Theory and practice of SCRs and PLLs - Electronic Circuits Projects Diagrams Free

winterhunter · 18th March 2007, 06:22 PM

Hi everyone,

I know that I'm asking about two different types of component, but I have two questions and did not want to start two consecutive threads.

First, let's start with thyristors.
I've bought a couple of thyristors to use them as signal triggers, but I can't get them to work!

First, I know that thyristors do have an anode, a cathode and a base. But when looking into the documentation of the one I have (BRX49), I find that:
Pin 1: anode
Pin 2: anode
Pin 3: cathode

So how do I connect it???

Also, I've tried to do the following circuit, assuming pin 2 to be the gate, which does not work (even though I've measured the voltage at the gate, and it goes from <200 mV to ~2V when it detects a signal). However, the led stays off...

About PLL's, how do they work internally? I know they are used as frequency multipliers and to sync the clock on "large" chip, but what else are they used for?

Could also anyone please explain how do you use a PLL as a frequency multiplier? (A real world example with a part number would be greatly appreciated!).

Thanks a lot!

Regards,

Gonzalo

ericgibbs · 18th March 2007, 06:34 PM

hi gonzalo,
Even though the gate voltage measures 2v or so to ground, it will not be so if you measure from the gate to the top of the LED connected to the SCR.

Place your LED and resistor in the 'top' line, apply the 2v to the gate and ground.

Eric

Hero999 · 18th March 2007, 06:39 PM

The LED won't turn on until the gate of the SCR reaches about 2.6V (depending what colour LED you used).

150

is a bit large for R1 and R3 is a bit too big for an LED. R1 shoud be around 10k and R3 should be around 270

to 330

. Check the minimum holding current for the SCR, it won't stay on if the current falls below below a certain value.

PLLs are a totally different part to SCRs, a tutorial can be found here.

Leftyretro · 18th March 2007, 06:45 PM

Hi;

A problem using SCR devices in DC applications is in how to turn them off once they fire on. Your circuit once fired on will stay on forever until you remove Vcc from circuit, as the base then has no further control of the device. Should be plenty of info via google on using these devices.

PLL are phase comparator circuits. They take two frequency inputs, a reference frequency and a controlled frequency. The controlled frequency is divided down either inside the PLL chip or externally to be a close match to the reference freq. The phase comparator drives a DC filter that controls a VCO (voltage controlled oscillator) that runs at the controlled frequency.
So in effect the PLL chip multiplies the the reference frequency by the divisor value. These chips vary in what features are available internally and if designed for micro interfacing and the frequency range of operation.

Lefty

Mike Stanley · 2nd April 2007, 03:06 AM

Gonzalo,
I use embedded (in SoCs) PLLs every day to multiply an external crystal frequency to higher CPU frequencies. Can't really say I've delved into the math - I just set a multiply factor in my software, wait for lock and switch over. But I can point you to a couple of sources for PLL information at http://www.eehomepage.com/query.php?Find=PLL. Hope that helps.
Regards,
Mike Stanley
http://www.eehomepage.com

nguyen ngoc duong · 17th May 2007, 01:32 PM

[IMG]c:\orcad\scr.jpg[/IMG]
I am sorry, I make a mistake! SW1 must be always closed.
when D2 in dark, adjust R6 so that Veb of Q2 less than 0,6v
when in bright , Q2 certainly in saturated state.
chose R4 depending kind of scr Q1.
Push SW1 to disconet LED D1 ( D2 must be in dark).
Sory! I can not post a image scr.jpg.
Are there anyone help me?
Contact to me incase anyone want to get a picture by mail:
duongnguyen1968@yahoo.com

Hero999 · 17th May 2007, 10:01 PM

Image tags only work if the file is stored somewhere on the Internet. You need to upload it somewhere, preferably to this place.

Also, it isn't a good idea to post your email address as you'll be inundated with spam.

Richard Principal · 26th October 2007, 07:08 PM

Dont you mean

Anode, C

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18th March 2007, 06:39 PM
Hero999 Experienced Member	The LED won't turn on until the gate of the SCR reaches about 2.6V (depending what colour LED you used). 150 is a bit large for R1 and R3 is a bit too big for an LED. R1 shoud be around 10k and R3 should be around 270 to 330. Check the minimum holding current for the SCR, it won't stay on if the current falls below below a certain value. PLLs are a totally different part to SCRs, a tutorial can be found here. __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser.

18th March 2007, 06:45 PM
Leftyretro Experienced Member	Hi; A problem using SCR devices in DC applications is in how to turn them off once they fire on. Your circuit once fired on will stay on forever until you remove Vcc from circuit, as the base then has no further control of the device. Should be plenty of info via google on using these devices. PLL are phase comparator circuits. They take two frequency inputs, a reference frequency and a controlled frequency. The controlled frequency is divided down either inside the PLL chip or externally to be a close match to the reference freq. The phase comparator drives a DC filter that controls a VCO (voltage controlled oscillator) that runs at the controlled frequency. So in effect the PLL chip multiplies the the reference frequency by the divisor value. These chips vary in what features are available internally and if designed for micro interfacing and the frequency range of operation. Lefty

2nd April 2007, 03:06 AM
Mike Stanley New Member	Gonzalo, I use embedded (in SoCs) PLLs every day to multiply an external crystal frequency to higher CPU frequencies. Can't really say I've delved into the math - I just set a multiply factor in my software, wait for lock and switch over. But I can point you to a couple of sources for PLL information at http://www.eehomepage.com/query.php?Find=PLL. Hope that helps. Regards, Mike Stanley http://www.eehomepage.com

17th May 2007, 01:32 PM
nguyen ngoc duong New Member	Trigger SCR [IMG]c:\orcad\scr.jpg[/IMG] I am sorry, I make a mistake! SW1 must be always closed. when D2 in dark, adjust R6 so that Veb of Q2 less than 0,6v when in bright , Q2 certainly in saturated state. chose R4 depending kind of scr Q1. Push SW1 to disconet LED D1 ( D2 must be in dark). Sory! I can not post a image scr.jpg. Are there anyone help me? Contact to me incase anyone want to get a picture by mail: duongnguyen1968@yahoo.com Last edited by nguyen ngoc duong : 17th May 2007 at 01:42 PM.

17th May 2007, 10:01 PM
Hero999 Experienced Member	Image tags only work if the file is stored somewhere on the Internet. You need to upload it somewhere, preferably to this place. Also, it isn't a good idea to post your email address as you'll be inundated with spam. __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser.

26th October 2007, 07:08 PM
Richard Principal Experienced Member	Dont you mean Anode, C Last edited by Richard Principal : 31st October 2007 at 05:13 AM.