1541-II-Supply

Plug-in power supply for the Commodore 1541-II

Introduction

This is a plug-in power supply for the Commodore 1541-II floppy disk drive. It's a bit of a spin-off of my 250466+ board as I re-used the overvoltage protection circuit and 5V creation from this project and put in on a small PCB that can be plugged directly into the power supply connector of a 1541-II. As for the 250466+ board, there is only a 12V DC power supply needed.

Features:

• Single 12V supply with common 5.6mm/2.1mm DC connector
• Small form factor
• Reverse polarity protection
• Over-voltage protection (~13.3V)
• Over-current protection (fuse)

Design

As this is a direct copy of the circuit used in the 250466+ board, it's also based on through-hole components. Then again, using SMD components would not have saved much space anyway.
The schematic is taken 1:1 from the 250466+ board:

The reverse current protection is realized through the body diode of the N-FET Q1 and the FUSE F1.
The over-voltage protection is implemented using a voltage reference TLE431 and a comparator TLC3702 (with push/pull output) which triggers the FET to blow the fuse. There is a 15V Zener diode in the supply of the comparator to protect both, the comparator and the FET's gate from higher voltages.

If the voltage rises above ~13.3V, the output of the comparator jumps from ground to its supply voltage. This triggers the FET which creates a deliberate short circuit to ground to blow the fuse.

Case

I designed a 3D printed case with FreeCAD that consists of two parts held together using self tapping M2 screws.

The FreeCAD design files and STL files can be found in the repository.

Hints and Links

• The schematic and PCB were designed with DipTrace. There is a free version available with up to 300 pins or even 500 pins if you register (this design uses only 58 pins).
• Use 1% resistors for the critical resistors in the voltage protection circuit (R2, R3, R4, R5, R6).
• As 5V DC/DC I used the Recom R-78B50-15L.
• Don't replace the comparator TLC3702 with a type that has an open collector or open drain output. The push/pull output is mandatory!
• For the 1541-II-connector I used an IEC 60130-9 connector by Lumberg (has to be taken apart).
• For the 12V DC connector I used a default 5.6mm/2.1mm connector.
• For fuse holder I used this one from Schurter with a very fast 2A fuse.
• When soldering in the IEC and DC connectors, leave as much space between the PCB and the connector as possible!!!
• The pins of the N-FET have to be bent to fit into the case. Bend them close to the body to leave some space above the FET for the case to fit.
• For the electrolytic capacitors I used one from Panasonic's SU series of bipolar aluminium capacitors.
• The 5.6µH inductor is the same as used on the 250466+ board.
• For the diodes, I used a Vishay BZX 85C15 (D1) and an OnSemi 1N 5339BG (D2).
• The TLE431 is a default tyoe. Any version in TO-92 package should fit.
• Use a proper, stable and safe 12V supply with at least 1A and a fitting (very) fast acting fuse. I used a 2A supply from Meanwell (MW GST25E12)  which is a bit on the safe side.
• The case is a tight fit. Cut off all the wires on the solder side as short as possible after soldering.

Repository

All files related to this project can be found in the BitBucket repository
https://bitbucket.org/fade0ff/1541-ii-supply

License Information

This is a spare time project I did without any commercial interest.
Everything is released under the Creative Commons CC-BY license.

In a nutshell this means that you can do share, modify and use everything released under this license even for commercial projects.
You just need to give me appropriate credit, indicate what changes you made and agree not to try to force a more restrictive license on my work.
See the CC BY license for details.