The four chips, uc3842/3843/3844/3845, are identified: vcc (7) and ground (5) with a 0-20v removable power supply for 384x, slowly increasing the power source voltage。
The order of the 5v voltage of the 8-foot ref varies from 3843, 3845 to 3842 and 3844. Specifically 3843, 3845 out of 10v and 3842, 3844 out of 16v。
Six foot out feet. In the absence of feedback, the driving will be the largest in output, so that 3842, 3843 is equal to approximately vcc when measuring the 6 foot voltage in 10,000 and 3844, 3845 is equal to about half of the vcc when measuring the voltage in 10,000。
The most commonly used integrated circuit type of power supply pwm to control circuits is uc 3842 (or ka 3842), which is briefly described below as a good and bad method of judging uc 3842:
In the original circuit, after replacement of the peripherally damaged metaware, no switch is installed, and the 7 foot voltage of uc 3842 is measured. If the voltage fluctuates between 10 and 17 v and the remaining feet fluctuate, it means that the circuit has been set on fire and the uc 3842 is basically normal; if the seven feet are low and the rest of the tubes are not voltage or non-voltage, the uc 3842 is damaged
The direct current voltage of 7 or 5 uc 3842 plus around +17v, measured at 8 feet with a stable 5v voltage and a different voltage of 1, 2, 4 and 6 feet, was generally normal, working with small electrical currents and was not easily damaged. The most common cause of damage was the burning of high voltage from the g extreme to its six feet after the short circuit of the power switch. In some cases, protection of the diodes at the g polar level was omitted, and in the case of damage to the power switch, the limit-of-flow electrical resistance of the uc 3842 and g outer poles was considered to be bad. At this point, a direct replacement is sufficient。
It is important to note that the power switch source (s) usually uses a small-value high-power resistance as an overflow protection to detect electrical resistance, which is less than 1 euro, which is more likely to be unloadable (i. E. Low subpolar voltage)。
Since both the working voltage and output power of uc 3842 (ka 3842) are significantly different from that of uc 3843 (ka 3843), there are also significant differences between the 3842 and 3843 series in the activation and shutdown of voltage. The former has a start voltage of 16 v and a shut down voltage of 10 v; the latter has a start voltage of 8. 5 v and a shutdown voltage of 7. 6 v. These two ic series cannot be replaced directly. Where it is necessary to replace the former, circuits should be modified. This must therefore be noted in the maintenance work。
