Unique method of obtaining positive and negative power in a single power supply loop

The core device of the polarity conversion circuit shown in FIG. 1 is an ordinary NOT gate. Since the input and output terminals are shorted together, the output voltage of the NOT gate is equal to the input voltage (Vi = VO); thus, the NOT gate is forced to work at the center point of the transfer characteristic curve, so the output voltage is limited to The threshold level of the gate circuit is equal to half the power supply voltage. If we use the output of the NOT gate as the DC ground terminal, we can convert the power supply voltage VCC to the dual supply voltage of ±VCC/2; Plays a role of a storage voltage regulator, the output impedance of the circuit is low, and the output voltage is also relatively stable.

The non-gates in the figure can use ordinary gate circuits such as 74HC00 or CD4069. Considering the limited ability of CMOS NOT gate drivers, it is better to use several NOT gates in parallel to increase the effective output current. Capacitors C1 and C2 in the figure From the decoupling effect, the capacity can be appropriately taken larger.

The operational amplifier shown in Figure 2 has a symmetrical series resistor divider connected to the noninverting input, and the op amp itself is connected to a voltage follower; The potentials between the partial pressure points are strictly equal. Since the output terminal of the operational amplifier is grounded, the power supply VCC of the operational amplifier is accordingly divided into two symmetrical positive and negative power supplies ±VCC/2.

When the output current of the op amp can not meet the actual demand, it cannot be used in parallel as simple as the gate circuit; at this time, the general-purpose low-power op amp can be replaced by a PA amplifier with a larger output current, such as the common TDA2030A. Similar to Figure 1, C1 and C2 are decoupling capacitors, and the capacitor C3 that loads the non-inverting output of the op amp serves as a mechanism to suppress interference and filter. For most OTL amplifier devices, the symmetry is usually set inside the device. Set the circuit structure, which makes its output terminal DC potential approximately half of the power supply voltage; according to the above principle, we can fully use the set to successfully put a single power into a bipolar positive and negative power supply of equal size, the specific circuit shown in Figure 3 As shown.

In fact, because of the discreteness of the content parameters and the influence of the bootstrap circuit structure, the voltage at the output terminal of the set is not an absolute VCC/2, resulting in a positive and negative output voltage imbalance. To do this, we need to connect a 10-100kΩ potentiometer in series between the positive and negative supplies. Connect the LM386 pin 3 input to the center tap of the potentiometer and leave pin 2 floating. After making the above improvements to the circuit, by adjusting the DC input level of the power amplifier, positive and negative voltage values ​​of very close size can be obtained at the output of the chip.