Delma DEM-F320LS type humidifier power supply circuit principle and maintenance - Power Circuit - Circuit Diagram

MOS power IC full range

Industrial Router Crystal 3.2*2.5mm 3225 26M (26.000MHZ) 12PF 10PPM 20PPM 30PPM

Photocoupler

This type of ultrasonic humidifier uses the power chip PR6228T. The chip has few external components, wide operating temperature, 18W power, DIP-8 package, high integration, low cost. It is a current mode PWM power conversion circuit with built-in 650V high voltage MOSFET with overvoltage, undervoltage protection and VDD voltage. The clamp function also uses frequency jitter technology to improve EMI characteristics and automatically enters the MODE and PFM modes of operation based on load changes. The functions and voltages and resistance values ​​of each leg of PR6228T are shown in Table 1. The whole circuit of the whole machine is shown in Figure 1.

First, the working principle analysis
The 220V mains is rectified by the F1 and D6-D9 full-bridge rectification and C14 filtering. The main winding of one switching transformer is sent to the 5th and 6th pins of the PR6228T (ie the drain of the internal MOSFET), and the other pass After R17 and R16 are stepped down, capacitor C4 is charged. When the voltage across C4 reaches 14.8V, IC1 starts, the secondary winding of the switching transformer induces voltage, and the DC voltage obtained by D2 rectification, R18 current limiting, and C4 filtering is sent to IC12. To replace the starting voltage. When the IC12 pin voltage is lower than 9V for some reason, the IC internal control circuit is turned off, and the chip enters the restart state.
When the protection circuit is working normally, the LED in the optical fault PC1 emits light normally, and the photosensitive receiving tube outputs a voltage of about 1.59V, which is sent to the 3 pin (feedback end) of IC1 and the external resistor R23 of 4 pin (SENSE) to form a current. Sampling input circuit. The duty cycle of the PWM controller inside the chip is determined by the feedback voltage of the 3-pin and the detection voltage of the 4-pin (SENSE). Once the circuit is abnormal, the protection functions such as overvoltage, undervoltage, and overcurrent of the power chip will immediately act and protect.

Second, the troubleshooting example 1 phenomenon phenomenon; no.
Analysis and overhaul: The test found that F1 was blown, and D6 and D7 were broken down. Test IC1 feet to ground resistance value and external components are no abnormalities, replace the above damaged components after the test machine, troubleshooting.
Symptom 2: None.
Analysis and overhaul: After testing with the resistance method, it was found that F1 was blown, D6-D9 broke down, there was a crack on the surface of IC1, and R23 was broken. After the above components are replaced, the red indicator light is turned on and off. It is measured that the voltage of pin 2 of IC1 fluctuates between 8V and 14V, and the voltage of C10 positive pole to ground fluctuates between 9V and 15V (normal value is 44V), C17 The voltage at both ends fluctuates between 6V and 10V. It seems that the peripheral components of the power chip are still faulty. Checking the peripheral components of the IC12 pin found that the power supply resistor R18 has been increased from 10Ω to 100kΩ. Because there is no chip resistor on hand, after switching to a 1/8W 10Ω metal film resistor, the voltage of IC12 pin is stable at 15V, but the voltage at C10 and C17 is only slightly improved, which is still unstable. After checking the pins 7 and 8 of IC1 and the ground connection of the power supply, the copper foil was broken. IC1 uses a flying wire to connect it and test the machine, and the fault is eliminated.
Fault phenomenon 3: The voltage of the whole machine is normal. When no water is added, the red light is on. When the water is added, the magnetic float rises, the reed switch pulls in, the green light lights up, and the fan runs. But no fog, the gas mist potentiometer has no effect.
Analysis and overhaul: Test the c-electrode voltage of the atomizing drive tube Q4 to the normal value of 44V, but the b-pole voltage is 2V, which is obviously wrong. In normal time, the b-pole voltage should be negative. When the test related components are all normal, the b-level voltage of Q4 is measured to be -1.3V. Replace the test machine after Q4, troubleshooting.