Series products for less than 23W low-power, low-cost and efficient switching power supply. For example, in the IC card paid watt-hour meter miniaturized switching power supply module, mobile phone battery constant voltage / constant current charger, power adapter (Powersupplyadapter), microcomputers, color TV, laser printers, video recorders, camcorders and other high-end household appliances the standby power supply (Standbypowersupply), also apply to ISDN and DSL network terminal equipment.
TinySwitch-II is easy to realize the optimization of the switching power supply design. Its switching frequency up to 132kHz, high-frequency transformer allows EE13 or EF12.6 of miniaturization cores and achieve high power efficiency. TinySwitch-II has a frequency jitter characteristics, only an inductor (You can also use two small resistors) and two capacitors in the output power less than 3W or less efficient acceptable to EMI filtering. Even in short-circuit conditions, do not need to use high-power rectifier.
Typical applications of 1 TinySwitch-II
1.1 2.5W constant current / constant voltage output of mobile phone battery charger
Mobile phone battery charger TNY264 (IC1) consisting of 2.5W (5V, 0.5A) AC wide range input circuit, as shown in Figure 1. RF fuse resistors. 85V ~ 265V AC VD1 ~ VD4 bridge rectifier, and then through the inductance L1 and C1, C2 consisting of π-type filter, the DC high voltage UI. R1 is L1 damping resistor. The use of the a TNY264 frequency jitter characteristics, and allows the use of a simple filter and low price of the security capacitor C8 (Y capacitors) can meet international standards suppression between primary and secondary conductive electromagnetic interference (EMI). Even under the most adverse circumstances the output capacitive load grounded shield to the increase in high-frequency transformer, able to effectively suppress EMI. Spike voltage protection circuit of a clamp diode VD6, capacitor C3 and resistor R2, can drain power MOSFET off limits in the safe range. IO lower than 500mA of output current, the voltage control loop work, the current control loop due to transistor VT cutoff does not work. At this point, the output voltage UO optocoupler IC2 (LTV817) LED's forward voltage drop (UF ≈ 1V) and the regulator VDZ regulator value (UZ = 3.9V) to jointly set, that of UO = UF + UZ ≈ 5V. Resistor R8 to the regulator to provide a bias current, so the VDZ stable current IZ close to a typical value. Secondary voltage via VD5 C5, L2 and C6 rectifier filter, the +5 V output voltage.
2.5w constant voltage and constant current cell phone battery charger
TinySwitch-II high switching frequency in the output rectifiers VD5 off the reverse recovery process will produce switching noise, easy to damage the rectifier. Although both ends in VD5 and on resistive and capacitive components in series of RC snubber circuit switching noise to play a certain extent, but the effect is still not ideal, Moreover, it will result in power loss in the resistance. The solution is in the secondary rectification filter series a bead.
Beads (Magneticbead) in recent years, the advent of an ultra-small amorphous alloy magnetic material, the case of two materials with ferrite. Similar to the commercially available bead appearance with plastic diode, tubular shape, but switch to magnetic materials package within small inductor and made to wear a wire. Dimensions of the common beads Φ2.5 × 3 (mm), Φ2.5 × 8 (mm), Φ3 × 5 (mm) and other specifications. Beads for chip switching power supply inductance is generally a few to tens of μH. The DC resistance of the beads is very small, and generally is 0.005Ω ~~ 0.01Ω. Usually noise filter can only absorb noise, are passive suppression; the bead role is different, can inhibit the generation of switching noise, therefore belongs to the active suppression-type, which is the fundamental difference between the two. The beads can be widely used in high-frequency switching power supply, video recorders, electronic measuring instruments, and a variety of very strict noise requirements of the circuit. The filter inductor L2 in Figure 1, on the selection of a 3.3μH the beads, can be filtered off VD5 switching noise generated in the reverse recovery process.
Transistor VT, current sense resistor R4 and optocoupler IC2 current control loop. When the output current IO is close to 500mA due to the voltage drop across R4 is elevated, so that the emitter voltage of transistor VT UBE also will increase, VT into the enlarged area, the current control loop starts to work, the output was constant current characteristics. Even if the output is short-circuit fault occurs, making IO ↑ UO → 0V, VT and optocoupler LED work properly able to maintain the total pressure drop of approximately 1.2V resistors R6 and R4. R3 is the base current limiting resistor.
1.2 15W PC, standby power circuit
An output power of 15W of the PC, the standby power supply circuit shown in Figure 2. The power supply provides two outputs: a main output of +5 V, 3A; auxiliary output compared to +12 V, 20mA. The total output power of 15.24W, power efficiency is higher than 78%. Circuit using two integrated circuits: the TNY267P type miniature monolithic switching power supply (IC1), SFH615-2 linear optocoupler (IC2). DC input voltage is 140V ~ 375V, this corresponds to the case of the AC input voltage is 230V ± 15% or 110/115V times of voltage input. The use of the TNY267P the undervoltage detection automatic restart and high-frequency switching characteristics, allows the use of smaller size, lower price EE22 high frequency transformer core. TNY267P chip is used in the form of a DIP-8 package, it can filter the output filter capacitor slowly discharges caused by auto-restart, burrs formed on the output voltage waveform. When the input voltage is below the undervoltage value, TNY267P automatically shutdown, play a protective role; work only when the input voltage is above the undervoltage threshold only. R2, R3 undervoltage threshold setting resistor. The total resistance of the two selected 4MΩ undervoltage threshold is set to DC 200V rectified DC high voltage UI must be higher than 200V in order to turn on the power. Once the power is turned on, it will continue to work until the UI down to 140V before shutdown. This lag shutdown characteristics, may be a standby power supply to provide the required holding time (Holdup).
The primary side auxiliary winding by VD2, C2 rectifier filter, +12 V output voltage, and power to TNY267P through R4. Work properly when TNY267P internal drain driver current source also stop charging on external bypass capacitor to reduce static losses in the meantime. R4 = 10kΩ, elect to bypass end to 640μA of the current, slightly higher than TNY267P current consumption, the excess part will be the chip internal zener clamp voltage of 6.3V security.
The secondary rectifier filter output of VD3, C6 and C7. L and C8 constitutes a rear stage filter mainly used to filter out the switching noise. When the output is short-circuited, automatic re-start circuitry limits the output current increases, and filtered out of VD3 overshoot voltage. By the optocoupler IC2 (SFH615-2), the regulator VDZ 5V output detection, R5 bias current to the regulator.
2 circuit design points
2.1 Use Caution
(1) The DC input voltage of the UI the minimum UImin may 90V to design. Enter a wide range of voltage (85V ~ 265V), the capacity of the input stage of the filter capacitor C1 according to the scale factor of 3μF / W to select; For example, when the output power PO = 10W, C1 = 30μF. For fixed voltage input AC 230V ± 15%, the ratio coefficient can be 1μF / W.
15w PC, standby power circuit
(2) In order to reduce losses and improve power efficiency, should adopt the secondary-side rectifier Schottky barrier diode (SchottkyBarrierDiode, abbreviation SBD), referred to as the Schottky diode. Such tubes have positive pressure drop (UF ≈ 0.4V), power loss, short reverse recovery time (trr can be as small as a few ns), etc., suitable for use as a low-voltage, high-current rectifier or freewheeling.
(3) Select the output power of a larger TinySwitch-II chip, helps improve the power efficiency. In the circuit shown in Figure 2, for example, select the TNY267 when the lower limit of the power efficiency is 78%; using TNY266 TNY264 sequentially reduced to 76%, 74%.
(4) In a particular application, the TinySwitch-II in the maximum output power over the thermal environment (including ambient temperature, cooling conditions, ventilation, and a power supply using the sealed or open type, and other factors), the size of the high-frequency transformer cores, work ways of design (continuous mode or discontinuous mode), the power required to change the condition of the minimum input voltage, the input stage of the filter capacitor, the forward voltage drop of the output rectifier.
(5) TinySwitch II to filter out the the audio noise produced by the high-frequency transformer. Allow using the general structure Impregnation transformer, and may also be without adhesive bonding between the core. When the switching power supply with the load mitigation audio interference, TinySwitch II by not continuously decreases the limiting current value, in order to filter the audio noise.
(6) in Figure 1 the LTV817 type linear photocoupler, available PC817 or PC817A instead. Their technical parameters are basically the same, the current transfer ratio CTR = 80% to 160%, and the reverse breakdown voltage U (BR) CEO ≥ 35V.
(7) In the circuit shown in Figure 2, standby power if select TNY266P chip, output power is reduced to the 10W. Optional EE16 type high frequency transformer core, and can also remove the filter capacitor C7.
2.2 PCB design points
TinySwitch-II chip PCB component layout, as shown in Figure 3, where the unused undervoltage protection resistor. The design of printed circuit board must note the following:
TinySwitch-II of the original layout of the printed board
(1) The following TinySwitch-II copper clad laminates not only as a source pole location, also to cool them. Figure 3 shadow area should be large enough to ensure good TinySwitch-II and rectifier cooling chip junction temperature below 100 ° C.
(2) The bypass the end capacitance CBP and the input filter capacitor C1 single point grounding method must be connected to the source terminal. Connection C1, the primary circuit of the high frequency transformer and TinySwitch-II should be as short as possible Jie.
(3) primary clamp circuit for limiting the turn-off of the peak voltage on the drain. Available R, C, VD type clamp circuit to achieve, also with 200V regulator or transient voltage suppressor (TVS) clamp the drain voltage. In any case, should the clamp components to the high frequency transformer and TinySwitch-II is the shortest distance.
(4) If the undervoltage sense resistor resistor as close as possible to the EN / UV end, in order to reduce the induced noise. Also need to consider the pressure value of the the undervoltage detection resistor R2 and R3. Select (1/4) of the resistance of W, generally can withstand the 200V voltage (refer to the continuous pressure, hereinafter the same); the resistance of W (1/2), the pressure value compared to 400V.
(5) Safety capacitors (Y capacitors) should be installed directly in the primary filter capacitor positive and secondary public land (Back end) between the maximum electromagnetic interference suppression and common mode surge voltage.
(6) the optocoupler to TinySwitch-II of the EN / UV end and the distance of the source should be kept as short as possible to reduce noise coupling. EN / UV pin to the optocoupler distance should be less than 12.7mm, the distance to the drain should be greater than 5.1mm.
(7) In order to improve the regulator performance, is connected to the secondary winding, the secondary rectifier, the secondary filter capacitor of the loop must be kept short. Secondary rectifier pad area must be large enough to ensure that the heat of the rectifier diode can be dissipated in a timely manner in the case of output short.
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