Using the TOP265KG power switching regulator manufactured by Power Integrations , can be designed a very simple and efficiency 12 V switching power supply electronic project. This TOP265KG 12 V switching power supply circuit is intended as a general purpose evaluation platform that operates from 110 VDC to 400 VDC input and provides a 12 V, continuous 30 W output.
This TOP265KG 12 V switching power supply offers various protection features using a low component count circuit: overvoltage protection (OVP) with latching shutdown and optional fast AC reset , primary-side sensed output overload protection, open-loop protection ,auto-restart overload protection , accurate thermal overload protection with auto-recovery using a large hysteresis .
Resistors R4, R5 and R6 provide a current into the VOLTAGE MONITOR (V) pin of U1 proportional to the DC voltage across high-voltage bypass capacitor C1. Resistor R10 provides an offset current into the V pin to reduce the current drawn from the DC bus via R4, R5 and R6.
An RCDZ clamp network (D1, R7, R8, R9, C2 and VR1) limits the drain voltage of U1 to below 725 V after the MOSFET inside U1 turns OFF.
Diode D3 rectifies the bias winding output of transformer T1. Resistor R13 and capacitor C6 filter the output of the bias winding. This provides the necessary bias supply for the optocoupler U2B. The voltage across capacitor C6 was adjusted via the bias winding turns to be ~9 V at no-load and 400 VDC input.
The secondary-side feedback circuitry maintains output voltage regulation via U2A .
Zener diode VR2 provides output overvoltage protection. Any fault condition which causes the power supply output to exceed regulation limits also causes the voltage across the bias winding to increase. Consequently, Zener diode VR2 breaks down and sufficient current flows into the V pin of U1 via D2 to initiate OVP. A resistor can be added in series with VR2 that limits the current into the V pin and changes the latching to self recovering shutdown.
Resistors R1, R2, R3 and R11 provide output power limiting. By reducing the current limit as a function of the input voltage a relatively constant overload power is achieved .
Diode D4 provides rectification for the 12 V output, and low-ESR capacitor C9 provides filtering. To eliminate high frequency switching noise, a post filter was added (L1 and C10).
The output voltage is controlled using shunt regulator U3. Resistors R19 and R20 sense the output voltage, forming a resistor divider connected to the reference input of IC U3.
Changes in the output voltage and hence the voltage at the reference input of U3 results in changes in the cathode voltage of IC U3 and therefore optocoupler LED current. This changes the current into the C pin of U1 and acts to maintain output regulation.
Capacitor C13 introduces a pole at DC, rolling off the gain of U3. Resistor R17 and capacitor C11 provides the additional phase boost to achieve stable power supply operation. Capacitor C14 was added after it was found that switching noise was being injected into the reference pin of IC U3.
Resistor R16 sets the overall loop gain and limits current through U3A during transient conditions.
To reduce power dissipation in the feedback circuit (and lower no-load consumption) a D rank optocoupler was selected with the value of resistor R16 increased to offset the increase in loop gain. A low minimum cathode current (150 uA) reference was selected
for U3 to also reduce dissipation.
In the table bellow you can see transformer electrical specifications that is required n this circuit project .
