LM324 Power Supply 0-25V 0-5A

Thread Starter

mike69

Joined Dec 22, 2012
83
Hello,
I have a few questions about the attached schematic of power supply.
1. Is the schematic functional ? If not, what are the mistakes in the schematic ?
2. Is the layout correct ? If not, how it can be improved ? The DRC does not return any error, but I am wondering about ground connection and other stuff like this...
3. Is the minimum output current really 0A ?
4. I will use R3=680R, R4=2K2, R7=12K, R11=120K, because I did not found the specified values at the local electronics shop. On the VT4 footprint I will solder the wires that go to the power transistors that will be on another PCB.
Here you can find the schematic image: https://imgur.com/NqGeRTi
 

Attachments

Last edited:

Papabravo

Joined Feb 24, 2006
16,778
Hello,
I have a few questions about the attached schematic of power supply.
1. Is the schematic functional ? If not, what are the mistakes in the schematic ?
2. Is the layout correct ? If not, how it can be improved ? The DRC does not return any error, but I am wondering about ground connection and other stuff like this...
3. Is the minimum output current really 0A ?
4. I will use R3=680R, R4=2K2, R7=12K, R11=120K, because I did not found the specified values at the local electronics shop. On the VT4 footprint I will solder the wires that go to the power transistors that will be on another PCB.
Here you can find the schematic image: https://imgur.com/NqGeRTi
The first thing that looks suspicious is that T2-T5 have their base terminals connected together, but the net has no driving source. What should be going on?
 

Thread Starter

mike69

Joined Dec 22, 2012
83
Regarding the attached schematic, what diodes can be used to replace the D2 (SB560) and D5 (BY500) ?
I saw that there are a few BY500 variants, with different reverse voltage. It is ok to use the 100V diode for D5 (BY500-100) ?
 

Attachments

Last edited:

danadak

Joined Mar 10, 2018
4,057
The 7812 regulator has a minimum load requirement of 5 ma to stay in regulation,
make sure that is met. The LM324 may not be enough current draw.

Capacitor ESR important (Polymers best for bulk)



Regards, Dana.
 
Last edited:

danadak

Joined Mar 10, 2018
4,057
Combination of heavy load at 30V coupled with high line voltage transient into bridge
is what that diode has to withstand. More margin is almost always better. Especially
if you don't know what your line looks like and its load disconnects, etc...

Regards, Dana.
 

AnalogKid

Joined Aug 1, 2013
9,352
If you are tying for a traditional supply that changes automatically between constant voltage and constant current regulation, there is something wrong with the way the current monitor ties into the voltage regulator in #1. It is correct in #4. Also, what is the purpose of C9 in #1?

ak
 

AnalogKid

Joined Aug 1, 2013
9,352
Only the schematic from post #4 is valid. You can ignore the schematic from post #1.
Pins 4 and 11 *need* bulk filter and decoupling capacitors to GND.

There is zero capacitance across the output. Some should be added to reduce high frequency noise. Be careful - too much can cause oscillation; the output capacitance and the emitter resistors form a phase shift network that can upset the control loop stability.

Not sure what R12 and R13 are for.

ak
 

Thread Starter

mike69

Joined Dec 22, 2012
83
It is possible that the power transistors (2N3055 in the schematic at post #4, but I used TIP35C in my project) to be destroyed if I make a short circuit on the output of the power supply ?
I am talking about the schematic at post #4 and I am talking about the situation when I use a properly large heatsink for the power transistors...
 

AnalogKid

Joined Aug 1, 2013
9,352
Depends on two things:

a) the size of the transformer. One 3055 is rated for20 A, so the peak short circuit current would have to be enormous.

b) C5. This sets the response time of the current regulator, how fast it turns down the voltage when it detects an output current greater than the setpoint.

ak
 

Thread Starter

mike69

Joined Dec 22, 2012
83
The transformer is sized at 24V and 160VA. The transistors that I use are 6x TIP35C in parallel. I am also planning to make a version with 4x 2N3055 in parallel or with 4xTIP35C in parallel.

Later edit: if I will reduce the value of C5, the power supply will start oscillating ?
 
Last edited:

AnalogKid

Joined Aug 1, 2013
9,352
It is possible that the power transistors (2N3055 in the schematic at post #4, but I used TIP35C in my project) to be destroyed if I make a short circuit on the output of the power supply ?
The transformer is sized at 24V and 160VA.
Possible, but very unlikely. The transformer is rated for under 7 A, so maybe 15-20 A short circuit (at greatly reduced output voltage). Any one of the transistors you have chosen should be able to handle this for a few seconds, way longer than the current limiter takes to act.

ak
 

Thread Starter

mike69

Joined Dec 22, 2012
83
Regarding the attached schematic, it is safe to use 10R resistor instead of 330R resistor (Imin) ?
I am asking because I need current to go down to 0mA. If I use 300R, then the minimum current is about 170mA. If i use 10R, the minimum current is about 1.7mA.

Later Edit: in the place of 2SC5200 and BD140, I used 4 NPN transistors with emitter resistor driven by a BD244.
 

Attachments

Last edited:
Top