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Step 3Building a PSU
There are many ways to build the psu. First I experimented with the +12V and -12V dc voltages that come from the standard computer psu. I found out that the devices work with only 12V but on some devices I was not able to adjust the zero point. Also the brightness of the display is not high enough using only 12V.
Next idea was to implement the psu using a transformer and linear dc-power regulators. This would be easy but then I would need to put 220V into the pc. That seemed to be a bad idea.
Finally I decided to generate the +-15V dc from the 5V of the pc psu. Therefore I needed step up converters. I used the components I found on other pcb boards that kalleb also offers on eBay. These are PIR boards, from a hands free kit for mobile phones build by com.n.sense http://www.greasemonkeyconversions.com/10609/Com_N_Sense_Hands-Free_Kit_(Nokia_3310_etc).shtml . I bought this pcb's for usage of the parts in future robotics projects.
The schematic of the psu is taken out of the data sheet of the MC34063A. This chip can be used to build positive and negative regulated step up converters. One problem using step up converters could be that the switching regulator could inject noise into the audio path. If I turn up the volume of the amplifier I can hear this noise. It is rather low, but you can here it.
The psu is build on an experimental pcb.
I build the psu on an experimental pcb board. You should have some experience in soldering when doing this. The components are very tiny. I did not optimize the design. The whole thing draws about 0.3A current in the end. The vu meter draws only about 0.16A current. This means that the psu is not very efficient. The main problem seems to be the coils I used. The positive and the negative switching regulators need different coils. I simply took the coils from the PIR pcb without taking care of their value. I could optimize that but efficiency of the psu is not important here.
The output voltage can be adjusted with small trimmers. It ranges from about 12V to about 17V. You can carefully experiment with voltage here ...
In any case, please test the psu before connecting it to the VFD's pcb!
Next idea was to implement the psu using a transformer and linear dc-power regulators. This would be easy but then I would need to put 220V into the pc. That seemed to be a bad idea.
Finally I decided to generate the +-15V dc from the 5V of the pc psu. Therefore I needed step up converters. I used the components I found on other pcb boards that kalleb also offers on eBay. These are PIR boards, from a hands free kit for mobile phones build by com.n.sense http://www.greasemonkeyconversions.com/10609/Com_N_Sense_Hands-Free_Kit_(Nokia_3310_etc).shtml . I bought this pcb's for usage of the parts in future robotics projects.
The schematic of the psu is taken out of the data sheet of the MC34063A. This chip can be used to build positive and negative regulated step up converters. One problem using step up converters could be that the switching regulator could inject noise into the audio path. If I turn up the volume of the amplifier I can hear this noise. It is rather low, but you can here it.
The psu is build on an experimental pcb.
I build the psu on an experimental pcb board. You should have some experience in soldering when doing this. The components are very tiny. I did not optimize the design. The whole thing draws about 0.3A current in the end. The vu meter draws only about 0.16A current. This means that the psu is not very efficient. The main problem seems to be the coils I used. The positive and the negative switching regulators need different coils. I simply took the coils from the PIR pcb without taking care of their value. I could optimize that but efficiency of the psu is not important here.
The output voltage can be adjusted with small trimmers. It ranges from about 12V to about 17V. You can carefully experiment with voltage here ...
In any case, please test the psu before connecting it to the VFD's pcb!
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7
Jul 10, 2011. 11:42 AM
uhclem
says:
uhclem
says:
How about summing the 5 and 12v (+ & -) supplies to get +/- 17V and just drop that down with a couple of 1A silicon diodes? I know you can combine the -5 and +12 to get +7, which some use to run fans slower.
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2
Jul 28, 2009. 10:39 PMcharlieb000
says:
instead of a DC DC converter, you can use a 555 (for the +15v)... have the 555 on the 12v and the output is to a negative of a capacitor. when the 555 output is off, the capacitor is charged with 5v (through a diode pointing from 5v to the cap's positive) and when the output is ON the negative of the cap is at 12v thus giving 17v on a second diode's output. and i dont think you can get any more efficient. may work also if you switch the voltages, same output. for the -15v, a cap where the positive is switched between +5v and 0v and the negative is on -12 (or switched between +12 and 0 and negative is on -5v) and thus -17v. probably a negative regulator needed or slowing the 555 will surfice. the diodes (and maybe the transistors in the 555 too) have voltage drops too so you may get around -15v and +15v in the end.
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2
Jul 28, 2009. 10:59 PMcharlieb000
says:
the diodes probably need to be high speed....
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