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1  Using Arduino / Motors, Mechanics, and Power / Is it safe to use the L78M05 to regulate 24 VAC ? on: July 11, 2013, 09:06:54 am
I used a bridge rectifier with four 1N4007 diodes to rectify 24VAC. I want to use the L78M05 regulator along with some capacitors before and after the regulator to get a 5VDC out. Is it safe to use the regulator for such an application? (in its datasheet it states clearly that the absolute maximum rating for its DC input voltage is 35 volts)
24 VAC RMS = 34 VAC peak to peak (24/0.707 = 33.9)
34 - 1.4V (forward voltage drop of the diodes) = 32.6V
32.6V is very close to 35V
in addition a non fully loaded transformer rated for 24VAC tends to have a higher voltage.

Thank you very much people
Regards
Void
2  Using Arduino / General Electronics / Suggestion for a standard triac and triac driver ? on: June 27, 2013, 03:15:04 pm
Do you people know of a standard triac able to handle at least 10 amps with a trigger current of no more than 50 mA and a suitable standard triac driver without zero crossing detection for it?

Thanks loads people. Cheers
3  Using Arduino / Motors, Mechanics, and Power / Re: Question: Driving a heating element on: June 26, 2013, 07:34:49 am
Is it okay and reliable to use a simple pnp transistor to trigger the power triac? or should i go for a triac driver?
4  Using Arduino / Motors, Mechanics, and Power / Re: Question: Driving a heating element on: June 24, 2013, 10:14:03 am
The MOSFETs have a full plastic body so yeah they were isolated from eachother.
5  Using Arduino / Motors, Mechanics, and Power / Question: Driving a heating element on: June 24, 2013, 03:39:53 am
I want to drive a 60 watt 24volt heating element of a 24volt 80 watt transformer. The trigger pin will be connected on a comparator that is capable of sinking up to 18 mA of current. I know that the ideal circuit for the job would be circuit 4 yet the MOC30xx family of triac drivers is incapable of handling 90 mA of current in order to latch the main triac. Moreover, i got 4 optocouplers and again none of them can handle 90mA of current.
> Which circuit do you suggest i use? (i was going to go with circuit 1 to be honest)
> Is there a better way of getting the job done?
> Do you know any other triac drivers capable of handling such currents?

Last question is a bit off topic:
Which would be the best way to switch ac current?
>Triac
> Full wave rectifier and a MOSFET (Tried it and the power wasted in the diodes of the full wave rectifier  is huge)
> 2 MOSFETs connected source to source and the drain terminals connected to the AC(Tried it and destroyed 2 MOSFETs one after the other by unknown cause {note: the MOSFETs were at all times cool, no magic smoke was released in any case} Still haven't figured out why they got destroyed as the circuit was correct at all times. After disconnecting the MOSFETs and measuring them out, some of their pins would be shorted, in one case the gate with drain showing 0 resistance or the drain with source showing 0 resistance. Do you have any idea why this might have happened? {The circuit is shown in one of the pictures. The MOSFETs are IRF630MFP with a max gate voltage of +- 20V})

I am really sorry for the crappy pictures. I know i need to change my mobilephone.

Regards
Void
6  Using Arduino / Motors, Mechanics, and Power / Re: Question: Zero crossing triac driver on: June 24, 2013, 02:58:46 am
Pancace that:

"So, maybe you're asking:
if the input got pulsed, say at line peak (90deg or 270deg), would the driver side sit "armed", as a latch, primed, ready for zero-cross, where it would turn the triac on?  Is that it?"

is exactly what i was asking about
7  Using Arduino / Motors, Mechanics, and Power / Re: Question: Zero crossing triac driver on: June 22, 2013, 02:47:16 pm
Therefore i can assume that the second example i gave is actually what needs to take place ("i need to keep the trigger signal going to the triac driver active until 181 degrees for the triac driver to activate the triac") and not the first one. Am i correct on that?
8  Using Arduino / Motors, Mechanics, and Power / Question: Zero crossing triac driver on: June 22, 2013, 04:49:19 am
Let's say i have a triac connected on a zero crossing triac driver. The sine wave of the triac is at 90 degrees. I trigger the triac driver with a signal from 95 degrees to 100 degrees and then remove the trigger signal. Will the triac driver activate the triac at 181 degrees? Or, will i need to keep the trigger signal going to the triac driver active until 181 degrees for the triac driver to activate the triac?

Thank you very much
Regards
Void
9  Using Arduino / General Electronics / Re: How do you supply an opamp with -12 volts? on: May 12, 2013, 09:07:41 am
Yes pito smiley I am currently designing the circuit for a temperature controlled soldering station and i want to get everything sorted out. I guess i am going to go with the lm324 since its cheaper. I will get it to swing to +5V by supplying it with more than 7 volts. By the way the lm324 contains 4 opamps. Do you guys know the package if there is one that contains one instead of all 4 opamps?
10  Using Arduino / General Electronics / Re: How do you supply an opamp with -12 volts? on: May 12, 2013, 06:41:07 am
Thank you very very much for the help people. It turns out that i only need the opamp to swing its output from 0 to +5 volts (no negative voltage involved). Is though the lm324 able to go as low as 0 volts and as high as +5 volts while being connected to +5volts and ground? I guess if not then i would have to raise the 5 volts and supply it with a negative voltage as well, or go for another opamp or implement your suggestions by using a DC to DC converter or a second center tapped transformer.
11  Using Arduino / General Electronics / Re: How do you supply an opamp with -12 volts? on: May 12, 2013, 02:40:05 am
Jackrae can you be a bit more explanatory please. I don't seem to understand what you are saying.

Mike thanks for the help man.
12  Using Arduino / General Electronics / Re: How do you supply an opamp with -12 volts? on: May 11, 2013, 12:21:59 pm
Should I go for a rail to rail opamp or a single supply one?
13  Using Arduino / General Electronics / How do you supply an opamp with -12 volts? on: May 11, 2013, 08:17:43 am
How do you supply a regular opamp (lm324) with -12V if you do not have a center tapped transformer? (ie regular  240 to 12 volt stepdown transformer with a single secondary coil)

Thank you in advance
Regards Voidugu
14  Using Arduino / Project Guidance / Re: Using an opamp to measure the voltage accross a RTD on: May 11, 2013, 06:44:42 am
Thank you very much for the help people smiley
15  Using Arduino / Project Guidance / Using an opamp to measure the voltage accross a RTD (SOLVED) on: May 11, 2013, 03:00:18 am
I am trying to measure the voltage drop across an RTD. Its resistance will vary from 50 to 100 ohms. A resistor of 75 ohms connected in series with the RTD, creating a voltage divider,connected to 5V DC gives a voltage range from 2V (R RTD = 50 ohms) to 2.857V (R RTD = 100 ohms) across the RTD. If this was fed directly to the ADC of the atmega328 then the resolution would be extremely poor.

My idea is that with a suitable amplifier circuit, this voltage range can be amplified around 5.83 times (5 /(2.857 - 2)= 5.83)to allow me to utilize the full potential of the atmega's ADC. The problem is that i am a complete novice with opamps since this is the first time using them.

Could you please help me by providing a suitable circuit or by providing me with some information on how to implement this?  

Thank you in advance.
Regards Voidugu
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