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Negative Voltage Design Problem

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transistance

New Member
Hello all,
I posted a representative schematic of my shot at 555 negative voltage generator. The problem is the lowest value I can get is around -8.2 V, in time it rises close to 0V - defeating the whole purpose.

How should redesign to make this unstable power supply work properly?
 

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audioguru

Well-Known Member
Most Helpful Member
The 555 needs to have a supply bypass capacitor. Use 470uF.
The output will be -8.2V all day if the load current is very low. If the load current is 200mA then the little 9V battery will be dead very quickly and then of course the negative voltage will drop to 0V.

What is the positive load current and what is the negative load current?
 

transistance

New Member
The 555 needs to have a supply bypass capacitor. Use 470uF.
The output will be -8.2V all day if the load current is very low. If the load current is 200mA then the little 9V battery will be dead very quickly and then of course the negative voltage will drop to 0V.

What is the positive load current and what is the negative load current?
I did not measure the positive load current. Negative output had no load when I measured. The 9V is a LM7809 regulated power supply - I used the standard circuitry with bypass capacitor right before feeding the circuit-, not a battery. Maybe this due to no load?

I thought the problem may be related to my output capacitor value.
 

audioguru

Well-Known Member
Most Helpful Member
The frequency is about 65kHz which is much too high for ordinary rectifier diodes.
Try 1N4148 diodes.
 

transistance

New Member
The frequency is about 65kHz which is much too high for ordinary rectifier diodes.
Try 1N4148 diodes.
I will try that thanks! I was using some germanium diodes I got for audio distortion effects.
 
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audioguru

Well-Known Member
Most Helpful Member
Your schematic does not show the polarity of the output capacitors. if their polarity is wrong then the 555 will get very hot and maybe stop working.
 

audioguru

Well-Known Member
Most Helpful Member
Everything seems to be fine. But since the circuit fails after some time without a load then maybe the 555 is defective. Replace it.
 
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