NOTE: Here is an Email from a person who built this.
These Errors are Now Corrected, As of Nov 29 2005.
Thanks Bob.........Gary
From : Bob
Sent : November 28, 2005 8:16:20 PM
To : "GARY XX"
Hello Gary,
Thank you! Your power supply board worked, and I was able to use it to replace the MC1466L in my power supply.
I found a small number of errors and notes that I'll pass along. At least they are errors when trying to use the board
as an MC1466L. The resistor from the junction of D12 and D13 to point 7 should be 7.50K as the schematic shows, but it
is marked 1.8K on the part diagram. 7.50K works; 1.8K stopped the current limit circuit from working.
The 15K resistor from Q1-e and Q2-e to point 7 is correct on the schematic, but it is shown on the part diagram as 10K.
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The 7.50K resistor from the base of Q4 to point 12 is correct on the schematic, but it is shown with the wrong value
(15K) on the part diagram, and it is connected to the wrong place (Q3-b instead of Q4-b) on the PC board. This correction
requires a small trace change on the circuit board (cut trace from 7.50K to Q3-b, jumper to Q4-b).
On the schematic, the junction of point 9 and the 499 ohm resistor should also connect to the bus running across the
schematic from D3 and Z1 on the left, to Q15-e and the 7.50K resistor on the right. This is a schematic error only;
the PC board has this connection.
Several of the transistor pads are backwards from "what I expected" (Q1, Q2, Q3, Q5, Q7, Q8, Q9, Q10, Q11 and Q13).
I used 2N2222A and 2N2907 transistors in TO-18 cases, and I did not notice the e-b-c arrangement of the TO-92 devices
in the layout diagram. I powered the unit with these devices backwards, but no harm was done. I unsoldered these units,
bent the base connections under the transistor bodies, and reinserted them, and the board worked. This is not a big deal,
but the reverse e-b-c connections should be noted in a readme file.
These problems did not damage the parts in live operation. I was able to correct the transistor lead connections, and
I had enough 7.50K resistors to make the needed part changes.
My 50-volt, two-amp supply is now working again, and I am very happy!
Bob
NOTE: The Transistor Pads are Actually Correct for the Specified Transistors.
Note: This is a Heavy Duty, "Lab Grade Supply" and can handle Hundreds of Volts and/or Very Large Currents.
The Info Presented Here Is Greater than the Origional IC.
I have added Most of the Extra Protection circuits as well as a E/I Mode Feature.
I Believe this documentation is Correct, But I will not assume any lialibility for Errors or Omissions.
Also Since this is Line Operated, Take Special care in this wiring to prevent Possible Electric Shock.
Although this Power supply LOOKS Complicated, It is Not that Difficult or Expensive to build.
The Transistors,Zeners and Diodes are Very Common types.
However, As with Any Power Supply, The "Main Power Transformer", "T2" in this Circuit, may be costly.
If Real Accuracy is Critical, the 1% Resistors can be Substituted with the Nearest 5% Values.
I Designed the board for a "Hammond" Transformer for "T1", because it is a good product made here in Canada
and readily Available to me. But you could substitue other types with the Approximate same voltage.
"RS" is Set to Drop 0.25 Volts at Full Current Out.
For 5 amps Maximum Current Out, RS would be .25 Divided by 5 = 0.05 Ohms
For 10 Amps Maximum Current Out, RS would be .25 Divided by 5 = 0.025 Ohms
"RX is a Value Equivalant to 1000 Ohms Per Volt.
As an Example, a 25 Volt Supply would use a 25 K Pot.
The Collector Resistor on Q16 is set for RX Divided by 10.
So on the Above Example, this resistor would be 2K5.
"C-Out" is Typically set at 100 uF Per Ampere Out.
So for 5 amps Maximum out, C-Out would be 500 uF.
"C-Supply" Should be a Reasonable Capacitance for the Maximum Supply Current.
I Would Recommend 1000 uF per Ampere.
For Optimum Regulation, Select the output Transistors such that:
Current Out, at Pin 5 Should not Exceed 0.5 mA. DC. (500 uA)
Therefore:
I Maximum
----------- = Less Than 0.5 mA. DC. (.0005 amps or 500 uA)
B1 B2
Where Imax = Maximum Short Circuit Current mA. DC.
Beta = HFE = Is the ratio of Collector Current to Base Current
For Example: If a 1 mA base Current cause the Collector Current
to go to 100 mA, that the Beta is 100.
Ic
Beta = -----
Ib
B1 = Minimum Beta of Q17
B2 = Minimum Beta of Q18
Although Pin 5 Will Source about 1.5 mA. DC,
Currents Greater than 500 uA will Result in Degration of the Regulation.
Examples:
A 2N3904 has a Minimum Beta of about 100
A 2N3055 has a Beta of about 20
100 X 20 X .5 mA (.0005 amps) = 1 Amp
In My Unit, I Used an MJE1100 with a Beta of 750
and 2N6328 with a Beta of about 35.
750 X 35 X .5 mA (.0005 amps) = 13 Amps
I also Paralleled 2 of the 2N6328's to give better Heat dissipation.
"I Assume No Liability from the Construction or Use
of this circuit"
Build and Use it at your own risk!
I Built a Dual, Isolated Version of this for my own use:
"Seperate Power Transformers for Each one"
They are Each rated at 35 Volts and 8 Amps, Continuous Output.
I can Parallel them for 16 Amps.
Or Series them for 70 Volts
Or use them in series connection as a Plus and Minus Supply, with center as ground.
I have also designed an Upgraded Version of this circuit with additional parts to display if it is operating
in Voltage Mode or Current Mode.
I Will be posting this as the Final Circuit circuit, a bit later and the PCB for it.
You can Either Add these few additional parts, Or leave them off. The choice is yours.
The Output Voltage and Current requires that Q17 and Q18 be capable of Handling both the Voltage and Current.
These create a Darlington pair and can be Multiple, Parallel Transistors.
The Main Requirement for High Output Current is:
First, having enough "Gain" in the Darlington Pair
Second, Parallel Transistors Capable of both the Voltage and Current Requirements.
More info to come about this later.
T1 Supplies power to the Control Circuitry and is Typically just a Small 50 mA, 18 VAC Transformer.
T1 is an Isolated Supply from the Actual Power Supply Transformer.
T2 is the Actual Supply Transformer and Must be capable of whatever Voltage and Current you require.
Because of Supply Filtering it should be Over-Rated in Current by at least 25%.
This is True for All Analogue Power Supplies, if you want the rated output.
The Filter Caps on the Supply for T2 should be at least 100 uF per Amp.
So for a 10 Amp Supply, it requires a "Minimum" 1000 uf Cap.
But I would Recommend Considerably More Capacitance.
Resistor "RS" is set to Drop 0.25 Volts at the Rated Amperage you have chosen.
If this resistor is well rated and doesn't change resistance with the Heat, resulting from Higher
Currents, A Milli-Voltmeter placed in Parallel with it can be Acurately Calibrated for the Output Current.
I used a 3 1/2 Digit, 199mv Digital Panal Meter for this purpose.
It Works Very Well and there is No Output Voltage Drop that always occurs when you place an
Amp-Meter in series with any supply.
In this case, This voltage drop is corrected within the circuit.
Additionally I use 10 Turn Pots for the Voltage and Current. Give a Very Accurate adjustment of both.
After Running this Circuit for over 20 years, The only failure I had was a set of
Output Transistors, Caused by a Very High Voltage Spike from a circuit I was Driving.
To Reduce Heat Sink Size, you can Add a Fan, Like I have done on Mine.
I also put a Thermal Switch on the Heatsink so the fan Only runs when necessary.
Design Considerations:
The Schematic
This is Updated to have the Current/Voltage Indicator.
Hopefully I have All Errors Corrected.
Here is a Picture of this Circuit in Operation.
This is a Slightly Advanced Circuit with a Current/Voltage LED,
telling you what the Mode of operation is.
Also,I am just using a Battery as the Supply's Actual Power Source.
And I am just using a Single TIP121 Darlington Transistor, just for Demonstration Purposes.
The PCB
Note: I have a 56 Ohm resistor that is not on the Schematic.
This is because I used a 20 volt transformer, not 18 Volts.
"M" on the PCB is for a Milli-Voltmeter, Calibrated to Measure Current.
All Imformation in this Article is "Copyright protected".
Chemelec
*Copyright © 2005*
