Re: Driving Triac Directly with 555 Output?

They are almost always your devices of choice.

John

And what's wrong with that?

If I can come up with a simple solution for a problem which can be easily and reliably solved with an inexpensive, ubiquitously obtainable device which will be available into the far future, should I not follow the KISS principle instead of kow-towing to your demands for increased complexity to accomplish the same end?

No. Larkin goes for ignorant simple... like assuming a transistor's Beta is 1000 ;-) ...Jim Thompson

As a special treat for Slowman and Larkin, I've found that a 555C is just perfection and light for implementing the 800-number kill features I'm designing ;-) ...Jim Thompson

Nothing special, just a 6-second pulse stretcher ;-) ...Jim Thompson

just flip everything, drive the gate negative (needs one more part)

AC>--+---+---------------------+---------+-----+ |+ | | | | [C1] | 1N4000 |8 | | | | +-->|--+ +----+----+ | | | | | | | Vcc _| | | | | +-[R2]-+-3|OUT R|4---+ | | | | | | MT1 | | [R2] +----2|TH DIS|7--[R3]---G | | | | |__ | MT2 | | +---+----6|TR 555| | | | | | GND | | | | [C1] +----+----+ | | | | |1 | +-[7905]---+--------------+ load | i o | V | T 1N4000 | AC>--+-----------------------------------------+

On Wed, 16 Feb 2011 05:36:41 -0800, SMS wrote:

--- Try this:

.AC>--+--------------------------------------------+ . |A | . [1N4002] | . | | . | |+ . +-------+-------------+---------+ [MR16] . |+ | | | | . [470µ] [680K] |8 | | . | | +----+----+ | | . | | | Vcc _| | | . | +-----7-O|D R|O-4-+ SSR | . | | | | +----+ | . | [300K] +--6-|TH OUT|-3--[1k]--|+ L|-+ . | S1 | | |__ | | | . | | --+-+-----+-------------+-------------+--------+

With S1 in the open position the MR16 will flash at about 2Hz with slightly greater than a 50% duty cycle, while with the switch closed it'll be on continuously.

Also, I suggest you use a CMOS 555 and a solid-state relay, as shown above.

The 7555 will eliminate the crossover transient the 555 suffers from and the SSR will eliminate any load nasties getting into the 555 through the triac's gate. (Thanks for the heads-up, Speff :-)

A nice one would be a Clare CPC1018N since it only needs 1mA to drive the output ON.

Mouser has them in stock at:

and a data sheet is available at that link.

Here's a simulation:

Version 4 SHEET 1 960 936 WIRE 672 112 -480 112 WIRE -480 192 -480 112 WIRE -352 192 -480 192 WIRE -176 192 -288 192 WIRE 144 192 -176 192 WIRE 464 192 368 192 WIRE 672 240 672 112 WIRE -176 256 -176 192 WIRE -128 256 -176 256 WIRE -16 256 -48 256 WIRE 16 256 -16 256 WIRE 144 256 96 256 WIRE 432 256 368 256 WIRE -16 320 -16 256 WIRE 144 320 -16 320 WIRE 512 320 368 320 WIRE 624 320 592 320 WIRE -480 368 -480 192 WIRE 400 384 368 384 WIRE -16 416 -16 320 WIRE -16 416 -288 416 WIRE -16 448 -16 416 WIRE 432 448 432 256 WIRE 432 448 -16 448 WIRE -288 464 -288 416 WIRE 672 464 672 320 WIRE -336 480 -416 480 WIRE 624 480 624 320 WIRE -416 512 -416 480 WIRE -176 512 -176 256 WIRE 400 512 400 384 WIRE 400 512 -176 512 WIRE -176 544 -176 512 WIRE -16 544 -16 448 WIRE -480 624 -480 448 WIRE -416 624 -416 592 WIRE -416 624 -480 624 WIRE -336 624 -336 528 WIRE -336 624 -416 624 WIRE -288 624 -288 544 WIRE -288 624 -336 624 WIRE -176 624 -176 608 WIRE -176 624 -288 624 WIRE -16 624 -16 608 WIRE -16 624 -176 624 WIRE 464 624 464 192 WIRE 464 624 -16 624 WIRE 624 624 624 528 WIRE 624 624 464 624 WIRE 672 624 672 544 WIRE 672 624 624 624 WIRE -480 720 -480 624 FLAG -480 720 0 SYMBOL Misc\\NE555 256 288 M0 SYMATTR InstName U1 SYMBOL voltage -480 352 M0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 3 24 104 Invisible 0 SYMATTR Value SINE(0 9 60) SYMATTR InstName V1 SYMBOL res -144 240 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 58 VTop 0 SYMATTR InstName R1 SYMATTR Value 680k SYMBOL res 0 240 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 300k SYMBOL res 608 336 M270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R3 SYMATTR Value 1000 SYMBOL cap 0 544 M0 WINDOW 0 -33 32 Left 0 WINDOW 3 -58 58 Left 0 SYMATTR InstName C1 SYMATTR Value .47e-6 SYMBOL diode -352 208 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D1 SYMBOL voltage -416 496 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 3 24 104 Invisible 0 SYMATTR Value PULSE(0 8 0 1e-6 1e-6 2 4) SYMATTR InstName V2 SYMBOL sw -288 560 M180 WINDOW 0 32 15 Left 0 WINDOW 3 32 44 Left 0 SYMATTR InstName S2 SYMBOL sw 672 560 M180 WINDOW 0 32 15 Left 0 WINDOW 3 32 44 Left 0 SYMATTR InstName S1 SYMBOL res 656 224 R0 SYMATTR InstName R4 SYMATTR Value 20 SYMBOL polcap -192 544 R0 SYMATTR InstName C3 SYMATTR Value 470e-6 TEXT -344 656 Right 0 !.tran 10 uic TEXT 376 176 Left 0 ;1 TEXT 376 240 Left 0 ;2 TEXT 376 304 Left 0 ;3 TEXT 376 360 Left 0 ;4 TEXT 120 368 Left 0 ;5 TEXT 120 304 Left 0 ;6 TEXT 120 240 Left 0 ;7 TEXT 120 176 Left 0 ;8 TEXT -464 688 Left 0 !.model SW SW(Ron=1 Roff=10Meg Vt=4 Vh=0)

--- JF

On Wed, 16 Feb 2011 10:05:03 -0600, John Fields wrote:

--- Oops...

R1 and R2 were 680k and 300k respectively, changed to 100k and 470k below:

.AC>--+--------------------------------------------+ . |A | . [1N4002] | . |D1 | . | LED1 |+ . +-------+-------------+---------+ [MR16] . |+ |R1 | | | . [470µ] [100k] |8 | | . |C1 | +----+----+ | | . | | | Vcc _| | | . | +-----7-O|D R|O-4-+ SSR | . | |R2 | | R3 +----+ | . | [470k] +--6-|TH OUT|-3--[1k]--|+ L|-+ . | S1 | | |__ | | | . | | --+-+-----+-------------+-------------+--------+

With S1 in the open position the MR16 will flash at about 3Hz with a 557% duty cycle, while with the switch closed it'll be on continuously.

Also, I suggest you use a CMOS 555 and a solid-state relay, as shown above.

The 7555 will eliminate the crossover transient the 555 suffers from and the SSR will eliminate any load nasties getting into the 555 through the triac's gate. (Thanks for the heads-up, Speff :-)

A nice one would be a Clare CPC1018N since it only needs 1mA to drive the output ON.

Mouser has them in stock at:

and a data sheet is available at that link.

Here's a simulation:

Oops, wiring error; here's the sim again, fixed:

Version 4 SHEET 1 960 936 WIRE 672 112 -480 112 WIRE -480 192 -480 112 WIRE -352 192 -480 192 WIRE -176 192 -288 192 WIRE 144 192 -176 192 WIRE 464 192 368 192 WIRE 672 240 672 112 WIRE -176 256 -176 192 WIRE -128 256 -176 256 WIRE -16 256 -48 256 WIRE 144 256 -16 256 WIRE 432 256 368 256 WIRE -16 304 -16 256 WIRE 144 320 80 320 WIRE 512 320 368 320 WIRE 624 320 592 320 WIRE -480 368 -480 192 WIRE 400 384 368 384 WIRE -16 432 -16 384 WIRE -16 432 -288 432 WIRE -16 448 -16 432 WIRE 80 448 80 320 WIRE 80 448 -16 448 WIRE 432 448 432 256 WIRE 432 448 80 448 WIRE -288 464 -288 432 WIRE 672 464 672 320 WIRE -336 480 -416 480 WIRE 624 480 624 320 WIRE -416 512 -416 480 WIRE -176 512 -176 256 WIRE 400 512 400 384 WIRE 400 512 -176 512 WIRE -176 544 -176 512 WIRE -16 544 -16 448 WIRE -480 624 -480 448 WIRE -416 624 -416 592 WIRE -416 624 -480 624 WIRE -336 624 -336 528 WIRE -336 624 -416 624 WIRE -288 624 -288 544 WIRE -288 624 -336 624 WIRE -176 624 -176 608 WIRE -176 624 -288 624 WIRE -16 624 -16 608 WIRE -16 624 -176 624 WIRE 464 624 464 192 WIRE 464 624 -16 624 WIRE 624 624 624 528 WIRE 624 624 464 624 WIRE 672 624 672 544 WIRE 672 624 624 624 WIRE -480 720 -480 624 FLAG -480 720 0 SYMBOL Misc\\NE555 256 288 M0 SYMATTR InstName U1 SYMBOL voltage -480 352 M0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 3 24 104 Invisible 0 SYMATTR Value SINE(0 9 60) SYMATTR InstName V1 SYMBOL res -144 240 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 58 VTop 0 SYMATTR InstName R1 SYMATTR Value 100k SYMBOL res 0 288 M0 SYMATTR InstName R2 SYMATTR Value 470k SYMBOL res 608 336 M270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R3 SYMATTR Value 1000 SYMBOL cap 0 544 M0 WINDOW 0 -33 32 Left 0 WINDOW 3 -58 58 Left 0 SYMATTR InstName C1 SYMATTR Value .47e-6 SYMBOL diode -352 208 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D1 SYMBOL voltage -416 496 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 3 24 104 Invisible 0 SYMATTR Value PULSE(0 8 0 1e-6 1e-6 2 4) SYMATTR InstName V2 SYMBOL sw -288 560 M180 WINDOW 0 32 15 Left 0 WINDOW 3 32 44 Left 0 SYMATTR InstName S2 SYMBOL sw 672 560 M180 WINDOW 0 32 15 Left 0 WINDOW 3 32 44 Left 0 SYMATTR InstName S1 SYMBOL res 656 224 R0 SYMATTR InstName R4 SYMATTR Value 20 SYMBOL polcap -192 544 R0 SYMATTR InstName C3 SYMATTR Value 470e-6 TEXT -344 656 Right 0 !.tran 10 uic TEXT 376 176 Left 0 ;1 TEXT 376 240 Left 0 ;2 TEXT 376 304 Left 0 ;3 TEXT 376 360 Left 0 ;4 TEXT 120 368 Left 0 ;5 TEXT 120 304 Left 0 ;6 TEXT 120 240 Left 0 ;7 TEXT 120 176 Left 0 ;8 TEXT -464 688 Left 0 !.model SW SW(Ron=1 Roff=10Meg Vt=4 Vh=0)

--- JF

Have you considered a schottky bridge to kep the DC operating losses down?

--- That's how much your load will be dissipating.

If your load draws 600mA and the maximum ON resistance of the relay is

P = I²R = 0.6A² * 0.5R = 0.18 watts,

so the CPC1018N should work OK.

Having said that, THE LCA710 has a lower ON resistance than the CPC1018N, and you've got the 10mA drive available from a CMOS 555, so I'd go with the LCA710 just for the safety of that extra 400mA the output can handle.

But, I forget how you said you were going to wire the thing up.

Do you have a schematic you can post?

--- Good idea. :-)

--- JF