When inductive loads such as motors and solenoid valves start or switch, or when communication equipment experiences sudden data transmission and reception surges, peak power levels may spike instantaneously. During this time, the load power consumption can far exceed its rated power (3-4 times or more), and this spike lasts for a short period, from tens of milliseconds to a few seconds, before stabilizing and returning to the rated power. Traditional power modules, upon detecting an overpower condition, will shut down the output to prevent internal semiconductor device current from exceeding set values or core device saturation from causing power failure. This approach cannot meet the load's requirement for several times the instantaneous peak power.
If the rated power is designed only to meet the over-power baseline to satisfy transient over-power requirements, it will lead to a significant increase in manufacturing costs and power supply size. At the same time, in practical applications, the power module will be operating below the rated power load for a long time, resulting in excessively low energy utilization, meaning that the design redundancy is too large and resources are wasted.
The following section will introduce three mainstream technical solutions in the industry, briefly explain their working principles, and compare their advantages and disadvantages.
1. Transient overpower power supply modules must meet the following requirements.
(1) Normal operation under overpower condition
Unlike conventional power modules, when an overpower load is detected, the transient overpower power supply enters a preset overpower mode, which can provide 3 to 4 times the rated operating power for a short period of time while maintaining stable output.
(2) Does not affect steady-state normal operation
Under normal conditions, the transient overpower power supply outputs the rated power, which is consistent with that of a conventional power module.
(3) To meet the transient requirements of overpower conditions without significantly increasing volume and cost.
2. Industry-leading transient overpower technology solutions
(1) Nonlinear magnetic devices (transformers)
When a flyback circuit is operating normally, the magnetic flux range of the core is within the maximum flux BMax. When the load switches from light load to heavy load or overload (transient overpower), the switching transistor will conduct at its maximum duty cycle, and the transformer is prone to saturation, leading to abnormal operation or failure. This can generally be solved by increasing the air gap in the transformer, but this also results in problems such as high leakage inductance and low efficiency. In this case, the core structure can be modified, as shown in Figure 1, to make the BH curve non-linear. As the output power increases, the effective distance of the transformer air gap increases, enhancing the transformer's anti-saturation capability. This makes the transformer less prone to saturation under different operating power conditions (especially overpower conditions), meeting the requirements of different power ranges without significantly increasing the transformer size.
Working principle: Output power P↑ → Air gap saturation → Effective air gap length lg↑ → H↓ → B↓ → Increased anti-saturation capability → Effective air gap length lg↑ → Lp↓ → P↑ increases output power.
Advantages: No complex control strategies are required, and overpower can be increased by more than 3 times.
Disadvantages: It is difficult to maintain consistency in the core air gap grinding process; the relationship between the parameters of the stepped air gap and the overpower multiple is non-linear, requiring cumbersome debugging steps.
(2) Frequency control
Currently, flyback control methods mainly include PWM control, PFM control, and PWM+PFM control. Within the full load range, the power converter enters different modes to maintain high conversion efficiency and control accuracy. Transient overpower technology adds a peak power mode to the above control methods. When the load switches from light load to heavy load or overload (transient overpower), it enters peak power mode, rapidly increasing the switching frequency. Since the output power is proportional to the switching frequency, stable overpower output can be achieved. Simultaneously, the conduction time within one cycle is shortened, and the change in magnetic flux density (i.e., the change in the transformer hysteresis loop) is reduced, preventing transformer saturation. To avoid prolonged operation in overpower mode, a timing function is also added to the system. When a peak load occurs and its duration exceeds the maximum allowable time, the PWM signal can be automatically shut off.
Working principle: From the equation P=1/2 * f * IP² * LP * η, we can deduce that frequency f↑→Pin↑→Pout↑→increase output power, as shown in Figure 2.
Advantages: The frequency modulation control strategy is easy to implement and is relatively simple compared to Scheme 3.
Disadvantages: Limited power increase, usually less than 3 times.
(3) Frequency control + adjustment of current limiting point
In peak current control mode, increasing the primary-side current limiting point increases the energy input to the system per unit switching cycle, thereby improving output power. Simultaneously, combining this with the peak power mode to increase the operating frequency further enhances peak power output capability, enabling transient over-power operation. A timed shutdown function can also be added to prevent the system from operating in an over-power state for extended periods.
By coordinating the adjustment of current limiting points and frequency control, the over-power state can be better achieved.
Working principle: Adjusting the frequency—frequency f↑ → Pin↑ → Pout↑ → Output power↑;
Adjust the limit point Ipp↑→Pin↑→Pout↑→output power↑.
Advantages: Overpower > 3 times, and overpower time can be set through control strategy.
Disadvantages: It requires a complex control strategy, and it is necessary to accurately judge the real-time power and adjust the frequency and current limiting point.
3. Summary
By employing transient overpower technology, under the premise of controlling the size and cost of the power module, nonlinear magnetic devices, frequency control, and frequency control + current limiting point adjustment technologies can achieve several times the peak power output in a short time without affecting the normal steady-state operation of the product. At the same time, the product also has complete protection functions, which can well meet the needs of practical applications.
