Diode in Amplifier

[Pim Driessen]

Hi, Yes it is true, I have an e-mail sent to Hitachi with the question of what the zener diode voltage is in the Mosfet.
I have now discovered again that Mosfets are not functioning properly, a type 2SK213 from China and 2SJ76.

2SK213 and 2SJ76 not function Gate input.
with 20-volt supply voltage is already current through the drain / source

 

[audioguru]

2SK213 and 2SJ76 not function Gate input.
with 20-volt supply voltage is already current through the drain / source

You did not tell us the polarity (positive or negative) of the 20V. You also did not say the gate-source voltage and its polarity.
The 2SK213 is N-Channel so its source is common and its drain and gate must be positive for it to pass current through the drain/source.
The 2SJ76 is P-channel so its source is common and its drain and gate must be negative for it to pass current through the drain/source.
When the gate has the same voltage as the source (0V) then a Mosfet should not pass current.

 

[MrAl]

Hi,

The zener(s) from the gate to source if present will conduct in both directions, plus or minus, but the drain and source voltages must be correct for the type of MOSFET either P or N type. This means you should check the gate with plus and minus (say) 12v, but the drain voltage must be correct for the type.

You also need a gate resistor to ground to make sure the MOSFET can turn off, because the MOSFET gate can charge up and stay charged up even without any signal applied (open circuit). So connect a 10k resistor from gate to source to check to see if the MOSFET can really turn off or not.

 

[Pim Driessen]

Hi, DC voltage test 20 volt : 2SK213 + volts, 2SJ76 - volt, 2SK3497 + volts.
The Mosfets which were not found good, was the Gate Source voltage is zero volts and the drain current 90 mA.

The Mosfets that were good was Gate Source Voltage 2.2 volts for 90 mA Drain Current.

 

[Pim Driessen]

Hi, I'm going to try it out with 10K between gate and source

 

[audioguru]

If your gate-source voltage was 0V then obviously the gate-source capacitance was not charged.

 

[Pim Driessen]

Hi, this is interesting, without 10K between Gate / source, the current flows in drain line at about 1 volt, and I can Gate / Source boost voltage above 12 volts.
But with 10K between Gate / source current is also running at about 1 volt, but the gate / source voltage, I can not pay more than 10 volts, is that the built-in zener

 

[audioguru]

Hi, this is interesting, without 10K between Gate / source, the current flows in drain line at about 1 volt, and I can Gate / Source boost voltage above 12 volts.
But with 10K between Gate / source current is also running at about 1 volt, but the gate / source voltage, I can not pay more than 10 volts, is that the built-in zener

But you do not show a schematic of how you connected the parts and the resistor values.
Maybe now you have a resistive voltage divider that limits a "payout" of more than 10V?

 

[Pim Driessen]

Hi, Here the schematic

 

[audioguru]

Your new schematic does not show a 10k resistor from gate to source.
The schematic does not show the resistance of the potentiometer.

With resistor R3 in series with the pot to ground then the gate-source voltage will never be 0V so of course the Mosfet conducts.

 

[Pim Driessen]

You are right,
but my test circuit was good connected between Gate / source with 10K

 

[audioguru]

That is what I thought.
The pot at maximum has an output of +20V.
The two 10k resistors divide the 20V in half so +10V maximum goes to the gate.

 

[Pim Driessen]

Hi, Thanks for your help.
I wonder if Hitachi will respond to my e-mail about the Zener diode in the MOSFET.

 

[Pim Driessen]

Hi, I have two amps to build according to the schedule shown earlier in this forum.
I have created a test setup, and wanted to measure all voltages of the amplifier.

I have current meters installed in my power lines to see if all goes well.

I was measured in the input stage and saw that the current of eindtansistoren climbed to 3 Ampere, the quiescent current is set at 1.4 Ampere.

Here is the schedule of the test points where I was measuring.

A print screen file was too big to post, so it's a PDF file

What could be the Cause.