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DC Motor Driver (SCR type)

BlackMelon

Aug 7, 2012
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Hello,

Is anybody familiar with this kind of driver? The input is 220Vac and the output is dc voltage feeding motor's + and - at M+ and M- respectively.

The bridge rectifier is used to rectify AC voltage to dc, supplying a trigger circuit of X1 and X2. And, there is a sub-circuit and a potentiometer to control two trigger signals. For simplicity, I omit the trigger circuit, leaving only power components. If you need to see the full detail, just tell me. :)

Thank you
BlackMelon
 

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Minder

Apr 24, 2015
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That is a common method of DC motor control, see KB products, but generally the two SCR's are part of the bridge to save on components, the bridge in the diag does not appear to be doing anything?
Some components seeming redundant?
M.
 

BlackMelon

Aug 7, 2012
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That is a common method of DC motor control, see KB products, but generally the two SCR's are part of the bridge to save on components, the bridge in the diag does not appear to be doing anything?
Some components seeming redundant?
M.

The file below is its full schematic. Now, I understand its power circuit. However, I can't comprehend the trigger circuit. All I know is that one can control the speed of a motor by turning a potentiometer Ri/o in the schematic. Could you please clarify it?


PS: Are power components redundant? I would say no. The group of U3, U4, U6 and U5 is a bridge rectifier, which provides a constant dc voltage supplying a triggering circuit. But X2 X1 U6 U5 is a controlled bridge rectifier, so its output voltage will vary accordingly to Ri/o,which controls trigger circuit. I think it's economical because the bridge rectifier and the controlled bridge rectifier, together, share U6 and U5.

Thank you
BlackMelon
 

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Last edited:

Minder

Apr 24, 2015
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There is no source of GND shown unless it is a CT transformer supply with the CT being GND otherwise the two SCR's do not make sense?
Also other sections are referenced to GND which shows Earth GND symbol, BTW.
M.
 

BlackMelon

Aug 7, 2012
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It's strange that there is no CT. Also, could you explain the word "a CT transformer supply with the CT being GND"?
 

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Minder

Apr 24, 2015
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One way of full wave rectification is to use a centre tapped secondary of the transformer and a diode in each outer connection and in this case the centre tap is the circuit common or "GND"
upload_2016-2-21_11-18-12.png
M.
 

BlackMelon

Aug 7, 2012
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Oh! Thank you. I was thinking of CT as "current transformer" rather than "center tapped" at first. LOL
 

BlackMelon

Aug 7, 2012
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There is no source of GND shown
Oh! Forgot to tell you that the ground source, which I define, is located at the anode of D9 in this new schematic.
The source is a 220Vrms 50Hz AC. All of these are depicted in the new file. The new schematic is just rearranging the old one. I found the circuit makes more senses.

As in this following site:
http://electronicsterms.com/wp-content/uploads/2013/12/SCR-Triggerig-using-UJT1.png
The junction between the gate and the cathode is a load of the UJT, and this pattern is also used in the new schematic.
However, driving high side SCRs requires a charge pump.

How could the circuit drive the SCRs?
 

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