Relay contact protection circuit, switching power supply RCD circuit, MOS tube construction, several issues 1. Relay coil and RC series circuit...

QWE4562009

Relay contact protection circuit, switching power supply RCD circuit, MOS tube construction, several issues 1. Relay coil and RC series circuit... [Copy link]

 

Several issues on relay contact protection circuit, switching power supply RCD circuit, and MOS tube structure

1. The relay coil is connected in parallel with the RC series circuit to absorb the self-inductance current when the coil is powered off. Is there any similarity between this and the primary RCD absorption circuit of the switching power supply? 2. The triode is composed of two PN structures, so what about the MoS tube? The MOS tube can also be seen as the structure of two diodes. Why is the triode a current control device, while the MOS tube is a voltage control device?

3. Field effect transistors are divided into junction field effect transistors (JFETs) and insulated gate field effect transistors (FETs) (Do MOS tubes belong to the FET category?) Both JFETs and FETs can be made into P/N enhancement and depletion types, for a total of four types?

maychang

1. The relay coil is connected in parallel with the RC series circuit to absorb the self-inductance current when the coil is powered off. Is there any similarity between this and the primary RCD absorption circuit of the switching power supply?

First of all, it must be said that relay coils are rarely connected in parallel with RC series circuits to absorb the "self-inductance current when the coil is de-energized". Instead, relay contacts are often connected in parallel with RC series circuits in order to eliminate sparks or arcs.

If the relay coil is connected in parallel with the RC series circuit, it is similar to the RCD absorption circuit of the switching power supply. Both use the RC circuit to absorb high voltage spikes.

maychang

In the third picture you posted, the RC circuit is not connected in parallel with the coil, but in parallel with the contacts.

maychang

2. The triode is composed of two PN structures, so what about the MoS tube? The MOS tube can also be seen as the structure of two diodes. Why is the triode a current control device, while the MOS tube is a voltage control device?

MOS tubes must never be "viewed as the structure of two diodes".

Although bipolar transistors have two PN junctions, the emitter junction and the collector junction, they cannot be viewed as two diodes simply connected together. You can never construct a transistor with two diodes.

maychang

3. Field effect transistors are divided into junction field effect transistors (JFETs) and insulated gate field effect transistors (FETs) (Do MOS tubes belong to the FET category?) Both JFETs and FETs can be made into P/N enhancement and depletion types, for a total of four types?

Junction field effect transistors cannot be made into enhancement type.

okhxyyo

Have you solved your problem? If you have, please share the solution.

QWE4562009

maychang posted on 2020-5-12 18:31 In the third picture you posted, the RC circuit is not connected in parallel with the coil, but in parallel with the contacts.

Control terminal and normally closed Control terminal and normally open Both sets are needed

QWE4562009

maychang published on 2020-5-12 18:34 2. The triode is composed of two PN structures, so what about the MoS tube? The MOS tube can also be seen as the structure of two diodes. Why is the triode a current control device, ...

Why not

QWE4562009

okhxyyo posted on 2020-5-13 07:34 Have you solved all your problems? ? If you have, please share your solutions.

These are things I encountered during the learning process, not at work.

QWE4562009

maychang published on 2020-5-12 18:35 3. Field effect transistors are divided into junction field effect transistors (JFETs) and insulated gate field effect transistors (FETs) (Do MOS tubes belong to the FET category?) Both JFETs and FETs can be made...

MOS tube is an insulated gate type.

maychang

QWE4562009 posted on 2020-5-14 08:19 Control end and normally closed Control end and normally open Both sets are needed

"Control terminal and normally closed Control terminal and normally open, both sets are needed."

As mentioned on the second floor: the two ends of the relay winding are rarely connected in parallel with an RC series circuit to absorb the "self-inductance current when the coil is powered off". There is no benefit in connecting RC in parallel, and it only increases the cost and circuit board area. Usually, a diode is connected in anti-parallel to the two ends of the relay coil to absorb the "self-inductance current when the coil is powered off".

The reason why RC is connected in parallel at both ends of the contact is that the relay contact controls the inductive load. When the contact is disconnected, the inductive current will suddenly change and generate an induced electromotive force, which will cause sparks at the contact. Sparks will affect the life of the contact. The parallel RC circuit can absorb the induced electromotive force energy and reduce sparks. This has been mentioned on the second floor. The relay contact cannot be connected in parallel with a diode to absorb energy, so an RC circuit must be used.

maychang

QWE4562009 posted on 2020-5-14 08:23 Why not

“Why not?”

The reason is very simple: if two diodes can form a triode, then why do we still need to make triodes? Diodes have been around for a long time, more than 50 years earlier than the transistor. The invention of the transistor won the Nobel Prize.

maychang

QWE4562009 posted on 2020-5-14 08:24 Is the MOS tube an insulated gate type?

"MOS tubes are of the insulated gate type, right?"

yes.

QWE4562009

maychang posted on 2020-5-14 09:23 "Control end and normally closed Control end and normally open Both sets are required" It has been said on the second floor...

Is it better to use RC or RCD?

maychang

QWE4562009 posted on 2020-5-15 17:10 Is it better to use RC or RCD?

Is it better to use RC or RCD?

You mentioned two situations: one is the relay contact (one mistakenly thinks it is a coil), and the other is the primary of the switching power supply. When you asked "is it better to use RC or RCD?" which situation do you mean?