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Andy

Tue Jan 20 2015, 04:46AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874

Hi, im trying to understand a circuit which I think I should beable to stack multable blocks for higher voltage, but the spice program is showing zero, or it crashs.
Im trying to convert ac mains to dc, then pass it throught a voltage divide network, when the switchs is turned on it should have full voltage across the load instead of half etc, with the cell to be stackable.

Thanks

Electra

Wed Jan 21 2015, 10:10PM

Registered Member #816 Joined: Sun Jun 03 2007, 07:29PM
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Posts: 156

Couple of things.
When using 'N' Fets like that on the high side, you need a floating/isolated gate drive that is just referenced to the source of the individual Fet. (move the Bat -ve symbol to the source). Or even re-arrange the Fets to switch the negative side of the rectifiers output.
Some of the diodes look redundant, unless your keeping them in series to increase the voltage rating.

The resistors across the fets are lower than the load, resulting in nearly 88% of the output across the 100k res all the time. Make the output resistor smaller or get rid of those in parallel to the fets.

The input voltage supplies have to be separate of course, but I think the way you drawn them is correct.

Andy

Thu Jan 22 2015, 03:46AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874

Thanks Electra, im think about driving the n mosfets with a circuit like this, if each fet as 340volt across it and they multiplier from one to the next, would a bridge have the isolation instead of the transofmer, would the inductor sort out the dc core walking, at 25_100khz would I use a couplering transofer for audio stuff.

Got like a thousand question just not sure what would be relavent.

Instead of the zener was going to use two 6.5v drop diodes in forward mode.

Would this transfomer be good

Wolfram

Thu Jan 22 2015, 03:26PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

I could tell you some things that are wrong with the circuit, but I think it will be more useful if I give you some tips on how to figure it out yourself, so that you can design better circuits in the future.

What is the load impedance?

For troubleshooting a circuit, it's often easiest to simplify the circuit as much as possible. When you have the simplest possible circuit that still doesn't work like you expect it to, then you can start to analyze it.

In general when designing a circuit, it's important to have a clear idea what each part does, and why you need it. Your circuits seem to have many redundant parts, and some parts that don't do anything, and some parts that actually ruin the operation of the circuit. When something doesn't work right in simulation, don't just add random parts hoping that it will suddenly start working.

Start with understanding the basic parts and simple circuits before trying to make something more complex. When something doesn't work, try to figure out why. If you can't, then reduce the complexity and try again, until everything works as expected. Then you can increase the complexity. You will not learn anything by just making complicated circuits that don't work.

Some helpful questions for your last circuit:

Do transformers work for DC?
What does the rectifier do?

hen918

Thu Jan 22 2015, 05:49PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Wolfram wrote ...

I could tell you some things that are wrong with the circuit, but I think it will be more useful if I give you some tips on how to figure it out yourself, so that you can design better circuits in the future.

What is the load impedance?

For troubleshooting a circuit, it's often easiest to simplify the circuit as much as possible. When you have the simplest possible circuit that still doesn't work like you expect it to, then you can start to analyze it.

In general when designing a circuit, it's important to have a clear idea what each part does, and why you need it. Your circuits seem to have many redundant parts, and some parts that don't do anything, and some parts that actually ruin the operation of the circuit. When something doesn't work right in simulation, don't just add random parts hoping that it will suddenly start working.

Start with understanding the basic parts and simple circuits before trying to make something more complex. When something doesn't work, try to figure out why. If you can't, then reduce the complexity and try again, until everything works as expected. Then you can increase the complexity. You will not learn anything by just making complicated circuits that don't work.

Some helpful questions for your last circuit:

Do transformers work for DC?
What does the rectifier do?

I think the transformers are gate drive transformers and therefore are used with pulsed DC. Other than that, it looks pretty well messed up...
Not sure what the inductors are for either.

Andy

Thu Jan 22 2015, 05:51PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Thanks Wolfram, I don,t thing it works properly with dc, Patrick awhile ago gave a link to a Smps site were the explained running onw with dc and using a inductor to help.
I think it would proable be better to have ac squarewave.
The diode bridge was a attempt to isolate one trigger signal to multiable stages with different voltages, type of like what a transfomer would do but the one linked only reachs 3 kv, and I might want more.

The tips Electra said helped, did remove the parrellel resistor, and just made the negtive side plan track, and moved the n mosfet there, also released I might need a 240/240v transformer for the ac source instead of just mains paralleled.

Thanks both for help.

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