Inductor, switch, snubber diode(flyback diode)

In summary, the conversation discussed the use of a snubber diode in a circuit to avoid voltage spikes and potential damage to components when opening a switch with an inductor in the circuit. The diode acts as a low resistance to allow for a slower decrease in current and prevent a high induced emf. This technique is commonly used in circuits with relays and can be safely measured using an oscilloscope.
  • #1
Bassalisk
947
2
Hello,

I am designing a simple circuit and I need some guidance over snubber diode.

When we open the switch, when we have a inductor in circuit, we will have that arc over switch which is something that we don't want.

Using this snubber diode, we can avoid this. I feel that we will have HUGE voltage spike, on inductor, when we open that switch.

How can I (safely) measure that voltage spike, in order to determine how much inverse breakdown voltage my diode has to have? I am assuming oscilloscope.

My source is 30V DC.
 
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  • #2
When the switch is closed current flows through the inductor and there is a magnetic field.
When you open the switch the current stops instantaneously and the magnetic field collapses very quickly.
This gives a high induced emf which can damage other components in the circuit, can cause a spark across the switch contacts and even cause electric shock to anyone in contact with the terminals of the coil.
The way to reduce this high emf is to arrange for the current to decrease slowly so that the magnetic field decreases slowly.
Before the advent of solid state diodes a common technique was to have a resistor (a lamp bulb) permanently connected in parallel with the coil. When the switch is opened any induced emf tries to maintain the current (lenz's law) and the resistor allows this to happen The current decreases slowly and there is no large induced emf.
The disadvantage is that power is wasted because of the resistor permanently connected.
The modern solution is to replace the resistor with a diode which is connected in reverse across the coil. No current will flow through the diode when the switch is closed and current flows through the coil.
When the switch is opened the polarity of the emf across the coil is to try to keep the current flowing (this is the opposite polarity to the supply voltage for the coil!)
The diode now acts like a low resistance and the current decreases slowly avoiding any large induced emf.
I do not think that reverse breakdown of the diode is an important matter.
This is a common technique used when relays are used in transistor circuits. A diode is connected across the relay coil (in opposite polarity to the power supply).
 
  • #3
technician said:
When the switch is closed current flows through the inductor and there is a magnetic field.
When you open the switch the current stops instantaneously and the magnetic field collapses very quickly.
This gives a high induced emf which can damage other components in the circuit, can cause a spark across the switch contacts and even cause electric shock to anyone in contact with the terminals of the coil.
The way to reduce this high emf is to arrange for the current to decrease slowly so that the magnetic field decreases slowly.
Before the advent of solid state diodes a common technique was to have a resistor (a lamp bulb) permanently connected in parallel with the coil. When the switch is opened any induced emf tries to maintain the current (lenz's law) and the resistor allows this to happen The current decreases slowly and there is no large induced emf.
The disadvantage is that power is wasted because of the resistor permanently connected.
The modern solution is to replace the resistor with a diode which is connected in reverse across the coil. No current will flow through the diode when the switch is closed and current flows through the coil.
When the switch is opened the polarity of the emf across the coil is to try to keep the current flowing (this is the opposite polarity to the supply voltage for the coil!)
The diode now acts like a low resistance and the current decreases slowly avoiding any large induced emf.
I do not think that reverse breakdown of the diode is an important matter.
This is a common technique used when relays are used in transistor circuits. A diode is connected across the relay coil (in opposite polarity to the power supply).

I understand. I will now open another thread regarding this matter. I will show what I have to make.
 

1. What is an inductor and how does it work?

An inductor is an electrical component that stores energy in the form of a magnetic field. It consists of a coil of wire that creates the magnetic field when current flows through it. The inductor resists changes in current, causing it to store energy when the current increases and release energy when the current decreases.

2. What is a switch and what is its purpose in a circuit?

A switch is an electrical component that can open or close a circuit, allowing or preventing the flow of electricity. Its purpose in a circuit is to control the flow of current, either by turning it on or off, or by redirecting it to a different path.

3. What is a snubber diode and why is it used in circuits?

A snubber diode, also known as a flyback diode, is a diode that is connected in parallel with an inductive load in a circuit. Its purpose is to protect the circuit from voltage spikes that can occur when the current to the inductor is suddenly interrupted. The diode provides a path for the current to flow, preventing damage to other components in the circuit.

4. Can a snubber diode be used in any circuit with an inductor?

Yes, a snubber diode can be used in any circuit that includes an inductor. It is especially useful in circuits that have high inductive loads, such as electromagnets or motors, to prevent voltage spikes and protect other components in the circuit.

5. Are there any drawbacks to using a snubber diode in a circuit?

The main drawback of using a snubber diode is that it can cause a small amount of power loss due to the diode always being in the circuit. However, this loss is minimal compared to the potential damage that can occur without the diode. Additionally, using a snubber diode can add to the overall cost and complexity of a circuit.

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