Need control circuit for induction heater

Thread Starter

mohan.n2293

Joined Jan 23, 2017
60
Hi ALL,
This is mohan I have built a induction heater by seeing the circuit in you tube(please see the attachment for the circuit 1),it is working fine but now i need to control the temperature in that core.
I went some of the datasheets in that i found that changing the frequency to the half bridge we can control the temperature in the core so i built the circuit(circuit 2) as attached .
But here when i test the circuit the input current is increasing with decrease in the input voltage(i have used RPS as a input) and bjts are getting heat.
Please check the circuit and suggest me better way to drive the BJT base.
1)Youtube circuit :
upload_2018-3-8_11-7-16.png

2)circuit2
upload_2018-3-8_11-5-39.png
 

Janis59

Joined Aug 21, 2017
1,383
1) The temperature is more easy to adjust by means of regulating the Vcc. The method is much more prost and fast
2) Changing the frequency there is only one thing which really changes - that is Focault deapth and therefore power. In most of cases that is contraindicated to variate the layer thickness.
3) Always lowering the frequency the layer will become more thick, but there will be more mechanical movement forces. If that is for example Zone Rectification heater then it is improper. And vice versa, at fixed frequency the highest possible frequency maximizes the temperature effects while minimizes the mechanical turbulences.
4) RE:""the input current is increasing with decrease in the input voltage"" But of course, that is determined by Ohm`s law!! If You want it vice versa, then You need a base junction with negative resistance :). More over, where is the rationale to change the meander voltage?? Just adjust it to minimum temperature and keep it. The deepest reason is that bjt stays `half`opened, what is thermally most dangerous regime.
 

ScottWang

Joined Aug 23, 2012
7,213
Could you upload your .asc file.

If the two input pulses all on low level at the same time and then it could causes the Q1 and Q2 to turn on at the same time and that situation as Vdd shorted to ground, you can measure the current to check out, so you need to change one side to invert whatever the up driver or low driver.
 
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