Help with 24+ circuit

Audioguru

Joined Dec 20, 2007
11,249
You talk about the LM350 and LM338 without looking at their datasheets?
They also reduce their maximum output current when the input to output voltage is too high.
 

mcgyvr

Joined Oct 15, 2009
5,394
You talk about the LM350 and LM338 without looking at their datasheets?
They also reduce their maximum output current when the input to output voltage is too high.
Which might not be an issue or maybe it is. Like I said you cannot pick the proper regulator until you know what you current requirements are. The transformer is only 200mA so talking about maximum current levels for the regulator is pointless too. But only he knows #1 if the transformer will even be enough #2 what his circuit actually is so again this thread can't go anywhere good till that information is provided.
 

Thread Starter

drycounty71

Joined Jan 16, 2012
30
Which might not be an issue or maybe it is. Like I said you cannot pick the proper regulator until you know what you current requirements are. The transformer is only 200mA so talking about maximum current levels for the regulator is pointless too. But only he knows #1 if the transformer will even be enough #2 what his circuit actually is so again this thread can't go anywhere good till that information is provided.
Schematic attached for 24+
 

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drycounty71

Joined Jan 16, 2012
30
You talk about the LM350 and LM338 without looking at their datasheets?
They also reduce their maximum output current when the input to output voltage is too high.

I did review and below is the graph for the LM350 with my notes. It looks close to 1.5 amps which is more that the 200mA the circuit requires from the limitation of the transformer specs from the factory. True I am wasting 500mA from my 2A tap but again the circuit is only requiring 200mA. Am I oversimplifying this?
 

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Audioguru

Joined Dec 20, 2007
11,249
The circuit does not use much current from +24V but the relays are unknown and might draw a lot.
With small relays it looks like any 24V regulator will work fine with a medium size heatsink.
 

Thread Starter

drycounty71

Joined Jan 16, 2012
30
The circuit does not use much current from +24V but the relays are unknown and might draw a lot.
With small relays it looks like any 24V regulator will work fine with a medium size heatsink.

are you refering to K1 and K2? If so, the specs on those off the parts list are:

3700 RELAY 2C 01AMP DC24 015MA PC-S

Oh and then there is the reverb pan:
Input Impedance 600 Ohms, Output Impedance 2250 Ohms
 

Thread Starter

drycounty71

Joined Jan 16, 2012
30
With small relays it looks like any 24V regulator will work fine with a medium size heatsink.
With that in mind a LM317 still has the issue of dealing with 48 vdc coming into it if I replace the 7824 with it. and that is 24volts difference. We are talking chernobyl-type heat.
 

Audioguru

Joined Dec 20, 2007
11,249
The numbers for the relay do not make sense. Google never heard of it since it does not have a manufacturer's name.

"01AMP"
Is it "1 Amp"? It it the rating of the contacts or the rating for the coil? Probably for the contacts.

"015MA"
Is it 15mA or 15uA? It it the rating of the contacts or the rating for the coil? Probably 15mA is the coil's current.

Then the entire circuit draws only about 50mA from 24V when both relays are activated.
 

Thread Starter

drycounty71

Joined Jan 16, 2012
30
The numbers for the relay do not make sense. Google never heard of it since it does not have a manufacturer's name.

"01AMP"
Is it "1 Amp"? It it the rating of the contacts or the rating for the coil? Probably for the contacts.

"015MA"
Is it 15mA or 15uA? It it the rating of the contacts or the rating for the coil? Probably 15mA is the coil's current.

Then the entire circuit draws only about 50mA from 24V when both relays are activated.
So what does this all mean?
 

Thread Starter

drycounty71

Joined Jan 16, 2012
30
So would it be safe to put a 12-15v 5w zener inline (cathode facing away from 7824) with the input of the 7824 and call it a day?
 

Ogu Reginald

Joined Oct 13, 2011
6
The max allowable voltage for 78** should not in any way be exceeded. You can reduce the voltage with a voltage divider arrangement and not with a single resistor.
 

Thread Starter

drycounty71

Joined Jan 16, 2012
30
The zener I tested is a 33v 5w zener and it was hot one of the leads started melting my breadboard. I am reducing down from 48v @ .2a to 33v the power dissipation would be 4.8w - 5w zener should do it. However, given the power dissipation and heat generated and the breadboard meltdown, a 10w or 50w shouldn't get as hot right? Especially since I have real-estate to mount a 50w zener vs. an extra ic chip. Thoughts???
 

Audioguru

Joined Dec 20, 2007
11,249
Simply look at the datasheet for the zener diode to see that its temperature is about 200 degrees C at its rated power which is extremely hot.
The datasheet shows its thermal resistance so you can calculate a suitable power for a reasonable temperature.

It is silly to use a power supply voltage that is too high then waste a lot of power making a lot of heat to reduce it.
 

Thread Starter

drycounty71

Joined Jan 16, 2012
30
Simply look at the datasheet for the zener diode to see that its temperature is about 200 degrees C at its rated power which is extremely hot.
The datasheet shows its thermal resistance so you can calculate a suitable power for a reasonable temperature.

It is silly to use a power supply voltage that is too high then waste a lot of power making a lot of heat to reduce it.

I know, I should be over on the "How to rewind a step-up transformer" forum.
 
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