# PWM controller ...help needed



## PrinzEugen (Dec 9, 2010)

from BDA's blog http://bda-train-blog.blogspot.com/2011/03/homemade-pwm-power-supply-for-h0.html

Here it my revisited scheme for PWM analog controller on split strip-board 




















summary 

This controller feeds the analog railway system with PWM impulses, with fixed amplitude (12 - 14V) and variable width. This means that the output voltage goes from 0 to 12-14V and back to 0 with a 25 kHz frequency. 
Do NOT use it to drive digital locomotives, until you change the C1 capacitor with a 470nF one! This will lower the frequency of the PWM, so that the digital decoders will know for sure that they work on an analog railway sistem.

- overcurrent above 1a and short circuit protected, 

- it can be used wit reverse polarity kipp switch for change direction 

- also no heatsink is needed for BD651 and LM7809, and all capacitors are ceramic, all resistors with at least 0.4w wattage 



so my problem....
I have checked board for 7 time literary. All connections on board are like on scheme. 

Potentiometer doesn't working, stuck to 14v as input. No min or max. 

Readings are 14v on output. Led dont lit. Motor dead on 14 DC voltage 
No cold solder joints also. 
Output and input are not short connected. 
Positive input is on + rail (checked). Negative input is on - rail 




5-6-7-8-9 cd4093 to ground . 4 and 10 free pins 


Q1: BD651 transistor 
Q2: BC547 
C1: 1nF capacitor 
C2: 0.33 microF capacitor 
C3: 0.1 microF capacitor 
D1 and D2: 1N4148 diodes 
D3: 1N4007 general usage diode 
R1: 2.2 KOhm resistor 
R2: 2.7 KOhm resistor 
R3: 0.68 Ohm resistor 
R4: 1 KOhm resistor 
P1: 100 KOhm potentiometer linear mono 

Maybe pot is wrong connected ?...i dunno...capacitors dont have polarity also. 


Can someone test this pls on test board...


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## tankist (Jun 11, 2009)

can't see images from work, will try to take a look later.

not much help, but just so you not feel alone. 
BTW, i would imagine dedicated electronics forum will be of much better help


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## PrinzEugen (Dec 9, 2010)

I must go to Geneva and CERN to solve this....


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## NIMT (Jan 6, 2011)

You must include the other side of the circuit board to solve this!
Your only showing half of the connections!


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## PrinzEugen (Dec 9, 2010)

Problem solved....


schematic is ok...pwm control fully operational


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