I. Reasons why the power supply cannot drive the load
A power supply's load capacity is typically measured by its output power. The higher the output power, the more electrical energy the power supply can provide to external circuits. When selecting a power supply, we need to determine the required output power based on the current and voltage needed by the external circuit. If the power supply's output power is insufficient, it will be unable to provide the necessary electrical energy to the external circuit, which may lead to circuit malfunction or damage.
The power supply may be unable to handle the load due to the following reasons:
1. Insufficient output power: If the power supply's output power is insufficient, it will be unable to provide the necessary electrical energy to the external circuit. In this case, the power supply may be overloaded or the circuit may fail to operate.
2. Power Supply Protection: Modern power supplies typically have built-in protection circuits to protect them from malfunctions or damage. If the load on the external circuit exceeds the power supply's capacity, the protection circuit may automatically shut off the power output. This is to prevent the power supply from being overloaded or damaged.
3. Incorrect power supply settings: If the power supply is not set correctly, it may fail to provide the necessary power to the load. For example, if the power supply's output voltage is set too low, it will not be able to meet the needs of the external circuitry.
4. Poor power supply: Poor power supply connections, or damage or failure of filters in the power supply line, may prevent the power supply from providing the required power to the load.
5. External circuit failure: Sometimes, the power supply's inability to provide the required electrical energy may be due to a fault or damage to the external circuit. For example, a short circuit in the external circuit can overload the power supply and prevent it from providing the required electrical energy to the circuit.
II. How to understand the internal resistance of a power supply? What impact does the internal resistance of a power supply have on a circuit?
The internal resistance of a power supply refers to the resistance between the output port and the source port of the power supply, usually represented by R.
The existence of internal resistance in a power supply is determined by its construction. The internal structure of a power supply consists of electrical components, including inverters, amplifiers, transistors, integrated circuits, capacitors, inductors, and resistors. These components all have a certain resistance value, so the internal structure of a power supply cannot be perfectly ideal. There will inevitably be resistance encountered by the current flowing through the internal components, resulting in phenomena such as voltage drops in capacitors and non-ideal currents in inductors.
The internal resistance of a power supply typically varies with the output current. As the output current increases, the internal resistance increases, thus reducing the output voltage. Therefore, when selecting a power supply, it is important to choose one with a higher required output current to ensure that the output voltage does not drop excessively due to high internal resistance, which could lead to system malfunctions.
The influence of the power supply's internal resistance on the circuit is mainly reflected in the following aspects:
1. Power supply voltage drop. The presence of internal resistance in the power supply can cause a drop in output voltage when the output current is high. Therefore, under high-power loads, the stability of the circuit needs to take into account the influence of the power supply's internal resistance, especially in DC power supplies and some long-term pulse power supplies, where the effect of the power supply's internal resistance is particularly significant.
2. Limiting output power. When the load resistance is small, the internal resistance of the power supply has a significant impact on the output voltage, thus limiting the output power. In this case, if you want to increase the output power, you need to use a larger power supply or a smaller load resistance.
3. Noise generation. The internal resistance of the power supply can also cause noise at the output port. The voltage drop caused by the internal resistance creates ripple voltage, which in turn generates oscillations and noise in the circuit. To reduce the impact of the power supply's internal resistance on noise, filtering or noise shielding techniques can be used to suppress interference.
4. Robust high-speed response and circuit stability. The internal resistance of the power supply also affects the high-speed response characteristics of the system. In scenarios such as rapid start-up and shutdown, power supply voltage adjustment, and the generation of transient voltages, the circuit will exhibit transient responses before and after steady-state operation.
5. Temperature affects the internal resistance of a power supply. The effect of temperature on the internal resistance of a power supply is very significant; generally, as the temperature increases, the internal resistance of the power supply will increase. This indicates that as the power supply heats up, its output voltage decreases, and the resulting losses increase accordingly.
In general, the internal resistance of a power supply has a significant impact on a circuit. Therefore, when designing a circuit, the influence of the power supply's internal resistance must be fully considered to ensure the circuit's stability, reliability, and efficiency.
