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Dave's Circuits:  Frequency to Voltage     Period to Voltage     Sine to Square Wave      Voltage Converters     Voltage to Frequency    DC to DC Power Supplies   High Voltage Power Supplies   
Switchmode Power Supplies  Voltage Controlled Oscillators

• 0.5V Negative Supply
  Although not very efficient, this simple circuit, consisting of two LEDs and a photo diode, generates a negative voltage with a current level of a couple milliamps.  It is ideal for supplying a negative rail to low power “rail to rail” op amp circuits, which need to have a true zero volts output.

• Battery Powered Plus-Minus 15v Supply
  Many classic operational amplifier circuits call for a split positive and negative 15 volt supply.  The circuit below makes the job of generating such a supply much easier by using an off-the-shelf DC to DC converter, powered from a cheap 6v battery made from four AA cells.  The converter, part number VESD1-S5-D15-SIP, is available from Digikey, their catalog number 102-1410, for about $6.00.  To insure clean voltages, I follow the output of the converter with two voltage regulators, also available from Digikey.  The result is a very nice supply rated at 30ma from each supply voltage.  This should be plenty of current for most circuits.

• Charge Pump Efficiently Divides Supply Voltage
  This circuit uses a few FETs and logic devices to down convert a DC voltage to about one half its value.

• Run Switching Type AC Power Adapters on DC  NEW
  I have received a couple emails from people looking for inexpensive DC to DC converters, which can convert 40v to 60v DC into say +5 or +12v.  Such input voltages are often found in new automotive and industrial applications with a typical DC voltage of 48 volts. It turns out that many, not all, but many, standard AC line operated power adapters, which use switch mode techniques, will indeed work great when supplied with DC instead of AC. The unit below works down to about 30v DC and delivers 500ma at 5v. If you draw less current, it will operate at even lower DC input voltages....