Author Archives: DP

Lab power supply build using old power bricks

via Dangerous Prototypes

Building a lab power supply from old computer power bricks:

Over the years, I have accumulated many used computer power bricks. Although I could just use them by themselves to power other electronics with similar voltage and current requirements, I thought I would combine a few of them together as the input to a linear regulator so that I can make a powerful lab power supply.

See the full post on Kerry Wong’s blog.

Reverse-engineering a low-power LED flasher chip

via Dangerous Prototypes

Ken writes, “How do you make an LED blink? A vintage way is the LM3909, a chip from 1975 that can flash an LED for a year from a single flashlight battery. This chip has some surprising features, such as a charge pump that lets you power a 2-volt LED from a 1.5-volt battery. This IC was designed for simplicity, using just an LED, external capacitor, and battery. In this blog post, I reverse-engineer its silicon die.”

More details on Ken Shirriff’s blog.

App note: MOSFETs withstand stress of linear-mode operation

via Dangerous Prototypes

App note from IXYS talking about MOSFET operating in linear region in application like electronic load. Link here (PDF)

Power MOSFETs are most often used in switchedmode applications where they function as on-off switches. But in applications like electronic loads, linear regulators or Class A amplifiers, power MOSFETs must operate in their linear region. In this operating mode, the MOSFETs are subjected to high thermal stress due to the simultaneous occurrence of high drain voltage and current, resulting in high power dissipation.
When the thermo-electrical stress exceeds some critical limit, thermal hot spots occur in the silicon causing the devices to fail. To prevent such failure, MOSFETs operating in the linear region require high power dissipation capability and an extended forward-bias safe operating area (FBSOA).

App note: Digital inrush controller

via Dangerous Prototypes

App note from IXYS about their unique digital inrush controller using Zilog’s 8-bit Z8F3281 MCU. Link here (PDF)

Digital control allows distinctive solutions to control inrush current in typical AC-DC rectifier with capacitive load by limiting capacitor pre-charge current to a predetermined value at each half sine-wave cycle. Capacitor charge is spread over a number of cycles until capacitor is charged proportion of peak value of AC voltage source. Capacitor is charged according to timedependent pulse train. The pulses are designed in a way to provide substantially equal voltage increment applied to capacitor to keep peak of charging current about the same value at each cycle. Number of cycles depends on capacitor value and charge current. For a given capacitor value which is selected depending on desired ripples amplitude, the charge current is a function of number of pulses and its timing position with respect to rectified sine wave. Detailed algorithm of creating pulse train for Digital Inrush Control is described in the Principles of Operation section.

Adjustable Lab power supply

via Dangerous Prototypes

Xristost built a DIY adjustable lab power supply:

With the original schematic at hand I took the liberty to make a few changes. First of all I replaced two transistor-zener regulators with LM317L/LM337L. Circuits are calculated to produce 33V positive and 3V negative voltages. Thus total supply voltage for the opamps does not exceed 36V and therefor we may use standard ones. I also made changes in the LED drive circuit and a few other minor changes.

See the full post on DIYfan blog.