PUSH-PULL output stage with transistors operating as switches. Drives Diode Capacitor ladder to produce complementary -19Vdc ( @ 150mA max ) from a 19 VDC laptop charger. The +/- 19 volt rails can power 7815 & 7915 regulators to provide a +/- 15 volt supply for powering opamp circuits. The 20 KHz Squarewave can be generated by any means, 555, logic gates or even a 2 transistor astable.
As there is likely to be a lot more current available from the charger ( mine can supply 3.42 A ) this could be used to generate other power rails like +5 V and +12 V, or even a variable supply of up to around 16.5 V
