First, the principle of brief introduction
Induction cooker is the application of the principle of electromagnetic induction heating, the use of current through the coil to generate a magnetic field, the magnetic field line through the bottom of the iron pot to form a closed loop will produce countless small eddies, so that the iron molecules of the iron pot body high speed to generate heat, and then heat the food in the pot.
Two, the principle of the induction cooker block diagram
Three, induction cooker working principle
1. The main circuit
The bridge integral DB1 in the figure changes the power frequency (50Hz) current into DC current, L1 is the throttle coil, L2 is the electromagnetic coil, IGBT is driven by the rectangular pulse sent by the control circuit. When IGBT is on, the current flowing through L2 increases rapidly. When IGBT is off, L2 and C12 are in series resonance, and the C pole of IGBT generates a high voltage pulse to the ground. When the pulse drops to zero, the driving pulse is again applied to the IGBT to conduct it. The process goes on and on, eventually generating a dominant frequency electromagnetic wave of about 25 kHz, which induces eddies from the bottom of the iron pot placed on the ceramic plate and heats the pot. The frequency of series resonance is the parameter of L2 and C12.
C11 is the power filter capacitor, CNR1 is the varistor (surge absorber). When the AC power supply voltage suddenly rises for some reason, that is, the instantaneous short circuit, so that the fuse quickly fuses, to protect the circuit.
2. The power supply
Switching power supply motherboard has two kinds of voltage regulator: +5V and +18V. The +18V after bridge rectifier is used for the IGBT drive circuit and the main control IC LM339 and fan drive circuit, and the +5V after three-terminal voltage regulator circuit is used for the main control MCU.
3. Cooling fan
The main control IC sends FAN drive signal (FAN), so that the FAN continues to rotate, inhaling cold air to the body, and then discharging hot air from the back side of the body, in order to achieve the purpose of heat dissipation in the machine, to avoid parts due to high temperature working environment caused by damage and failure. When the fan stops or the heat is not good, IGBT meter attached thermistor will send the overtemperature signal to the CPU, stop heating, to achieve protection. The CPU will send out a fan detection signal at the moment of power on, and then send out a fan drive signal to make it work when the machine is running normally.
4. Constant temperature control and overheat protection circuit
The main function of the circuit is based on the thermistor (RT1) placed below the ceramic plate and thermistor (negative temperature coefficient) on the IGBT to detect the temperature and change the resistance with A temperature of A voltage unit transmitted to the main control IC(CPU), CPU after A/D to compare with the temperature set value and make A running or stop running signal.
5. Lampboard wiring pin function
(1)12V voltage, touch power supply.
(2) Feedback voltage of furnace surface temperature measurement.
(3)IGBT temperature feedback voltage.
(4) Buzzer drive signal
(5) Fan drive signal
(6) Switch K signal
(7) Pot detection signal
(8)PWM power control
(9) Interrupt signal (overcurrent or pulse detection)
(12) High and low pressure detection
(13) Current detection feedback (power judgment)
6. Load current detection circuit
In this circuit, T2(transformer) is connected in series to the line in front of DB1(bridge rectifier), so the AC voltage at the secondary side of T2 can reflect the change of the input current. This AC voltage is then converted into DC voltage through D6-D9 full-wave rectifier, and the voltage is directly sent to the AD pin of CPU after R42 voltage divider. The CPU judges the current according to the converted AD value and calculates the power with the software, and controls the PWM output to control the power and detect the load.
7. Drive circuit
The circuit amplifies the output pulse signal from the pulse width adjustment circuit to the signal strength enough to drive the IGBT on and off. The wider the input pulse width, the longer the IGBT on, the greater the output power of the wire plate, namely, the higher the firepower.
8. Synchronous oscillation loop
The synchronous detection circuit consists of R4, R5, R7, R19, R20, R22, R23, C1, C2, C13 and 339;
The oscillation circuit (sawtooth wave generator) composed of D3, R8, R15, R9 and C7 synchronizes the oscillation frequency with the working frequency of the pot under the modulation of PWM. The synchronous pulse is output to the drive through the 13th pin of 339 to realize smooth operation.
9. Surge protection circuit
The surge protection circuit is composed of R45, R13, R16, R47, R39, R40, C20 and C18. When the wave surges, negative pressure of the same amplitude is transmitted on R45 through the transformer, so that the comparison end of 339 turns over, and pin 2 outputs low level. On the one hand, MUC is informed to stop the power; on the other hand, K signal is turned off through D4 to close the drive output.
10. Dynamic voltage detection circuit
The other two ends of D13, D14, R18, R2, R52, D8, EC2 and DB form a voltage detection circuit. After rectifying pulsating wave AD is directly transformed by CPU, the power supply voltage is detected whether it is within the range of 145V~270V.
11. Instant high-pressure control
The circuit is composed of R22, R23, R24, R26 and 339. When the voltage is normal, the circuit will not work. When the backvoltage instantaneous high voltage exceeds 1100V, the 339 will output a low level, pull down the PWM, reduce the output power, control the back voltage and protect the IGBT from over-voltage breakdown.
IV. Failure and maintenance
Fault 1. No power and no response on the button
Fault 2. Do not start (power off after a while, the buzzer will ring once every few seconds)
Fault 3. Automatic shutdown (shutdown after a few minutes, or shutdown at irregular intervals)
Failure 4. Slow heating, intermittent heating or too low firepower
Fault 5. Big noise
Failure 6. Fan failure
(1) There is abnormal sound from the fan
(1) Whether the fan blade is broken;
(2) whether there is foreign body interference;
(3) blade deformation, quality problems or caused by external forces.
(2) The fan does not operate
(1) whether the fan 18V power supply is open;
(2) Whether the fan socket and connection are open, and whether the fan blade is stuck;
(3) fan motor due to lack of oil dry damage;
④ Fan drive triode Q1, CE electrode open circuit or BE electrode short circuit.
⑤ Single-chip microcomputer control fan output in the boot state without high level output, I/O port damage.
(3) The electric rotation of the fan is out of control
① Drive triode Q1 CE electrode short circuit.
The MCU output is damaged, and the level is always high.
Fault 7. The buzzer is long or not ringing.
(1) Long sing, whether there are other faults with the MCU out of control;
(2) does not sound, the buzzer is damaged; R29 whether open circuit, virtual welding; Microcontroller control bee I/0 port damage.
Fault 8. Power can not be adjusted, too large or too small.
(1) whether the power “plus and minus” button is out of control, while other function files can be adjusted to change the button;
(2) check whether the power regulating potentiometer VR1 is in bad contact/open circuit;
(3) Check whether the current transformer T2 is deteriorating/leakage;
(4) check whether D6, D7, D8, D9 and four IN4148 are open or short circuit;
(5) Check whether the distance between the surface of the microcrystalline plate and the surface of the wire disk is within the normal range of 10-11mm.
(6) check whether the wire disc is deformed and the surface is black.
(7) Check whether the PWM filter capacitor EC8 leaks.
(8) Check whether the capacity of C11 (5uF) high voltage filter capacitor is smaller.
(9) Check the voltage detection circuit EC2 whether leakage, R2, R52 resistance value is increased, D2 whether breakdown.
Fault 9. Power instability (on/off)
(1) Use a multimeter to measure whether the power grid fluctuates too much, so that the surge protection works;
(2) Check whether the pins of C12 and C11 high voltage capacitors are welded and ignited, and whether the wiring end of the wire tray is loose and ignited, resulting in the protection of the single chip microcomputer.
(3) check whether the socket plug is loose and fire.
(4) Check whether the capacity of C11(5uF) high voltage capacitor is reduced.
(5) Check whether the power supply of 18V and 5V is normal, and replace LM339.
(6) Check whether the transformer secondary is open, whether D6, D7, D8 and D9 are breakdown, and whether EC7 is leakage.
Failure 10. There is abnormal noise at the bottom of the pot during operation
(1) check whether the pot is too thin, so that the vibration in the heating process is too large.
(2) Check whether the grid clutter is too large, so that the induction cooker is modulated.
(3) Check whether the 18V and 5V filter capacitors EC6, EC13, C10, C8 and EC5 fail;
(4) Check whether the PWM capacitor EC8 capacity has decreased.
Fault 11. Display operation normal, no E0, no power output.
(1) the power grid interference is too large, so that the impact protection circuit has been working.
(2) Check whether the current/impact protection circuit is wrong to work, whether C6, C20, C18 are invalid, and whether the resistance value of R15 is increased. Single chip interrupt pin (INT) is low level.
(3) Check whether the transformer is leaking, so that the single-chip current detection pin in the standby state level is higher than 0.5V
(4) Check whether C11 and C12 high-voltage capacitors fail;
(6) Replace LM339, whether the lampboard row plug has bad contact.
Fault 12. Startup shows E0
(1) Check whether the material and size of the pot >10cm are within the specified range;
(2) check whether there is bad oxidation contact in the lampboard insert;
(3) check whether Z1 leakage, breakdown.
(4) Check whether the oscillation circuit C3 and D3 have been damaged.
(5) Check whether the synchronous loop R19, R20, R22, R23, R4, R5, R7 is open, and whether C1, C2, C13 is leakage. Replace 339.
(6) Check whether Q2 and Q3 are damaged, and whether R49 is open to make the drive without 18V.
Failure 13. If the machine is not switched on, there will be beep on the power
(1) Check whether the lamp panel is in bad oxidation contact;
(2) Check whether the boot button is in good condition; Check whether other keys have short circuit phenomenon.
Fault 14. Power on silent, no response,
(1) Check whether the 220V power cord is normal and whether the plug is burnt black;
(2) Check whether the power connector is welded or not.
(3) check whether there is a fracture of the main board;
(4) Check whether the switching power supply is normal, and whether D5, L4, Z3 and IC1 are normal.
(5) SCM 5V power supply is normal, check IC2(78L05), replace Y1 crystal oscillator, SCM;
(6) check whether the lampboard wiring is oxidized or loosened;
Fault 15. It works normally, but the digital tube shows lack of pen and drawing
(1) whether the digital tube is damaged;
(2) Whether 164 is normal;
(3) whether the light-emitting diode leakage short circuit damage phenomenon;
(4) whether the circuit board has weld, crack, water;
(5) whether the SCM is normal.
Fault 16. Explosion
(1) only burn insurance, check the varistor ZNR or insurance quality is poor, direct replacement.
(2) IGBT, bridge stack and insurance are burned without any reason, and the quality of components or the impact of the power grid is too big, so they should be replaced directly.
(3) There are the following reasons for the explosion:
A. High voltage capacitor C11, C12 capacity deterioration, dummy welding ignition.
B. The wire panel terminal is falsely welded, and the connection is loose and kindling.
C. The wire coil is blackened and damaged.
D. Drive circuit Q6, Z1 damaged.
E. Lower 18V power supply
Bad F.L M339.
G. Silicone grease drying makes IGBT poor heat dissipation, so that the thermistor attached to the IGBT surface temperature measurement is not accurate, comprehensive damage.
H. Inlet water into machine board, short circuit of cockroach and fire.
I. Switching power supply is damaged, so that 18V power supply is damaged instantly.
J.P. WM filter capacitor EC8 open circuit or no capacity
Five, general fault display code
1. No pot: E0
2. Too low voltage (
3. High voltage (>270V):E2
4. Short-circuit or dry burning fault of furnace surface sensor :E3
5. Open circuit of furnace surface sensor :E4
6. IGBT overtemperature (90 ° C) or sensor short circuit :E5
7. IGBT sensor open circuit fault :E6