JSR03 - information

[peranders]

Good that you succeeded after all.

From zero load to max the voltage should not drop more than a few millivolts.

Have you checked that you min voltage isn't under 34 volts. You must also include the ripple. I think the voltmeter should read 36-37 volt in your case, which is a bit much if you have a 35 V cap at the input.

The LED should be lit all the time, if not the power stage hasn't got enough base current. How much current are you taking out?

If the output voltage isn't 100% stable you won't get low noise either.

[Keljian]

Good that you succeeded after all.

From zero load to max the voltage should not drop more than a few millivolts.

Have you checked that you min voltage isn't under 34 volts. You must also include the ripple. I think the voltmeter should read 36-37 volt in your case, which is a bit much if you have a 35 V cap at the input.

The LED should be lit all the time, if not the power stage hasn't got enough base current. How much current are you taking out?

If the output voltage isn't 100% stable you won't get low noise either.

C1 is 50v

voltage in is 33.5 approx

I'll check current soon

[Keljian]

Good that you succeeded after all.

From zero load to max the voltage should not drop more than a few millivolts.

Have you checked that you min voltage isn't under 34 volts. You must also include the ripple. I think the voltmeter should read 36-37 volt in your case, which is a bit much if you have a 35 V cap at the input.

The LED should be lit all the time, if not the power stage hasn't got enough base current. How much current are you taking out?

If the output voltage isn't 100% stable you won't get low noise either.

C1 is 50v

voltage in is 33.5 approx

I'll check current soon

Well I tried with a 30v AC (500mA) transformer, the same thing happened.

I'm only driving an m3.. which (while the quinescent current draw has been set to 130mA on each fet) should be drawing less than 500mA

ok the M3 is drawing (measured) exactly 309mA

So it isn't the transformer. (which is capable of 24v AC/0.87A)

Also the transformer worked with the old power supply design wihout voltage sag.

[peranders]

Do you have a tin blob at the SENSE pads at the solder side?

If you meassure in the sense hole, X6. Stable voltage?

Just wondering but what does Morsel and the rest of the design team say about recommend power supply? Do you follow their instructions?

Personally I think 29 volt stabilized with 24 VAC is too little. A rule of thumb is to have the same AC voltage as DC so in your case 26-28 V AC for 29 V DC.

If you want 300-350 mA out you must have a transformer with 500-700 mA AC. I would have chosen 28 VAC, 1 A.

How much smoothing do you have? Have much ripple voltage do you have at 300 mA out?

[Keljian]

Do you have a tin blob at the SENSE pads at the solder side?

If you meassure in the sense hole, X6. Stable voltage?

Just wondering but what does Morsel and the rest of the design team say about recommend power supply? Do you follow their instructions?

Personally I think 29 volt stabilized with 24 VAC is too little. A rule of thumb is to have the same AC voltage as DC so in your case 26-28 V AC for 29 V DC.

If you want 300-350 mA out you must have a transformer with 500-700 mA AC. I would have chosen 28 VAC, 1 A.

How much smoothing do you have? Have much ripple voltage do you have at 300 mA out?

Sense pads are tinned

How do I measure ripple?

as for their instructions, they're based on the opamp voltages but 24-29v/300ma is ok

8000uF worth of smoothing caps.. should be plenty..

Surely the JSR couldn't be drawing 300mA on its own..

if it worked with the other power supply (which was a snubberised steps clone)

[Keljian]

the transformer is rated to .87A

I'm only trying to draw 300ma..

[peranders]

The tricky part is that the current in theory will get 1.4 times more on the AC side plus in your case 8000 uF is considered as rather heavy smoothing and this increases losses in the transformer.

A thumb of rule is if you have heavy smoothing you can take out 50% in watts of the VA rating.

In your case: 300 mA x 34 volts = 10.2 Watts => 20.4 VA is required

3300-4700 uF is a normal max especially if you have a super regulator. If you want to have less you must have an oscilloscope in order to judge a safe lower limit.

With 24 VAC I don't recommend more than 24-26 volts DC unless you can get an oscilloscpoe.

BTW: How hot gets the LM317 with the rather small heatsink? The heastsink shouldn't be hotter than 60-70 degrees C.

[Keljian]

The tricky part is that the current in theory will get 1.4 times more on the AC side plus in your case 8000 uF is considered as rather heavy smoothing and this increases losses in the transformer.

A thumb of rule is if you have heavy smoothing you can take out 50% in watts of the VA rating.

In your case: 300 mA x 34 volts = 10.2 Watts => 20.4 VA is required

3300-4700 uF is a normal max especially if you have a super regulator. If you want to have less you must have an oscilloscope in order to judge a safe lower limit.

With 24 VAC I don't recommend more than 24-26 volts DC unless you can get an oscilloscpoe.

BTW: How hot gets the LM317 with the rather small heatsink? The heastsink shouldn't be hotter than 60-70 degrees C.

The transformer is 20VA.

I had the same problem with only 4700uF worth of caps, the caps I have are low ESR panasonic FM

The problem is still occuring with 25.7v (changed R8 value)

25.7v unloaded

23v loaded.

(26 going into the jsr when loaded)

[peranders]

Have you checked X6, voltage drop also there?

The LED is lit also?

You have 10 mA base current available for T3/T4 which means that at least 1 A is possible, that assumes current gain of 100. It may be possible that used used transistor has a but low current gain. datasheet says min 20-40 so maybe you should decrease R14 to 47 or even 27 ohms. This will create more base current.

If you have such problems you will see a difference in voltage between the inputs of the opamp. The inverting input, pin 2 should have exactly the same voltage as the LM329.

[Keljian]

Have you checked X6, voltage drop also there?

The LED is lit also?

voltage drop is at x6 also

led is not lit

when I switch it on the led goes on for a second, then goes off. If I unplug the load while running it lights up again

[Keljian]

the transformer is rated to .87A

I'm only trying to draw 300ma..

max is 870mA, if I divide by 1.4 I get 614mA.. which is more than enough..

[peranders]

If the LED is not lit, then you may increase the base current => decreasing R14.

The current is calculated like this:

(Ledvoltage-0.7)/R14 => (1.7-0.7)/R14

[Keljian]

If the LED is not lit, then you may increase the base current => decreasing R14.

The current is calculated like this:

(Ledvoltage-0.7)/R14 => (1.7-0.7)/R14

changed R14 to 27 ohms..

no change in output.

LED is  still off

[peranders]

How much voltage across the LED?

How much voltage across R14?

Do you have 1 volt over R14 when you have a small load?

[Keljian]

How much voltage across the LED?

How much voltage across R14?

Do you have 1 volt over R14 when you have a small load?

0 load

LED = 1.8v

R14 = 1.07v

300mA load

R14 = 0.1v

LED = 0.8v