Pass "DeLite" Amp from BAF

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ra7

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Joined 2009
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Hey guys,

Just got back from work and measured the current. Its sourcing about 8A. I don't know how the fuse didn't blow. Perhaps, its a 10A one :eek:

I'm stumped.

Stefano, I'm looking at that diagram and seeing how the drain voltage is set. But I'm getting about 20V at the drain any way. Hmmm... :(
 
R

ra7

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Joined 2009
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juma said:
You still think that your CCS is ok? ;)
Click to expand...

Well, maybe not. Here is the schematic. I've used the parts at hand. Components that have different value compared to fig2. in ZV9 are: the two 470uF caps, the NPN transistor is BC550B and the MOSFETS are IRFP140. I think all substitutions are ok, but let me know if they are not.

The CCS current is controlled by the source resistor on the second MOSFET - R6 in my schematic. The NPN transistor develops 0.66V across it and so, a value of 0.33R means 2A current. This is what I had set it up as. Changing the value of the R6 should give me different currents.

I drew this up in LTSpice, so if you guys have models for the three transistors, that would be great.

Thanks!
 

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P

Puffin

Member
Joined 2006
Fran. I seem to have the same problem you had, in that when I power-up I lose all the volts and the bulb does not light. I have wired a 15R resistor in parallel with the bulb, but still no joy.

My bulbs are 300w 130volts (not 240v) The bulb cold measures about 4.5ohms, so I thought that adding a 15R resistor might work.

Any ideas?

rob.
 
Nelson Pass

Nelson Pass

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Joined 2001
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ra7 said:
Well, maybe not. Here is the schematic. I've used the parts at hand. Components that have different value compared to fig2. in ZV9 are: the two 470uF caps, the NPN transistor is BC550B and the MOSFETS are IRFP140. I think all substitutions are ok, but let me know if they are not.

The CCS current is controlled by the source resistor on the second MOSFET - R6 in my schematic. The NPN transistor develops 0.66V across it and so, a value of 0.33R means 2A current. This is what I had set it up as. Changing the value of the R6 should give me different currents.
Click to expand...

I don't see any bias for the Fet. You need about +4v from
Gate to Source, often provided by a resistor from Drain
to Gate and divided by resistors from Gate to Ground.

:cool:
 
R

ra7

Member
Joined 2009
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The bottomost FET is the IXTH part and the top 2 are IRFP140. I thought just replacing the light bulb with a CCS would work and it won't need a special biasing arrangement - like used for the FET in Zen-lite. And I used the CCS from ZV9. Is there a simpler route or am I missing something obvious?

Thanks for help, Papa. Greatly appreciated, as always.
 
Nelson Pass

Nelson Pass

The one and only
Joined 2001
Paid Member
ra7 said:
The bottomost FET is the IXTH part and the top 2 are IRFP140. I thought just replacing the light bulb with a CCS would work and it won't need a special biasing arrangement - like used for the FET in Zen-lite. And I used the CCS from ZV9.
Click to expand...

You need a method of balancing the currents of the two,
otherwise the Drain voltage will be either full + or full -.

The Lite bulb is a resistor, so it tends to self balance.

:cool:
 
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Peter M.

Member
Joined 2005
How about a resistor from the drain of M3 and a trimpot to ground, and disconnect R8 at the source end and connect it between the resistor and the trimpot.
Just like R14, P1 and R15 in the Zv9 schematic.

If the CCS draws more current than M3 then the drain voltage of M3 becomes to high, if it draws less it becomes to low.
 
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P

Puffin

Member
Joined 2006
Hi guys. I need some help with my De - Lite.

Can you cast an eye over my board and see if I have done anything silly. What is happening is that the volts are dropping to 0.6v (same as woodturnerFran). I have tried a 15R in series with the bulb (bulb measures 4.5ohms) but still no joy. The 50w resistor gets quite warm and the bulb is doing something as it gets mildly warm, bit you would not know it was on unless you put your hand on it.

The bulbs are 130v 300w

I seem to have done something wrong.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
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