Positive 12V to negative 12V circuit diagram

Positive 12V to negative 12V circuit diagram (I)

This circuit uses the TPS5340 step-down chip, and Figure 1 shows a simplified buck-boost circuit and the switch voltage that appears across the inductor. The similarity of this circuit to a standard buck converter becomes immediately clear. In fact, it is exactly the same as a buck converter, except that the output voltage and ground are reversed. This layout can also be used for a synchronous buck converter. This is where the similarity with the buck or synchronous buck converter side ends, because the operation of this circuit is different from that of a buck converter.

The voltage that appears across the inductor when the FET is switched is different from the voltage in the buck converter. Just as in the buck converter, it is necessary to balance the volt-microsecond (V-μs) product to prevent the inductor from saturating. When the FET is on (the ton interval shown in Figure 1), the full input voltage is applied to the inductor. This positive voltage on the "dot" side of the inductor causes the current to ramp up, which results in the V-μs product of the inductor's on time. During the FET off (toff) period, the voltage polarity of the inductor must be reversed to maintain the current, pulling the dot side negative. The inductor current ramps down and flows through the load and output capacitor and back through the diode. The V-μs product when the inductor is off must be equal to the V-μs product when it is on. Since Vin and Vout are constant, it is easy to derive the expression for the duty cycle (D): D = Vout / (Vout "Vin). This control circuit maintains output voltage regulation by calculating the correct duty cycle. The above expressions and the waveforms shown in Figure 1 assume operation in continuous conduction mode.

Figure 1 Buck-boost inductor requirements balance their volt-microsecond product

Interestingly, there are two ways to connect the input capacitor return that affect the rms current in the output capacitor. In contrast to the typical capacitor placement between +Vin and Gnd, the input capacitor can be connected between +Vin and “Vout”. Using this input capacitor configuration reduces the rms current in the output capacitor. However, because the input capacitor is connected to “Vout”, a capacitive voltage divider is formed on “Vout”. This creates a positive peak at the output during the turn-on time before the controller starts to function. To minimize this effect, it is usually best to use an input capacitor that is much smaller than the output capacitor, see the circuit in Figure 2. The input capacitor current alternates between sourcing dc output current and sinking the average input current. The rms current level is worst at low input voltages at the highest input current. Therefore, care should be taken when selecting the capacitor to not make its ESR too high. Ceramic or polymer capacitors are usually a good choice for this topology.

Figure 2 The dual role of the buck controller in buck-boost

Positive 12V to negative 12V circuit diagram (II)

MIC4680 can also be used to convert positive and negative voltages. Figure 5 shows a positive and negative voltage conversion circuit composed of MIC4680. This circuit can convert a +12V input voltage into a -12V output voltage and obtain an output current of 150mA.

Positive 12V to negative 12V circuit diagram (Part 3)

Use a transformer with a center tap to convert the 12V DC into 34V AC through PWM. The center tap is used as the ground, and each side is 17V. Then, through half-wave rectification and filtering, positive and negative 12V are obtained.

Black is usually negative, and black and white (black wire and white dot wire) are positive. A normal transformer or power input interface has a label to mark the polarity.

Conventionally, the inside is positive and the outside is negative, but there are special cases where the general transformer has a switch to change the polarity. It is recommended to measure the polarity with a multimeter before use to avoid the danger of incorrect connection.