emitter, and in FETs there is gate, drain and source, but what is the fourth grounded connection opposite the gate in this NMOS circuit?

1 answer  ·  posted 7mo ago by NMOS lover‭  ·  last activity 7mo ago by Andy aka‭

50%
+3 −3
What reactance actually is?

I saw that equation of reactance is written like this $$I=\frac{V}{|R+X_L j|}$$ $$I=\frac{V}{|R-X_c j|}$$ When there's capacitor and inductor in a single circuit then it is written like : $$I=\...

4 answers  ·  posted 10mo ago by deleted user  ·  last activity 7mo ago by Andy aka‭

80%
+6 −0
DAC controlled high side current source.

I'm designing a high side current source that can be controlled with a Digital-to-analog and can source up to 100mA with voltage supply up to 36V. By high side I mean one side of load will be alwa...

1 answer  ·  posted 9mo ago by DeadMouse‭  ·  last activity 7mo ago by Olin Lathrop‭

66%
+2 −0
Level shifting of a 3 state logic pin

I want to design a simple battery charger using MCP73831/2. This chip has a 3-State state pin according to the table below: I have a 3.3V MCU and I want to connect this pin to a GPIO. The MCU is...

1 answer  ·  posted 8mo ago by dekker‭  ·  last activity 8mo ago by Olin Lathrop‭

77%
+5 −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 8mo ago by 2kind‭  ·  last activity 8mo ago by TonyStewart‭

66%
+4 −1
Duty cycle of buck-boost converter

I have the following problem: - Using Wikipedia I find that during CCM we have the relation: - $$\frac{V_{out}}{V_{in}} = -\frac{D}{1-D} $$ Solving for $D$ and inserting values gives me $...

2 answers  ·  posted 9mo ago by Carl‭  ·  last activity 9mo ago by Olin Lathrop‭

40%
+0 −1
SMPS Requirements [closed]

I want 3 SMPS (AC-DC) : Vout/Iout - 5V/20A , 12V/75A , 24V/30A Vin (AC) ~ 220V/50Hz I want it such that I can use Hard &amp; Soft Kill Switches for turning off. Can you help me with the same. I tho...

0 answers  ·  posted 9mo ago by Sye‭  ·  closed 9mo ago by Olin Lathrop‭

72%
+6 −1
How to protect RF switches from ESD?

Assume that I have some generic antenna connector, followed by a pi-filter/50ohm impedance matching components, then a DC blocking cap (as per the RF switch recommendations) and then a RF switch fo...

4 answers  ·  posted 10mo ago by Lundin‭  ·  last activity 9mo ago by Nick Alexeev‭

71%
+3 −0
Case temperature of MOSFET

Homework problem A MOSFET has a power dissipation of $P_{d} = 10\text{W}$. The MOSFET is mounted on a heatsink. There is an isolation pad between the MOSFET case and the heatsink. We are given t...

1 answer  ·  posted 9mo ago by Carl‭  ·  edited 9mo ago by Olin Lathrop‭

50%
+0 −0
How do "O-ring circuit" differ from an "ORing circuit" or "OR-ing circuit", or are they synonyms? [closed]

I've seen a few different circuits (a) (b) (c) (d) described as "an O-ring circuit" or "an optimal O-ring circuit". What does the "O" and the "ring" refer to in such circuits? How do "O-ring circ...

0 answers  ·  posted 9mo ago by DavidCary‭  ·  closed 9mo ago by Olin Lathrop‭

66%
+4 −1
How to choose the right value for input voltage ripple of an SMPS?

Which important system design parameters need to be locked in order to estimate the maximum allowable level of the input voltage ripple of an SMPS? I have encountered ballpark figures of &lt;1%, &...

1 answer  ·  posted 10mo ago by 2kind‭  ·  last activity 9mo ago by Olin Lathrop‭

83%
+8 −0
Why are some PCB design software programs considered to be 'hobbyist' programs?

Recently I have heard this opinion from experienced engineers when discussing PCB design software. The common opinion was that Allegro and Altium are supposedly professional programs whereas Eagle ...

2 answers  ·  posted 10mo ago by Wilkins Ticklebum‭  ·  last activity 10mo ago by Andy aka‭

77%
+5 −0
Press fit PCB receptacle for plated holes (Marked for non-plated holes)

I saw that this PCB socket: Is marked as pressfit for non-plated holes. However, can it be used with plated holes as well, or will it damage the plating inside?

1 answer  ·  posted 10mo ago by Wilkins Ticklebum‭  ·  last activity 10mo ago by Olin Lathrop‭

PCB
50%
+2 −2
Inductance vs frequency

Suppose we have a sine signal applied to a inductive load. Is the inductance of the load changed if the frequency of the signal is changed?

3 answers  ·  posted 1y ago by MissMulan‭  ·  last activity 10mo ago by coquelicot‭

75%
+4 −0
PNP Darlington pair as a current limiter

I am trying to analyse what is controlling the load current in the below Darlington configuration. Is it the base current of transistor Q3 which is controlling current through R14 / emitter curr...

1 answer  ·  posted 10mo ago by kadamrohan16‭  ·  last activity 10mo ago by Olin Lathrop‭

81%
+7 −0
How long does it take for energy to propagate in a circuit?

The premise In a recent video by the pop-sci channel Veritasium, the concept of the flow of electricity and energy transmission in a circuit was discussed. In that video a thought experiment is pr...

5 answers  ·  posted 1y ago by Mu3‭  ·  last activity 10mo ago by coquelicot‭

75%
+4 −0
Why are there more N type than P type MOSFETs?

I was looking at different transistors, especially MOSFETS and I saw that N type MOSFETs seem to be way more popular to be used in circuit design. Is there a reason for that, or am I mistaken?

2 answers  ·  posted 10mo ago by crusadEEr‭  ·  last activity 10mo ago by Olin Lathrop‭

66%
+2 −0
Flyback transformer for Vout > Vin

This question is asked in an addition to https://electrical.codidact.com/posts/276436 Here is a Flyback converter mentioned there: Design parameters are: Input voltage 125 volts Output volt...

2 answers  ·  posted 10mo ago by 2kind‭  ·  last activity 10mo ago by Andy aka‭

33%
+0 −2
What happened to my headphones? [closed]

I recently started working at a construction office in another country. I usually listen to music when working, and I saw a headphone jack in the wall, so I thought it is radio or something, I plug...

0 answers  ·  posted 10mo ago by Headphone Jackson‭  ·  closed 10mo ago by Olin Lathrop‭

66%
+2 −0
H(jω) does not exist for unstable systems, but we still use it when designing controllers - contradiction?

According to Signal processing and linear systems by Lathi, the transfer function $H(j\omega)$ does not exist for systems with poles in the RHP: - This makes sense to me, since $H(j\omega) = \fr...

2 answers  ·  posted 10mo ago by Carl‭  ·  last activity 10mo ago by a concerned citizen‭

66%
+4 −1
How to calculate the RC filter of a TXCO for a RFIC reference?

I have a 30MHz TCXO circuit (TXCO datasheet) like this serving as local oscillator to a RFIC: The RFIC manufacturer recommends to "add filtering caps" for high RF output cases. That is &gt;20d...

1 answer  ·  posted 10mo ago by Lundin‭  ·  edited 10mo ago by Lundin‭

57%
+2 −1
Choosing Y value in photoresistor graph

I have designed a graph of the current in a photoresistor related to the brightness of light which hits the photoresistor. Our professor told us that it is more correct to draw the Current/Brigh...

1 answer  ·  posted 10mo ago by MissMulan‭  ·  last activity 10mo ago by Olin Lathrop‭

28%
+0 −3
Electromagnetic induction

If I connect a battery to an LC tank and then to an antenna and then on the other side at a distance x, I connect an antenna to another LC tank and this to a diode and this to an LED, Do a I have a...

1 answer  ·  posted 11mo ago by Voyager ll universe probe‭  ·  last activity 11mo ago by Olin Lathrop‭

80%
+6 −0
Standardized schematic/layout file formats for PCB CAD tools?

As we know there exists numerous different kinds of PCB CAD software. The big ones seem to be Eagle, KiCAD, Altium, OrCAD, Solidworks, DesignSpark and probably a few more. When it comes to mechani...

1 answer  ·  posted 11mo ago by Lundin‭  ·  last activity 11mo ago by Olin Lathrop‭

77%
+5 −0
Location of AGC in a superheterodyne RX chain

RF novice here. If using a superheterodyne receiver for the purpose of FM/FSK modulated signals, I'm wondering if the location of an optional automatic gain control (AGC) circuit is always placed o...

0 answers  ·  posted 11mo ago by Lundin‭

77%
+5 −0
How do I design a flyback converter? What are the basics I should know?

I need to design a simple flyback converter like this: - I want to control duty cycle from another circuit such as an MCU but, I'm unsure how to proceed. My requirements are: - Input voltage 125 ...

2 answers  ·  posted 2y ago by Andy aka‭  ·  last activity 11mo ago by Andy aka‭

77%
+5 −0
Why do large RAM chips not have a serial interface?

I have a PIC32MZ2048ECG064, a 64-pin 32-bit microcontroller with 512kB RAM. This is not enough for my purposes, I need to extend it by at least 32MB, preferably 64 or 128. I believe this means I ca...

0 answers  ·  posted 11mo ago by Keelan‭

22%
+0 −5
Why won't this Globe Electric Dimmable LED securely fit my IKEA November Lamp? [closed]

On the LEFT is what I just bought today — Globe Electric 4W (40W Equivalent) Daylight (5000K) Dimmable LED Light Bulb, G9 Bi-Pin Base, 400 Lumens, 15,000 H. Here's Globe Electric's Dimmer Compatibi...

0 answers  ·  posted 11mo ago by TextKit‭  ·  closed 11mo ago by Olin Lathrop‭

75%
+4 −0
PCB Copper Layer Spacing & Voltage Rating

One standard used for spacing conductors based on voltage is the IPC-2221. This standard differentiates spacing requirements for inner and outer conductors. Does the IPC minimum separation betwee...

1 answer  ·  posted 12mo ago by DavidE‭  ·  edited 11mo ago by Lundin‭

77%
+5 −0
Design considerations for a differential pair

Differential pairs, such as for ethernet or a CAN bus, can be designed to be loosely coupled or tightly coupled. For a loosely coupled differential pair, the odd-mode and even-mode impedances are ...

1 answer  ·  posted 12mo ago by DavidE‭  ·  last activity 12mo ago by Olin Lathrop‭

75%
+4 −0
Via on pad: acceptable or not?

I am designing a PCB with somewhat limited space. To save space, I am placing some vias on component pads. However, I am not sure if this is a good practice in PCB design. As far as I understand, t...

1 answer  ·  posted 12mo ago by Mu3‭  ·  last activity 12mo ago by Olin Lathrop‭

28%
+0 −3
Phase shift between phase and line quantities [closed]

In a 3 phase Star source-Star load circuit the phase voltage has different phase than line voltage and in a 3 phase Delta source-Delta load circuit the phase current has different phase than the li...

0 answers  ·  posted 12mo ago by MissMulan‭  ·  closed 12mo ago by Olin Lathrop‭

37%
+1 −3
Bandwidth of serial signal

Suppose we have this stream of data.Let's assume the data stream lasts 1 sec. How do we find the bandwidth of the data?Do we Fourier transform the signal in order to find its components in the ...

1 answer  ·  posted 12mo ago by MissMulan‭  ·  last activity 12mo ago by Olin Lathrop‭

42%
+1 −2
Splitting of message inside the layers [closed]

Assume a app generates a message (stack on computer).Each layer of the sending entity will put then control information in the data depending on the protocol and transmit the data to the next lowe...

0 answers  ·  posted 12mo ago by MissMulan‭  ·  closed 12mo ago by Nick Alexeev‭

84%
+9 −0
208VAC triple-phase to single-phase conversion

The question: Is there a way to convert from triple-phase 208VAC to single-phase 208VAC? Background: Hi everyone, I am stuck on a project I'm working on. I'd like to convert 208VAC (three phase,...

2 answers  ·  posted 1y ago by cosined‭  ·  last activity 12mo ago by Andy aka‭

75%
+4 −0
ESD USB Shield Connection & Filtering

I have a handheld ARM Cortex M based device, which has a USB input port. The product is battery powered and there is no metal chassis. We are going through CE testing, and are having ESD issues a...

4 answers  ·  posted 2y ago by leroy105‭  ·  last activity 1y ago by Pete W‭

60%
+1 −0
Asynchronous connection question

Assume we have a channel and send 7-bit data(0100100) asynchronously with 1 parity bit(0).Suppose the start bit is 1.The end bits are in the same logic level with the idle state of the channel(0).H...

2 answers  ·  posted 1y ago by MissMulan‭  ·  last activity 1y ago by Olin Lathrop‭

50%
+0 −0
What is minimum resolution here?

In this datasheet it says that the minimum resolution is 0.1uA for the 10mA range.What is this minimum resolution?Is it the sensitivity of the multimeter for the 10mA range?

1 answer  ·  posted 1y ago by MissMulan‭  ·  last activity 1y ago by dsr‭

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 1y ago by Sriram14‭  ·  last activity 1y ago by Olin Lathrop‭

60%
+1 −0
Resistance of digital ampmeter

Can we find the internal resistance of a multimeter ,when we use the multimeter like a ampmeter, from its datasheet? I am trying to find the internal resistance of IDM 505 and I went to the datash...

2 answers  ·  posted 1y ago by MissMulan‭  ·  edited 1y ago by Canina‭

66%
+4 −1
What is sacrificed when buying cheaper oscilloscope probes (of same BW/cap/R/gain)

I'm wondering if there are particular aspects of an oscilloscope probe's performance that tend to suffer, or failure points to look out for, if/when buying lower-end makes of oscilloscope probes (l...

1 answer  ·  posted 1y ago by Pete W‭  ·  last activity 1y ago by Olin Lathrop‭

81%
+7 −0
Low-frequency PWM-controlled Mosfet heater circuit

The circuit above is used to control a 240W ceramic heater by means of a PWM signal at 30Hz, generated by a microcontroller, with 5V logic. The input is a standard 280W AC-DC external power adapt...

2 answers  ·  posted 1y ago by francesco‭  ·  last activity 1y ago by Pete W‭

50%
+1 −1
MOSFET not turning completely off

Hello everyone, I have a simple circuit in which I control some LEDs via an MCU and DMG2302UK ( N-channel MOSFET ) The EN pin is connected to an MCU gpio pin that works at 3.3V. The circuit wo...

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

71%
+3 −0
3+3 doesn’t show 6

I have a problem which I don’t understand how to solve. I have this 2-bit adder, but when I select A1AO to be (11)2 3 and B1BO to be (11)2 3 and run it on Logisim it doesn’t show me 6. Instead it s...

2 answers  ·  posted 1y ago by MissMulan‭  ·  edited 1y ago by Peter Mortensen‭

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} \c...

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

66%
+2 −0
Diodes used in mixers

Suppose we have this circuit which is supposed to be an unbalanced frequency mixer. But how does the diode generate a signal with new frequencies at the output?

2 answers  ·  posted 1y ago by MissMulan‭  ·  edited 1y ago by Peter Mortensen‭