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Old 3rd October 2006, 01:39 PM   #1
mr.duck is offline mr.duck  United Kingdom
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Default Could somone please check my Jung regulator?

Its my 1st PCB layout. I found a cheap board house that will make single PCBs for just a few pounds. But the PCB must be single sided and the traces cannot be too thin. I like to keep the components all tightly packed together and it was a challenge but i think i have done it

If somone could just give it a quick look over to see if there is no obvious errors with it that would be great. Or sugest improvments?

It is a single regulator. I plan to duplicate the whole regulator and have two on the same board so that I can have a +/- PSU to power an amp.
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Old 3rd October 2006, 01:44 PM   #2
mr.duck is offline mr.duck  United Kingdom
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Here is the schematic. The PCB layout does not have the first star ground point like it is drawn in the schematic, but it does have the star ground point by GND_SENSE. I dont know how important it is.
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Old 3rd October 2006, 01:49 PM   #3
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I can't comment on the correctness of the connections. If you drew the circuit in a schematic program and then generated the netlist for the PCB this will automatically be right of course.

With pin 4 at the error amp you just did the right way too connect it at the load point. As it was in the schema it is not optimal, because the pin 4 voltage would get some voltage developed over part of the track between load gnd and the return to the reservoir caps. But the layout is OK here.

You may want to put in a series resistor to the -input of the error amp, and a cap from that point to gnd. With the remote sensing, there ia a possibility for instability, depending on layout, cable type/length etc. You mat get away without it, and then just bridge the resistor and leave out the cap, but if it oscillates use like 1k and 100pF to try.

Anyway, if this is your first layout, it's pretty, pretty good! Nice and compact.

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Old 3rd October 2006, 03:53 PM   #4
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Thanks for your comments, Jan.

Its my 1st PCB layout but it took a few attempts before i got it. I dont even want to know how long it took me to do the whole thing from start to finnish lol.

I may use OPA134 for the error amp. It seems be good spec. Decent slew rate, very low noise and low distortion... and less prone to oscillate?

Also I will use BC560 for the bias transistor. I think thats the only other modification I've made.

I have not heatsinked the pass transistor. Is it correct that the pass transistor will have 2.3v across it all the time with the rest being droped accross the pre reg? By my calculations the regulator can provide up to 0.5A before it needs a heatsink. Thats based on a 75*C/W junction to ambient resistance for the pass transistor.

I think thats all. Thanks for your help.


oh and are 1/4W resistors ok? The regulator will have to supply about 0.25A
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Old 4th October 2006, 08:10 AM   #5
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LM329 has three pins (yes?), it's smart to have three holes if you want to use a LM431. It's also smart to choose a LM431 because it's easier to fit in a LM329 in a LM431 footprint than vice versa. A small remark.

R3 =1k can sometimes be a bit high. Most manufactures recommend 220 ohms but I have noticed problems only in a few occations. If R3 is too high the regulation gets worse.

If you plan to use OPA134 or similar it will probably work but AD825 or similar may not work becasue of the grounding in particular. If you use a 45 MHz opamp the pcb layout become much more critical than for slower opamp. You should try to implement a "current free" ground, really look at the star concept (compare the schematic). You should also make the ground traces as wide as you can. That's a good start.

It's smart to have four resistors in the feedback, then you can trim the voltage easier. You can see how I have done.

I would add 100 nF or something at the input. 2000 uF only will not be particulary good at higher frequencies.

The series transistor will become rather hot with 2.3 x 0.25 W but you won't kill it. A thing to consider though is electrolytic caps rather near, not good for the lifetime of those.
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Old 8th October 2006, 11:04 AM   #6
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Hi,
that layout looks really compact. Well done.

The ground connections from r5 & c7 could be starred into the output connection.

If you move the ground track down to the bottom of the PCB then the space created allows the whole right hand side to be moved down and that releases space for the TL431 and it's two Vset resistors up at the top.

Check the gap bc560 pin2 to track above, looks a bit close.

Your power dissipation calculation is correct, but I would limit a zero sink dissipation to no more than 500mW (3V & 165mA) and preferably 300mW (3V & 100mA).

A little 20C/W sink will allow 1000mW (3V & 330mA) and not get too warm.

I would join in a mini order if it suits you. Letter post would cover about 4 or maybe 6 PCBs.
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Old 8th October 2006, 11:36 AM   #7
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Hi,
I think the LED is reversed. The -ve (flat side) leg should be towards the +ve supply side.

Are you planning to decouple the opamp direct from pin 7 to pin 4 on the track side? 100nF ceramic fits nicely here.
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Old 8th October 2006, 11:49 AM   #8
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Quote:
Originally posted by AndrewT
Hi,
I think the LED is reversed. The -ve (flat side) leg should be towards the +ve supply side.
Question to Andrew: The LED should be lit. Why? You wamt 1.6 volts over it. How should you connect it in order to achieve that?
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Old 8th October 2006, 11:52 AM   #9
AndrewT is online now AndrewT  Scotland
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Hi,
I think he has the LED inserted like a diode which will try to block the current flow.

When an LED is used as a voltage reference the current flows (and lights) when the +ve supply comes into the -ve leg.
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Old 8th October 2006, 11:53 AM   #10
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Quote:
Originally posted by AndrewT
Are you planning to decouple the opamp direct from pin 7 to pin 4 on the track side?
This is not a good idea. Adding a high Q capacitor at the output might get you into trouble. Oscillations.
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