SSR03 new board +/- 15V w/ LM329 and LT1028 ...

[yo4frj]

Hi P-A,

Happy New Year 2014!

Well, I'm facing something strange with my first SSR03 15V board version, based on LM329(LT version) and LT1028 (SOIC version). Parts were double checked accordingly with your last LM329 15 Vdc BOM. I've secured J1, J2, J3, J4 with a tin bulb. DZ1 & DZ2 installed correctly without LED (both negative and positive areas got PL6V8 paired at 6.78V for the same current). VR1 & VR2 installed correctly (as the thin marked area on the board). H1 installed correctly. Input voltage +21 Vdc from my variable bench power supply, with current protection set for 100mA. Loading was set for 55 mA by a set of 12 Vdc LEDs. 

Step 1 - positive regulator - data same as above
First power on: variable voltage (oscillation???) at output as 10.0-11.55 Vdc every 2s. However, H1 - Red LED - it's on, however showing a variable light as the variable output!
 
I could cure the output voltage 2s oscillation after taking out C57(100uF - Panasonic FM), and therefore measuring the following points, facing GND, I've got the next set of parameters:
- LT1028 - N1: U2=+3.77V, U3=+3.76V, U4=0.0V (GND), U6=4.02V, U7=10.09V
- voltage across H1 = 1.89V (red LED light on stable)
- voltage across DZ1 = 6.78V
- voltage across VR1: 5.00V
- R27 = 1000R as in BOM
- R31 = 4700R as in BOM
- R33 = 1000R as in BOM
Well, I was expecting Vout = Vref x (1000/825 + 1) = 6.9 x 2.2121 = 15.26V, but I've got only +10.67V output stable dc after C57 removal !!!

I was trying to change R27 in order to force VR1 to reach the nominal 6.9V function and put N1 to work. By  simple paralleling R27 with 1000R, I could get the following results:
- Vout = 14.91V no load
- LT1028 - N1: U2=+8.00V, U3=+7.39V, U4=0.0V (GND), U6=8.02V, U7=14.00V
- voltage across H1 = 1.92V
- voltage across DZ1 = 6.78V
- voltage across VR1: 6.91V 
- voltage across Q7 B-E = 0.65V
I was expecting much lower output voltage based on formula  Vout = Vref x (500/825 + 1) = 6.9 x 1.606 = 11.08V so the whole circuit is behaving strange in my opinion with reverse results as expected by theory of operation. I assume N1 is oscillating? Installing 100pF (C51) didn't help at all ...  However, I decided to test the positive regulator under 0.5A loading. So I've just put back C57 (no problems as before), changed my variable DC PS to max. 1A current while keeping the same +21V as Vin, also replaced the R47 wire with a 5W - 1R5 vishay resistor. I ended up installing a 30R/15W loading resistor for simulating an resistive 0.5A load for this positive regulator stage. Vin was monitored with another voltmeter and remains stable as 20.92V, but the positive regulator Vout changed down to +6.86V, and I could measure aprox. 10V over pin 3-2 of LM317. At a first view based on such a simple test I've just proved myself the +15V module is not regulating properly.


Step 2 - negative regulator installed as BOM - data same as above
First power on: variable voltage (oscillation???) at output as -15.0 to -17.55 Vdc every 2s. H2 - Red LED - it's off. LM337 installed.
 
Again I could cure the output 2s oscillation after taking out C58(100uF - Panasonic FM). In order to separate the Jung regulator from LM337, I took out the IC2(LM337), including R16, and also reduced the input voltage from -21V to Vin = -19.1V, while installing R48 (1R5 / 5W).
Measuring the following points, facing GND, I've got the next set of parameters:
- LT1028 - N2 got very hot: U2=-8.43V, U3=-8.37V, U4=-13.33V, U6=-12.02V, U7=0.0V (GND)
- voltage across H2 = 1.65V (H2 light off!)
- voltage across DZ2 = 0.13V
- voltage across VR2: 6.91V
- R28 = 1000R as in BOM
- R32 = 4700R as in BOM
- R34 = 1000R as in BOM

During the first tests I may be powered this negative regulator in reverse by mistake while LM337 was installed, but I'm not 100% sure. Most likely N2 is damaged, as far the rest of Q2, Q4, Q8 looks okay B-E (0.65V) and no shorts on C-E.

Please advice what're your thoughts about all above, positive and negative regulators different results, and I'll thank you a lot in advance for any suggestion/advice.

Warm regards,

Adrian 

[peranders]

Is the LM329 soldered in the small outline, not the fat?

Tell me what input voltage you have when you test.

What are the voltages on the opamp, pin 2, 3, 6 and 7? I see that the pin 2 and 3 have similar voltages = feedback is working. Please the LM329!

Can you take some close-up pictures?

[yo4frj]

Indeed, on both positive and negative sides LM329 was soldered in the small outline.

Pse see various N1 and N2 voltages in my text: U2, U3, U4, U6, U7 is the voltage between pin 2, pin 3, pin 4, pin 6, pin 7 and GND.

Input voltage for Step 1 - positive 15V side of the regulator was always +21V. With no load the output was +14.91V, then with 55mA load output decreased to +14.67V, and with 30R/15W load the output get as down as +6.86V.

Input voltage for Step 2 - negative 15V side of the regulator was always +19v after LM337 + R16 + C58 removal.

By the way: I installed Q1=Q6=Q7=BC560C and Q2=Q5=Q8=BC550C from Farnell.

Thanks

[yo4frj]

How to send the high def pics? Current forum will allow a max. size of 0.25M pics ....

[peranders]

The positive side seems to work but you may have to increase the input voltage and/or change the series resistors you have in the rectifier bridge and smoothing. You must have 5 volts more in than you have out,

If you have had the wrong polarity (the negative half) you will much likely have fried the Q8 and possibly the opamp.

[yo4frj]

I just fixed the negative side by replacing the N2-LT1028. For Vin = -21V I've got Vout = - 15.3V and this fits exactly as in formula while using the standard 15V LM329 BOM values for R28-R32-R34 resistors. C58 was soldered back as far there was no oscillation anymore, and last but not the least the regulation works as was supposed to be at 0.65A.

Tomorrow I just hope to find some time to carefully check why the positive side needs to lower the value of R27 from 1000R down to 500R in order to make the feedback work for N1, while the Vout formula didn't fit. I'll suspect a partially damaged N1-LT1028 ... but let's not anticipate ...

I'll keep you all posted.   

[yo4frj]

FYI, I just fixed the positive side by replacing the N1-LT1028 too.

Got similar results as the negative regulator. So far both negative and positive regulators now fits the Vout formula as it should. For Vin = +21V I've got Vout = + 15.3V and this fits exactly as in formula while using the standard 15V LM329 BOM values for R27-R31-R33 resistors. C57 was soldered back as far there was no oscillation anymore, and last but not the least the regulation works as expected at 0.65A.

Because I paired VR1 with VR2, DZ1 with DZ2, and resistors in feedback (R27 and R28, R31 and R32, R33 and R34) I've got similar voltage at both outputs, i.e. +/- 15.3V at 0.65A. 

Now I need to review my initially building notes just to understand what, and/or how I damaged both LT1028s. However, at a first view, all  the snubber resistors (R1, R2, R3, R4 as 2R2/3W) were installed on top of the rectifiers, including R9 and R10 (as 1R5/5W). This allowed that a fraction of the +21V DC voltage applied before R9 from my bench PS to be seen as reverse voltage at the input of the negative section, and viceversa. Probably that was enough for the LTs. Then you all know the story, as above.

This lead to the my own next adds & conclusions:
1 - If you don't want to use the xxVac trafo in the early test stages, and you're looking to use your bench PS, I will suggest you all to install R9/R10 only after both regulator and pre-regulator works on each positive and negative sides. This way you'll avoid loosing time, and burned N1/N2.
2 - Start your tests first with Jung regulators. That means you populate each Jung regulator side with parts at a time. No need to install R15 and LM/LT317, and R16 and LM/LT337 at this early stage in order to keep things simple.
2.1 - carefully check all the resistors to fit with BOM's values, and pair R27-28, R31-32 and R33-34 within 1% or less before installation. Do remember the output voltage should fit with the formula shown in P-A's SSR03 technical presentation. P-A's BOM on each output voltage will give you the required values to get you very close to the selected voltage.
2.2 - pair VR1 with VR2 separate. Take a 2k2 resistor in series with VR1/VR2 outside the board and power properly with 15Vdc while you check voltage over VR1 in case you decide for using LM329, and do the same with the 6.8v zenners DZ1 with DZ2.
Both 2.1 and 2.2 steps should allow you to get the same, or very close values at the outputs, if that's what're looking for. You can do some fine tuning in the end, over the output voltage, using the same Vout formula based on the influence of R31-R33 and R32-R34 values.
2.3 - do your math based on your maximum DC current requirements on each side of the SSR03 board in order to further calculate properly R47 and R48. In the end will help you to decide over the AC input value for the both sections of the transformer and the overall power for the transformer.
2.4 - try to format all the new electrolytic capacitors for a few minutes before installation. There is a particular case when few of us may have trouble with a new elco if not formated properly, and that's the case for C57 either C58. Each of those capacitors can influent the correct functionality of the feedback in his own Jung regulator section. The inrush current at the first start-up may lower the LM329 voltage, and therefore you may face an unexpected but strange Vout value until the capacitor will get formated, etc. 
3 - prove that the Vout calculated based on the measured values for VR1, R27, R31, R33 fits with your output voltage measured on each regulator side, no matter negative or positive section. If it fits, then everything should work properly, and deliver your selected BOM output voltage, and the current as R47, either R48 will allow you. Check that with a load resistor at the output. If everything looks as expected, then go ahead and install LM/LT317 and R15. Do the same with LM/LT337 and R16. You'll discover that the pre-regulator will always work after the Jung regulator works properly. If your measurements does not fit with the selected BOM voltage, or Vout formula, then something it's wrong, and you need to recheck everything.
4 - in the end do remember that P-A's boards and technical parameters for each voltage section will always fit with his specs if parts are okay and values as the selected BOM's, and everybody follows P-A's installation instructions in detail, and of course own expertise ...   

Thanks P-A for support!

Adrian