Searching \ for '[EE]: Driving a triac' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=driving+triac
Search entire site for: 'Driving a triac'.

Exact match. Not showing close matches.
PICList Thread
'[EE]: Driving a triac'
2000\11\07@093708 by John Walshe

flavicon
face
Hi guys,
   I'm having a bit of a problem driving a triac from a pic.
The electrical main is 220Vac 50Hz.
I have the Vdd of the pic connected to the live and Vss is 5v less than
live.
I have a PNP transistor: emitter to live, collector to triac trigger,base
via resistor (1k) to the pic i/o pin. The base is also connected to the live
via 10k resistor (to prevent false trigger at powerup).

My theory is that with the pic i/o pin high the transistor is off and
therfore high z to the trigger so no leakage current can trigger it.Thus the
triac doesn't conduct.
With the pic i/o pin low the transistor is switched on and the trigger gets
all the current it needs and the Triac conducts.

The triac I'm using is a BTA12 from Philips (logic level driven device).

My target use is for a small motor but I'm using a lightbulb for testing.

The Problem: The bulb is always on!

I thought I had all the bases covered but obviously I'm missing something.

Has anyone got an idea what this 'something' is.

Thanks in advance
John

--
http://www.piclist.com hint: To leave the PICList
spam_OUTpiclist-unsubscribe-requestTakeThisOuTspammitvma.mit.edu




2000\11\07@094741 by staff

flavicon
face
John Walshe @Inpact wrote:
{Quote hidden}

The BTA12 is a pretty high gain device, seems you are relying
in "high z" to stop the triac being gated. I would think
you need some resistor to hold the triac gate "off" rather than
relying on high-z which basically allows leakage or even RF
to activate the traic.

Also check you haven't fried the transistor, what current
limiting (resistor?) are you using in the collector circuit?
-Roman

--
http://www.piclist.com hint: To leave the PICList
.....piclist-unsubscribe-requestKILLspamspam@spam@mitvma.mit.edu




2000\11\07@123230 by Harold M Hallikainen

picon face
       Sounds like you're using a transistor in an AC circuit, so half the time
the transistor has reverse polarity on it. I just did a triac drive
circuit using the MOC3023 opto coupler. For noninductive loads, it's real
simple. See Motorola Ap Note AN780A, if you can find it...

Harold


On Tue, 7 Nov 2000 14:35:27 -0000 "John Walshe @Inpact"
<John.WalshespamKILLspamINPACTMICRO.COM> writes:
{Quote hidden}

FCC Rules Online at http://hallikainen.com/FccRules
Lighting control for theatre and television at http://www.dovesystems.com

________________________________________________________________
YOU'RE PAYING TOO MUCH FOR THE INTERNET!
Juno now offers FREE Internet Access!
Try it today - there's no risk!  For your FREE software, visit:
dl.http://www.juno.com/get/tagj.

--
http://www.piclist.com hint: To leave the PICList
EraseMEpiclist-unsubscribe-requestspam_OUTspamTakeThisOuTmitvma.mit.edu




2000\11\07@124418 by Chris Eddy

flavicon
face
Roman is pointed in the right direction.  Triacs have a parameter called dv/dt.
The gate of the triac is capacitive, and as such a high dv/dt can push enough
charge over to the gate to false trigger the device.  This dv/dt parameter also
applies to opto triacs when they are in use.  You may have to use some form of RC
snubber to protect the Triac and properly hold the gate off.  I saw some great app
notes in SGS territory that covered the microprocessor driven tirac with details,
and even more in the area where they have a new multi channel triac trigger device
that mates up with your processor.

Do you have to pass UL and CE?  You might carefully study your non-isolated
strategy to see if you will pass.

Chris~

Roman Black wrote:

{Quote hidden}

--
http://www.piclist.com hint: To leave the PICList
piclist-unsubscribe-requestspamspam_OUTmitvma.mit.edu




2000\11\07@225007 by PDRUNEN

picon face
part 1 1432 bytes content-type:text/plain; charset="US-ASCII" (decoded 7bit)

Hi John,

Attached is a Triac schematic I have used for controlling an AC source with a
PIC I/O.  The SCR is really a TRIAC device.  Also, you will have to find a
different TRIAC as I think the T2800 is rated up to 200V.

Cheers,

Paul

In a message dated 11/7/00 8:39:31 AM Central Standard Time,
@spam@John.WalsheKILLspamspamINPACTMICRO.COM writes:

<< Hi guys,
    I'm having a bit of a problem driving a triac from a pic.
The electrical main is 220Vac 50Hz.
I have the Vdd of the pic connected to the live and Vss is 5v less than
live.
I have a PNP transistor: emitter to live, collector to triac trigger,base
via resistor (1k) to the pic i/o pin. The base is also connected to the live
via 10k resistor (to prevent false trigger at powerup).

My theory is that with the pic i/o pin high the transistor is off and
therfore high z to the trigger so no leakage current can trigger it.Thus the
triac doesn't conduct.
With the pic i/o pin low the transistor is switched on and the trigger gets
all the current it needs and the Triac conducts.

The triac I'm using is a BTA12 from Philips (logic level driven device).

My target use is for a small motor but I'm using a lightbulb for testing.

The Problem: The bulb is always on!

I thought I had all the bases covered but obviously I'm missing something.

Has anyone got an idea what this 'something' is.

Thanks in advance
John >>


part 2 6523 bytes content-type:application/pdf; name="triac.pdf" (decode)

part 3 107 bytes
--
http://www.piclist.com hint: To leave the PICList
KILLspampiclist-unsubscribe-requestKILLspamspammitvma.mit.edu




More... (looser matching)
- Last day of these posts
- In 2000 , 2001 only
- Today
- New search...