0-45V 8A DC switching power supply circuit

Today I recommended the 0-45V 8A DC switching power supply circuit as a circuit that is capable of a higher common linear circuit but it has a lot of detail.

Special feature:
– Output voltage……….0-45V
– Output current continuous 8 hour at a lower voltage than 35V and 6A at 40V
– ripple and noise :5mVp-p at 6Ampere 13volts
:10mVp-p at 8Ampere 18volts
:40mVp-p at 8Ampere 35volts
-Minimum output current:….800mA
-Maximum output current:….8.2A
– Display while use over voltage that setting and while voltage no regulated
– Can cut off the output load without the wires
– Adjustable constant voltage such as 13.8V.

Learn: What is switching power supply

Basic working
Figure 1 is shown the simple circuit of this switching power supply. The transistor Q1 will serves as the on/off switch circuit, we control them by lighting connection. This controller circuit will control the Q1 to on/off circuit by the frequency 20KHz.

basic of DC switching power supply circuit

Figure 1 the basic of DC switching power supply

Both Q1 and D2 will be passed to a high current, this will work alternately. During the Q1 performance, the current is passed through C8, C9, L1 and Q1, When Q1 stop or open circuit Energy stored in L1 will evolve through D2 and C8, C9 in the same direction, makes the output voltage is constant on all times.

And, if the pulse that send to control Q1, have the low duty cycle range. The current flow through Q1 and L1 are too low,so the output is also low. Which the duty cycle of this pulse switching will have high or low value depending on adjusting the output voltage that.

Learn to Build: 0-50V 3A Adjustable Regulator Power supply

How it works
Figure 2 is complete circuit of this switching power supply. IC5/4 is reference voltage booster circuit, which the output of IC5/4 will depending on adjusting VR3. This reference voltage from output of IC5 / 4 will send to pin 7 of IC3/2, to compare with the signal at pin 6 of IC3/2 that connected from IC3/1, which is 20KHz frequency ramp generator circuit.

the full circuit diagram of 0-45V 8A switching power supply
Figure 2 the full circuit diagram of 0-45V 8A switching power supply

IC3/2 will compare the voltage at both pins, if reference voltage has too much the output of IC3/2 will be a switching pulse (the square wave pulse) that has many duty cycle range. But if the reference voltage has less switching pulse value so low duty cycle as Figure 3

A comparison of the signals VP and VE

The pulse signal from the compare circuit will be sent to Q3 and Q4, Which is the buffer circuit to drive the LED in IC, that is the opto-isolator. It will detect the light as switching pulse signal then send to Q2 to Raise the signal. Next IC2/1 will set the signal waveform, then send to IC2/2-IC2/6. It drive the gate of Q1 that use as inverter in parallel to 5 pcs. To the current sufficient to drive the gate of Q1 up.

The switching of Q1 in sometimes will cause the voltage brief moment at leg drain may be higher than the source. As a result of the inductor coil L1. Thus, so the D1 and ZD3 to prevent this voltage, which may cause the FET crash. The limited voltage circuit while only 75 volts. This means that, If the voltage does not exceed 75V. This voltage would drop all ZD3, No effect to the circuit. If momentary voltage exceeds 75V, it can trigger the effect of making it through Q1 D1 conduct another stroke should not be working.

IC4 /1 and IC5/1 per share, to serve conditional no regulated. That IC4 / 1 will compare voltage between pin 6. Which is switching pulse and steady voltage at pin 7. When the negative pulse come in, output of IC4/1 will high, can through to charge C23 at pin 2 of IC5/1. And when output of IC4/1 lower the capacitor C23 at pin 2 of IC5/1 will higher up. The LED1 will no display, if Q1 get trigger gate at all times or Irregularities. The output voltage of circuit will lower in unregulated form. Capacitors C23 at pin 2 of IC5 / 1 are discharged, Until the output of IC5 / 1 high up, LED1 is lighted indicator non regulated.


Normally, the switching power supply output is not constant. If the Supply Current is very low. Or while no load. Thus, you must have the load of the circuit. To apply current lowest at all times.

While the output voltage up to 10volts, R24 and R43 connected in parallel 2 pcs, Will act as a load to the circuit. When voltage ranges from 5V to 10V, the output of IC4/2 will be the compare circuit will has high current cause Q6 works. R40 are connected to the load to the circuit and when output voltage lower than 5volts The output of IC4/3 will high instead makes Q5 works and R41 will be to provide a load of circuit.

IC3 / 3 acts to reduce the output current. When detected load use current over than 9 Amperes, will cause voltage across R1 and R2 are more valuable (more than 0.45 volts)As a result, output of IC3 / 3 low, and to pull the reference voltage at pin 7 of IC3 / 2 to IC3 / 2 to produce the switching pulse with a lower duty cycle as a consequence, the output dropped to a value less than 2A.

During the current over than the value set by the VR1, output of IC5 / 3 would be lower, according to the IC3 / 2 through D8, Make output IC4 / 4 higher. LED2 will show whether the current exceeds a preset.

How to build it

See the copper PCB layout and Component layout below.


The PCB layout

components-layout-of-45V-8A- Switching power supply

The components layout of this projects

We sorry not clear how to build it.

Parts you will need

0.25W 5% Resistors
R1, R2, R42, R43: 1K 5W
R3: 390 ohms 0.5W
R4: 270 ohms
R5, R11, R21, R32, R45: 1K
R6, R50: 100 ohms
R7, R34, R35: 470 ohms
R8, R17: 6.8K
R9, R18, R57:47K
R10, R30:18K
R12, R14, R15, R16:100K
R19, R27, R28, R29, R54:100K
R13, R23, R24, R26:10K
R22:270 ohms
R25, R30, R37, R38, R39:2.2K
R33, R46:22K
R40:39 ohms 5W
R41:10 ohms 5W
R48:820 ohms
R51, R52:0.1 ohms 5W
R53:47 ohms
R55:220 ohms
VR1, VR3:10K (B) Volume
VR2:500 ohms:trimpots
VR4, RV5:50K:trimpots

C1 – C5: 4,700uF 50V Electrolytic
C6, C7, C15, C23: 0.1uF 50V Polyester
C26, C28, C29: 0.1uF 50V Polyester
C8, C9, C12, C14: 100uF 50V Electrolytic
C10, C21, C22, C24: 1uF 16V Electrolytic
C11: 0.001uF 50V Polyester
C16, C17: 0.1uF 25V Polycarbonate
C18: 1,000uF 25V Electrolytic
C19, C25, C27: 10uF 16V Electrolytic
C20: 820pF 50V Ceramic

BD1:35A 100V
D1, D3-D6:1N4004
IC2:74C14 or CD40106
IC3, IC4:LM339
Q5, Q6:BC639
ZD1: 15V 3W
ZD2: 4.7V 1W
ZD3: 75V 1W
ZD4: LM336Z-2.5
F1: Fuse 7.5A
L1, L2: See circuit

L1:Toroidal core, Outside diameter of 46.7 mm, Rounds in 24.1 mm, 18 mm thickness; L1 is 10 turns of 17 AWG (1.2mm)
L2:Toroidal core, Outside diameter of 33 mm, rounds in 19.8 mm, 11.1 mm thickness; L1 is 5 turns of 17 AWG(1.2mm)

M1, M2: 1mA Meter
S1:ON/ OFF 10A Switches
S2: 3 leg, normally open pushbutton switch
S3: 10A On/off switches
S4:2 way switch
T1:transformer toroidal core
220V, 35-0/35-0 V, 300 VA
T2:Transformer 220V 12.6V 150mA
Box,PCB, Wires, and more.

Note: we sorry this circuit not have full building guide.

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9 thoughts on “0-45V 8A DC switching power supply circuit”

  1. Hi Salim Khan,
    I sorry for not clear how to builds it,

    L1____Toroidal core, Outside diameter of 46.7 mm, Rounds in 24.1 mm, 18 mm thickness; L1 is 10 turns of 17 AWG (1.2mm)
    L2____Toroidal core, Outside diameter of 33 mm, rounds in 19.8 mm, 11.1 mm thickness; L1 is 5 turns of 17 AWG(1.2mm)

  2. Hai, can u please give me a solution for my question it is that how to produce 7amps current as an output by giving dc voltage as an input to the circuit , one important thing is that without using transformer please help me guys.

  3. First I want to thank you for this project,
    Second could you please tell us the usage S2 and S4 switches?
    Best regards.

    • Hello Mrrobot,

      Thanks for your visit.

      You are a great person. You feel interested in this circuit.

      I am very sorry. I have never built it. I am not sure. Did it work?

      I will update it to clearly view for you. Please wait for me.

      For VR4 is selecting voltage 13.8V and adjust volt.
      And, VR3 for a control current to load.

      Thanks again.


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