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Sunday, December 23, 2018

Experiments with the LM2575

The standard buck regulator circuit delivers a +5V output. This is a rather straightforward circuit and will operate with a wide spread of component values. Optimal values should be selected however to get minimal ripple, minimal noise to the power source, maximum efficiency etc. Note that the quiesent current is about 10 to 14mA.

Here is a nice way of using this regulator, Experiments with the LM2575 this can be used for CMOS opamps as you have a -5V too. That means a portable instrument may find this design useful.

The TI Datasheet Layout Guidelines

LM2575 Switching Regulator

LM2575 - Step-Down Adjustable Voltage Switching Regulator with Output Enable

The Spirit of Hacking and Fixing, Giving back Life to Old Instruments.

Fluke 8050A LCD display replaced with LED seven-segment

"Recently I was able to cheaply buy a second hand Fluke 8050A made in the early eighties. It is a nice 4.5 desktop digit meter, but a typical problem seems to be that the LCD wears out and goes black. Replacement LCD displays are hard to find, not cheap and probably lead to similar problems in due time."

Friday, December 07, 2018

LM317 based Regulated Power Supply

This is a Regulated Power Supply based on the LM317 IC. It will need a Boost Power Transistor and heatsink for higher currents. It is a versatile building block for stable instrumentation supplies. Consumer Electronic gadgets can use a SMPS chip. In case you wish to use a SMPS for a Precision Instrumentation Block, then take extreme care on Shielding and EMI-RFI.

LM317 based Regulated Power Supply

This is a General Purpose Chip, Series Regulation. It can be varied or trimmed. There is an Internal temperature compensated reference. The minimum trim value is around 1.2. In case you want a Low value voltage like 0.5 with a good current, then use a good negative supply to offset the 1.2 V.

See more at my Power Supplies Section.

The transformer can be s Split Bobbin with Pri-Sec copper shield foil.  This can be earthed along with the metal enclosure. C4 sends any hi-freq components to earth.  It is better if you do not earth the ground but use such capacitors. A Supply should simulate a a battery with both ends floating wrt Earth. A option to eartth the ground is fine. This also helps the user to configure his own dual supplies.

Q1 and R5 form a Short Circuit OR current fold back OR constant current mechanism. TP1 can be used to vary the output voltage.  Better use something like a Bourns 10T trimpot. An open preset may introduce a noise due to dust and vibration. I don’t remember why i added a zener DZ1, a diode may suffice.

Tuesday, December 04, 2018

MyCPU - A Computer made of Logic Gates

Look no CPU! - Built with MyCPU which is made of discrete logic gates as the Bricks. Homebrew Computer for Education and Experimenting. Dennis Kuschel is  the developer of MyCPU.

Homebrew Computer - MyCPU

The MyCPU is a "Central Processing Unit" that is completely built with discrete logic gates. Over the years the project has grown, and now the MyCPU is the brain of a real Personal Computer. The computer has the following capabilities and features

Homebrew Computer - MyCPU

This can also be roasted on a single FPGA Board.

The “MyCPU v2.3” is ideal for education, and is a nice project for enthusiastic hobbyists. The system uses COM1 for terminal communication and COM2 for file service. The personal computer acts as file server. There are several applications you can use on the MyCPU.