Does the forward voltage drop of diodes have a significant impact on communication power supply?

一, The physical essence of forward voltage drop and the particularity of communication scenarios
The forward voltage drop of a diode is due to the weakening process of the built-in electric field in the PN junction. When the forward bias voltage exceeds the threshold (about 0.6-0.8V for silicon tubes and about 0.2-0.3V for germanium tubes), carrier diffusion forms a current, but at the same time, irreversible voltage drop occurs due to resistance effect. This characteristic presents a dual contradiction in communication power supply:
Sensitivity to low voltage scenarios: Modern communication devices commonly use supply voltages of 3.3V, 1.8V, or even lower. The voltage drop of silicon diodes at 0.7V accounts for as much as 21% -39%, directly leading to a cliff like decrease in power conversion efficiency. For example, in the DC-DC conversion module of a 48V communication power supply, if traditional silicon rectifier diodes are used, only the secondary rectification link can lose 1.4V, reducing the overall efficiency by nearly 3 percentage points.
The integrity challenge of high-frequency signals: In high-frequency applications such as 5G base stations, nonlinear distortion caused by diode voltage drop may disrupt the phase consistency of carrier aggregation signals. Experimental data shows that when the forward current fluctuation exceeds 20% of the rated value, the voltage drop of the silicon diode can change by up to 0.15V, which is enough to cause the EVM (error vector amplitude) of the OFDM signal to deteriorate by more than 3dB.
二, Multidimensional impact of forward voltage drop on communication power supply system
1. Quantitative analysis of efficiency loss
Taking a certain 48V/12V communication power module as an example, IN4007 silicon diode (Vf) is used= 0.7V@1A )When the rectifier circuit is fully loaded at 10A, the diode loss alone reaches 7W, accounting for 35% of the total module loss. If Schottky diode (Vf) is used instead= 0.3V@1A )The loss can be reduced to 3W, and the efficiency can be improved by 2.2 percentage points. For data centers that consume over a million kilowatt hours of electricity annually, this improvement can save hundreds of thousands of yuan in electricity bills each year.
2. The critical impact of signal integrity
In the bias circuit of PD (photodetector) in fiber optic communication, the temperature drift characteristic of diode voltage drop may cause fatal problems. The voltage drop of silicon diodes decreases at a rate of -2.2mV/℃ with increasing temperature. Within the industrial temperature range of -40 ℃ to+85 ℃, the voltage drop changes by 0.28V. If temperature compensation design is not used, it will cause the PD bias voltage to deviate from the optimal operating point, resulting in a decrease of more than 1dB in receiving sensitivity and directly shortening the transmission distance by several kilometers.
3. Long term reliability risks
Local overheating caused by positive voltage drop is one of the main causes of communication power failure. Tests have shown that under a current of 10A, the junction temperature of silicon diodes can reach 125 ℃ (ambient temperature of 40 ℃), exceeding their maximum rated junction temperature. Long term high-temperature operation will accelerate metal migration and electromigration, leading to a more than tenfold increase in diode leakage current and ultimately causing short-circuit faults. According to statistics from a certain operator, the repair rate of power modules caused by improper diode selection is as high as 18%, of which 70% are directly related to voltage drop related thermal failures.
三, Optimization Strategies and Practical Cases of Communication Power Supply System
1. Innovative selection of materials and devices
Schottky diode: With an ultra-low voltage drop of 0.15-0.45V, it has become the preferred choice for low-voltage communication power supplies. For example, in LTE base station power supply, MBR2045CT Schottky diode (Vf) is used= 0.38V@2A )Afterwards, the rectification efficiency increased from 88% to 92%.
Synchronous rectification technology: Replacing traditional diodes with MOSFETs to achieve a low on resistance of m Ω. A certain type of 5G micro base station power supply adopts a synchronous rectification scheme controlled by LTC4359, with a voltage drop of only 56mV at 3A current and an efficiency exceeding 96%.
SiC/GaN wide bandgap devices: SiC Schottky diodes (Vf) in high-voltage and high-power scenarios= 1.2V@10A )It exhibits a 50% lower voltage drop and 3 times higher switching frequency than silicon devices, and has been applied in high-end fields such as submarine cable repeater power supply.
2. Fine compensation for circuit design
Temperature compensation network: dynamically adjusts diode bias current through a combination of thermistor and voltage divider resistor. In a certain type of OTN device, this technology reduces the fluctuation of PD bias voltage to less than 0.05V across the entire temperature range, and improves the stability of receiving sensitivity by 0.3dB.
Multi level voltage drop balancing technology: In high-voltage rectification circuits, a cascaded diode array is used in conjunction with a current sharing resistor to control the voltage drop difference between each diode within 5%. After adopting this scheme, the current imbalance of a certain type of 400V communication power supply decreased from 15% to 3%, and the lifespan was extended by three times.
3. Innovative breakthroughs in system architecture
Diode free power supply architecture: In the backup power supply system of the data center, a solution using supercapacitors and bidirectional DC-DC converters is adopted to completely eliminate diode voltage drop losses. Actual testing shows that the energy conversion efficiency of this architecture in a 48V system reaches 98.5%, which is 6 percentage points higher than the traditional solution.
Intelligent voltage drop management chip: a dedicated IC that integrates voltage drop monitoring and dynamic adjustment functions, such as TI's TPS2419, can sense load current in real time and adjust gate drive voltage, so that the voltage drop of synchronous rectification MOSFET is always maintained at the optimal value. In a certain type of AI server power supply, this technology improves light load efficiency by 8% and full load efficiency by 2%.