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Old 6th May 2005, 09:37 AM   #11
mikeks is offline mikeks  United Kingdom
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Originally posted by AndrewT
I am not advocating Reg output stage, just suggesting a solution.
I personally prefer reg supply to input & drivers and brute force PSU to the output stage.


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Old 6th May 2005, 10:56 AM   #12
k1jroth is offline k1jroth  Finland
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I`v heard about that book but it`s expensive and not on my mother language so it takes too much time to study it.
I think that straight line current limitign is enough and i want to keep schematic simple as possible.

I will use multiple transistors in parallel to reduce power of them.
Yes power dissipation is still a problem but if voltage is +-50V and current is 8A power warms load and power dissipation of transistor is 25W (4 parallel).

Worst case scenario of dissipation is a short circuit of outputs
8Ax60V=480W (voltagedrop of transformer not included)
That means all 4 transistors have to dissipate 120W exremely much i think but i will never use supply with low voltages and high current i have no need for that.
There will be over heating protection because of that.
These transistors are bipolar

It is a bench supply for testing all kinds of stuff

I can design power supplly with these properties but not with
currentlimiting which will work allways no matter how load is connected.
(For example +V to ground, -V ground, +V to -V.)

Please correct if i`m wrong in some case
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Old 6th May 2005, 06:21 PM   #13
AndrewT is offline AndrewT  Scotland
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thanks for clarifying that you are building a bench supply.
I was on the wrong track.
All those nice transistors going to waste!
You could intercept each winding and take off lower voltage taps.
Then change the tapping as you change the output voltage.
My bench supply has relays that do the switching automatically. As I ramp up the voltage with the control pot the relays come in & out selecting the appropriate voltages.
This arrangement reduces the dissipated power considerably at lower output voltages and allows the use of a constant current control. The constant current control should be adjustable to protect a faulty circuit.
regards Andrew T.
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Old 6th May 2005, 09:21 PM   #14
dhaen is offline dhaen  Europe
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Current limiting is normaly done by including a small value resistor in the current path, either in the +, - or ground lines, then measuring the voltage across it. (The voltage regulation is not affected by the presence of the resistor if the error voltage signal is taken after the resistor).
The voltage across this "current sense resistor" can be measured best by an opamp, but that requres external floating supplies. An simpler way is to use a small bipolar transistor which is biased by the voltage developed across the resitor.
Here is an example

Language: I believe that your grammar is rather different from European languages, so understand your reluctance to read Horowitz & Hill. However, if you can understand my muddled and sometimes confusing English, you will have no trouble to understand the clear and concise text of the book
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