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DC Power Supply: SCR-Regulated, Voltage and Current Bridges with Automatic Cross-Over (Kupferberg & Ash, Forbro, US 3,305,763, 1967)
A variable DC supply regulated by controlled rectifiers instead of a series transistor. Two of the four rectifiers in the bridge are silicon controlled rectifiers; how late in each half-cycle they are fired sets the output. A voltage bridge and a current bridge each make an error signal, an analog OR gate passes whichever is larger, and the supply crosses over automatically between holding the voltage and holding the current.
Result: a variable voltage / current regulated DC supply with automatic cross-over.
Source: K. Kupferberg and J. Ash (Forbro Design), US 3,305,763 (1967), Fig. 1. Unknown: component values and the firing-angle circuit. Picture: the patent drawing.
Advanced
Unknown
Instructions
1
1
Build the controlled rectifier bridge
Build the controlled rectifier bridge
In a case, wire the cord through a switch and fuse to a transformer. Feed its secondary into a bridge of two ordinary rectifiers and two silicon controlled rectifiers. Smooth the negative output through a choke and a capacitor, then through a current-sensing resistor (with a second capacitor forming a further filter) to the negative output terminal; the positive goes straight to the positive terminal. Ours: the case, switch and fuse. Not given: the ratings.
Materials for this step:
Aluminium Enclosure Box1 piece
Flexible Cord with Plug1 piece
Toggle Switch1 piece
Fuse1 piece
Step-Down Transformer1 piece
Diode2 pieces
Thyristor (SCR)2 pieces
Filter Choke1 piece
Electrolytic Capacitor2 pieces
Binding Post2 output + and -Tools needed:
Hand Drill
Screwdriver Set2
2
Build the two bridges
Build the two bridges
Current bridge: the sensing resistor, a reference Zener, a fixed resistor and the variable current-control resistor. Voltage bridge: the load across the output, the variable voltage-control resistor, a fixed resistor and a second reference Zener. Feed both Zeners from a small separate supply. Not given: the values, the Zener supply.
Materials for this step:
Zener Diode2 pieces
Rheostat2 voltage and current controls
Resistor1 sensing and bridge resistorsTools needed:
Soldering Iron3
3
Build the control chain and use it
Build the control chain and use it
Invert the current bridge's error in a phase-reversing amplifier and feed it, with the voltage bridge's error, to an analog OR gate that passes the larger. Amplify the result and feed it to a firing-angle control circuit that fires the two controlled rectifiers' gates later or earlier in each half-cycle. In use, set the voltage and the current: for any load larger than the cross-over resistance (voltage setting divided by current setting) the supply holds the voltage, for a smaller one the current. Not given: the amplifier, OR-gate and firing circuits in this form.
Materials for this step:
Printed Circuit Board1 piece
Transistor Assortment1 amplifiers
Unknown Material1 OR gate and firing-angle circuit
Solder Wire1 as neededTools needed:
Soldering IronMaterials
17- 1 piecePlaceholder
- 1 piecePlaceholder
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- 1 piecePlaceholder
- 1 piecePlaceholder
- 2 piecesPlaceholder
- 2 piecesPlaceholder
- 1 piecePlaceholder
- 2 piecesPlaceholder
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- 2 piecesPlaceholder
- 2 voltage and current controlsPlaceholder
- 1 sensing and bridge resistorsPlaceholder
- 1 piecePlaceholder
- 1 amplifiersPlaceholder
- 1 OR gate and firing-angle circuitPlaceholder
- 1 as neededPlaceholder
Tools Required
3- Placeholder
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- 2 vendors sell this, none ship to you yetPlaceholder
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