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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.
Classic Linear 5v Supply Using
6.3vac Transformer
A classic method for producing a regulated +5v DC supply is shown below. This
circuit consists of an iron core transformer, a bridge rectifier, a filter capacitor
and a voltage regulator. Many people are tempted to use a very popular 6.3v
transformer for this +5v supply but they will often discover that there just isn’t
enough voltage from the transformer to make the circuit work properly under all but
very light load conditions. Higher transformer voltages will work but at the
expense of much more power being dissipated in the voltage regulator....
Run Switching Type AC Power Adapters on DC
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....
