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Old 24th December 2010, 07:31 PM   #161
jaycee is offline jaycee  United Kingdom
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Originally Posted by MJL21193 View Post
Hi jaycee,
What can I say about simulation? I use it extensively myself.
I can say that the circuit does not behave that way in Multisim and, more importantly, it does not do that in reality. The addition of a 1A load causes less than 10mV deviation in the supply voltage at 12VDC.
You might want to check the ground references for your measurements to ensure they are on the regulated side of the current sense resistor (0 volt side). This tripped me up a few times in the beginning.
Oh sh... yeah! It's measuring with reference to the ground node, not to the 0V_OUT node. It was a "what have I done wrong?" post, not the usual "Hey, the sim says it doesnt work, you suck!" post you get on here - I know your design skills well enough to know they are a) way better than mine and b) you make stuff that works !

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I like to be efficient and run everything from one transformer. Less mains voltage wires to run, less space taken up inside the case. The implementation in this supply is in no way inferior to a separate supply and the results speak for themselves.
Yep, it's good ! It'd leave me to use a small transformer for 5v/12v to power the display control circuitry i'd put in (I'd probably use a microcontroller).

What i'm thinking of next is a prereg - some way to get the dissipation down when using eg 3.3v or 5v.

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Not sure what you mean by 'any short, not just a short to ground'. The supply limits current on a dead short between the positive volts terminal to the 0 volts terminal to less than 2.2A. Here that is in action:
<snip>
Hmm good point as there isn't really any node it could short to. I was thinking for example, if you shorted to Earth (Protective Ground), what would happen.. but of course nothing would happen as the supply floats!

I did wonder though, what happens if you tie 2 channels together to get a symmetric supply, and one of the channels goes faulty...
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Old 24th December 2010, 08:00 PM   #162
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Originally Posted by jaycee View Post
I did wonder though, what happens if you tie 2 channels together to get a symmetric supply, and one of the channels goes faulty...
With all of the protection diodes in place (thanks again Mega ), there isn't much that can happen. I have done some testing on it with both supplies in series and the only 'wrinkle' I can see is that the current limiter works on one channel first rather than both at the same time. This would create an asymmetrical supply, with one dropping below the other. This is an issue I'd like to fix but for now, I'll accept it as it will rarely (if ever) cause a problem.

Last edited by MJL21193; 24th December 2010 at 08:15 PM.
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Old 24th December 2010, 08:17 PM   #163
jaycee is offline jaycee  United Kingdom
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OK, i guess that's not too bad. I guess now I'll explore two extra features:

* Constant Current/Constant Voltage mode light. The supply would be in CC mode if Q9 is conducting.

* Rather than current limit, a mode that as soon as the supply draws too much current, it turns off. Again I guess this can be done by checking Q9 and if it conducts too much, clamp the voltage at the A of D2 to ground.
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Old 24th December 2010, 08:36 PM   #164
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Originally Posted by jaycee View Post
OK, i guess that's not too bad. I guess now I'll explore two extra features:

* Constant Current/Constant Voltage mode light. The supply would be in CC mode if Q9 is conducting.

* Rather than current limit, a mode that as soon as the supply draws too much current, it turns off. Again I guess this can be done by checking Q9 and if it conducts too much, clamp the voltage at the A of D2 to ground.
The advantage of meters for both channels becomes clear when you want to set CC. With a dummy load attached, rotating the V adjust pot to the desired voltage and then rotating the I adjust to the desired current sets it up quickly. For example: 22VDC at 200mA and the supply will not exceed that current under any load conditions.
The current limit is active at all times and restricts draw to 2.2A at any voltage (with the current limit pot at max). This can be increased or decreased by changing the value of R27 and/or the sense resistor R23.
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Old 28th January 2011, 09:06 AM   #165
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I want to replace the buz900p-buz905p on the musical fidelity a220 with irfp240-irfp9540. I will appreciate your help.
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Old 17th February 2011, 11:54 PM   #166
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Have you thought about putting a thiele/zobel/pi/whatever network at the output to improve stability and pulse behavior? If a pulse is fast enough (in terms of slew rate), it will saturate the feedback circuitry and this may cause a long recovery time.

Also, I wonder if adaptive power limiting could be achieved using one of those analog multipliers from Analog Devices?

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Old 18th February 2011, 02:43 AM   #167
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Have you thought about putting a thiele/zobel/pi/whatever network at the output to improve stability and pulse behavior? If a pulse is fast enough (in terms of slew rate), it will saturate the feedback circuitry and this may cause a long recovery time.

Also, I wonder if adaptive power limiting could be achieved using one of those analog multipliers from Analog Devices?
Hi Kean,
During construction, I tried many different things to stabilize the supply and finally successful with the relocation of cdom. Adding the 100uF cap to the output helped also.
Transient response is very good (see HERE) - actual scope shots of the supply in action. The slew rate looks fine to me. It is just a power supply, after all.
The current limiter has exceeded my original expectations. I had no idea it would work as well as it does and it's hard to imagine a more effective method that is as simple.
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Old 3rd March 2011, 10:10 AM   #168
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How does it fare with large film cap bypass?

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Old 3rd March 2011, 11:20 AM   #169
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Not sure what you mean, kean. Can you be more specific?

Last edited by MJL21193; 3rd March 2011 at 11:23 AM.
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Old 3rd March 2011, 11:40 AM   #170
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Say 1uF film, connected to output without series resistor, and tested with a square wave. Many regulated supplies will oscillate. I notice you have a 100nF cap with .3R series resistance. Some circuits may have a number of 100nF bypass, and for a lab supply to be useful it needs to be stable into these.

Just like in amplifiers, a Zobel will help with this. Maybe it is better to leave HF regulation up to capacitors near the circuit, and isolate the regulator at HF.

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