goldenreference low voltage power supply

[sorenb]

6 hours ago, mwl168 said:

Fed by a transformer with 2 X 24vac/2A secondaries, my GRLV was not able to sustain regulation for 24 VDC output when the current draw was about 1A per rail. The output sagged down to about 23 VDC.  

The same setup works fine when I reduce the current draw to about 500mA pre rail. It also works fine for 1 A per rail draw once I lowered the regulated output to 22 VDC.

As you can see from my previous post (edited to include transformer information), I was able to pull 4.2A at 20V without any problems (had a scope on the output).
I suggest you measure the actual input pins of the OpAmp and pin6 at the lt1021, to verify all those are at 10V when you experience the output is sagging. If that is ok Check if you have >4V Vce across the pass transistor (for my experience it works already at 3V when the current is 1A) 

[mwl168]

Thanks Soren. I will measure as suggested and report back.

Since you have the same spec transformer I have (24vac, 100VA), do you mind testing it at 4.2A and 24VDC regulated output and see what you observe?   

[sorenb]

6 hours ago, mwl168 said:

Thanks Soren. I will measure as suggested and report back.

Since you have the same spec transformer I have (24vac, 100VA), do you mind testing it at 4.2A and 24VDC regulated output and see what you observe?   

23.6VDC 2.1A, regulation when Vce>3V

[mwl168]

So, at 2.1A draw, the regulated voltage dropped to 23.6VDC? Were the two LEDs next to the MJF1503x devices lit?

[sorenb]

No, didn't care to get excatly 24V ... got 23.6V from the resistors I had at hand
Yes, the diodes are fully lit hence the regulation comment

Edited January 4, 2018 by sorenb

[Kerry]

I updated the BOM for the GR78xx.  The GR79xx will be very similar.

I'm having an issue exporting it so here's a screen shot. 

 

Note:  Don't use the 10uF cap from the first BOM.  

[Pars]

Brings up an interesting issue... what is the difference between European style and US style SMD parts?

[cspirou]

11 minutes ago, Pars said:

Brings up an interesting issue... what is the difference between European style and US style SMD parts?

I thought they were the same but just used a different code?

[mwl168]

On 1/3/2018 at 2:11 PM, sorenb said:

"could not maintain regulation" meaning what exactly?

(edit after adding the transformer info to the previousposting)
You probably want to check the voltages in the input pins of the OpAmp (directly on the OpAmp) against the pin6 at the LT1021, when you experience the regulation doesn't work

Checked 3 GRLV and observed very similar measurements. 

Under load, which is only 300mA - 400mA in these cases, the transformer secondaries measured right around spec. However, I am getting < 3VDC Vce on MJW21194 and MJW21193 and it seems to drift a bit, I measured between 2.3VDC - 2.9VDC at different time and the lower Vce is also reflected as dimmer LEDs next to the MJF190303/19031. I don't have the GRLV schematic on hand. What do I need to do to raise the Vce of the MJW devices to 3 - 4 VDC? 

EDIT: Forgot to mention that I did measure the input pins of the OP (pin 2 and 3) and pin6 of LT1021 and they all measured 10VDC.

Edited January 5, 2018 by mwl168

[Pars]

If you look on Mouser, for example, there is a metric case code and an In case code. There for example isn't a 0805 case code for metric, but there is for inch.

[luvdunhill]

If you look on Mouser, for example, there is a metric case code and an In case code. There for example isn't a 0805 case code for metric, but there is for inch.

0805 == 2012 in metric parlance. 2012 means 2.0 mm x 1.2mm. Convert and voila!

[Pars]

How fucking intuitive

.08" = 2.032 mm. .05" = 1.27mm

I also take it this doesn't have anything to do with the "Resistor - European Style - 0805" in Kerry's BOM?

[Kerry]

Interesting/funny/

I imported European style resistors/capacitors for the symbols on the schematic.  The packages though are in inches (as imported). 

[kevin gilmore]

you need transformers with higher output voltages. probably custom transformers.

[sorenb]

5 hours ago, mwl168 said:

Checked 3 GRLV and observed very similar measurements. 

Under load, which is only 300mA - 400mA in these cases, the transformer secondaries measured right around spec. However, I am getting < 3VDC Vce on MJW21194 and MJW21193 and it seems to drift a bit, I measured between 2.3VDC - 2.9VDC at different time and the lower Vce is also reflected as dimmer LEDs next to the MJF190303/19031. I don't have the GRLV schematic on hand. What do I need to do to raise the Vce of the MJW devices to 3 - 4 VDC? 

EDIT: Forgot to mention that I did measure the input pins of the OP (pin 2 and 3) and pin6 of LT1021 and they all measured 10VDC.

So you have 24VAC 100VA connected to a GRLV configured for 24VDC, and have less than 3VDC drop, while the transformer secondaries are at 24VAC? numbers doesn't seem to add up - at least 3-5V is missing as far as I can see: 24VAC*1,4VDC/VAC - 3VDC (regulation drop) - 2VDC (diode drop) - Load_drop = 24VDC =>  Load_drop ~ 3-5V
 

[mwl168]

I measured the GRLV I am using on my SS Dynalovwith transformers with 20vac secondaries. I am getting the ac input of 19.3vac under load (less than 500mA) but the rectified raw DC measured at the 1N4007 diode is only 22.7VDC and the Vce at MJW21194 is only 2.6VDC. As a result the GRLV is barely maintaining regulation for the 20VDC output, the LED s next to the MLF15030 is lit but rather dim. Ditto on the negative rail.

[sorenb]

What is the drop of those special diodes you are using? 2.8V drop seems to be about twice what could be expected.
In any case you might consider using higher secondaries to provide the regulation some 'room' ... as far as I have experienced 3V is minimum to get regulation, but if the current is above 1.5A is more likely to be 4V .... as for your experience it seem like you have some loss between the VAC input and collector of the pass transistor 

[mypasswordis]

https://en.wikipedia.org/wiki/Ripple_(electrical)

[mwl168]

4 hours ago, sorenb said:

What is the drop of those special diodes you are using? 2.8V drop seems to be about twice what could be expected.
In any case you might consider using higher secondaries to provide the regulation some 'room' ... as far as I have experienced 3V is minimum to get regulation, but if the current is above 1.5A is more likely to be 4V .... as for your experience it seem like you have some loss between the VAC input and collector of the pass transistor 

I first suspected the special diodes I am using as well but eliminate that possibility after observing the same thing with a GRLV using the regular bridge rectifiers. In this case a GRLV configured for 15VDC regulated output and fed by a 15vac transformer. It maintains regulation under load (about 300mA) and the LEDs are all lit but I was getting only 17.7VDC rectified DC at the 1N4007 and the Vce on the MLF15030 is between 2.9 - 3VDC.

I do plan to use transformer with higher secondaries in the future. Your GRLV load-testing post is what prompted me to revisit this whole issue.

In another case (I built quite a few GRLVs), I could not get 28VDC regulation from a transformer with 28vac secondaries when the load is over 1A and the voltage drop here between the raw rectified DC and the regulated output is over 10VDC.    

Edited January 5, 2018 by mwl168

[JoaMat]

Law of nature. You always need a sufficient transformer.

[Kerry]

I'm getting better with Eagle, so here's an updated version of the GR78xx boards (still need the GR79xx version).

This version supports higher voltages and more current (some infamous designer wanted that ).  The board is the same size at .8" x 1.16".

GR78xx.xlsx

GR78xx-Gerber.zip

And some pics...

[cspirou]

Are pins 1 & 5 for higher current capacity?

[JoaMat]

Great work! Reason for KST42/92 replacing PBSS4140DPN? - need for higher collector-emitter voltage?

[Kerry]

2 hours ago, cspirou said:

Are pins 1 & 5 for higher current capacity?

Yes - For most applications I'd use just the center three pins.

58 minutes ago, JoaMat said:

Great work! Reason for KST42/92 replacing PBSS4140DPN? - need for higher collector-emitter voltage?

Yes - It took a bit of thinking to make the two sot23's fit.

[JoaMat]

Did this today. Positive golden reference regulator. I managed to make a Kerry device in my kitchen but I think he is pushing the envelope now. I’ll try to make negative regulator as well and if this succeeds  I’ll put them in a T2 PSU.

Dark picture so you can see the small red LEDs on the board.

Hope the small GRLV hit the market soon.