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Questions tagged [scr]

A Silicon Controlled Rectifier - A PNPN or NPNP semiconductor device that once triggered stays in permanently conductive state until the current is removed. USed in protective circuits and chopper style light dimmer switches. Also know as a thyristor.

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Why on shutdown the SCR can be compared to a power diode?

I have this as a homework question and can't seem to find the answer in my notes, book or internet. I know they will behave similarly when there is a reverse polarity on both, but the way my professor ...
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80 views

Xenon Flash thyristor trigger

I'm building a xenon flash unit with a power of 50Ws (300V 1000uF capacitor). I need to trigger it from a microcontroller. For that I use a MOC3041 to opto isolate my µC from the HV circuit and ...
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79 views

What happens for the SCR if I connect gate with ground when it is turned on?

When I connected a silicon control rectifier by applying positive voltage in anode and negative voltage in cathode, after that I triggered the gate by pulse voltage and it connected, after that I want ...
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240 views

What distinguishes an ordinary thyristor from a GTO thyristor?

A thyristor, I know, is a four-layer PNPN structure, with an anode on the first P section, a gate on the second P section, and a cathode on the second N section. This simple structure suggests that ...
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76 views

Trouble with simulating an SCR

I was reading about SCRs and I'm trying to simulate 2N5060 SCR but having some issues when I plot the currents and voltages: First by looking at the datasheet, I set the R4 to keep the gate current a ...
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47 views

Confused with turn on time definition of an SCR

The following question I encountered is asking about the minimum time for applied voltage to the gate of an SCR to turn it ON: And below is the solution: I can understand the solution looking for ...
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3answers
46 views

Testing a thyristor

I have a very large high voltage device that a friend asked me to take a look at. It has a bunch of BIG thyristor packages (Semikron, SKKT 106/18 E, Dual Thyristor Module, 600A 1800V). I'm testing ...
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31 views

Help With Latching Shutdown Circuit Using SCR

I am considering using the following circuit for a shutdown circuit that latches when a sensor goes above a certain voltage. My intention is for the circuit to remain latched until the main power ...
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29 views

Gate behaviour on triggered SCR

I'm having trouble understanding this crowbar circuit, which I'm trying to implement as an overvoltage protection for a 5V linear power supply. V1 simulates the regulator's output while V2 is the ...
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71 views

TCA785 phase angle controller design problem?

this shematic is taken directly from TCA785 datasheet i have one question: 1- what is the need for the negative rail in this TCA785 application circuit ?
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1answer
74 views

Switch operating at particular touch IC voltage [closed]

Is there any circuit to perform such task more efficiently? I am trying to control a small motor (like a smartphone vibration motor) with specific outputs from the touch IC, so that it can be turned ...
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3answers
94 views

“Active Low” SCR

Background: I'm working on a circuit that uses an ATmega 328 processor, and a hall effect sensor. We're creating a small wireless sensor, so what we're focusing on now is power consumption. We want ...
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34 views

UJT provides a trigger operation to the SCR

hello everyone i want to know how to solve this problem if anyone cane help me to solve this question i will really appreciate it
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167 views

Dimensioning SCR crowbar circuit

I need to dimension an SCR crowbar circuit to reach a certain level of protection against overvoltage, without increasing much the complexity of the circuit of my control card. The need is to protect ...
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67 views

What's the best way to detect zero crossing in this design?

The design that I am talking about: I want to be able to detect the zero point with an MCU of which pin can withstand only 3.3 V. I'll forgo optocoupler because A. I want everything to be as cheap as ...
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1answer
165 views

Thyristor/SCR \$i^2t\$ and \$i^2\sqrt{t}\$ Rating

I have commonly seen the \$i^2t\$ rating for fusing in a SCR datasheet. This is a helpful rating for assessing if pulses which exceed the surge current rating (Itsm) of the SCR will damage it. ...
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95 views

GTO Driver circuit

i am new to power electronics.I am working in project where input is pulsating dc and i have to control it, i try with scr but we can control only on of scr not off so in some case the cycle cut ...
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510 views

Ideal component to switch 84V DC?

I wanted to control a 84V LED strip using a ATtiny13a microcontroller with minimal power wasted. I just want to turn it on and off, don't need any PWM dimming. The strip uses 270mA current and is ...
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243 views

What is the purpose of the SCR in this circuit?

I am trying to repair an old SMPS. The first step is to reconstruct the schematic and work from there on. The schematic on the low voltage side is completed for the +12V and the +5V circuits. However ...
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98 views

Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

See attached circuit. Circuit is designed to have the bulb light, when a very low amperage momentary switch is pressed. In the final circuit, the bulb will draw 4 to 5 amps for a short period of ...
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159 views

SCR switching conducted emissions

I have a circuit that drives a 240Vac line to line power to a resistive load. I am testing for radiated and conducted emissions. Radiated emissions went fine but conducted emissions failed with "broad ...
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1answer
96 views

How to know if a SCR is still working?

I'm using a TIC116 to control the power over an electric grill. However, I didn't use a heatsink and it got very warm. On the data it says that its upper limit is 110 °C. I suspect that the gate is ...
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1answer
105 views

Problem with using SCR to control power for an electric grill

I'm doing a power controller for an electric grill, where through PWM I allow to pass x number of cycles from the 124V @ 60 Hz source of my lab. Here you have the diagram: simulate this circuit &...
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2k views

Why are bulky SCR power controllers used when the same can be achieved with a relay?

This is kinda noob question. I recently got an SCR Power controller (WATLOW DIN-a-mite DB20-24CO-0000 Style B). This is the first time I actually got to test an SCR controller for myself. The input ...
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2answers
343 views

Turn-off an scr by a transistor

Hello. I understand that one of the method to turn-off an scr is by connecting a transistor parallel to it in order to short it. I would like to turn on the transistor(BC547B)by touching the wires ...
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1answer
623 views

SCR triggering using DIAC

I've found this method of triggering of the SCR through DIAC and I'm trying to understand it. I was able to figure out the whole trigger circuit and how to compute the values of RC in order to have ...
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1k views

How to use SCR to control the power of a heater

I would like to point out that I am not an expert (as it is perceived by the question) in the use of scr, diac, and triac and that this question is more for academic purposes than use in real life. ...
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686 views

Formula of snubber capacitor capacitance for SCR dv/dt protection

I have a formula here for finding the suitable value of shunt capacitance to be put on an SCR snubber. \$C=\frac{1}{2L}(\frac{0.546V}{dv/dt})^2\$ where L is the snubber inductor, V is the DC supply ...
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831 views

Wiring for 10000W 220V SCR Voltage Regulator Speed Controller

I live in the US and have the Twist Lock Electrical Plug 4 Wire, 30 Amps, 125/250V, NEMA L14-30P. It has 2 hots, 1 ground, and 1 neutral wire. I saw the following scr controller on ebay and am ...
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1answer
415 views

DC bus inversion to 3 phase AC modified sine wave using IGBTs

I'm working with a variable voltage inverter. I have 3 phase AC voltage coming in at 480V RMS line to line. It hits a full wave SCR front end, has a DC bus link, and is inverted with IGBTs to created ...
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94 views

Why does this transformer have an additional winding on the side of the core?

This photograph is of a wire feed welder. This unit consists of a step-down transformer with a bunch of taps on the primary side. It is fed from 115 Volt 60 hz supply. The switch on the left allows ...
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242 views

Identify a Thyristor

Hello would anybody be able to find the spec's of this SCR Thyristor General Electric C50FX425 937 Thanks in advance.
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719 views

Is this a good inverse parallel SCR drive circuit?

I have a design for a dimmer circuit, but I am unsure of its correctness or if there are issues with it. It's meant to be controlled by a 50% duty cycle PWM signal - the dimming responds to the phase ...
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1answer
214 views

Does this capacitor discharge? SCR and capacitor doubts

I'm having some doubts about this circuit and about capacitors charge/discharge in general SCR CIRCUIT; Igt= 100MicroAmps;Vgt = 0.7V Ok I have like 5 questions 1) Is flowing current through R2 and ...
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1answer
356 views

How to automatically turn off an SCR after being latched for DC supply

How to automatically turn off an SCR after being latched for DC supply? Type of switches that turns on/off a circuit with a certain voltage But when i try it in multisim it doesnt work.
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1k views

How do I find the firing angle of SCR practically? [closed]

Our teacher told us to find out the time period and then multiply it by 18.Then 180-(∆t*18) gives firing angle.Why 18 as a multiplier?
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3answers
586 views

SCR fail safe protection

I would like to use 2 SCRs in antiparallel configuration to control the power to a all resistive load (20A) using 240Vac (line to Line). Pretty typical configuration and part of a lot of SCRs ...
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1answer
490 views

SCR circuit falsely triggered during capacitor charging

I am building a coil gun. Above is the complete schematic of the voltage boost circuit plus the trigger circuit. Not shown in the schematic, there is a push button switch between the regulated +9V ...
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4answers
367 views

Verification of SCR Driving Circuit

Several years ago I attempted to build a coil gun, but gave up in frustration after burning out several SCR's when designing the trigger circuit. The SCR is used as the switch that dumps the energy ...
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173 views

Cycloconverter , MOC3021 problems?

i am doing a cycloconverter single phase design and i have a problem , i use microcontroller to control the firing angle ,i have used zero crossing voltage (741) to trigger INTERRUPT port of MCU , i ...
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1answer
550 views

LTSpice Simulation Problem - Controlled Rectifier Single Phase Dual Converter

So I am having problems simulating a Single Phase AC/DC Dual Converter on LTSpice. At the first converter I am getting the perfect output but when I take the voltage probe from the second converter ...
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1answer
430 views

Why is that the gate current cannot be negative for SCR?

Why is that the gate current cannot be negative for SCR ? If the gate current is negative it should only increase the breakover voltage , why is that the SCR does not work ?
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2answers
509 views

Precision control of current to an inductive coil (coilgun)

I have students building a coilgun. At first they used a manual switch, despite my suspicion that it would not switch on cleanly. After looking on the oscilloscope at the trace of a one shot, we can ...
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2k views

SCR Gate to negative

Is a short circuit that occurs for as long as an instance safe? In the following schematic done from here, I have a silicon controlled rectifier that is used as a latch (the circuit simulation doesn'...
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2answers
447 views

thyristor equation

I know how does an I-V curve of a thyristor look like, but is there any thyristor equation that can represent the curve?
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1answer
2k views

How should I step down 220V (ac) to 180V for a DC motor?

I have many treadmills motor of rating 180V 10A which I would like to use for power tools. Locally we have 220V ac 50Hz. I thought of using iron-core transformers. But having one for 1800W+ is ...
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1answer
891 views

Is it possible to replace a DIAC circuit with an SCR circuit to drive a TRIAC

I have a triac DIAC cirtcuit. I don't have any DIACs on hand, but I do have plenty of TN1215s. Is it possible to generate the required pulses using an SCR to drive the TRIAC's gate?
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Is there a good reason to use an SCR based speed controller instead of a TRIAC?

I tried to purchase a switch for a reciprocating saw with variable speed for my Dewalt DW304. I discovered the part is no longer available. Instead, I bought a similar switch used on the later model ...
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2answers
144 views

How to mount a TO-200AB

I'm looking into high power SCRs. The two common cases i'm finding are TO-209AB and TO-200AB. The TO209AB are straight forward to mount and connect. The other, TO-200AB is strange looking and ...
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123 views

Why isn't the switches being bypassed in this triac/diac circuit?

Just when you think you understand circuits, there's always a curve ball to derail you and leave you scratching your head. The diagram below is a Triac/Diac speed controller for a reciprocating saw. ...