Electronics > Beginners

Wattage Limiting Device

<< < (3/4) > >>

TerminalJack505:

--- Quote from: DrG on February 06, 2020, 04:52:09 am ---
--- Quote from: TerminalJack505 on February 06, 2020, 04:43:57 am ---Okay.  Thanks for answering my questions.  That is a 1.5uF cap.  Which means that they are powering the circuit using a capacitive power supply.  So, from a power supply standpoint, it likely looks like the attached.

I'm not sure about the rest--so far as how the AC current is being sensed and how they are using the LM324 to 'latch' and require a power cycle when it trips.

--- End quote ---

1.5uF? oops yes, sorry about that

http://kaizerpowerelectronics.dk/theory/capacitor-code-table/
Third digit=5 so the multiplier is 100,000 = 1500000 pF = 1.5 uF

Need more time with the schematic you posted - thanks

Edit: Actually understanding *some* of it, seems like the input to the 7812 would be well beyond the 35V max?

--- End quote ---

The input to the regulator, in the simulator, is steady at 14.08V.

The circuit is kind of hard to understand but the capacitor that is in series with the 120VAC will only allow so much charge to pass through.  This, and the fact that the circuit will use a minimum amount of current prevents the voltage from rising any further.  Basically, the circuit has to burn off as much charge as the capacitor feeds in.

This would be very inefficient for circuits that have dynamic current requirements.  In the case of this particular circuit, when it trips and cuts the current to the relay (which is an exceptional condition), that current has to go somewhere else.  In the circuit as shown, it would go through the Zener diode.

DrG:

--- Quote from: TerminalJack505 on February 06, 2020, 06:08:46 am ---
--- Quote from: DrG on February 06, 2020, 04:52:09 am ---
--- Quote from: TerminalJack505 on February 06, 2020, 04:43:57 am ---Okay.  Thanks for answering my questions.  That is a 1.5uF cap.  Which means that they are powering the circuit using a capacitive power supply.  So, from a power supply standpoint, it likely looks like the attached.

I'm not sure about the rest--so far as how the AC current is being sensed and how they are using the LM324 to 'latch' and require a power cycle when it trips.

--- End quote ---

1.5uF? oops yes, sorry about that

http://kaizerpowerelectronics.dk/theory/capacitor-code-table/
Third digit=5 so the multiplier is 100,000 = 1500000 pF = 1.5 uF

Need more time with the schematic you posted - thanks

Edit: Actually understanding *some* of it, seems like the input to the 7812 would be well beyond the 35V max?

--- End quote ---

The input to the regulator, in the simulator, is steady at 14.08V.

The circuit is kind of hard to understand but the capacitor that is in series with the 120VAC will only allow so much charge to pass through.  This, and the fact that the circuit will use a minimum amount of current prevents the voltage from rising any further.  Basically, the circuit has to burn off as much charge as the capacitor feeds in.

This would be very inefficient for circuits that have dynamic current requirements.  In the case of this particular circuit, when it trips and cuts the current to the relay (which is an exceptional condition), that current has to go somewhere else.  In the circuit as shown, it would go through the Zener diode.

--- End quote ---

Some of this is actually sinking in. When I have used a 78L series regulator with mains, it has always been mains to transformer to bridge rectifier to regulator and filter caps before and after. Just didn't focus on the R1, R2, C1 (as in your sim). Ignoring certain sections is probably a very bad way to try to understand a circuit. This is why I posted it in beginner's section.

Not so embarrassed though. I am a retired research scientist (unrelated field as you might guess) and I really appreciate folks, like yourself, taking the time to explain some things. It does have an effect. Thanks again.


The red denotes where the rocker switch is attached, connecting/disconnecting L out of the circuit.

TerminalJack505:
The lack of a transformer means this particular circuit isn't isolated from mains voltage.  So be careful if you play around with it while it is powered up!

DrG:

--- Quote from: TerminalJack505 on February 06, 2020, 05:20:10 pm ---The lack of a transformer means this particular circuit isn't isolated from mains voltage.  So be careful if you play around with it while it is powered up!

--- End quote ---

Noted!

DrG:
I decided to go in another direction.  :)

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod