firing angles

SgtWookie

Joined Jul 17, 2007
22,210
Are you talking about "firing angles" in regards to ignition spark advance in gasoline powered engines? Or perhaps firing angles in regards to thyristors (SCRs, TRIACs, DIACs, etc)
 

SgtWookie

Joined Jul 17, 2007
22,210
I'd considered that too, but this would not really be the forum to ask that kind of question in.

Our OP was most likely asking about some form of thyristor.
 

bountyhunter

Joined Sep 7, 2009
2,512
here's what I was talking about:
The Electronic Measurements Inc. TCR series are SCR phase controlled regulated power supplies. Output is controlled by modulating the conduction angle of the controlled SCRs. Input AC is applied to three pair of bi-directionally connected SCRs placed within the delta connected primary of the main power transformer. Secondary voltage is rectified and double L/C filtered to provide a low ripple DC output.
 

thatoneguy

Joined Feb 19, 2009
6,359
I want a Triac that will let me chop a full 120VAC cycle into a few hundred PWM pseudo-squarewave "slices". Just for kicks.
 

joeyd999

Joined Jun 6, 2011
4,375
I want a Triac that will let me chop a full 120VAC cycle into a few hundred PWM pseudo-squarewave "slices". Just for kicks.
You can't do that with a Triac.

A triac turns on with the gate trigger, and turns off at the zero current crossing. Therefore, you can only control the position in each 1/2 wave where the triac turns on (or, as you originally stated, the firing angle). Turn-off will always occur at the same position in each 1/2 wave (which may or may not be the zero *voltage* crossing if you have a reactive load).
 

jimkeith

Joined Oct 26, 2011
540
@ bountyhunter

This is the phase control circuit that Lambda uses--old brute force, but very reliable technique--uses expensive 60HZ transformers, but provides DC with very low ripple and a 360HZ ripple component.

I have applied this technique with good success in NEMA D high slip motors for variable speed pump applications.

The SCR anti-parallel current is 58% of the line current--substantial thermal advantage.

Line synchronization is also immune to phase rotation.
 

Attachments

Last edited:

BillB3857

Joined Feb 28, 2009
2,532
@ bountyhunter


Line synchronization is also immune to phase rotation.
Can you expand on this? Any drive I worked with required phase synchronization with the trigger circuitry. If the phasing on only the line feeds to the SCRs was rotated without rotating the trigger sync lines, we got a lot of smoke. Is this what you meant?
 

jimkeith

Joined Oct 26, 2011
540
You got it--the phase control ramp generators (whether linear or digital) are reset at line voltage zero crossing--generally the synchronization voltage is taken phase to phase, but this does not exactly work out so the signal must be delayed 30 or 60° (do not remember which) to make it work properly--then when the phase rotation is reversed, the timing is really out of whack and the SCRs will snap on at quite a high voltage.

The best design creates an artificial neutral and synchronizes the ramp control circuits in respect to line to neutral voltage--this technique is immune to phase rotation.
 
Top