The TOP223P pulse width modulation ic is designed to work in switch mode power supply (smps). It is mainly used in the audio/video electronic equipment. Computer monitor rarely use this type of ic. In this article, I would like to share with you that not all switch mode power transformer must use the combination of uc3842 and power or chopper fet in order to function. SMPS designed are getting compact nowadays and this TOP223P ic actually consisted of the oscillator circuit and power fet integrated into it. Thus, do not search for the power fet at the surrounding circuit. If you look at the photo of this Thompson DTH5008FEK power supply, you could notice that there are not many components in the primary section. What you see are fuse, bridge rectifier, filter capacitor, top223p ic, optoisolator and couples of diodes, resistors and capacitors. If this type of power supply breakdown, it would not take you much time to repair it. Some TOP SWITCH IC have only three terminal but this type have 8 pins.
The secondary section consisted of fast recovery diodes, filter capacitor, coils and two voltage regulator ic with the part number of PQ05RD11. Both ic are the general purpose low power-loss voltage regulator with a 1 ampere output. Normally a voltage regulator has 3 pins but this type have 4 pins. The extra pin is for the on/off control functions. The pinouts functions for this ic are pin 1= DC input (vin), pin 2= DC output (vout), pin 3= Ground and pin 4= on/off control terminal (vc). It is important to know the specification of this type of ic if you want to be successfully tackle the power supply problem. Here are the spec for this type of family ic PQ03RD13 =3.3 volt output, PQ05RD11= 5 volt output, PQ09RD11= 9 volt output and PQ012RD11=12 volt output.
By measuring the output of this ic pin, you will have a rough figure whether the power supply is working or not. For example, when you put your meter's red probe to pin 2 of this PQ05RD11 ic with power on, you should expect a 5 volt. If the output voltage has only 2-3 volts then suspect a low dc input voltage problem, a faulty voltage regulator, a high esr ohm in filter capacitor or even bad components somewhere further down the line.
Conclusion-Troubleshooting power supply that used the TOP223P ic or other family type is very easy if you understand how power supply work and if you have the schematic diagram of a particular equipment. Below is a schematic diagram of a 20 watt universal input power supply using the TOP224P ic. One word, make sure you must know how to check all the electronic components before you repair it.