New Application of Fenghua High Voltage Resistors 0603 300V and 1206 500V in 250W Small Chargers

The core contradiction of using 0603/1206 packaged high-voltage resistors in a 250W high-power density charger (50 × 45 × 10mm) lies in the balance between miniaturization and high-voltage safety. The following is the design logic analysis of specific models:

1、 The core function of high-voltage resistors
1. Voltage resistance requirement
The charger input is AC 220V, and the rectified DC bus voltage reaches over 300V. The ordinary 0603 resistor has a withstand voltage of only 75V (such as the Vishay Dale model), while the RVS03KxxxFT series increases the withstand voltage of 0603 to 300V through thick film technology and special structures (such as resistance tuning optimization), meeting the safety margin of high-voltage division and detection circuits.

2. Functional positioning
470K/124K resistors (RVS03K4703FT, RVS03K1243FT): used for AC input detection or feedback voltage divider network, directly withstand high voltage pulses.
10M resistor (RVS06K106JT): used for discharging circuits or small current sampling. The 1206 package avoids arc breakdown due to its larger creepage distance (500V withstand voltage).
34.8K resistor (RVS03K3482FT): It may be used to supply power to PWM control chips or generate reference voltage, and high voltage noise isolation is required.

2、 The selection logic of miniaturized packaging
1. The necessity of space compression
Under a volume of 50 × 45 × 10mm, traditional plug-in resistors cannot be laid out. 0603 (1.6 × 0.8mm) and 1206 (3.2 × 1.6mm) surface mount resistors save over 90% of space and are compatible with automated mounting.

2. Balance between power and withstand voltage
|Model | Packaging | Resistance | Voltage Resistance | Power | Applicable Scenarios|
|RVS03K4703FT | 0603 | 470K Ω | 300V | 1/10W | Input voltage divider/surge protection|
|RVS06K106JT | 1206 | 10M Ω | 500V | 1/4W | High voltage discharge/leakage current detection|
|RVS03K1243FT/RVS003K3482FT | 0603 | 124K/34.8K | 300V | 1/10W | Feedback regulation/IC bias|
0603 power limitation (0.1W) is solved by sharing multiple resistors in parallel to avoid local overheating.
1206 is used for 10M high resistance: the higher the resistance, the more likely it is to cause dielectric breakdown, and the larger the size, the higher the safety margin.

3、 Special Design of High Voltage Resistors
1. Material and process upgrades
Thick film slurry optimization: The Fenghua RVS series uses high-voltage glass glaze material to reduce leakage current caused by electric field concentration.
No impedance tuning design: Some high-voltage resistors (such as the RESI HVCR series) abandon laser impedance tuning and retain the complete ceramic substrate to enhance voltage resistance (such as 500V).

2. Safety redundancy design
300V nominal withstand voltage actual test ≥ 500V, ensuring tolerance to grid fluctuations (such as 264V AC peak 374V).
0603 resistor series use: If the withstand voltage of a single resistor is insufficient, multiple resistors are used in series for voltage division (such as 2 × 150K instead of 300K).

4、 Summary: The selection of small high-power power supplies
The use of 0603/1206 high voltage resistors in a 250W charger is essentially an engineering compromise between "power density" and "high voltage safety":
Advantages: Utilizing surface mount technology to achieve millimeter level layout, supporting compact PCB design required for GaN high-frequency solutions (>100kHz).   
Risk control: By selecting high-voltage specialized models (such as Fenghua RVS), increasing creepage spacing, and conducting strict aging tests, we ensure that we can withstand a continuous operating voltage of 300V+even in small volumes.   

If pursuing higher reliability, 1210 packaging (withstand voltage 600V) or modular design can be considered, but it will sacrifice volume. The current selection is the optimal solution for miniaturization and cost.