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I am not an expert at electronics.I am trying to build a pulse induction metal detector. I have this circuit Pulse induction metal detector design using PIC microcontroller

from that Book

I am using it with stm 32 blue pill but I have to stabilize the 9v supply to make works perfectly so i tried to use a 9v 1A adapter instead of 9V battery The transistor gets very hot and produce sound like beeps and after a while it is about to burn.I investigate the circuit on oscilloscope it produces a similar output on both cases adapter and 9v battery.

I thought it is a problem of logic level(between stm32 and PIC) so i tried to convert the 3.3V to 5V using open drain but it produces the same unpredictable performace.

finally it do the same with 2*3.7 li-ion battery What should i do to overcome this problem to be able to drive the circuit with 3*3.7 through 9V regulator to stabilize the circuit.Thanks.

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  • \$\begingroup\$ Did you calculate the value of L1 correctly...? \$\endgroup\$ – Natsu Kage Feb 7 at 23:09
  • \$\begingroup\$ Thanks for your comment . It is about 448 uH .How could inductance affect the circuit . \$\endgroup\$ – Romyo Feb 7 at 23:13
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Place a 1 ohm resister in the source of your P channel drive fet Q2 .Measure the voltage across the resister with a scope .If you see big spikes like several volts then excess current is heating the Fet. More Inductance ,less on time ,More delay time will cool things down .Next place the scope between the Drain and ground noting a positive swing of almost 9V and a big negative backswing .If thin negative going backswing exceeds the VDs rating of your 200V P channel fet the Fet will zener and heat up because the inductive energy is going into the avalanche region of the Fet . Reduce on time ,Increase L1 ,Decrease R2 .High voltage P channel devices are hard to find .Next check the gate drive waveform on the scope expecting a clean square wave .Long fall times and parasitics will cook the Fet .

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  • \$\begingroup\$ Thanks that helped me a lot.However the problem was the off time it was very short ON 100us OFF 50 us. I made it 8ms. \$\endgroup\$ – Romyo Feb 8 at 13:30

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