Q:Triac Switch

No.

1. The +5V rail is shorted to ground through the base-emitter junctions of Q1 and T3
2. T2, R2 and T5 are redundant

Why is the Q output AC-coupled? Is it to pulse the opto-triacs to save power?

You can just connect the opto-LEDs, through current-limiting resistors, directly to the Q output.

it's an unusual looking circuit (there's a short circuit through the two first output transistors) what's the intended purpose of C3

you can simpply connect the optocouplers (and resistors) above and below the output of an NE555 to have them firing alternately.

you have the 555 configured to be on for upto about 4 seconds (adjustable) and then off for about 15 miliseconds (or approx one mains cycle) - is that what you want?

if you want an even mark-space (on and off for the same length of time) connect the 250K pot between pins 3 and 2 and disconnect pin 7 and remove R10 something like this

0V +--------------+--+5V | | . . . . . | . . . . . +------(---.1 . . 8.--+-[220R]---.1 6. | 22u | . ~ . .MOC3022. +--||--(-+-.2 7. +--------.2 5. | | . NE555 . | . . +------(-(-.3 6.--+ | .3 4. | | | . . | | . . . . . +---+ +-(-.4 5. | | | | | . . . . . | | . . . . . | v | | +--------.1 6. +-[250K]-+------------+ | .MOC3022. | | +--.2 5. +-----------------------+ | . . | .3 4. 0V--[220R]--+ . . . . .

The stuff on the other side of the optocoupler seems needlessly complex but I guess that depends on what the load is you intend to drive. doing that part the way you plan won't cause any problems.

It appears that you copied the a "solid state relay" schematic from somewhere (and got atleast one copy wrong)

You don't need the whole solid state relay input stage if the input has a predictable voltage range. a simple resistor is sufficient... the 3022 has a 10mV input sensitivity and Fairchild suggests feediing it about 15mA in case it degrades a little, the internal LED has a voltage drop of about 1.5V so 15ma at 3.5V comes to 233 ohms so 220 is close enough.

Bye. Jasen

You can probably get by with fewer transistors and lower operating current.

The MOC3022 needs at least 10mA to trigger, so you work backwards from there. Its input forward voltage is less than 1.5V, and a saturated

2N4401 is something like 0.3V. Thus, you will have 3.2V, and you want to have 10mA through it, so you need at most 320 ohms of resistance. Make it 300 ohms. Passing 10mA through a signal NPN will probably require 500uA into the base, so use an 8.2k resistor from Q to the base. This will reliably turn on a MOC3022 when Q is high, and turn it off when Q is low.

Now, the other side of the coin is turning one on when Q is low. To do that, you use a PNP transistor in an inverted configuration, emitter to

5V, collector to the MOC3022, and the other MOC input terminal to a 300 ohm resistor which then goes to ground. Again, connect the base to Q using an 8.2k resistor, and your MOC3022 will turn on when Q is low, and turn off when Q is high.

When you turn off the 555, both branches will go off. If you want it to stay on after the 555 goes away, use what is called a latching relay. There are two coils, and they latch the relay one way or the other.

Good luck.

--
Bob Monsen