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Old 21st February 2006, 05:23 PM   #1
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Default Power supply need help...

Hi

Is it good schematic?I need too get +-40V DC from power supply +-70V?
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Old 21st February 2006, 05:32 PM   #2
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Default Regulator

Viktor,

Your Q2, MJE340 is backwards. Try flipping the Collector and Emitter. This should keep either of the MPSA42s from blowing.

How much current are you passing? If it is more than a few hundred mA, then you should consider using a switching regulator, as your conduction losses would be considerably less and efficiency would go way up, keeping things much cooler.

A common buck regulator can be used for the (+) rail, and a variation of the boost (flyback) regulator can be used for the (-) rail. Heck, they can even be synchronized to eliminate any beat frequencies that would be generated!

Hope this helps!

Cheers,

Steve
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Old 21st February 2006, 05:41 PM   #3
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Default !

Is it good now?I need around 10-20mA
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Old 22nd February 2006, 01:08 AM   #4
clem_o is offline clem_o  Philippines
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How much regulation do you need? It looks ok in the simulation. You can try putting a dynamic load on it and looking at how much the output changes with the load.
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Old 22nd February 2006, 01:44 AM   #5
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Now you are on the right track. If you're loading only 10-20mA, the nyour disspation will be less than 1 watt per rail, and you should be fine.
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Old 22nd February 2006, 08:23 AM   #6
Eva is offline Eva  Spain
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The circuit is likely to work fine with real components, but you should check for frequency stability. In case of oscillation, a small miller capacitor in each output device may solve it. If part count is not critical, I would include some basic overload protection achieved with two current sense resistors in series with the emitters of the output devices and two transistors to clamp the base drive in case of overcurrent, when the voltage drop across the said resistors goes above one diode drop.
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Old 22nd February 2006, 08:45 AM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
I would look for heatsinks on the pass devices (Q1 & Q2).

is your load continuous constant current on each rail? If not then what is the real maximum current on each rail. Allow a percentage above this and then calculate your power dissipation with maximum voltage on the supply.

You have a 30V loss across the pass device. Have you thought about using your input caps as low pass filters? Add a power resistor, 2W or 3W wirewound would be perfect as a voltage dropper.
680r would drop 13.6V at your 20mA load and if C3&4=1mF//100nF give 680mS RC timeconstant to kill the majority of high frequency rubbish coming from the previous supply. It would also provide a modicum of overload/short circuit protection.

The ground sensing leads are shown in the sym and schematic as common with the main ground current return. The ground for Z, R5 & R9 should have a separate track to the output node and same for negative.
A simple constant current for Z would improve performance but constant voltage is maybe not that important to your circuit.
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Old 22nd February 2006, 03:07 PM   #8
CBS240 is offline CBS240  United States
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small film caps across the zener won't hurt either as zeners can generate some noise.
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Old 22nd February 2006, 08:05 PM   #9
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Default !

Hi

If I want too change output voltage what schood I do?Could I change value R9,R10 or value R7,R8?

With value's on the picture I got +-65V DC!
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Old 22nd February 2006, 11:37 PM   #10
clem_o is offline clem_o  Philippines
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If that's the output you're getting you can bet that there's a mistake in how you wired up your (physical) circuit. Take your DVM and start measuring voltages against the voltages printed in the simulation of Circuitmaker, to find the problem.

After you've corrected the problem the output voltage will be much closer to your target +-40V. If you're still not happy with it, you can modify (R7 and R8) OR (R9 and R10), pick a pair.
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