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Can someone please explain this circuit for me?

Oluwatimilehin

Apr 12, 2016
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Please explain it in such a way that I will be able to even teach someone else. I want to know what each component does and if possible how they arrived at the component values. Thank you
 

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Arouse1973

Adam
Dec 18, 2013
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Where did you get the circuit from? Is it some kind of power supply?
Adam
 

Oluwatimilehin

Apr 12, 2016
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It's a power supply. It got sent to me by someone to use for a power supply project I posted a while back.
 

Arouse1973

Adam
Dec 18, 2013
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Do you not have the reference website for this PSU. It will take some time to go through this to work out all the values chosen.
Adam
 

duke37

Jan 9, 2011
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My word, that is complicated, you would be better using an LM317T or similar.
There is a string of Zener diodes to give a variable voltage between 4.7V and 10.7V. This is compared to the output voltage and if there is a difference, the output power transistors are driven to correct this.

You should be able to find out what each component does by finding a book to introdce you to electronics. My memory is too poor to remember the circuit in detail and I cannot get it on screen with my reply.
To get component values you look up the data sheets to see what is necessary
 

Herschel Peeler

Feb 21, 2016
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Please explain it in such a way that I will be able to even teach someone else. I want to know what each component does and if possible how they arrived at the component values. Thank you

Is something like this what you were looking for?

TR1, the two 1N4148 diodes and the 150 ohm resistor are a constant current source. One diode cancels out the 0.6 V or so across the E-B of TR1, the other diode sets the voltage across the 150 ohm resistor. 0.6 V / 150 ohms gives a consistent 4 mA down through the three Zener diodes. This current will be consistent even as the voltage out of the power supply section (the two 1N5401s and the 2,700 µF capacitor) may vary with line voltage. It is worth noting that the voltage across the Zener diodes will vary a bit as current through them changes, so if you want a steady voltage use a constant current source instead of just a resistor. The 22K resistor beneath the two 1N4148 diodes controls the current through the diodes, which controls the voltage drop across the diodes, which controls the voltage across the 150 ohm resistor and thus the current level at the output.

The 47 ohm resistor will drop about 0.188 volts (47 ohms x 4 mA). The two 3 V zeners will drop about 6 Volts across them and about 4.7 V above ground at the bottom end. The pot gives us an adjustable voltage between 4.7 V and 10.7 V.

TR3 and TR4 make up a differential amplifier that compares this pot voltage to the output of TR5 and TR6.

TR5 and TR6 make a Darlington amplifier that gives us the voltage regulator function.

So we have an adjustable voltage regulator. With the 1N5401 diodes used we can assume we have 2 or 3 Amps available. (LM317 alone won't cut it. Maybe LM317 with a boost transistor.)

TR2 monitors the voltage drop across Rx. When the current through Rx causes a voltage drop of about 0.6 V TR2 turns on, killing the constant current circuit, turning off the power supply. So we also have current limiting as well as voltage regulation. Not knowing the value of Rx we can't say what the current limit is set to.
 
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dorke

Jun 20, 2015
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Is something like this what you were looking for?

TR1, the two 1N4148 diodes and the 150 ohm resistor are a constant current source. One diode cancels out the 0.6 V or so across the E-B of TR1, the other diode sets the voltage across the 150 ohm resistor. 0.6 V / 150 ohms gives a consistent 4 mA down through the three Zener diodes. This current will be consistent even as the voltage out of the power supply section (the two 1N5401s and the 2,700 µF capacitor) may vary with line voltage. It is worth noting that the voltage across the Zener diodes will vary a bit as current through them changes, so if you want a steady voltage use a constant current source instead of just a resistor. The 22K resistor beneath the two 1N4148 diodes controls the current through the diodes, which controls the voltage drop across the diodes, which controls the voltage across the 150 ohm resistor and thus the current level at the output.

The 47 ohm resistor will drop about 0.188 volts (47 ohms x 4 mA). The two 3 V zeners will drop about 6 Volts across them and about 4.7 V above ground at the bottom end. The pot gives us an adjustable voltage between 4.7 V and 10.7 V.

TR3 and TR4 make up a differential amplifier that compares this pot voltage to the output of TR5 and TR6.

TR5 and TR6 make a Darlington amplifier that gives us the voltage regulator function.

So we have an adjustable voltage regulator. With the 1N5401 diodes used we can assume we have 2 or 3 Amps available. (LM317 alone won't cut it. Maybe LM317 with a boost transistor.)

TR2 monitors the voltage drop across Rx. When the current through Rx causes a voltage drop of about 0.6 V TR2 turns on, killing the constant current circuit, turning off the power supply. So we also have current limiting as well as voltage regulation. Not knowing the value of Rx we can't say what the current limit is set to.

Looking at the TIP31 SOA graph,
the max current of this power supply can be 2A.
 

Herschel Peeler

Feb 21, 2016
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Looking at the TIP31 SOA graph,
the max current of this power supply can be 2A.

Good point. I didn't look at that.
For the original poster, SOA is Safe Operating Area. It depends on the maximum voltage across the transistor and the allowable current through it. Not really much to calculate, just look at the graph. Voltage x current = watts being dissipated. Derated for temperature. Then throw out the calculations and use a heat sink on the transistor.
 
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73's de Edd

Aug 21, 2015
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Sires . . . .

And so . . . .its like this . . .I had blown that schema up 4X and started to COLOR box it up in sections for separate areas of clarity of its design :

A . . .The RAW DC portion
B . . .The constant current derivation from TR1 and its feed down to the to the Zener diode string.
C . . .The TR2 base as the sense for output current control . . . .with the Rx resistor being its sampling point.
( the idea of this unit is for proper selection of Rx value to be having a 1 ma meter shunting it, and the meter scaled to be reading out the 1 amp output capacity of the supply.)
D . . .TR3 and TR4 are configured as a differential pair.
TR3 base goes over and gets a regulated voltage reference from the Zener diode string from the wiper of the 50K pot.
Simultaneously TR4 base is taking a 22k resistor to go over and pick a fixed reference voltage from the Zener string BUT it is ALSO receiving a sample of the power
supplys voltage output at the emitter of TR6 via a 33k resistor. The difference between those two different voltage levels with "give and take" cause the 1K emitter resistors voltage and currrent to vary.
BUT that's actually where the differential pair aspect of this design comes into play, since TR4 and TR3 share that COMMON 1K resistor the voltage /current fluctuations, EQUALLY affect
the two collector load resistors of TR3 . . up at top page.
That voltage divider pair gets some voltage transition stability with the 10 ufd cap but it then feeds into the ***** Sziklai ***** configured TR5 - TR6 for final series power control.

And that's being just about how THIS ball rolls.


So I now have about 1/3 of the schematic partitioned and what do I see but SM0VPO . . . . .none other than Harry Lythall . . .frum Sveden !

So four internet clicks and I am in Sweden and then to his home page and then the logical "Power Circuits" and then

BAM there I am . . . . . .

http://213.114.136.42/use/psu3.htm

So read it all there . . . .that info, along with my initial write up above . . . . should tell all.

There is even enough show through image of the PCB's foil to replicate his lay board layout.


73's de Edd
 
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