# Charging large capacitor banks with an LDO regulator

• DragonPetter
In summary, using a large capacitor bank with a limited current LDO may be feasible, but care must be taken to ensure the LDO remains stable. Another option may be to use an adjustable LDO.
DragonPetter
I'm trying to see if charging large capacitor banks with a limited current LDO is feasible.

If the capacitors draw current past the maximum current of the LDO, will the LDO become unstable or will it be current limited?

I suppose it depends on the LDO and the proposed input to the LDO.

I think most just turn off when they hit the current limit (not what you want). Others just stay fixed current until the strong load is removed (this is what you want).

Another option might be to use an adjustable LDO that takes an external reference. You can then slowly ramp up the reference with a dv/dt that limits max I for your C. You have to be careful with this though because at the beginning there will be lag on the output and the error signal could cause the LDO pass element to saturate, which would likely blow it out (depending on how much C were talking about).

What were you planning on using as the input to the LDO, about how much C is in the bank?

Another, possibly better option (assuming the reason you want the LDO is to make a precise voltage on the cap) would be to over charge the caps on purpose, then remove that power source, and finally slowly bleed off the excess charge with a weak parallel R. Remove the R when the right voltage has been obtained.

Oh ya, even more simply... You can also just put a power resistor in series with the output of the LDO to limit max I into the caps. Ipeak = Vout/R. The LDO feedback point needs to be the input to the series R to keep it stable. Then make sure the R can handle Ipeak*Ipeak*R Watts.

This assumes you don't need a good transient response on the LDO (and presumably you don't since there is a lot of output C).

Thanks so much for the responses

## 1. How does an LDO regulator work when charging a large capacitor bank?

An LDO (low-dropout) regulator provides a constant output voltage, even when the input voltage changes. When charging a large capacitor bank, the LDO regulator will regulate the voltage to ensure that it does not exceed the maximum rating of the capacitors. This prevents damage to the capacitors and ensures a safe and efficient charging process.

## 2. What is the maximum voltage that an LDO regulator can handle when charging a large capacitor bank?

The maximum voltage that an LDO regulator can handle when charging a large capacitor bank depends on the specific regulator being used. However, most LDO regulators have a maximum input voltage of around 5-20V. It is important to select an LDO regulator with a maximum input voltage that is higher than the desired charging voltage of the capacitor bank.

## 3. Can I use an LDO regulator to charge multiple capacitor banks at the same time?

Yes, an LDO regulator can be used to charge multiple capacitor banks at the same time. However, the total current drawn from the regulator should not exceed its maximum output current rating. It is important to consider the total capacitance and desired charging rate of all the capacitor banks when selecting an LDO regulator.

## 4. How long does it take to charge a large capacitor bank using an LDO regulator?

The charging time of a large capacitor bank using an LDO regulator depends on the capacitance of the bank and the output current of the regulator. For example, a 1000μF capacitor bank being charged at 10mA would take approximately 100 seconds to reach its maximum voltage. It is important to consider the desired charging time when selecting an LDO regulator and to ensure that it can provide enough output current for the desired charging rate.

## 5. Is it safe to leave a large capacitor bank connected to an LDO regulator after it has been fully charged?

It is generally safe to leave a fully charged capacitor bank connected to an LDO regulator. However, it is recommended to disconnect the bank from the regulator to prevent any potential damage or discharge of the capacitors. It is also important to ensure that the LDO regulator is not continuously applying a voltage to the bank, as this can cause unnecessary stress on the capacitors and potentially lead to failure over time.

• Electrical Engineering
Replies
3
Views
2K
• Electrical Engineering
Replies
4
Views
330
• Electrical Engineering
Replies
17
Views
2K
• Electrical Engineering
Replies
11
Views
1K
• Electrical Engineering
Replies
3
Views
1K
• Electrical Engineering
Replies
35
Views
5K
• Electrical Engineering
Replies
4
Views
1K
• Electrical Engineering
Replies
5
Views
1K
• Electrical Engineering
Replies
10
Views
1K
• Electrical Engineering
Replies
14
Views
950