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L200 Bench Power supply.

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OK, I found some of your suggested mods to this PSU audioguru, I never realised there was a forum to read over there about it.

I'm up to page 7 now lol.

I'm sure I might get this lot read by next new year!

I'm gonna make mods as you sugest ;)

hackableFM.

**EDIT** Ohhh and thanks again! Doesn't this forum have a 'Thanks' button anywhere?
 
The moderator there thinks the original project works fine even though the site's owner made it and it blew up!

It is a kit. They must have many complaints.

I have asked the moderator to sort the 140 pages about it in the forum into construction, modifications, parts substitutions and troubleshooting but he won't.
 
When one had built any power supply, one should really test out how the power supply performs. Its no use just saying to the world I now own a 30V 3A regulated supply.

Can it produce regulated 30V, 3A without problem? Is the output voltage steady?

Can one short circuit the output at any output voltage level? For how long?

How much voltage is dropped when a 3A loading is connected to the output?

The last one is particularly important and will show both the design skill of the circuit designer and the wiring skill of the constructor. Don't ever miss it.
 
eblc1388 said:
When one had built any power supply, one should really test out how the power supply performs. Its no use just saying to the world I now own a 30V 3A regulated supply.

Can it produce regulated 30V, 3A without problem? Is the output voltage steady?

Can one short circuit the output at any output voltage level? For how long?

How much voltage is dropped when a 3A loading is connected to the output?

The last one is particularly important and will show both the design skill of the circuit designer and the wiring skill of the constructor. Don't ever miss it.

In fact it has to be tested at 10% extra load to be sure on specification.
 
mvs sarma said:
In fact it has to be tested at 10% extra load to be sure on specification.

All true!

I used to test & Repair PC P.S.U.'s back when I left school, even they had to be tested at just over their max ratings ASWELL as being baked in a walk in oven whilst on soak test!

@ Audioguru.... I like your .... what's the word... I dunno but I like the way you keep your cool in that 140 page thread, I have only read the first 30 or so pages then the last 10, I was up ALL NIGHT considering my options on this PSU, I have already printed the PCB and mounted most 'originals' components. I now plan to buy the relevant parts and CORRECT rather than improve the psu as it appears you aren't allowed to call it lol.

Since I can't make head nor tale from the 140 pages (I simply end up on autopilot and get confused over the number of suggestions!), I don't suppose you could supply your latest list of required mods for this PSU including things like the track mod for Q1 rather than just the component changes please AudioGuru?

I've had a dig about and found some TIP31A's already lol. and I'm gonna double up (Piggyback) the rectifying 4Amp diodes I already have in place.

It would be much appreciated if you can supply the latest list of updates, I thought I had it at one point then someone posted a picture listing the latest mods! I'm just so puzzled with the ammount of changes there's been!

Many Thanks!!

HackableFM...
 
audioguru said:
I have asked the moderator to sort the 140 pages about it in the forum into construction, modifications, parts substitutions and troubleshooting but he won't.

Moron, He just doesn't want to make you look better for pointing out the obvious mods that were required. Even though it would make it easier for people like me to just look and find the info we need.

Double MORON!!

oops, sorry for my outburst! The guy owes me a full nights sleep! :mad:
 
Hi Hackable,
My best "cool" replies in the power supply thread were deleted by the moderator when I explained that it is bad practise to operate an opamp with a supply voltage higher than its absolute max allowed voltage. He thinks it is OK to have the supply voltage too high if the temperature is not also too high. He also thinks that if the transformer can supply more current than is needed then the circuit will draw too much current.

Leave the wiring of Q1 like in the original schematic which is correct, it doesn't make much difference.
Change the wiring and resistor for the offset voltage adjustment so it is correct for the opamp you use for U2.
Here is my latest corrected parts list without a BD139 for Q2 which nobody tried yet:
 

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OK, thank you very much!

I appreciate this list, I have phoned my local electronics shop and they can't get the OPA445 I.C's. There were a couple of other types listed in that thread namely... MC34071AP & TLE2141CP, Would you recommend using them as a second best or might I just aswell stick with the TL081's? and watch the fireworks?

If they have the BD139 then I might just be the first to try it! :D
 
Digikey get about 1000 OPA445AP high voltage opamps every couple of months then they run out in about 6 weeks before the next shipment. They recently ran out again.
With a 30VAC transformer and no load on the circuit then the total supply voltage for the opamps is 48VDC. It is higher if your mains is high.

The MC34071 and TLE2141 have an absolute max allowed supply voltage of 44V. The TL081 has a max of 36V.

The OPA604AP has a max allowed total supply voltage of 48V and is inexpensive, but Digikey has also run out of it recently.
 
OK, I've been to the electronics store, They had everything I asked for except the bloody OpAmp chips. They do have the TL081's as I bought them a couple of days ago, Now they did also have the LF356's in stock but they had the 'N' type, now when I refer to the datasheet for these the 'N' type are the same voltage as the TL081's so they're no good, I asked for the LF356B as they are +-22V and I feel these would have done the job but nope, they ain't got them and they're unlikely to get them either.

So, I now have a pile of bits which I can use to build this supply WITH the mods to make it work properly but I'm stuck without the chips, I thinkI'll go have a spooch about on the net and see if I can find any!

Oh @ audioguru.... You suggested the BD139 for which transistor? I got a couple anyway so I can try them if I ever get this project completed.

R15 was changed to allow more voltage on the output of the PSU only if you fit the TIP31A??? is this correct? And If I fit the BD139 do I still need to change this resitor nto 100R???

hackableFM....

Thanks again audioguru.
 
Ohh sorry, another question, My transformer from the L200 PSU I made gave me approx 36.4VDC after rectifier and smoothing cap, I intnd to use the same TX, BD & cap in this PSU... Will the OPA604AP work ok for me with that voltage??

I can get some from the states for a reasonable price!
 
hackableFM said:
OK, I've been to the electronics store, They had everything I asked for except the bloody OpAmp chips. They do have the TL081's as I bought them a couple of days ago, Now they did also have the LF356's in stock but they had the 'N' type, now when I refer to the datasheet for these the 'N' type are the same voltage as the TL081's so they're no good, I asked for the LF356B as they are +-22V and I feel these would have done the job but nope, they ain't got them and they're unlikely to get them either.

So, I now have a pile of bits which I can use to build this supply WITH the mods to make it work properly but I'm stuck without the chips, I thinkI'll go have a spooch about on the net and see if I can find any!
Connect a 9VAC/4A transformer in series with the 30VAC transformer out-of-phase to reduce the voltage to 21VAC. Then without a load it will make a positive unregulated +29.7V which adds to the regulated negative -5.6V supply to make a total of 35.3V for the ordinary opamps with a max allowed voltage of 36V. R14 must remain at the original vlue of 1.5k.
Then when you can get OPA445AP high voltage opamps remove the 9V transformer and change R14 to 1.2k.
With a 21VAC supply the project will have a max output voltage of about 22VDC at 3A.

You suggested the BD139 for which transistor?
The BD139 is a very fast transistor and improves the circuit's transient response when it is used for Q2. It will need a good heatsink because its max allowed power dissipation is low.

R15 was changed to allow more voltage on the output of the PSU only if you fit the TIP31A??? is this correct?
No. R15 wastes about 2V (3 or 4V if the output transistor is a single 2N3055 with low gain) when the output current is 3A and the transistors have minimum gain. With 100 ohms then the loss is only 0.2V.

If I fit the BD139 do I still need to change this resitor nto 100R???
Yes, to avoid too much voltage loss at high output current.
 
Okie Dokie.... I away to work on it now!

What do you think? BD139 for both Q1 and Q2? or just BD139 for Q1 and TIP31A for Q2? I bought enough just incase! :D
 
Q1 is just a switch that turns on when the mains is turned off. Any little power transistor is fine.

Q2 works hard and gets hot. A BD139 will have good transient response but needs a good heatsink. A TIP31A is slow and causes transients but conducts heat very well.
 
Why not use MC33071 for the op-amps?

They're rated for 44V when driven from a single supply.

I've haven't studded the circuit that well but you might be able to get away with the :mu:A741 if you're really stuck but don't expect a wonderful transient response.
 
The MC33071 has an industrial/vehiclular temperature range from -40 degrees C to +85 degrees C.
The MC34071 has a commercial temperature range from 0 degrees C to +70 degrees C.
They use a 100k offset adjustment trimpot but 10k is shown on the datasheet for a +-80mV range.
 
Right, thanks for the input, I have tried to get MC34071AP and TLE2141CP OPA445 and OPA604 Op-Amps, Non of which are stocked at my local shop.The only LF356 they had I believe was rated for +-18V and hence no good.

I can however get ahold of OPA604AP OP AMP FET Input Low Distortion Op-Amps from the net. Will these work ok or not?

I will contact the local shop tomorrow and ask about the MC33071 you mentioned Hero999. Thanks.

I will go and dig out the voltage rating for a 741. :D

As usual, thanks for the help!
 
Bloody hell man!!

I might just have some LM741's kicking about in the shed somewhere if I can get past all the junk! According to the datasheet, they are as good as the others mentioned. +-22Volts!!!

Someone hire me a skip to get rid of all this junk in the shed!
 
The OPA604 has a max allowed supply voltage of 48V.
Some brands of 741A opamps have a max allowed supply voltage of 44V.
 
hackableFM said:
Bloody hell man!!

I might just have some LM741's kicking about in the shed somewhere if I can get past all the junk! According to the datasheet, they are as good as the others mentioned. +-22Volts!!!

Someone hire me a skip to get rid of all this junk in the shed!
+-22V = 0 to 44V.

The maximum working voltage is the potential difference between the + and - supply pins. You could run you 741 of a single 44V supply, a bipolar 22V supply or a +12V -32V supply and as far as your op-amp's concerned the potential difference between the supply pins is 44V so it'll be happy.

The absolute maximum AC supply you can have from the transfomer without exceeding the rating or your 741 is actually 32V, given that (44V+1.4V)/root(2) =32V, (1.4V comes from the volt drop across the rectifier).

If you can't get an op-amp that's rated to the full power supply voltage then you can often run it of a lower supply voltage using a zener diode but this will depend on the voltage on the inputs and what voltage the output is expected to swing to.
 
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