APD - カスタム電源設計ソリューション

【Customized Power Supply】Impact of Parameter Controls on Yield during the Research & Development Stage

With rising market competition pressure and a simpler PSR primary side feedback circuit being more competitive than the SSR secondary side feedback circuit, an increasing number of power supplies are now designed with PSR circuit framework. However, PSR does has its disadvantages. For example, it has far inferior peak load and dynamic load attributes compared to the SSR framework. In particular, PSR relies on primary side detection to control output voltage, leading to a low power supply yield.


Common issues include:

  • Exceedingly high output voltage during regular working conditions
  • Exceedingly low output voltage during regular working conditions
  • Blue screen display or inability to switch on during poor weather conditions

Typically, overly high or low voltage output is due to collocation caused by component tolerance after mass production. On the other hand, APD’s power supply devices adopts DFMEA and Limited condition testing during the product design stage to control component parameters that affect voltage output, in order to avoid such flaws.


PSR IC voltage sampling is typically done in 2 ways:

  • Delay Voltage Sampling method
  • Slope Sampling method for inflection voltage which uses IC technology and reflected by higher costs. Hence most PSR products on the market use the delay method (as shown in Diagram 1)

Delayed sampling control formula:


Vout= Vsampling/Naux*Ns-Vd

Vout: Voltage Output

Vsampling:Sampling Voltage Output

Naux: Auxiliary Winding Turns

Ns: Number of secondary turns

Vd: Diode Voltage drop on the secondary side


The voltage output will change according to the sampling point voltage, which is affected by the Transformer winding process, auxiliary diode Trr,  Clamping Resistor , and IC FB voltage precision. Therefore, a good control of component parameters is key to solving the issue of unstable voltage output.


APD conducts limit testing on component parameters for all PSR products and ensures voltage output stability through limit cross testing, in order to prevent interruptions to client systems due to overly high or low voltage output.