Hi, i have the schematic below i downloaded from a YT video, its a power supply circuit. it uses the lm358 op amp. notice that the datasheet of lm358 can handle upto 32V vcc. my problem is my power supply at the filter cap is having 40v, which i think its a lot for lm358 vcc, how can i lower it so that it will be suited on the lm358 vcc? take note that i will be building a 30v 3a linear bench ps, and i want to copy the schematic below. thanks

 

Use a power-tab voltage regulator like the 78 24 to provide a stable voltage that will not fry the LM358.
But I would not trust a youtube circuit to work, especially this one. Running a device at the abs max voltage rating is seldom a good choice.

 

Use a power-tab voltage regulator like the 78 24

I think the MC7824 is rated to 40V.
There are two resistors, Base-Collector of TIP142, should be 332//332. I think 333 is an error.

 

hi,
He is asking for a 10V drop at 3 Amps, rating 30 Watts, will need a decent size regulator and heat sink.
E

 

He is asking for a 10V drop at 3 Amps,

I think the idea from Post #2 is to regulate the voltage to the LM358 only. Very little current.

 

Why not replace LM358 with a high voltage op-amp?

 

hi Ron,
I 'think' he intends connecting the +40V input to the input marked as +30Vin.
If he reduces the supply to the LM358 to 30V, he will have to make some modifications to left side circuitry, considering the LM358 Vout swing range will be limited.
E

 

Use a power-tab voltage regulator like the 78 24 to provide a stable voltage that will not fry the LM358.
But I would not trust a youtube circuit to work, especially this one. Running a device at the abs max voltage rating is seldom a good choice.

But to get 30V output the LM358 outputs must get to 30V.

 

hi Ron,
I 'think' he intends connecting the +40V input to the input marked as +30Vin.
If he reduces the supply to the LM358 to 30V, he will have to make some modifications to left side circuitry, considering the LM358 Vout swing range will be limited.
E

View attachment 275118

exactly, since lm358 vcc max input is 32V, which in my case i have 40V, which if i connect lm358 vcc(pin 8) will too much

 

Use a power-tab voltage regulator like the 78 24 to provide a stable voltage that will not fry the LM358.
But I would not trust a youtube circuit to work, especially this one. Running a device at the abs max voltage rating is seldom a good choice.

i choose this diagram because it uses tl431 and op-amp. which i think is a versatile one?

 

exactly, since lm358 vcc max input is 32V, which in my case i have 40V, which if i connect lm358 vcc(pin 8) will too much

Use a zener diode to provide V+ to the opamp.

If the 40V isn't regulated well enough, you'll need a larger capacitor.

 

Use a zener diode to provide V+ to the opamp.
View attachment 275120
If the 40V isn't regulated well enough, you'll need a larger capacitor.

is that c1 a non polar cap?

 

Back in 1980 I built this supply. I used a uA723 IC. I also had problems with 40V like this supply.
I added a 10V calculator adapter to power the IC. The 10V supply, negative went to the output or Emitter of the power transistor. The IC turns on the Power Transistor from the +10V supply. The feedback was a little hard to understand. I looked for a schematic but could not find it. I am certain it is in an application note somewhere. I also made a 500V version (low current) using the same floating 10V supply. Maybe a search for uA723 high voltage supply will turn up the design.

 

is that c1 a non polar cap?

The component I used isn't polarized, but you could use a polarized cap. A ceramic cap would be the least expensive and you don't even need a temperature stable variety.

 

hi muno,
This is your original circuit running in LTspice, with a 8R load, not bad.
E
Please check for any circuit errors.


Added the Wattage plot for the TIP.!!!

 

hi muno,
This is your original circuit running in LTspice, with a 8R load, not bad.
E
Please check for any circuit errors.


Added the Wattage plot for the TIP.!!!

View attachment 275124

hello, i havnt ise ny simulation software before, but somehow, can you recomment the circuit?

 

hi,
The best I can get from that circuit is 25V at 2.5A, is that what you want.?
E

 

take note that i will be building a 30v 3a linear bench ps, and i want to copy the schematic below

That may be problematic using LM358 as the control element because the output voltage can only get to within 3-5V of the maximum output voltage for the opamp. What is the lowest output voltage you want?

 

The MC33171 is a low-cost, single-supply, 44V op amp, which should replace the LM358 without problem.
(Edit: It also generally has better performance with lower power, slightly higher output voltage, nearly double the frequency response, four times the slew-rate, and no crossover distortion.)

Adding a second diode in series with D2 should allow a slightly higher maximum output voltage.

 

The MC33171 is a low-cost, single-supply, 44V op amp, which should replace the LM358 without problem.

Adding a second diode in series with D2 should allow a slightly higher maximum output voltage.

Need to do this for D1 as well.