How to achieve current balance for multiple power supply outputs?

乱世煮酒论天下

How to achieve current balance for multiple power supply outputs? [Copy link]

 

If the load requires a large amount of power, and a single power supply cannot meet the demand, but there is no large power supply for the time being, then how can two or more identical power supplies achieve equal output and current sharing without backflow? Is there any solution and what is the principle?
For example, the two LDO output chips are both converted from 3.3 to 1.8V, but since the chips cannot be completely consistent, one is always a little higher than the other, which may cause only one power chip output during operation, which is far from meeting the load requirements. What are the measures for this application?
Another example is a charging pack, which is used for energy storage. When the output current is required to be larger than the output current of a single battery pack, the battery pack will not share the current and may even backflow. I seem to remember that the solution is to add reactance to the output of the two battery packs respectively, in the order of the same end, so that there will be no backflow and the current sharing effect can also meet the requirements.

fxyc87

1. The output voltage must be accurate enough, and the error cannot be too large

2. Connect a small resistor in series to each output, and then connect a capacitor to the final load after the small resistor comes out.

乱世煮酒论天下

What is the principle of connecting resistors and capacitors? There is one output, but it is given by multiple power supplies. Although the difference in power supply output is very small, in microelectronic circuits, a small difference will cause output imbalance.

maychang

[For example, in two LDO output chips, both convert 3.3V to 1.8V, but since the chips cannot be completely consistent, one is always a little higher than the other. This may result in only one power chip output during operation, which is far from enough to meet the load requirements.]

Your example is not [multi-channel power output] as mentioned in the title. The output is still one channel, but the voltage stabilization uses two LDO chips in parallel.

maychang

Therefore, your question should be [When several linear regulated power supplies with the same output voltage are connected in parallel, how can each linear regulated power supply achieve current sharing].

乱世煮酒论天下

maychang posted on 2024-4-28 15:58 So, your question should be [When several linear regulated power supplies with the same output voltage are connected in parallel, how can each linear regulated power supply achieve current sharing].

Not only is the linear regulated power supply outputting current evenly, but if the power is slightly higher and the battery pack is output in parallel, how can we prevent backflow?

maychang

Luan Shi Zhu Jiu Lun Tian Xia published on 2024-4-28 16:15 Not only the linear voltage regulated power supply has a current-balanced output, but if the power is slightly larger and the battery pack is connected in parallel, how can we avoid backflow?

[Not only the linear voltage-regulated power supply has a current-balanced output, but if the power is slightly higher and the battery pack is connected in parallel, how can we avoid backflow? ]

[Current sharing] and [backflow] are two different things. [Current sharing] means that the output current is evenly distributed among the parallel units, and [backflow] means that the output current of a parallel unit flows into another parallel unit to charge the other parallel unit.

maychang

Luan Shi Zhu Jiu Lun Tian Xia published on 2024-4-28 16:15 Not only the linear voltage regulated power supply has a current-balanced output, but if the power is slightly larger and the battery pack is connected in parallel, how can we avoid backflow?

For linear voltage regulator chips, "backflow" is impossible, as can be seen from the internal structure diagram of voltage regulator chips such as 7805. Batteries can "backflow", so batteries of different ages should not be used in parallel. Batteries of the same age have almost the same terminal voltage when loaded with an open circuit. If two such batteries are connected in parallel, even if there is "backflow", the current is very small. Moreover, "backflow" means that the battery with a slightly higher terminal voltage charges the battery with a slightly lower terminal voltage. The battery with a slightly lower terminal voltage will increase its voltage after charging, and the terminal voltages of the two batteries will be equal in the end.

乱世煮酒论天下

Or maybe it’s not backflow, but when two power chips have different voltage outputs, if a diode is connected in series with the output and one voltage output is higher, will it affect the normal output of the other power supply and thus affect the load power?

baopodao

Current balancing is only considered for large currents, but it is most reliable to handle small currents all the way.

maychang

乱世煮酒论天下published on 2024-4-28 22:00 Or it is not backflow, but when the two power chips have different voltage outputs, if the output is connected in series with a diode, and one voltage output is higher, will it affect...

[Or it may not be backflow, but when two power chips have different voltage outputs, if a diode is connected in series with the output, and one voltage output is higher, will it affect the normal output of the other power supply?]

Are you replying to the 7th floor or the 2nd floor?

乱世煮酒论天下

maychang posted on 2024-4-29 10:44 [Or it is not backflow, but when the two power chips have different voltage outputs, if the output is connected in series with a diode, and one voltage output is higher, then...

Reply at the same time

maychang

Talking about the world over wine in troubled times published on 2024-4-29 10:46 Reply at the same time

【Reply at the same time】

Then you should discuss it with the second floor first.

乱世煮酒论天下

maychang posted on 2024-4-29 10:47 [Reply at the same time] Then you can discuss with the second floor first.

Now let me reply to you, if two voltage regulator chips output a series diode, if the difference in the chips causes a slight difference in the output voltage, one of the voltage chips will block the output, which will result in insufficient load power. How to solve this problem? What is the principle of series resistors and capacitors?

maychang

乱世煮酒论天下published on 2024-4-29 14:04 Then I will reply to you now, if two voltage regulator chips output series diodes, if the difference in the chips causes a slight difference in the output voltage, there is a voltage core...

[Then I will reply to you now. If two voltage regulator chips output a series diode, and if the difference in the chips causes a slight difference in the output voltage, one of the voltage chips will block the output. In this case, the load power will be insufficient. How to solve this problem? ]

I have never suggested connecting diodes in series with the outputs of two voltage regulator chips.

maychang

乱世煮酒论天下published on 2024-4-29 14:04 Then I will reply to you now, if two voltage regulator chips output series diodes, if the difference in the chips causes a slight difference in the output voltage, there is a voltage core...

[What is the principle of series resistor and capacitor? ]

I also didn't suggest series resistors and capacitors.

maychang

乱世煮酒论天下published on 2024-4-29 14:04 Then I will reply to you now, if two voltage regulator chips output series diodes, if the difference in the chips causes a slight difference in the output voltage, there is a voltage core...

In the first post, what you are talking about should be [When several linear regulated power supplies with the same output voltage are connected in parallel, how can each linear regulated power supply achieve current sharing], which I have already mentioned on the 5th floor.

The above requirement is impossible to achieve. No matter what method is used (external circuits are not allowed, otherwise they will not be several identical linear regulated power supplies), the current passing through each linear regulated power supply cannot be the same.

To make the currents passing through each power supply equal, only one power supply with a regulated output (the output current of this power supply is not enough for the load) can be used, and the other is a current follower, whose output follows the previous regulated output power supply. In this way, the currents output by the two power supplies are the same, and they are added together to supply the load. Of course, the number of current followers can also be increased to two or three...

Connecting power supplies with the same regulated output in parallel can only prevent each power supply from burning out, but cannot make the current passing through each power supply equal.

maychang

乱世煮酒论天下published on 2024-4-29 14:04 Then I will reply to you now, if two voltage regulator chips output series diodes, if the difference in the chips causes a slight difference in the output voltage, there is a voltage core...

Many linear voltage regulator chips have built-in current limiting functions, and many switching power supply modules also have automatic current limiting functions. Such power supplies are not afraid of output short circuits. When the output is short-circuited, the output current of the voltage regulator chip or voltage regulator module will be automatically limited to a certain value.

Some voltage regulator chips output current limiting by detecting the output current, which is actually a kind of negative feedback, but the current negative feedback does not work when the output current does not reach the set value. Similarly, the output voltage negative feedback of this voltage regulator chip does not work after the current reaches the set value. Simply put, both voltage comparison feedback and current comparison feedback are "whichever reaches the set value follows the other".

maychang

乱世煮酒论天下published on 2024-4-29 14:04 Then I will reply to you now, if two voltage regulator chips output series diodes, if the difference in the chips causes a slight difference in the output voltage, there is a voltage core...

The voltage regulator with automatic current limiting described on the 18th floor can be directly connected in parallel with two or more of them (no external components are required). For multiple voltage regulators connected in parallel, when the load current is very small, only one voltage regulator will output current, and the other voltage regulators will be "blocked" and have no output. When the load current exceeds the current allowed to be output by a single voltage regulator, the output current of this voltage regulator is limited, and the second voltage regulator starts to output current. Therefore, the current in each voltage regulator is not equal, but each voltage regulator will not be damaged due to overcurrent.

It is easier to understand using the voltage/current characteristic curve to illustrate the parallel operation of multiple regulators with current limiting.

振动试验仪器

In the high-current power amplifier output stage, twenty MOSFET tubes are generally used for parallel output. For even greater power, dozens of 50A power amplifier modules are connected in parallel for output. Good tubes have the ability to self-balance current. The principle is that if the current output of a certain tube is large, the internal resistance of the tube will increase due to heat, which will reduce the output current. Ultimately, each tube can achieve current balance through heat generation, and there is no other measure.