Ⅰ. The principle of generating circuit diagram of negative voltage

We frequently need to employ negative voltages in electronic circuits. For instance, we frequently need to create a negative voltage for him when we employ op amps. Here is a straightforward illustration of his circuit from a positive 5V voltage to a negative 5V voltage.

I normally choose to utilize a specific negative voltage generation chip, such as the ICL7600, LT1054, and so forth, when I need to use negative voltage, however these chips are very expensive. Oh, I nearly completely overlooked the MC34063. The most usage is of this chip. I won't go into detail about the information found in the datasheet regarding the 34063's negative pressure producing circuit. Let's take a look at the two types of negative pressure generating circuits that we commonly use in single-chip electronic circuits.

Figure. 1

PWM output is currently present in many single-chip microcomputers. PWM is frequently ineffective when we utilize a single-chip microcomputer. It is a wise decision to employ it to help create negative pressure.

One of the simplest circuits for producing negative voltage is the one shown above. He uses the least of the originals. It's very easy to do; all we need to give him is a square wave at roughly 1 kHz. It should be noted that this circuit has a very low generation load capacity, and the voltage drop after adding the load is also quite substantial.

The following circuit is produced for the above reasons:

Figure. 2

Ⅱ. Analysis of Negative Voltage Generation Circuit

Voltage is a physical quantity that represents the energy difference of a unit charge in an electrostatic field due to various potentials. It is sometimes referred to as potential difference or potential difference. The effort a unit positive charge must perform to move from point A to point B due to the force of the electric field determines its magnitude, and the direction of the voltage is described as travelling from high potential to low potential.

Simply explained, the voltage is the difference between potentials with respect to a reference point at a certain location. E - E parameter equals V. Typically, we use the negative pole of the power source as our point of reference. The voltage of the power source is Vcc=E power positive - E power negative.

Simply allow it to have a lower potential in relation to the negative pole of the power supply if you wish to generate a negative voltage. Another power source must be involved for the cost to be reduced. The basic idea is to link two power supply in series with one another. The reference power supply 1's negative pole and the power supply 2's positive pole are connected in series. The negative voltage is present at power supply 2's negative terminal.

Figure. 3

A circuit that produces negative voltage: By charging the capacitor, a new power source is equivalently created. The capacitor becomes comparable to power supply 2 once it is linked in series with GND. There is a negative voltage produced.

Figure. 4

1. Capacitor charging: The charging circuit is VCC-Q2-C1-D2-GND, and when PWM is low, Q2 is turned on, Q1 is turned off, and VCC charges C1 through Q2. Right negative and left positive on C1.

Figure. 5

2. The charge on Capacitor C1 is complete.

Figure. 6

3. The high potential pole of the capacitor C1 is linked in series with the reference point. C1 serves as the power source. A negative voltage results from C1 discharging and freewheeling from C2.

Q2 is switched off, Q1 is turned on, and C1 starts to discharge when the PWM is low. C1-C2-D1 is the discharge loop, and C2 is actually being charged during this operation. The bottom of C2 is positive and the top is negative once it has been fully charged. The voltage of -5V can be output if the VCC potential is 5:00 volts.

Figure. 7

Ⅲ. Scheme for generating negative voltage (-5V)

Figure. 8

The output capability of 7660 and MAX232 is limited, and it is very difficult to make an oscilloscope with a high-speed op amp, so Wei Kun also has to use 4 slices in parallel to expand the current.

The first version is 7660 two in parallel.

Ordinary DC/DC chips can produce negative voltage, and they do it with accuracy equal to that of positive voltage. In addition, they have a very high driving capability that can reach more than 300mA.

The generic switching power supply chip has a negative voltage generation capability. The switching power supply's PWM output cannot be used to drive the charge pump at all. Additionally, it has a relatively low cost and can produce a huge current. The necessary amount of ripple is unknown to me. The ripple is fairly tiny after LC filters the charge pump. Because the 7660 is a charge pump, the current is really low.

How should the digital ground and the analog ground be handled? The +5V of the digital power supply and the +5V of the analog power supply are powered separately in the design of the complete oscilloscope.

The analog ground and the digital ground must be connected in order for the circuit to function.

The two grounds should be joined together at a stable ground reference since the ground return current of the digital part cannot pass through the analog part.

Ⅳ. The meaning of negative voltage

1. Rules created by humans. For instance, the telephone system is powered by -48V, preventing galvanic corrosion of the telephone line. Of course, answering the phone backwards is also an option; all that is required is a modification in the voltage reference point.

2. The interface for communication is necessary. For instance, negative voltage is required for the RS232 interface. -3V15V equals 1, and +3V+15V equals 0. When the communication interface was first created, this protocol was used, and it can only be adhered to. PS: Interface chips with their own charge pumps and the ability to produce negative voltage include those like the MAX232.

3. Give (non-rail-to-rail) op amps electricity rails. Rail-to-rail input/output capabilities are not available in traditional op amps like the OP07. The output voltage range is always 2V lower and the input voltage range is always 1V lower than the power supply voltage range. This means that if VEE uses 0V, the input voltage must be greater than 1V and the output voltage cannot be less than 2V. Some requirements for circuit design might not be met in this situation. It is necessary to provide the op amp with a negative voltage, such as -5V, in order for the op amp to function normally under input/output situations close to 0V. But as rail-to-rail op amps gain prominence, this circumstance is fading away.

4. This one has a self-destructing circuit and Chinese traits. Generally speaking, the chip's internal safety circuit is not well-protected against negative voltage, thus the chip can be successfully destroyed as long as the current is somewhat higher and a low negative voltage is not required.