TOPSwitch-FX series microcontroller power supply IC, can be widely used general-purpose and special switching power supply, standby power supply, switching power supply module.
First, to limit the external 12V, 30W Switching Power Supply
Constituted by the TOP234Y 12V, 30W high efficiency switching power supply circuit shown in Figure 1. The AC input voltage range is AC85 ~ 265V, full load power efficiency up to 80%. AC voltage u followed by electromagnetic interference (EMI) filter (C10, L1), the input rectifier filter (BR, C1) to obtain DC high voltage UI. Through R1 and R2 UI followed by M-side partial pressure, can limit the current with the UI increases. R1 provides voltage feed-forward signal, when the UI automatically reduced when the high maximum duty cycle to reduce the output ripple. For the current limit set resistor R2, the set Ilimit ≈ 0.7Ilimit = 0.7 × 1.5A = 1.05A, slightly higher than the low voltage input value when the peak current Ip. Here the factor of 0.7 is taken into account TOP234Y in a wide range input, the maximum continuous output power Pom = 45W, while the actual output power P'om = 30M, which P'om / Pom = 30/45 = 0.67 ≈ 0.7. With this design method allows the selection of high-frequency transformer cores smaller size, by increasing the primary inductance Lp TOP234Y to reduce power consumption, and to prevent magnetic saturation. In addition, the use of lower voltage feedforward technology Dmax even if the input voltage induced voltage UOR UI and junior high, switching power supply can work properly. It allows the use of cost of R, C, VD-type drain clamp circuit (R3, C7, VD1), as an alternative to higher prices of TVS (transient voltage suppressor), VD-type clamp circuit, to absorb the TOP234Y off by the high-frequency transformer leakage inductance voltage spike generated on the drain has protective effects.

After secondary voltage VD2, C2, C3, L2 and C4 rectifier filter obtained after +12 V, 2.5A voltage regulator output. To reduce the rectifier loss, VD2 type 10A/60V by MBR1060 Schottky diodes. VD2 R7 in parallel with C9 and ends, to prevent high frequency switching state VD2 produce self-oscillation (ringing). When the switching power supply with no load, TOPSwitch-FX can be used to further reduce the skip cycle mode the maximum output duty cycle, making Dmax1.5%, therefore, no need to take leave at the output load, which can reduce the load or standby under power.
The power supply regulator used with the optocoupler feedback circuit. IC2 is LTV817A linear optocouplers. VDZ by 1N5240C-type regulator, the regulated voltage Uz = 10 (1 ± 0.02) V. Optocoupler LED's forward voltage drop in the UF ≈ 1V. Output voltage is determined by:
Uo = Uz + UF + UR4
Now its regulator principle is as follows: When the cause for some reason Uo ↑, UoU2 + UF + UR4, the resulting error voltage Ur '= Uo-(Uz + UF + UR4) to make LED's IF ↑, after coupler, the receiver tube IE ↑, makes the control terminal current Ic ↑, while the duty cycle D ↓, led Uo ↓, for the purpose of the realization of the regulator. On the contrary, Uo ↓ → IF ↓ → IE ↓ → Ic ↓ → D ↑ → Uo ↑, also play a role in regulation.
1N5240C the stability of the current is typically 20mA, taking R4 = 150 Ω can only 6.7mA supply current, and further increase the resistance will be LED Current IF (typically 3.5 ~ 7mA) limit. To this end, the other provided by the resistor R6 13.3mA operating current, so VDz the stability of the current Iz = 3.7mA +13.3 mA = 20mA, the voltage characteristics are also improved. After the feedback winding voltage VD3 and C6 rectifier filter, the resulting feedback voltage 12V, after the end of IC2 to provide bias control TOP234Y. C5 is a bypass capacitor, it also posed with the R5 control loop compensation circuitry.

Second, multi-output 35W switching circuit set-top box
5, the 35W has a set-top box output switching power supply circuit shown in Figure 2. This 5-way voltage is: Uo1 (+30 V, 100mA), Uo2 (+18 V, 550mA), Uo3 (+5 V, 2.5A), Uo4 (+3.3 V, 3A), Uo5 (-5V, 100mA). Which, +5 V and +3.3 V as the main output, the rest are supplemented by output from various quarters. When the AC input voltage u = 220 (1 ± 0.15) V, the total output power of 38.5W; the use of a wide-range voltage input (u = 85 ~ 265V AC), the total output power to drop into a 25W, can be used as set-top boxes ( Set-top Box), VCR (VCR), camcorder (CVCR) and the DVD of the switching power supply. The power supply uses 3 IC: TOP233Y (IC1), optocouplers LTV817A (IC2); adjustable precision shunt regulator TL431C (IC3). In order to reduce the volume and enhanced high-frequency magnetic field coupling transformer, and the secondary windings stacked around the method used. R4 and C14 formed by the absorption of the RF circuit can reduce noise interference from TV and other video equipment. When necessary, select the end of the switching frequency (F) change the access control side (C), select the half-frequency mode to further reduce the sensitivity of the TV on the video noise level.
R6, R7 and R8 as the ratio of feedback resistance, the 5V and 3.3V power supply according to a certain percentage of the feedback, the two outputs of the load adjustment rate of up to ± 5%. R9 and C16 constitute the TL431C frequency compensation network. C17 for the soft-start capacitor, take C17 = 22 μF 4ms soft start time can increase the time, coupled with their existing soft-start time 10ms, for a total of 14ms. The rest of each output feedback does not increase the output voltage by the high-frequency transformer turns ratio to determine. -5V power supply due to low output power, is through the resistor R2 and voltage regulation regulator VDz2. R9 is a +30 V output of the dummy load, it can reduce the road load and light load voltage. In view of 5V, 3.3V and 18V power supply output power of larger, three levels have increased after the LC filter (L3 and C9, L4 and C11, L2 and C7), to reduce the output ripple voltage.
TOP233Y with frequency jitter, which helps reduce electromagnetic interference. In addition, another reasonable choice of security and the EMI filter capacitor C15 (C6, L1) of the component values, can make the switching power supply to electromagnetic radiation generated by CISPR22 (FCCB) international standards. One end of the C15 positive terminal of U1, TOP233Y the common mode interference can be reduced to a minimum. Have pointed out, C15 and C6 are called safety capacitor C15 is connected to the pressure difference and the ground can filter out the primary and secondary coupling capacitance of the common mode interference in the international standard IEC950 called "Y capacitors. C6 is connected to the AC power line side, the specialized filter power line between the series mode interference is called "X capacitor."
Possible from the grid to withstand lightning voltage line fleeing into the AC input voltage is also parallel U1mA = 275V only the nominal varistor VSR. U1mA that adopted when the varistor 1mA DC current, voltage across the device.

Third, 5V and 3.3V standby power output of 17W PC
Provide 5V, 2A and 3.3V, 2A output of two main PC, the standby power circuit shown in Figure 3. The power supply has also increased the minimum cost 15V, 30mA auxiliary output. Circuit using a TOP232Y MCU power supply, the total output power of 17.05W. DC input voltage range is 200 ~ 375V. Can choose a fixed input voltage 220/110V AC, only rectifier filter access without the need to increase the input voltage doubler for times on 110V AC voltage rectifier. The design leverages TOP232Y soft start, undervoltage protection, strictly limiting characteristics and good characteristics of higher switching frequency, making high-frequency transformer optional EE19-type core. In addition, increased TOP232Y extreme high and low end of the drain spacing, reducing the leakage between the pin, so power can be in a more harsh environments. C1 for the DC high voltage high frequency decoupling capacitors, as close to U1 and standby power can be omitted from the C1. Line under-voltage detection circuit is used to set the value of R1 UUV. Take R1 = 3.9M Ω when, UUV = IUV · R1 = 50 μA × 3.9MΩ = UI195V DC when it is re-connected to power.
After the feedback winding voltage VD4 and C6 15V rectifier filter resulting from the feedback voltage, on the one hand as a +15 V output (not with the initial isolation), on the other hand has also been sensitive to the TOP232Y control transistor to provide bias side. R4, R6 and R7 are the sampling resistor, used to detect 3.3V and 5V output voltage variation. R2 is the LED provides bias limit TL431C. C8 for the soft-start capacitor, can eliminate the power generated when the first voltage overshoot phenomenon. No-load characteristics using TOP232Y skip cycle, PC, meet low standby power consumption targets.