All About Circuits Forum  

Go Back   All About Circuits Forum > Electronics Forums > General Electronics Chat

Notices

General Electronics Chat Discussion forum for general chat about anything electronics related, including asking questions about material in the All About Circuits E-book, Worksheets, and Videos.

Reply   Post New Thread
 
Thread Tools Display Modes
  #1  
Old 04-25-2011, 11:25 AM
danda suredra danda suredra is offline
Junior Member
 
Join Date: Apr 2011
Location: Manglore
Posts: 12
Default pulse transformer details for scr firing

i am using 4503 1:1:1 pulse transformer to generate the triggering pulses to trigger scr. scr is able to trigger when a resistive load is connected. but when i connect an highly inductive load it's not able to trigger the scr. scr used is tyn 410. and pulse transformer is driven by (sl-100) which is fed by 556 timer with 180us on time.
can any one plese give the specifications about 4503 pulse transformer.
thanks in advance.
Reply With Quote
  #2  
Old 04-26-2011, 12:28 AM
t_n_k t_n_k is offline
Senior Member
 
Join Date: Mar 2009
Posts: 4,805
Default

The likely reason that the SCR isn't turning on with the highly inductive load is that the gate pulse is not on for sufficiently long enough time for the SCR to reach latching current in the forward conduction condition. Increasing the firing pulse duration will probably solve the problem.
Reply With Quote
The Following User Says Thank You to t_n_k For This Useful Post:
danda suredra (04-26-2011)
  #3  
Old 04-26-2011, 04:44 AM
danda suredra danda suredra is offline
Junior Member
 
Join Date: Apr 2011
Location: Manglore
Posts: 12
Default firing pulse duration

thank you. but how can i increase the firing pulse duration its all decided by the pulse transformer. and i am stuck with that. i dont know any thing about the pulse transformer it is mentioned as 4503 with 1:1:1.
Reply With Quote
  #4  
Old 04-26-2011, 04:48 AM
danda suredra danda suredra is offline
Junior Member
 
Join Date: Apr 2011
Location: Manglore
Posts: 12
Default firing pulse duration

the input for the pulse transformer is around 185us pulse. and it has 24v bias supply for the input. and input resistance is 200ohms and gate resistance used is 220ohms. one pulse transformer is able to drive the scr.
but other one of the same type is not able to drive it. but both are driving for resistive loads.
Reply With Quote
  #5  
Old 04-26-2011, 05:05 AM
t_n_k t_n_k is offline
Senior Member
 
Join Date: Mar 2009
Posts: 4,805
Default

There's most likely a solution for your problem, but without a schematic diagram no one can really comment or make specific suggestions. If your pulse is derived from a 556 timer then I would be very surprised if you can't stretch the pulse to something longer.

The only limitation of the pulse transformer will be the Volt-μsec rating of the transformer. That should be known from the data sheet if you have access to the data sheet for that type no.

If you can post a schematic of your existing circuit that would be very useful.
Reply With Quote
The Following User Says Thank You to t_n_k For This Useful Post:
danda suredra (04-26-2011)
  #6  
Old 04-26-2011, 05:35 AM
danda suredra danda suredra is offline
Junior Member
 
Join Date: Apr 2011
Location: Manglore
Posts: 12
Default firing pulse duration

but i dont know the volt usec rating of the pulse transformer i even not able to find the data sheet of that one. its "pulsetek thyristor trigger RPTYPE 4503 pulse transformer isolation". i have attached the circuit. the ckt name file is fed from phase_shifter. where i wil get inverse cosine wave. and firing angle can be controlled by the -Vc.
Attached Files
File Type: pdf ckt.pdf (16.9 KB, 360 views)
File Type: pdf phase_shifter.pdf (8.9 KB, 248 views)
Reply With Quote
  #7  
Old 04-26-2011, 10:04 AM
t_n_k t_n_k is offline
Senior Member
 
Join Date: Mar 2009
Posts: 4,805
Default

It looks like the SCR gating control is a pulse train derived from half of a 556 timer running in gated astable mode. The gating control comes from a 4538 monostable.

There are timing capacitors which could be adjusted - C2,3,6,8.

For instance in the top half of your schematic C2 & C3 are associated with either R4 (monostable gating circuit) or R5,6 & 7 (astable circuit).

Do you know the values of C2, C3 & R4,5,6 & 7?

Increasing C2 would increase the monostable gating duration and increasing C3 would increase the width of the gated pulses. If you know these values it would help if you posted them .....

Unfortunately, not knowing the pulse transformer spec is going to make it hard to determine how much one might increase the capacitor values.

Another option may be to introduce some capacitance across the gate-cathode terminals on the SCR's and perhaps also changing (increasing) the astable frequency at the 556 timer. In other words extending the pulse width at the gate terminals directly using an AC-DC converter action through the pulse transformer & secondary side diodes (D7A or D10A).

Post the component values if you can and there may be some ideas forthcoming from other members as well.
Reply With Quote
The Following User Says Thank You to t_n_k For This Useful Post:
danda suredra (04-26-2011)
  #8  
Old 04-26-2011, 10:40 AM
danda suredra danda suredra is offline
Junior Member
 
Join Date: Apr 2011
Location: Manglore
Posts: 12
Default component values

c2 = c6 = 47nf ; R4 = R7 = 150k; for 4538b which is used as monostable multivibrator with 4.7ms pulse.
c4 = c3 = c7 =c8 = 10nf; R7 = R20 = 27K; R6 = R19 = 1K; for 556 timer. which wil give 185us(approx.) on time pulses (12).

can u please suggest any pulse transformer which i can know the rating in such away i can take care the req. gate current of the scr. i am using tyn410 scr. Igt = 15mA; Vgt = 1.5V(both are max.)tgt = 2us;
Reply With Quote
  #9  
Old 04-26-2011, 10:50 AM
danda suredra danda suredra is offline
Junior Member
 
Join Date: Apr 2011
Location: Manglore
Posts: 12
Default firing pulse duration

if i keep a capacitor across the gate cathode terminals what does it wil do.is it increase the pulse duration across gate cathode terminals. rc time constant. please suggest a proper pulse transformer.
Reply With Quote
  #10  
Old 04-27-2011, 06:40 AM
t_n_k t_n_k is offline
Senior Member
 
Join Date: Mar 2009
Posts: 4,805
Default

Hello danda suredra

I'll give some further thought to the values you have posted and a possible solution.

One other thing that is worth knowing is the SCR load side power schematic.

You mentioned you are attempting to turn on a highly inductive load. What exactly is the load (values) and high side power supply type & value.

This is worth knowing because (you) the designer can then decide what the minimum gate pulse on time is required to ensure the load will be turned on. I notice from the data sheet that the TNY410 SCR has a latching current of 50mA
Reply With Quote
The Following User Says Thank You to t_n_k For This Useful Post:
danda suredra (04-27-2011)
Reply   Post New Thread

Tags
, , , ,


Related Site Pages
Section Title
Worksheet Timer circuits
Worksheet Thyristors
Worksheet Thyristor application circuits
Textbook The TRIAC : Thyristors
Textbook The Silicon-Controlled Rectifier (SCR) : Thyristors
Textbook CMOS 555 LONG DURATION FLYBACK LED FLASHER : 555 Timer Circuits
Textbook CMOS 555 LONG DURATION BLUE LED FLASHER : 555 Timer Circuits
Textbook CMOS 555 LONG DURATION MINIMUM PARTS RED LED FLASHER : 555 Timer Circuits
Textbook LED sequencer : Digital Integrated Circuits


Similar Threads
Thread Thread Starter Forum Replies Last Post
Assessing an unknown transformer someonesdad General Electronics Chat 37 05-27-2010 05:22 AM
Pulse Transformer for Rectifier Circuit ZaaRz The Projects Forum 4 01-02-2010 09:58 AM
SCR Firing using pulse transformer dingdong The Projects Forum 8 08-26-2009 12:51 PM
pulse Transformer Far General Electronics Chat 12 08-09-2009 08:12 AM
What Pulse Transformer needed to drive MCR100-6 thyristor for AC/DC converter whywhy68 General Electronics Chat 3 08-11-2008 02:19 PM

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 08:25 AM.


User-posted content, unless source quoted, is licensed under a Creative Commons Public Domain License.
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.