Misc circuits

• +5v from RS-232 using LM78L05
• Advanced polarity protection with MOSFETs - Advanced Power Switching and Polarity Protection for Effects
• A Simple Capacitance Multiplier Power Supply For Class-A Amplifiers - A mentohd which providess good noise filtering but no actual voltage regulation
• Automaatti-sulake - This is an automatic fuse circuit for 24V power. Thsi circuit uses transistors which control an output relay. The text of this document is in Finnish.
• Circuit combines power supply and audio amplifier - This circuit can helpful if you must transfer dc power and audio over a pair of copper wires. The circuit uses only one IC, the well-known LM317, a low-cost power-supply regulator. Using this chip, you can modulate the adjustment-pin input with the audio signal from an electret condenser microphone, connected between the output and the adjustment terminals of the IC.
• Clamping circuit dissipates minimal power - quasi-linear regulator
• Drive high-voltage varactor diodes from just 5V - how to connect two International Rectifier (El Segundo, CA) PVI1050s photovoltaic-isolator ICs in series to provide a 20V tuning drive for the varactor diode
• Electronic Fuse for Power Supply - This circuit offers effective protection against overcurrent in power supply with output voltage through to 45V DC and output current form 0.1A to 5A.
• High-Voltage EL Lamp Driver
• Micropower, 10ppm/°C, +/-5v reference
• MOSFET replaces switch - you can use a single-pole switch to turn a bipolar power supply on and off without consuming extra power
• Power switch provides soft start
• Quickly discharge power-supply capacitors - A perennial challenge in power-supply design is the safe and speedy discharge, or "dump," at turn-off of the large amount of energy stored in the postrectification filter capacitors. If you let the capacitors self-discharge, dangerous voltages can persist on unloaded electrolytic filter capacitors for hours or even days. This design idea gives one alternative approach for faster discharge than normal bleeder resistors provide.
• Rectification using a Gyrator Circuit
• Series Lamp Limiter - connect a 100W lamp bulb in series with the supply to the equipment being repaired to avoid very nadty high short circuit current is something goes seriously wrong, useful for power supply testing and repairing
• Smoke Detector Power Supply - This power supply normally supplied power from AC mains power source thrpgh transformer nad charges a battery. When AC mains power dissapears, the power is supplied from the battery.
• Soft-Start Circuit For Power Amps - This circuit reduces the current spike large transformers take when switched on.
• Soft Power On Tester for Amplifiers - The worst thing that can happen is that when you turn an electronics device you are fixing on, it immediately pops a fuse - or worse yet a valuable part you've just installed! If you don't have a variac with a current meter so that you can make power on gradual, the next best thing is this widget. It can be whipped up from parts in your local home supplies store.
• Time-delay relay reduces inrush current - A transformer switching onto a line can sometimes cause a circuit breaker to trip or a fuse to blow. This phenomenon occurs even if the transformer presents no load, such as when the secondary is open. The problem arises because of the heavy magnetizing inrush current in the transformer. This design solves the problem in one way.
• Transistors offer thermal protection for controller - You can use standard bipolar transistors to implement a low-cost thermal-shutdown circuit for switched mode power supply.
• Transistor latch improves on/off circuitry
• Versatile power-supply load uses light bulbs - Improvising loads for bench-testing and designing power supplies is often a frustrating and sometimes hazardous experience. Many electronic loads are on the market but are usually expensive and of laboratory-type precision and often represent overkill for the average designer. Incandescent light bulbs make excellent loads, able to handle large amounts of power. Moreover, they come in small packages and require no heat sinks. The drawback is that the resistance of an incandescent lamp changes dramatically with the power input. A simple approach to this control problem is to pulse-width-modulate a power MOSFET in series with the load.
• Voltage follower with 1G ohm input resistance