Questions tagged [flyback]

A flyback diode is a diode used to eliminate flyback, which is the sudden voltage spike seen across an inductive load when its supply voltage is suddenly reduced or removed. A flyback transformer, also called a line output transformer, is a special type of electrical transformer designed to generate high voltage sawtooth signals at a relatively high frequency.

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How to choose a flyback diode for a relay?

A diode is put in parallel with a relay coil (with opposite polarity) to prevent damage to other components when the relay is turned off. Here's an example schematic I found online: I'm planning on ...
Nate's user avatar
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Correct use of Flyback or Snubber diode across Motor or Transistor?

From seeing a few schematics where the flyback or snubber diode has been placed across the transistor C-E terminals (Right Configuration), instead of what I typically seen as the the flyback being ...
Passerby's user avatar
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18 votes
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How to calculate air gap in flyback transformer?

I’m designing (or at least trying to design) a flyback converter on LM3478. I chose the EFD20/10/7-3F3 core [1]. Using a PDF from Infineon [2] I calculated that I need a primary winding inductance of ...
urhen's user avatar
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17 votes
3 answers
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Can a Zener diode that protects a switch against inductance when the switch opens, affect turn on speed of the valve when you close it again?

As you probably know, in the applications that the turn off speed of the solenoid valves are crucial, the simple flyback diode is not effective. Some people put a resistor in series with the flyback ...
arudino.tyro's user avatar
15 votes
4 answers
13k views

Why is flyback air gap needed for energy storage?

Why do so many sources say something along the lines "since a flyback transformer stores energy, an air gap is needed"? I have seen this reasoning in textbooks and app notes. I thought air gaps ...
EwokNightmares's user avatar
15 votes
4 answers
7k views

What are the effective power limitations of the flyback converter topology, and why?

Looking at several different isolated converter topologies, flyback looks like it's the simplest at first glance. There's only one switch, so there's only one driver, which (all other things being ...
Stephen Collings's user avatar
14 votes
4 answers
4k views

H-Bridge Fly-Back

Sorry if this question is a little long, but I though it prudent here to discuss the state-of-the art as I know it before asking the question. ISSUE When using an H-bridge to drive a bidirectional ...
Trevor_G's user avatar
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13 votes
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Why do most flyback converters / LED drivers operate under 100 kHz?

Most of the LED drivers and flyback converters I have come across operate in the 60-100 kHz range. Is there any particular reason behind this - example - ferrite cores not being able to handle higher ...
Whiskeyjack's user avatar
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13 votes
4 answers
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Why don't flyback diodes in H-bridge damage power supply?

I'm currently learning about driving a small DC motor (~ 5V). My research so far indicated that a L298N might be a good choice to quickly get something up and running. However, I'm also trying to ...
s1m0n's user avatar
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12 votes
4 answers
3k views

What keeps the kickback voltage from reaching an infinite voltage?

We know that the voltage over an inductor is defined by the formula: \$V = L * \frac {di}{dt} \$ So in the case where the current flow is suddenly interrupted (like when a mechanical contact is ...
C K's user avatar
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11 votes
4 answers
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Does a diode flyback protection decrease the life of the relay?

I am currently making an automotive circuit that controls some automotive accessories (personal project not for production). In my circuit, I will be controlling some automotive relays and in any ...
DrakeJest's user avatar
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11 votes
2 answers
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Flyback diodes issues and pull-in & hold current issues in this Relay circuit

Although this may be a basic question but I'm still struggling with it. In this schematic, two zener diodes D1 and D2 are connected back-to back across relay coil L1. The BVds = -30V for Q1. Can I use ...
jacks's user avatar
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10 votes
5 answers
2k views

MOSFET broke after attaching capacitor bank

I have a solenoid that has a coil resistance of \$0.3\Omega\$ and accelerates a steel projectile here. I've posted the schematics below. Normal Version that acts as a control The GPIO8 goes to 5V to ...
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10 votes
2 answers
9k views

Do I need a flyback diode?

I have some experience using automotive relays and triggering them using the output from a two-way radio aux pin so I am aware of the need to add a diode in parallel with the coil to protect the radio'...
Chef Flambe's user avatar
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10 votes
4 answers
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What is a flyback?

Trying to find this answer is so difficult that I can't even tell whether What is the difference between a transformer and a coupled inductor? is asking the same thing. Some reading suggests that a "...
feetwet's user avatar
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10 votes
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Is a balancing diode really necessary for the Balanced Boost converter?

Please pardon all of the information that precedes the question -- I didn't want you to actually have to go read the paper itself. This question is in two parts, but they are really equivalent, so it'...
MicroservicesOnDDD's user avatar
9 votes
3 answers
4k views

Practical way to generate 1500V?

In designing the power supply for an radiation detector, I need to supply up to 1,500V at 2 mA from mains (170 Vdc). I've largely considered a flyback converter, but cannot find a flyback transformer ...
A.S.'s user avatar
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9 votes
3 answers
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Protecting microcontroller from inductive loads

I'm working on a project where I will be controlling a variety of loads (relay, solenoid, motor) from an Arduino and I'd like to make sure I build in enough protection for the microcontroller and ...
Aleksander's user avatar
9 votes
1 answer
5k views

Use of Flyback Diodes

A flyback diode is commonly use to eliminate sudden voltage spike when current drop across an inductive load. These kind of diode can be found close to relay, motor or sometime MOSFET. simulate this ...
M.Ferru's user avatar
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8 votes
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MOSFET Diode design

I'll start this off by simply saying I am not an Electrical Engineer. I am, however, an embedded programmer who has had some experience with circuit design and setup (give me 1's and 0's and I can ...
Cory Russell's user avatar
8 votes
3 answers
8k views

Making LM78xx fail safe against short, open, reverese bias, flyback, etc

I want to use LM78xx for various applications. What I am concerned about is its failure modes. 1. Failure to Short Not shorting Vcc to ground!! I mean shorting V_input to V_output. Assume that you ...
arudino.tyro's user avatar
8 votes
2 answers
2k views

Flyback diode forward voltage drop

In an ideal flyback diode selection, one would seek a diode which has very large peak forward current capacity (to handle voltage transients without burning out the diode), low forward voltage ...
emperor_penguin's user avatar
7 votes
4 answers
2k views

Bench power supply with no minimum output voltage

Just like many other electronics hobbyists, I am trying to build a variable bench power supply with 0-30 V and 0-5 A output. I have gone through various sources to get a basic idea of how to design ...
tinkerer's user avatar
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7 votes
5 answers
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Can the inductive kick be discharged without a freewheeling diode, in this example?

In literature we commonly see the use of a freewheel diode to protect the circuit against the inductive kick when the switch goes from closed to open (Fig 1). However, what would be the pros/cons of ...
Big Al's user avatar
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7 votes
3 answers
1k views

Are flyback diodes needed for this op-amp voltage controlled inductor?

I understand the need for flyback diodes when trying to change inductor current abruptly with a mechanical switch or when using a BJT/MOSFET as a switch. Now, assume I (linearly) control the voltage ...
GummiV's user avatar
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7 votes
3 answers
3k views

Is it possible to store flyback voltage in capacitors?

I recently put together a circuit that I use to control an electrical motor. I use an Arduino's PWM through darlington-pair transistors to control the speed of the motor. During construction of this ...
0xhughes's user avatar
  • 261
7 votes
2 answers
782 views

What's the purpose of the MOSFET on the output of the flyback buck converter in this circuit?

Below is an EVL8030 for MP8030 POE PD and DC/DC controller. They have put a MOSFET on the secondary winding. At first I thought it was used as a snubber but I'm unsure about this. It's a flyback buck ...
Sam Alamad's user avatar
7 votes
3 answers
2k views

In a flyback transformer with multiple windings, how are voltages controlled for different current loads?

This is the flyback transformer I will be referring to: Wurth 760871543 There are three output windings as follows, 24 V at 0.30 A, 5 V at 1.15 A, 14 V (unspecified but in mA range aux winding). ...
A.S.'s user avatar
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7 votes
2 answers
7k views

Does a fan need a flyback diode?

I'm aware that inductive loads like relays need a flyback diode. Since a motor is also an inductive load, I'm inclined to put a reverse-biased 1N400x diode across the terminals of this fan. However, ...
user31708's user avatar
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7 votes
2 answers
2k views

High Step-up Ratio DC-DC Convert (12V-to-150V) - Boost, Flyback, Coupled-inductor Boost?

I am trying to design an on board DC DC converter that generates 150V from a 12V input. I'd like to design it to handle at least a 30-50mA load, but in reality the load will most likely be smaller. ...
newothegreat's user avatar
7 votes
3 answers
2k views

Detecting sparks at the output of a high voltage flyback transformer

I was trying to generate plasma inside a cylinder for a hobby project, so I decided to use a flyback transformer from an old TV and drive it with a 555 timer as shown in the schematics. It solves my ...
Kadyan's user avatar
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6 votes
2 answers
2k views

What are these four diodes doing?

I am working with a MC33186DH1 5A H-bridge IC. It seems to simplify things quite a lot. The data sheet shows this simple schematic: I found a break out board that mostly follows that design: My ...
AndrewT's user avatar
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6 votes
5 answers
3k views

Using a large resistor instead of a flyback diode

In a video lecture a professor is explaining how to prevent an electric arc caused by the switching operation in an RL circuit. Here is the section (at around 18:26) where he explains it: https://...
user16307's user avatar
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6 votes
1 answer
820 views

PCB Design position of flyback diode for motor

I have a simple question: If I design a PCB, does it physically matter at what position my flyback diode for my motor is? Does it matter if it's "in front" of my MOSFET or not? I made two ...
Stackoverflowsuperbad's user avatar
6 votes
3 answers
1k views

Why does a flyback converter in DCM mode have a different oscillation waveform at start and end of MOSFET turn off?

As seen from the waveform, when the MOSFET turns off, it has some high-frequency oscillations (shown in red) whereas before MOSFET turns on it has low-frequency oscillations. I have found that the ...
Arun Kumar Thawait's user avatar
6 votes
2 answers
3k views

Is a flyback diode necessary for a small sg90 servo motor?

I am powering a small sg90 servo motor (see datasheet) directly using a 12V battery and a simple circuit to step down the voltage to the appropriate one for the servo. I noticed the servo has some ...
mickkk's user avatar
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6 votes
4 answers
2k views

Solenoids causing Arduino to malfunction despite protection diode

simulate this circuit – Schematic created using CircuitLab I have an Arduino Mega that I'm attempting to control some solenoids and LEDs with. The LEDs are 3.3V, controlled through an open ...
zacaj's user avatar
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6 votes
3 answers
966 views

Intermittent MCLR reset on PIC32 - involves switching electromagnets

I am working on a project that involves a lot of switching of electromagnets. The switching is controlled by a PIC32MX6xx-series microcontroller, which determines the required states of 80x 12 VDC ...
wave.jaco's user avatar
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6 votes
1 answer
1k views

How to safely generate 200V from low voltage supply

Unfortunately, this post requires quite a bit of background if it's going to be useful to anybody (including me). I have been trying to build a relatively high voltage power converter for part of my ...
deltamac's user avatar
  • 121
6 votes
2 answers
897 views

Mazzilli flyback driver mosfets keep failing

I've been trying to build a high voltage generator consisting of a high-voltage transformer and a Cockroft-Walton multiplier. I have actually tried several different drivers to drive a high-voltage ...
user198606's user avatar
6 votes
2 answers
676 views

PNP BJT as a 'switchable' flyback diode?

I have an automotive ignition coil which I'm using as an ignition source for a project I'm working on. During normal operation, the primary coil current will be interrupted periodically to induce ...
christopher.robot's user avatar
5 votes
3 answers
4k views

Determine adequate speed of flyback diode for a relay

I have already looked at this question which looked like it would provide the answer: How to choose a flyback diode for a relay? But it didn't, so I also checked out these: https://electronics....
Jodes's user avatar
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5 votes
5 answers
949 views

Is it possible to produce 30W (5V 6A) using a flyback topology without opto-isolation?

The circuit steps the voltage down from POE (class 4) input to 5V 6A The circuits I have found so far use opto-isolation to regulate the feedback voltage (for 5V 6A). I'm wondering is it feasible to ...
Sam Alamad's user avatar
5 votes
2 answers
1k views

What´s the purpose of this diode?

I'm trying to build my own relay board to use with a 3.3V controller. I found the schematic of the board, so I'll try to replicate it. I'm only having trouble understanding what's the purpose of the ...
Josy Sclei's user avatar
5 votes
2 answers
2k views

Won't the back EMF from the relays hurt the LEDs?

In this ULN2803 based relay driver schematic, why won't the back-EMF from the relays hurt the relay status LEDs?
VAN's user avatar
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5 votes
2 answers
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Why can't flyback work when the duty cycle is greater than 0.5?

I read this document talking about flyback design, and I am curious about why, when the duty cycle is greater than 0.5, do we need to adjust the VOR to make sure the duty cycle is less than 0.5? What'...
Power JJ's user avatar
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5 votes
3 answers
2k views

Braking a brushed DC motor with a flyback diode

I've seen many references to braking a brushed DC motor by shorting its terminals. As I understand it, the motor torque is relative to the current through it, which should dissipate relative to its ...
Christian's user avatar
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5 votes
3 answers
3k views

Isolated DC/DC flyback/SEPIC

As far as I understand the flyback topology, it can be used in both buck and boost converters. What I am not sure about is: Does it also work for the case where buck-boost is needed, i.e. \$V_{\text{...
Junius's user avatar
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5 votes
2 answers
1k views

Multiple inductors in series/parallel, flyback diodes required?

Considering the following setup, 4 equal inductors (4.5V DC, 90 mA pager motors of unknown inductance values) in both parallel and series connection, how many flyback diodes should be used? Is one ...
Passerby's user avatar
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5 votes
1 answer
280 views

Are bypass caps reason why uC don't have flyback diode across ferrite bead in the sample schematics?

Often the IC datasheet recommends putting a ferrite bead before AVCC pin. First I started wondering if I don't need a flyback diode but than I realized that capacitor is probably able to absorb the ...
Maciej Piechotka's user avatar

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