The inverters Ula and Ulb form a 20 kHz oscillator, and the square wave output of the oscillator (on the one hand shaped by D2. R4 and R5, and on the other hand by D5. R6 and R7) drives the power FETs Q2 and Q3. The two P-channel and N-channel FETs are alternately turned on in a push-pull structure. When Q2 is turned on, the positive charge of Cout forces diode D4 to also conduct, thereby generating a positive voltage at terminal A that is determined by Zener diode D5. Similarly, when Q3 is turned on, the negative charge on Cout forces D7 to turn on. Therefore, a negative voltage is generated at the B terminal, the level of which is determined by D6.
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