Sinrace Power Supply Technology (Shenzhen) Co., Ltd.

TEA1733 is applied to the vast majority of system which is no more than 75W power consumption, typical applications include: the netbook adapter, LCD monitor and printer adapter. The controller supports the discontinuous conduction mode (DCM) and continuous conduction mode (CCM). It can improve the work efficiency in entire load range to combine the fixed frequency operation under high output power with down operation under low output power.

TEA1733 integrated frequency jittering function can reduce electromagnetic interference (EMI), also provides several protection features to ensure the durability and reliability of device.

Fixed-frequency flyback converter

Flyback converter is the most common form of switching power supply topology. Figure 1 shows layout form of TEA1733 typical flyback topology. TEA1733 uses peak current control, output power is adjusted by the CTRL pin. Load results is measured by optocoupler and sent back to CTRL pin. Primary current flowing through the external resistor R1 is detected by the ISENSE pin. Peak voltage is compared adjusted throughthe internal voltage, and present ratio change with CTRL voltage. To relevantly adjusted duty cycle by controlling the peak current, when duty cycle is more than 50% ,to active slope compensation ,to avoid harmonic distortion. Maximum duty cycle is not more than 74%.

Low-power operation, reduce switching losses by reducing the switching frequency. Internal voltage controlled oscillator (VCO) can gradually reduce the frequency to 0Hz. In order to avoid audible noise, with the frequency step down, the peak current be 25% of maximum current. Figure 2 shows the corresponding relation graph of frequency and peak current control .

TEA1733 integrated frequency jittering function can reduce EMI interference. Controlling center frequency to be 66.5kHz ± 4kHz by dithering Oscillator. Jitter Oscillator Frequency Select 260Hz to avoid audible noise.

During startup, the power supply voltage VCC charge through the current of startup resistor, the chip consumes is only about 10μA, so needn’t high-voltage to startup circuit. When VCC reaches the start voltage of 20.6V and all other conditions are met, the controller began to work. Since then, the power supply voltage is in charge by from the transformer auxiliary winding. The normal work current of pin load without DRIVER is 0.5mA. Low power consumption is help for improving efficiency.

As small power consumption and low frequency, using TEA1733 standby power does not exceed 100mW. If accompanied by the appropriate resistors and capacitors and other external devices X, usually 65W/19.5V power standby power measurement is 48mW (115Vac) or 84mW (230Vac).

If you provide an external "run / power" signal indicating the standby mode, such as battery-operated devices, standby power consumption can be further reduced to less than 30mW by shutting down the whole system This is the so-called "zero-power" design. "Activity off" state of the basic application schematic Figure 3, the standby mode external "power" signal is high. Then turn down VINSENSE transistor Qx voltage activated restart protection. Stop switching chip, into power saving mode. Power-saving mode, the chip consumes only 10μA. Meanwhile, VCC control by clamping the voltage dropped to slightly below the starting voltage level to ensure quick restart from standby.

TEA1733 has multiple protection features such as: input over / under voltage protection, output over-voltage protection, overload protection, internal / external thermal protection. These protection functions can protect secure restart or latch. To achieve safe restart, firstly chip gets into power-saving mode, when all conditions are met, then resume running. When power-saving mode, OPTIMER pin rapidly charge to 4.5V, then slow down to 1.2V. Start blocking protection, the chip also firstly gets enter power-saving mode of operation, but the VCC voltage keeping in around 6V by clamp controlling. To reset the latch protection, it can be achieved to need unplug the main power plug ,and reduce the VCC voltage to a certain level. 6V clamping voltage is just a little higher than voltage level about quickly resetting after lockout protection .

PROTECT pin of TEA1733 has a special double protection functions: external thermal protection and output overvoltage protection, refer to Figure 4. PROTECT pin provides 32μA current and absorbing 107μA current. Internal circuit usually adjust PROTECT pin voltage to 0.68V. If the PROTECT pin voltage is between 0.5V - 0.8V, no protection. If the VCC voltage is too high, the maximum absorption current can not be pulled PROTECT to lower than 0.8V, so that the test results is the output overvoltage. The protection can meet the general application requirements. As the temperature increasing, the thermistor of negative temperature coefficient (NTC) connected by PROTECT pin reduces its resistance .If the maximum power supply current can not upgraded PROTECT voltage to 0.5V, then the test results is the external heat. Both cases as below will activate the latch protection .

If OPTIMER pin connections is shown in Figure 5, allows short-term overload to operate If ISENSE peak voltage exceeds 400mV, OPTIMER pin output current 11μA charge for external capacitor C2 , overloading timer start timekeeping. Overload operation is for a long time, once OPTIEMR pin voltage exceeds 2.5V, overload protection will be activated. For a short time overload, before the OPTIMER voltage reaches 2.5V, ISENSE the following peak voltage down to 400mV, C2 will discharge immediately, without protection action. Through setting different values for the C2 and R3 to adjuste overload running time.

For a fixed frequency CCM, a maximum output power not only depends on a peak point current, but also affected by duty cycle and input voltage. TEA1733 integrated input voltage compensation circuit can ensures an extremely stable main voltage overload protection. Overload compensation circuit measuring the main circuit through VINSENSE pin, and change it into ISENSE pin output current. The output current generate voltage through soft boot resistor R2 shown figure 1, to limit the maximum output current of sensor resistor R1. By adjusting R2, the maximum output power won’t be controlled by the input voltage.

TEA1733 offers several different versions to meet different application requirements. Standard version supports the safety overload timeout restart. TEA1733L is used for overload timeout blocking protection. 90kHz working devices are included TEA1733A and TEA1733M, the former is safety restart, the latter is used for blocking protection. In addition to conventional SO8 package form, TEA1733 (L) chips can also use the DIP8 package, also called as TEA1733 (L) P.

NXP TEA1733 has become the first model which is newly launched by NXP. the new GreenChip series low power AC / DC converter control chip, the feature of highly integration make it fully be able to meet the low-cost, compact power supply design and the growing market demand. "Zero-power" design of standby power consumption is less than 30mW. Compared with similar products, TEA1733 power performance, especially characteristics of low-power dissipation under standby mode has a strong competitive edge in the low-power consumption of computing and communications applications,.