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Similiar to a 7805, but more efficient. Output 3.3 volts.
My attempt was to make a three pin module which could be soldered into the place of a 78xx type of voltage regulator, making use of the switchmode control chips in order to implement a more efficient solution.
This one makes use of the TC105333 integrated circuit manufactured by Microchip. This contains all the components of the power supply except the switching transistor, freewheeling diode and inductor. The TC105503 can be used for 5 volts output, thus creating an efficient 7805 replacement which needs no heatsink.
The switching device is a TPS1101 PMOS Transistor manufactured by Texas Instruments.
The freewheeling (schottky) diode was extracted from an old hard drive board. The inductor has a resistance of about 1.8 ohms and was extracted from an ancient VCR board.
With no load, and an input supply of 6 volts, this circuit draws about 17 microamperes. With a resistor of 33 ohms connected (load 100 mA) the current is about 63 milliamperes. This computes to an efficiency of around 87%.
My attempt was to make a three pin module which could be soldered into the place of a 78xx type of voltage regulator, making use of the switchmode control chips in order to implement a more efficient solution.
This one makes use of the TC105333 integrated circuit manufactured by Microchip. This contains all the components of the power supply except the switching transistor, freewheeling diode and inductor. The TC105503 can be used for 5 volts output, thus creating an efficient 7805 replacement which needs no heatsink.
The switching device is a TPS1101 PMOS Transistor manufactured by Texas Instruments.
The freewheeling (schottky) diode was extracted from an old hard drive board. The inductor has a resistance of about 1.8 ohms and was extracted from an ancient VCR board.
With no load, and an input supply of 6 volts, this circuit draws about 17 microamperes. With a resistor of 33 ohms connected (load 100 mA) the current is about 63 milliamperes. This computes to an efficiency of around 87%.
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Signing UpStep 1The circuit
The figure shows the circuit, shamelessly copied off the datasheet provided by Microchip.
I have been more inventive with the parts. I had to get a modern P channel MOSFET from Texas Instruments because old hard drive boards were seriously deficient in this one critical component.
However, using the parts as specified would be necessary to get 1. A more compact layout 2. higher efficiency.
As it is, my circuit is small enough to fall off the desk and be lost among the crud on the floor. I feel an increase in efficiency to 90% would be wonderful, but three points less is good enough.
This small integrated circuit has a maximum tolerable input of around 12 volts. It has terminals for driving external power devices, and that makes it more versatile.
For example, replacing that inductor with a transformer and arranging things so that the bulk of the power and voltage is handled by a second hefty transistor and diode can make this little circuit control a power supply operating off the rectified mains.
I have been more inventive with the parts. I had to get a modern P channel MOSFET from Texas Instruments because old hard drive boards were seriously deficient in this one critical component.
However, using the parts as specified would be necessary to get 1. A more compact layout 2. higher efficiency.
As it is, my circuit is small enough to fall off the desk and be lost among the crud on the floor. I feel an increase in efficiency to 90% would be wonderful, but three points less is good enough.
This small integrated circuit has a maximum tolerable input of around 12 volts. It has terminals for driving external power devices, and that makes it more versatile.
For example, replacing that inductor with a transformer and arranging things so that the bulk of the power and voltage is handled by a second hefty transistor and diode can make this little circuit control a power supply operating off the rectified mains.
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You certainly proved the old Art of Electronics maxim that component values aren't nearly as important as mathematicians would have you believe. I'll have to do some random-salvaged-crap experimenting of my own...
Mimicing the 78xx pinout for a switching regulator is great. Dimension Engineering has some sepic-based designs in the same form factor, though they appear to be sold out at the moment.